We thank Ryan Johnson and Leah Miller for their assistance in collecting the data.

<ol>
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The authors have no disclosures to report.

First, it is critical that the net application is correct and that impedances are lowered. Second, it is important to explain to the parent what the EEG net application and paradigm will entail and how the parent can help calm the infant if they become fussy without speaking to or making eye contact with the infant, which would blur the lines between the social and non-social conditions. Further, instruct parents to keep infants from pulling on the net, which can affect the EEG data and cause damage to the net. Third, consistent paradigm administration is crucial. This includes using the same tone of voice and affect during all conditions and with all participants; making sure to get the infant&#39;s attention before beginning each joint attention trial; and keeping the infant focused on the experimenter during the social engagement condition. If there are multiple experimenters, their tone of voice and affect should be similar so as not to introduce experimenter effects. Fourth, follow the alternating sequence of social and nonsocial conditions to sustain infant cooperation throughout the protocol. Lastly, confirm that infants engaged in the conditions as intended by coding infant looking behavior during the social engagement and joint attention conditions.
There are multiple modifications to this technique. If the infant becomes fussy, it is possible to modify the paradigm by stopping halfway through. The entire paradigm includes 8 x 2.5-min blocks (with each condition repeated twice) and each condition happens once in the first four blocks. Therefore, if necessary for the infant or parent, it is possible to end the paradigm half way and still have completed each condition once. The order and administration of blocks in this protocol was the same for all infants. If researchers are concerned with making certain that the order of the blocks does not influence neural activity, the order of the blocks can be counterbalanced across participants. However, based on piloting, counterbalancing requires two constraints: (1) each condition needs to be represented in the first four blocks in case the paradigm needs to end early and (2) the blocks need to alternate between social (joint attention and social engagement conditions) and nonsocial (language-only and nonsocial conditions) to maintain infant interest.
This paradigm has only been piloted with 11 - 14-month-old infants. However, if researchers are interested, this paradigm could be used at other ages. The time window that this paradigm is most likely to be appropriate is from 6 months, when joint attention and capacity for gaze following are well established 29, through 24 months. This age range is when joint attention is the most important developmentally for nonverbal social communication and language learning13,14. If using the paradigm for other ages, modifications of the conditions are likely not needed. However, the most effective block length may vary depending on infant age. Specifically, the blocks may need to be shortened for younger ages to maintain infant cooperation and attention.
If a laboratory&#39;s technical capabilities do not allow for the presentation of two computer screens, it is possible to modify the paradigm to be completed with only one screen. The main consideration is whether interests lie in assessing whether infants are complying with the experimenter&#39;s directions to look at the left or right screen. This requires two screens to allow for an assessment of the amount of time each infant looks at the correct or incorrect screen, which would not be possible if only using one screen. If individual differences in responding to adult joint attention bids are not part of the research question, a single screen could suffice.
To further disentangle how EEG power varies by social context, infant EEG could be parsed within the joint attention and social engagement conditions based on whether the infant was attending to the experimenter or the computer screens. In addition, infant EEG could be analyzed when the infant was engaging in the condition as intended, such as only including EEG data from the social engagement condition when the infant was looking at the experimenter.
While parents were mostly compliant with the instructions to not socially interact with their infant, researchers may be concerned with parent interference during EEG recording. A modification would be for the parent to wear headphones and/or a visor so that they would not know what was happening during EEG recording. Further, as the infant was sitting on their parent&#39;s lap, the infant could be affected by the parent&#39;s body language. The infant could sit in a high chair, instead of the parent&#39;s lap, however this may lower the amount of time the infant can tolerate the EEG recording. Another option would be to use an event marker to mark in the EEG data when the parent engaged with the infant and not include this data. However, it is notable that despite the potential for parent interaction, there are significant condition differences in the representative data. Lastly, in the presented protocol, trials and blocks for coding were marked in the video post-hoc, based on the auditory tones signifying block and trial onsets. An alternative would be to synchronize the video to the EEG and mark transitions during EEG recording.
Recording EEG with infants is challenging and a limitation of this protocol is that not all infants will have useable EEG data in each condition. In this sample, 73 out of 85 infants (85.88%) of whom EEG was successfully recorded had useable data for at least one condition. To maximize the potential of useable EEG data, blocks are frequently alternated to maintain infant interest. However, it can be a challenge for infants to maintain interest for the entire protocol (20 min) and infants were fussier during the conditions where the experimenter was behind the curtain (nonsocial and language-only conditions). Of the 73 infants with useable EEG data, 78.1% (57 infants) had useable EEG in the nonsocial condition and 71.20% (52 infants) had data for the language-only condition. In contrast, 91.80% (67 infants) of infants had useable data in the joint attention condition and 87.85% (63 infants) had useable data in the social engagement condition. Finally, it is possible that infant affect could vary across blocks. To address this, infant affect could be coded and compared across conditions. An overall limitation of EEG research is that it is difficult to know exactly where the EEG activity recorded from the scalp is generated from in the cortex. However, it is noteworthy that the reported pattern of regional differences in EEG activity across conditions is consistent with adult fMRI research 24,27,30,12.
The primary significance of the reported EEG paradigm is the inclusion of controlled social and nonsocial conditions to systematically examine functional neural activation during social interactions. Conditions were designed to tease apart the effects of different elements of social interaction &#8212; such as the presence versus absence of language and face-to-face interaction &#8212; to understand the contributions of different social inputs in patterns of infant EEG power. The conditions were validated by coding infant looking behavior to ensure infants socially engaged as intended. Many infant EEG studies use &#34;resting state&#34; or baseline recording conditions that include both social and nonsocial elements 5,8,9. This paradigm demonstrates significant differences in infant EEG power between the social and nonsocial conditions, suggesting the relevance of this paradigm for assessing the development of social engagement in infancy. Further, it demonstrates the importance of using clearly social or nonsocial conditions during EEG recording to maximize consistency across infants, as there could be variability in what infants are attending to if both social and nonsocial stimuli are present during recording.
This paradigm and results demonstrate how context affects functional neural activation, assessed with EEG power. Future studies can leverage this technique to examine functional neural development taking into account the role of recording context. This includes using clearly social or nonsocial conditions as well as using multiple contexts to have a more comprehensive and thorough understanding of functional neural activation. In addition, future research should build on the results from this paradigm by using other measures such as EEG coherence or cross frequency coupling to further examine the differential patterns of brain activity associated with social input. Further, different domains of infant development are likely linked. Thus, this paradigm assessing the neural bases of social interactions could be used with other EEG paradigms tapping cognitive and motor development 31. Assessing infant EEG across these multiple domains as well as using multiple neural measures, would provide a broader picture of infant development and further an understanding of how these domains are related in the brain. In addition, pairing EEG with other neural techniques such as fMRI would help to better understand how patterns of cortical activity relate to underlying brain regions.
This paradigm took a first step in teasing apart factors that might underlie differences between the joint attention and nonsocial conditions including language input and face-to-face interaction. However, joint attention is complex and multi-faceted. It includes components such as gaze following, alternating gaze, and pointing. Future research could break down these components into different conditions, such as having a pointing-only condition and a condition of the experimenter only alternating gaze, to further parse how the different components of joint attention relate to infant EEG. Further, assessing how individual differences such as infant age and socioeconomic status relate to patterns of infant EEG power and coherence during each condition of this paradigm is another important future direction. It could be, for example, that EEG recorded during social versus nonsocial contexts has differing sensitivity to environmental factors such as poverty or culture. Thus, examining EEG across several controlled recording contexts may allow for a more nuanced picture of environmental influences on infant functional neural activation.
In the reported paradigm, the experimenter socially engaged with the infant. Having the infant socially interact with their caregiver during EEG recording would allow for examination of how individual differences in the interaction quality of parent and infant relate to patterns of EEG power. In addition, clinical diagnoses such as Autism Spectrum Disorder (ASD) are typically associated with impairments in social interactions. Using this paradigm with clinical populations at high risk for social difficulties would further an understanding of the neurobiological underpinnings of certain diagnoses, such as ASD. Moreover, many studies use baselines that are not clearly social or nonsocial, which would also be especially relevant when comparing the EEG of typically developing individuals to those with ASD. It is possible that differences in EEG between these groups could in part be a function of differences in where the groups are looking during the baseline (e.g., at the experimenter or at an object). Lastly, the concept and design behind the reported paradigm could be applied to other states beyond social inputs. In this paradigm, the nonsocial and joint attention conditions differed in three ways: the joint attention condition had language-input, face-to-face interaction, and the presence of joint attention. Additional conditions were included to tease apart which social inputs drove the difference between the joint attention and nonsocial conditions. This within-subjects design of using conditions to separate out different environmental contributions could be applied in other domains.

