Supported by KIST Grant (2E21510), National Honor Scientist program of the Ministry of Education, and the Original Technology Research Program for Brain Science through the National Research Foundation of Korea funded by the Ministry of Education, Science and Technology (2010-0018944).

1. Summary
C57BL/6J - 129S4/SvJae hybrid mice (12~15 weeks old) are anesthetized with ketamine (120 mg/kg i.p.) and xylazine (6 mg/kg, i.p.) cocktail. Tail or toe pinching precedes the surgery to inspect the depth of anesthesia. The mouse is fixed by stereotaxic apparatus (David Kopf Instruments, Model 902, Calif, USA). The scalp is incised on the midline about 25 mm to expose the skull under the lidocaine treatment for pain reduction. Any debris on the skull is wiped off by saline-soaked cotton tips to enhance the adherence of the electrode to the skull. The bregma and lambda points are marked and set in the same horizontal plane. The polyimide based microelectrode array (PBM-array) is positioned so that its vertical midline meets the midline of the skull. The bregma point should be located at the middle of the 5th layer of the anterior of PBM-array. Two or three microscrews are used at the null space in the edge of skull to help secure the position of the electrode with dental cement. For propping the PBM-array connector, we position a strut on the middle of the head, and cover it with dental cement. After curing, the incised skin is sutured, and at least 5 days are given for recovery. During recovery, the mice are housed in individual cages with free access to food and water. After recovery, EEG recording is performed. Animal care, surgical, and recording procedures were in accordance with the guidelines for the Institutional Animal Care and Use Committee, following Act 1992 of the Korea Lab Animal Care Regulations and associated guidelines. The PBM-arrays in this manuscript were fabricated as described by Choi. et. al.1 Please contact the authors to use the same PBM-array in the video.
2. 	Procedure
<ol>
<li>Prepare the sterilized surgical instruments and stereotaxic apparatus.</li>
<li>Anesthetize the mouse with anesthesia (e.g., ketamine/xylazine with a dose of 120 and 60 mg/kg i.p., repectively). Tail or toe pinching precedes the surgery to inspect the depth of anesthesia.</li>
<li>Mount the mouse onto the stereotaxic apparatus by placing ear bars into the mouse's ear canal and tightening it in place. The eyes can be covered with biocompatible jelly (e.g., petroleum jelly) to keep the eyes from drying up by the surgery light. After moisturizing the mouse's head with 70% ethanol, shave the fur off its head.</li>
<li>Incise the head about 25 mm with a scalp. It is recommendable to apply a little amount of 2% lidocaine hydrochloride under the scalp. Pinch the skin with micro clamps (Fine Science Tools (USA), Inc., 18052-03, Calif, USA) to keep the incision wide open.</li>
<li>Wipe any remaining tissue debris on the skull with saline-soaked cotton swabs enhance adherence of the PBM-array to the skull. Using peroxide for removing the residue of the membrane is also effective.</li>
<li>Find the bregma and lambda points on the skull, and mark them with an oil-based marker pen. Place the PBM-array so that its vertical midline meets the midline of the skull as shown in Figure 1. Position the bregma at the middle of the 5th layer of the anterior of PBM-array with one drop of tap water. Swab the film electrode from the medial to lateral carefully for better adherence. In order to help the film electrode stick tighter to the skull, the film electrode should be completely dry on the skull. The film electrode remains to be fixed on the skull by van der Waals force. When re-positioning the electrode, another drop of tap water is necessary to prevent the electrode from being