Social interactions are crucial for infant neural development 1,2. Although recent research has begun to focus on the development of the social brain 3,4, the neural processes involved in social engagement are not well understood. The goal of the reported method was to assess how infant electroencephalography (EEG) power, a measure of voltage released from neuronal communication, varies across controlled social and nonsocial contexts. This method allows for assessment of how specific aspects of social input differentially relate to neural activation and has implications for future studies to consider the role of recording context when assessing functional neural activation.
EEG is a well-suited method to measure infant brain activity, as it is noninvasive and robust to infant movement. A cap composed of electrodes is placed on the infant&#39;s head to record electrical activity from the cerebral cortex released during neuronal communication. EEG power is a measure of voltage at each electrode site over a period of time. EEG is a functional measure of neural activity and thus reflects in part the immediate context under which EEG is recorded. Due to its functional nature, EEG power has the potential to be compared across contexts using a within-subjects design and thus to index context-specific activation. Therefore, EEG can be used to assess both the neural underpinnings of social interactions specifically and of context-specific activation more generally. However, this potential has not been fully realized as infant EEG is often recorded during only one condition.
Many studies have recorded infant EEG power during a &#34;resting state&#34; or baseline, which does not always clearly differentiate between social and nonsocial input. In some cases, EEG is recorded as infants watch an experimenter spin a bingo wheel 5,6,7, watch an experimenter blow bubbles 8 or watch an experimenter shake a rattle 9,10. However, infants can attend to either the experimenter or the object, and infant characteristics could influence how they direct their attention. Thus, for some infants the baseline could be social if they are attending to the experimenter and for other infants the baseline could be nonsocial if they attend primarily to the object. As EEG reflects the recording context, observed individual differences in baseline EEG that researchers might interpret as stable or developmentally meaningful could simply be due to differences in what the infants were attending to at the time of recording. Indeed, one study recorded EEG while infants watched a woman singing while holding an object 11. Infant EEG power varied depending on whether the infant paid attention to the woman or the object. This demonstrates both the functional nature of infant EEG power to assess the neural bases of social interaction and also the methodological importance of using controlled conditions during EEG recording.
Social interaction is complex and multi-faceted. Therefore, if EEG was recorded during a naturalistic interaction, it could be difficult to tease apart the neural processing of different aspects of the interaction (e.g., hearing language, interacting face-to-face, or engaging in joint attention). A strategy to address this issue involves including different conditions that each involve a certain aspect of social interaction. Thus, this paradigm is designed to systematically compare how EEG power varies according to the specific type of social input.
The reported within-subjects paradigm involves recording infant EEG during 4 conditions. The conditions were designed both to examine the functional nature of infant EEG power &#8212; how it varies depending on recording context &#8212; and to assess the roles of specific types of social inputs. First, a nonsocial condition was included where the infant saw objects on two computer screens. By presenting objects on computer screens instead of having an experimenter manipulate an object, this condition is clearly nonsocial and involves no form of social input. Next, a joint attention condition was included where the experimenter directed the infant&#39;s attention to pictures and talked about the pictures. The joint attention condition thus involves three types of social input: face-to-face interaction, language input, and the added component of joint attention. Therefore, the nonsocial and joint attention conditions differ on three dimensions (face-to-face interaction, language input, and the presence of joint attention). Thus any differences in EEG power between the nonsocial and joint attention conditions could be attributable to any of these three social inputs. Therefore, 2 additional conditions were included to tease apart which aspect of social input explained any observed differences in neural activity between the nonsocial and joint attention conditions. To assess the effect of language, a language-only condition was included where the infant could hear the experimenter comment on the pictures on the computers, but could not see the experimenter. Thus, if EEG power was similar during the joint attention and language-only conditions compared to the nonsocial condition, this effect could be attributed to language. Lastly, to assess the effect of face-to-face interaction, a social engagement condition was included where the experimenter was face-to-face with the infant and contingently engaged with the infant. If EEG power was similar during the joint attention and social engagement conditions compared to the nonsocial condition, the difference between the joint attention and nonsocial conditions could be attributed to face-to-face interaction. If the difference between the joint attention and nonsocial conditions was not explained by the language-only and social engagement conditions, this would suggest that the presence of joint attention specifically was explaining differences in EEG power. This paradigm was piloted with 12-month old infants, as this is an age when the capacity for joint attention is well established12. In addition, joint attention during this time is particularly important for language development in the 2nd year of life 13,14, so neural activation in this context was of particular interest at this age.
The paradigm is designed to maintain infants&#39; interest while also ensuring that the conditions are standardized and only differ in the type of social input. Each of the four conditions is repeated once for a total of eight blocks, which alternate between experimenter being present (joint attention and social engagement conditions) or absent (nonsocial and language-only conditions). To maintain consistency, photographs of objects are presented in all conditions and the same utterances are used across blocks. During each block, 10 photographs of nonsocial objects appear sequentially on computer screens. There are 10 categories of objects (e.g., flower, glove) and four colors of each object. Thus, the same 10 categories of objects are presented in each block with the color of the objects varying across blocks. The stimuli were selected to be interesting for the infants. During the joint-attention and language-only conditions, the experimenter makes a scripted utterance as each object appears on the screen. There are 10 specific utterances (with specified directions to point to the left or right computer screen in the joint attention condition). Utterances are the same for the joint attention and language-only conditions but are said in a variable order to maintain infant interest and to prevent associating particular categories of object with particular utterances. The order of utterances is the same for the first joint attention block and first language-only block. The order then changes for the second joint attention and language-only blocks. Lastly, the direction of pointing varies for each joint attention block and is pseudo-randomized so that infants cannot anticipate the direction.

<table><tbody><tr><td>EEG Amplifier</td><td>EGI</td><td>N/A</td><td>We used a net amps 300 system. Contact EGI for more information or to purchase. https://www.egi.com/</td></tr><tr><td>EEG Sensor Nets</td><td>EGI</td><td>N/A</td><td>We used HDGSN 130 nets with 128 channels in pediatric sizes. Contact EGI for more information or to purchase. https://www.egi.com/clinical-division/geodesic-sensor-nets</td></tr><tr><td>EEG Recording Software</td><td>Netstation</td><td>N/A</td><td>Contact EGI for more information or to purchase. https://www.egi.com/clinical-division/net-station</td></tr><tr><td>EEG Recording Computer</td><td>Apple</td><td>N/A</td><td>An apple computer is required to run the Netstation software. The operating system just has to match the version of Netstation used.</td></tr><tr><td>Stimulus Presentation Computer</td><td>Dell</td><td>N/A</td><td>E-Prime 2.0 is compatible with PCs running Microsoft Windows&lt;br/&gt; XP SP3, Vista SP1, 7 SP1, 8/8.1 and 10</td></tr><tr><td>Stimulus Presentation Software - E-Prime 2.0 Professional Edition</td><td>Psychology Software Tools, Inc.</td><td>http://www.psychology-software-tools.mybigcommerce.com/e-prime-2-0-professional/</td><td></td></tr><tr><td>Stimulus Presentation Monitors</td><td>Dell</td><td>N/A</td><td>LCD monitors are appropriate.</td></tr><tr><td>Potassium Chloride</td><td>Sigma-Aldrich</td><td>http://www.sigmaaldrich.com/catalog/product/sigma/p9541?lang=en&amp;amp;region=US</td><td></td></tr><tr><td>Pipettes</td><td>Karter Scientific Labware Manufacturing Co.</td><td>http://www.kartersci.com/7ml_&lt;br /&gt;Volume_3ml_Graduated_&lt;br /&gt;Transfer_Pipette_Karter_&lt;br /&gt;p/206h2.htm</td><td></td></tr><tr><td>Disinfectant-Control 3 Disinfectent Germicide</td><td>Maril Products Inc</td><td>https://www.amazon.com/Control-Disinfectant-Germicide-Cntrl3-Concntr/dp/B007AZ37VC</td><td></td></tr><tr><td>EEG Processing Software</td><td>MATLAB</td><td>https://www.mathworks.com/products/matlab/</td><td></td></tr><tr><td>Data Analysis Software</td><td>SPSS</td><td>https://www.ibm.com/marketplace/cloud/statistical-analysis-and-reporting/purchase/us/en-us#product-header-top</td><td></td></tr><tr><td>Coding Software - The Observer XT</td><td>Noldus</td><td>http://www.noldus.com/</td><td></td></tr><tr><td colspan="4">&lt;strong&gt;General Note:&lt;/strong&gt; This equipment list includes what was used in the presented study, however other systems and products with the same capabilities are also appropriate.</td></tr></tbody></table>

a within-subjects experimental protocol to assess the effects of social input on infant eeg

Despite the importance of social interactions for infant brain development, little research has assessed functional neural activation while infants socially interact. Electroencephalography (EEG) power is an advantageous technique to assess infant functional neural activation. However, many studies record infant EEG only during one baseline condition. This protocol describes a paradigm that is designed to comprehensively assess infant EEG activity in both social and nonsocial contexts as well as tease apart how different types of social inputs differentially relate to infant EEG. The within-subjects paradigm includes four controlled conditions. In the nonsocial condition, infants view objects on computer screens. The joint attention condition involves an experimenter directing the infant's attention to pictures. The joint attention condition includes three types of social input: language, face-to-face interaction, and the presence of joint attention. Differences in infant EEG between the nonsocial and joint attention conditions could be due to any of these three types of input. Therefore, two additional conditions (one with language input while the experimenter is hidden behind a screen and one with face-to-face interaction) were included to assess the driving contextual factors in patterns of infant neural activation. Representative results demonstrate that infant EEG power varied by condition, both overall and differentially by brain region, supporting the functional nature of infant EEG power. This technique is advantageous in that it includes conditions that are clearly social or nonsocial and allows for examination of how specific types of social input relate to EEG power. This paradigm can be used to assess how individual differences in age, affect, socioeconomic status, and parent-infant interaction quality relate to the development of the social brain. Based on the demonstrated functional nature of infant EEG power, future studies should consider the role of EEG recording context and design conditions that are clearly social or nonsocial.

Infant Looking Behavior
Representative results are from 73 x 12-month old infants 12. Conditions were effective in changing infants&#39; looking behavior 16. In the social engagement condition, infants spent the majority of the time looking at the experimenter, as intended (on average, 60.06% of the time during the social engagement condition). Further, every infant looked at the experimenter more than 50% of the time. In the joint attention condition, infants accurately followed the experimenter&#39;s gaze and pointing: infants spent 2.88 times more looking at the correct screen where the experimenter had pointed compared to the incorrect screen. Infants also spent the majority of time engaging in joint attention, defined as the amount of time both looking at the experimenter and the correct screen (on average 67.93%; for more details, see original article 16). The paradigm was also effective in maintaining infant interest among infants of varying temperaments. Specifically, there were no relations between infant temperament as assessed with a parent report measure 17 and the amount of useable EEG data for each condition. This demonstrates that the paradigm is not biased to yield different amounts of useable EEG data depending on individual differences in temperament.
EEG Data Analysis Strategy
Repeated measures analyses of variance (ANOVAs) with condition and region as repeated measures and post-hoc comparisons with Bonferroni corrections were used in the present study. However, mixed modeling is also appropriate. In the initial model, the joint attention and nonsocial conditions were included as they differ on several dimensions: joint attention includes language, face-to-face interaction, and the presence of joint attention while the nonsocial condition has none of these inputs. Separate models were used for each frequency band. Whenever condition main effects or interactions with condition were observed in this initial model, the model was repeated two times: once adding the language-only condition and a second time adding the social engagement condition. This is to determine which dimensions of social input explain the difference in EEG power between the joint attention and nonsocial conditions. Including the language-only condition in the model is to assess whether language input explains the difference in EEG power between the joint attention and nonsocial conditions. If EEG power in both the language-only and joint attention conditions differs from the nonsocial condition, this suggests that the difference between the joint attention and nonsocial conditions is partially explained by the neural processing of language input. Including the social engagement condition in the model is to examine whether face-to-face interaction explains the difference in EEG power between the joint attention and nonsocial conditions. If EEG power in both the social engagement and joint attention conditions differs from the nonsocial condition, this suggests that face-to-face interaction explain the difference between the joint attention and nonsocial conditions.
EEG Power
Infant EEG power (both overall and within regions) varied by condition in the expected pattern 16, validating the presented paradigm. Infant EEG power was assessed in the 4 - 6 Hz and 6 - 9 Hz frequency bands, which are widely used in infant research 6,18,19,20. In infants, these frequency bands are thought to reflect slow wave brain activity, so lower power in these frequency bands is thought to index greater neural activation 6,18,19,21,22. Infant 4 - 6 Hz and 6 - 9 Hz power was assessed in frontal, temporal, and parietal regions, based on the proposed involvement of these regions for social interaction 6,23,24,25,26,27. The amount of useable data varied by condition. On average, infants had 78.08 s of useable data in the nonsocial condition; 82.60 s of useable data in the language-only condition; 125.75 s of useable data in the joint attention condition; and 118.36 s of useable data in the social engagement condition. The amount of useable data in each condition was unrelated to infant EEG power.
Results were similar for each frequency band 16. Joint attention and the nonsocial conditions were included in the initial model. Power was lower in the joint attention condition compared to the nonsocial condition both overall and within each region. Therefore, the language-only and social engagement conditions were added to the model to tease apart whether language-input and face-to-face interaction were contributing to the power difference between the joint attention and nonsocial conditions (see Figures 2 &#38;&#160;3). The frontal regions are involved in orienting and shifting attention 24,27 and power recorded from frontal scalp regions was lowest, indexing greater activation, in the joint attention condition compared to the other conditions. This is consistent with the demands in the joint attention condition (for results in each region and condition, see Figures 4 &#38; 5) and demonstrates that language-input and face-to-face interaction do not explain the difference in frontal scalp power between the joint attention and nonsocial conditions. The temporal regions play a role in facial processing 26 and power recorded from temporal scalp regions was lowest, indexing greater activation, in both of the conditions with face-to-face social interaction (joint attention and social engagement) compared with the nonsocial condition. This demonstrates that the difference in neural processing between the joint attention and nonsocial conditions in the temporal scalp region can be attributed to face-to-face interaction. The parietal regions are involved in spatial orientation and gaze following 6,23,25,26, demands which were unique to the joint attention condition as the infant had to respond to the experimenter&#39;s bids for attention. Accordingly, power recorded from parietal scalp regions was lower, indexing greater neural activation, in the joint attention condition compared to all other conditions. Thus language-input and face-to-face interaction do not explain the difference in parietal scalp power between the joint attention and nonsocial conditions. The power values (transformed using the natural log) ranged from 7.21 - 7.71 in 4 - 6 Hz and 6.32 - 6.71 in 6 - 9 Hz. These are consistent with past research that used the same EEG recording system and comparable processing parameters 28. However, EEG power values may vary based on factors such as the EEG system used and choices of reference and artifact parameters.
<img alt="Figure 2" src="/files/ftp_upload/55596/55596fig2.jpg" /> 
Figure 2. Mean 4 - 6 Hz Power in Each Condition. In this sample of 12-month-old infants, 4 - 6 Hz power was lower in the joint attention condition, indexing greater neural activation, compared to all other conditions. This demonstrates that the presence of language-input and face-to-face interaction do not fully explain the difference in power between the joint attention and nonsocial conditions. The error bars represent standard errors. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55596/55596fig2large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 3" src="/files/ftp_upload/55596/55596fig3.jpg" /> 
Figure 3. Mean 6 - 9 Hz Power in Each Condition. In this sample of 12-month-old infants, 6 - 9 Hz power was lower in the joint attention condition, indexing greater neural activation, compared to the nonsocial and language-only conditions. There was no difference in 6 - 9 Hz power between the joint attention and social engagement conditions. The error bars represent standard errors. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55596/55596fig3large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 4" src="/files/ftp_upload/55596/55596fig4.jpg" /> 
Figure 4. Mean 4 - 6 Hz Power in Each Condition and Region. In this sample of 12-month-old infants, 4 - 6 Hz power in the frontal and parietal regions was lower in the joint attention condition, indexing greater neural activation, compared with the other conditions. Temporal 4 - 6 Hz power was lower in both the joint attention and social engagement conditions compared with the nonsocial condition. The error bars represent standard errors. This figure has been modified from 16. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55596/55596fig4large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
<img alt="Figure 5" src="/files/ftp_upload/55596/55596fig5.jpg" /> 
Figure 5. Mean 6 - 9 Hz Power in Each Condition and Region. In this sample of 12-month-old infants, 6 - 9 Hz power in the frontal region was lower in the joint attention condition, indexing greater neural activation, compared with the language-only and nonsocial conditions. In the temporal region, 6 - 9 Hz power was lower in both the joint attention and social engagement conditions compared with the nonsocial condition. The error bars represent standard errors. This figure has been modified from 16. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55596/55596fig5large.jpg" target="_blank">Please click here to view a larger version of this figure.</a>
Supplemental Figures. Stimuli Used in the Paradigm. The supplemental file &#39;List of photos in each block&#39; includes the names of stimuli files that accompany each block in the paradigm. The stimuli files are also included. <a href="https://cloudflare-jove-com.remotexs.ntu.edu.sg/files/ftp_upload/55596/Supplemental_Figures.zip" target="_blank">Please click here to download these figures.</a>

Watch this Scientific Journal Video about A Within-subjects Experimental Protocol to Assess the Effects of Social Input on Infant EEG at JoVE.com

A Within-subjects Experimental Protocol to Assess the Effects of Social Input on Infant EEG

This novel protocol is designed to assess the neural bases of social interaction in infants. The paradigm is designed to tease apart how various social inputs such as language, joint attention, and face-to-face interaction relate to infant neural activation. Infant EEG power is recorded during both social and nonsocial conditions.

Despite the importance of social interactions for infant brain development, little research has assessed functional neural activation while infants ...

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7.7K Views.  Boston University. This novel protocol is designed to assess the neural bases of social interaction in infants. The paradigm is designed to tease apart how various social inputs such as language, joint attention, and face-to-face interaction relate to infant neural activation. Infant EEG power is recorded during both social and nonsocial conditions.

Video: A Within-subjects Experimental Protocol to Assess the Effects of Social Input on Infant EEG

Cortical Source Analysis of High-Density EEG Recordings in Children

EEG is traditionally described as a neuroimaging technique with high temporal and low spatial resolution. Recent advances in biophysical modelling and signal processing make it possible to exploit information from other imaging modalities like structural MRI that provide high spatial resolution to overcome this constraint1. This is especially useful for investigations that require high resolution in the temporal as well as spatial domain. In addition, due to the easy application and low cost of EEG recordings, EEG is often the method of choice when working with populations, such as young children, that do not tolerate functional MRI scans well. However, in order to investigate which neural substrates are involved, anatomical information from structural MRI is still needed. Most EEG analysis packages work with standard head models that are based on adult anatomy. The accuracy of these models when used for children is limited2, because the composition and spatial configuration of head tissues changes dramatically over development3.&#160;
In the present paper, we provide an overview of our recent work in utilizing head models based on individual structural MRI scans or age specific head models to reconstruct the cortical generators of high density EEG. This article describes how&#160;EEG recordings are acquired, processed, and analyzed with pediatric populations at the London Baby Lab, including laboratory setup, task design, EEG preprocessing, MRI processing, and EEG channel level and source analysis.&#160;

In recent years, there has been increasing interest in estimating the cortical sources of scalp measured electrical activity for cognitive neuroscience experiments. This article describes how high density EEG is acquired and how recordings are processed for cortical source estimation in children from the age of 2 years at the London Baby Lab.

EEG is traditionally described as a neuroimaging technique with high temporal and low spatial resolution. Recent advances in biophysical modelling and ...

Infant Auditory Processing and Event-related Brain Oscillations

Rapid auditory processing and acoustic change detection abilities play a critical role in allowing human infants to efficiently process the fine spectral and temporal changes that are characteristic of human language. These abilities lay the foundation for effective language acquisition; allowing infants to hone in on the sounds of their native language. Invasive procedures in animals and scalp-recorded potentials from human adults suggest that simultaneous, rhythmic activity (oscillations) between and within brain regions are fundamental to sensory development; determining the resolution with which incoming stimuli are parsed. At this time, little is known about oscillatory dynamics in human infant development. However, animal neurophysiology and adult EEG data provide the basis for a strong hypothesis that rapid auditory processing in infants is mediated by oscillatory synchrony in discrete frequency bands. In order to investigate this, 128-channel, high-density EEG responses of 4-month old infants to frequency change in tone pairs, presented in two rate conditions (Rapid: 70 msec ISI and Control: 300 msec ISI) were examined. To determine the frequency band and magnitude of activity, auditory evoked response averages were first co-registered with age-appropriate brain templates. Next, the principal components of the response were identified and localized using a two-dipole model of brain activity. Single-trial analysis of oscillatory power showed a robust index of frequency change processing in bursts of Theta band (3 - 8 Hz) activity in both right and left auditory cortices, with left activation more prominent in the Rapid condition. These methods have produced data that are not only some of the first reported evoked oscillations analyses in infants, but are also, importantly, the product of a well-established method of recording and analyzing clean, meticulously collected, infant EEG and ERPs. In this article, we describe our method for infant EEG net application, recording, dynamic brain response analysis, and representative results.

High-density electroencephalography (dEEG) is being used increasingly to study brain development and plasticity in the early years of life. Here we present an application of sophisticated analysis techniques that builds on traditional EEG recording to understand the oscillatory dynamics of rapid auditory processing in the infant brain.

Rapid auditory processing and acoustic change detection abilities play a critical role in allowing human infants to efficiently process the fine spectral ...

Applying Stereotactic Injection Technique to Study Genetic Effects on Animal Behaviors

Stereotactic injection is a useful technique to deliver high titer lentiviruses to targeted brain areas in mice. Lentiviruses can either overexpress or knockdown gene expression in a relatively focused region without significant damage to the brain tissue. After recovery, the injected mouse can be tested on various behavioral tasks such as the Open Field Test (OFT) and the Forced Swim Test (FST). The OFT is designed to assess locomotion and the anxious phenotype in mice by measuring the amount of time that a mouse spends in the center of a novel open field. A more anxious mouse will spend significantly less time in the center of the novel field compared to controls. The FST assesses the anti-depressive phenotype by quantifying the amount of time that mice spend immobile when placed into a bucket of water. A mouse with an anti-depressive phenotype will spend significantly less time immobile compared to control animals. The goal of this protocol is to use the stereotactic injection of a lentivirus in conjunction with behavioral tests to assess how genetic factors modulate animal behaviors.

Stereotactic injection of lentiviruses expressing cDNAs or shRNAs can modulate gene expression in specific brain areas of mice. Here, we present a protocol to combine stereotactic injections with behavioral tasks, such as the Open Field Test (OFT) and the Forced Swim Test (FST).

Stereotactic injection is a useful technique to deliver high titer lentiviruses to targeted brain areas in mice. Lentiviruses can either overexpress or ...

The Social Dimension of Stress: Experimental Manipulations of Social Support and Social Identity in the Trier Social Stress Test

In many situations humans are influenced by the behavior of other people and their relationships with them. For example, in stressful situations supportive behavior of other people as well as positive social relationships can act as powerful resources to cope with stress. In order to study the interplay between these variables, this protocol describes two effective experimental manipulations of social relationships and supportive behavior in the laboratory. In the present article, these two manipulations are implemented in the Trier Social Stress Test (TSST)&#8212;a standard stress induction paradigm in which participants are subjected to a simulated job interview. More precisely, we propose (a) a manipulation of the relationship between different protagonists in the TSST by making a shared social identity salient and (b) a manipulation of the behavior of the TSST-selection committee, which acts either supportively or unsupportively. These two experimental manipulations are designed in a modular fashion and can be applied independently of each other but can also be combined. Moreover, these two manipulations can also be integrated into other stress protocols and into other standardized social interactions such as trust games, negotiation tasks, or other group tasks.

Previous research on the social dimension of stress has focused on two important variables: social identity and social support. This protocol introduces an effective experimental manipulation of these two social variables and describes their implementation in a standard stress induction paradigm (Trier Social Stress Test).

In many situations humans are influenced by the behavior of other people and their relationships with them. For example, in stressful situations ...

Experimental Research Examining How People Can Cope with Uncertainty Through Soft Haptic Sensations

Human beings are constantly surrounded by uncertainty and change. The question arises how people cope with such uncertainty. To date, most research has focused on the cognitive strategies people adopt to deal with uncertainty. However, especially when uncertainty is due to unpredictable societal events (e.g., economical crises, political revolutions, terrorism threats) of which one is unable to judge the impact on one&#8217;s future live, cognitive strategies (like seeking additional information) is likely to fail to combat uncertainty. Instead, the current paper discusses a method demonstrating that people might deal with uncertainty experientially through soft haptic sensations. More specifically, because touching something soft creates a feeling of comfort and security, people prefer objects with softer as compared to harder properties when feeling uncertain. Seeking for softness is a highly efficient and effective tool to deal with uncertainty as our hands are available at all times. This protocol describes a set of methods demonstrating 1) how environmental (un)certainty can be situationally activated with an experiential priming procedure, 2) that the quality of the softness experience (what type of softness and how it is experienced) matters and 3) how uncertainty can be reduced using different methods.

To date research has focused on cognitive strategies people adopt to cope with uncertainty. This research examines instead an experiential way of dealing with uncertainty and introduces a set of experimental methods showing how the experience of haptic softness can serve as a tool to deal with uncertainty.

Human beings are constantly surrounded by uncertainty and change. The question arises how people cope with such uncertainty. To date, most research has ...

A Method for Evaluating the Reinforcing Properties of Ethanol in Rats without Water Deprivation, Saccharin Fading or Extended Access Training

Operant oral self-administration methods are commonly used to study the reinforcing properties of ethanol in animals. However, the standard methods require saccharin/sucrose fading, water deprivation and/or extended training to initiate operant responding in rats. This paper describes a novel and efficient method to quickly initiate operant responding for ethanol that is convenient for experimenters and does not require water deprivation or saccharin/sucrose fading, thus eliminating the potential confound of using sweeteners in ethanol operant self-administration studies. With this method, Wistar rats typically acquire and maintain self-administration of a 20% ethanol solution in less than two weeks of training. Furthermore, blood ethanol concentrations and rewards are positively correlated for a 30 min self-administration session. Moreover, naltrexone, an FDA-approved medication for alcohol dependence that has been shown to suppress ethanol self-administration in rodents, dose-dependently decreases alcohol intake and motivation to consume alcohol for rats self-administering 20% ethanol, thus validating the use of this new method to study the reinforcing properties of alcohol in rats.

This protocol describes a novel and efficient method to quickly initiate operant responding for ethanol in rats that, contrary to standard methods, does not require water deprivation or saccharin/sucrose fading to initiate responding.

Operant oral self-administration methods are commonly used to study the reinforcing properties of ethanol in animals. However, the standard methods ...

A Novel Experimental and Analytical Approach to the Multimodal Neural Decoding of Intent During Social Interaction in Freely-behaving Human Infants

Understanding typical and atypical development remains one of the fundamental questions in developmental human neuroscience. Traditionally, experimental paradigms and analysis tools have been limited to constrained laboratory tasks and contexts due to technical limitations imposed by the available set of measuring and analysis techniques and the age of the subjects. These limitations severely limit the study of developmental neural dynamics and associated neural networks engaged in cognition, perception and action in infants performing &#8220;in action and in context&#8221;. This protocol presents a novel approach to study infants and young children as they freely organize their own behavior, and its consequences in a complex, partly unpredictable and highly dynamic environment. The proposed methodology integrates synchronized high-density active scalp electroencephalography (EEG), inertial measurement units (IMUs), video recording and behavioral analysis to capture brain activity and movement non-invasively in freely-behaving infants. This setup allows for the study of neural network dynamics in the developing brain, in action and context, as these networks are recruited during goal-oriented, exploration and social interaction tasks.

This protocol presents a novel methodology for the neural decoding of intent from freely-behaving infants during unscripted social interaction with an actor. Neural activity is acquired using non-invasive high-density active scalp electroencephalography (EEG). Kinematic data is collected with inertial measurement units and supplemented with synchronized video recording.

Understanding typical and atypical development remains one of the fundamental questions in developmental human neuroscience. Traditionally, experimental ...

Investigating Social Cognition in Infants and Adults Using Dense Array Electroencephalography (dEEG)

Dense array electroencephalography (dEEG), which provides a non-invasive window for measuring brain activity and a temporal resolution unsurpassed by any other current brain imaging technology1,2, is being used increasingly in the study of social cognitive functioning in infants and adults. While dEEG is enabling researchers to examine brain activity patterns with unprecedented levels of sensitivity, conventional EEG recording systems continue to face certain limitations, including 1) poor spatial resolution and source localization3,4,2) the physical discomfort for test subjects of enduring the individual application of numerous electrodes to the surface of the scalp, and 3) the complexity for researchers of learning to use multiple software packages to collect and process data. Here we present an overview of an established methodology that represents a significant improvement on conventional methodologies for studying EEG in infants and adults. Although several analytical software techniques can be used to establish indirect indices of source localization to improve the spatial resolution of dEEG, the HydroCel Geodesic Sensor Net (HCGSN) by Electrical Geodesics, Inc. (EGI), a dense sensory array that maintains equal distances among adjacent recording electrodes on all surfaces of the scalp, further enhances spatial resolution4,5,6 compared to standard dEEG systems. The sponge-based HCGSN can be applied rapidly and without scalp abrasion, making it ideal for use with adults7,8, children9,10,11, and infants12, in both research and clinical4,5,6,13,14,15 settings. This feature allows for considerable cost and time savings by decreasing the average net application time compared to other dEEG systems. Moreover, the HCGSN includes unified, seamless software applications for all phases of data, greatly simplifying the collection, processing, and analysis of dEEG data.
The HCGSN features a low-profile electrode pedestal, which, when filled with electrolyte solution, creates a sealed microenvironment and an electrode-scalp interface. In all Geodesic dEEG systems, EEG sensors detect changes in voltage originating from the participant's scalp, along with a small amount of electrical noise originating from the room environment. Electrical signals from all sensors of the Geodesic sensor net are received simultaneously by the amplifier, where they are automatically processed, packaged, and sent to the data-acquisition computer (DAC). Once received by the DAC, scalp electrical activity can be isolated from artifacts for analysis using the filtering and artifact detection tools included in the EGI software. Typically, the HCGSN can be used continuously for only up to two hours because the electrolyte solution dries out over time, gradually decreasing the quality of the scalp-electrode interface.
In the Parent-Infant Research Lab at the University of Toronto, we are using dEEG to study social cognitive processes including memory, emotion, goals, intentionality, anticipation, and executive functioning in both adult and infant participants.

Investigating Social Cognition in Infants and Adults Using Dense Array Electroencephalography dEEG

Dense array electroencephalography is being used increasingly to study social cognitive functions in infants and adults. Here we present an established methodology that represents a significant improvement on conventional methodologies for studying EEG in infants and adults.

Dense array electroencephalography (dEEG), which provides a non-invasive window for measuring brain activity and a temporal resolution unsurpassed by any ...

Neuroscience

A Novel Approach to Assess Motor Outcome of Deep Brain Stimulation Effects in the Hemiparkinsonian Rat: Staircase and Cylinder Test

Deep brain stimulation of the subthalamic nucleus is an effective treatment option for Parkinson&#39;s disease. In our lab we established a protocol to screen different neurostimulation patterns in hemiparkinsonian (unilateral lesioned) rats. It consists of creating a unilateral Parkinson&#39;s lesion by injecting 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle, implanting chronic stimulation electrodes into the subthalamic nucleus and evaluating motor outcomes at the end of 24 hr periods of cable-bound external neurostimulation. The stimulation was conducted with constant current stimulation. The amplitude was set 20% below the individual threshold for side effects. The motor outcome evaluation was done by the assessment of spontaneous paw use in the cylinder test according to Shallert and by the assessment of skilled reaching in the staircase test according to Montoya. This protocol describes in detail the training in the staircase box, the cylinder test, as well as the use of both in hemiparkinsonian rats. The use of both tests is necessary, because the staircase test seems to be more sensitive for fine motor skill impairment and exhibits greater sensitivity to change during neurostimulation. The combination of the unilateral Parkinson model and the two behavioral tests allows the assessment of different stimulation parameters in a standardized way.

Deep brain stimulation (DBS) is an effective treatment option for Parkinson's disease. We established a study design to screen novel stimulation paradigms in rats. The protocol describes the use of the staircase test and cylinder test for motor outcome assessment in DBS treated hemiparkinsonian rats.

Deep brain stimulation of the subthalamic nucleus is an effective treatment option for Parkinson&#39;s disease. In our lab we established a protocol to ...

Real-Life EEG and ECG Synchronization in Infant-Caregiver Interactions

Home-Based EEG Hyperscanning for Infant-Caregiver Social Interactions

Prior hyperscanning studies that record the brain activities of caregivers and children concurrently have primarily been conducted within the confines of the laboratory, thus limiting the generalizability of results to real-life settings. Here, a comprehensive protocol for capturing synchronized electroencephalography (EEG), electrocardiography (ECG), and behavioral recordings from infant-caregiver dyads during various interactive tasks at home is proposed. This protocol demonstrates how to synchronize the different data streams and report EEG data retention rates and quality checks. Additionally, critical issues and possible solutions with respect to the experimental setup, tasks, and data collection in home settings are discussed. The protocol is not limited to infant-caregiver dyads but can be applied to various dyadic constellations. Overall, we demonstrate the flexibility of EEG hyperscanning setups, which allow experiments to be conducted outside of the laboratory to capture participants' brain activities in more ecologically valid environmental settings. Yet, movement and other types of artifacts still constrain the experimental tasks that can be performed in the home setting.

Author Spotlight: Capturing Infant-Caregiver Interactions Through Synchronized Multimodal Data Collection

This protocol describes how synchronized electroencephalography, electrocardiography, and behavioral recordings were captured from infant-caregiver dyads in a home setting.

Prior hyperscanning studies that record the brain activities of caregivers and children concurrently have primarily been conducted within the confines of ...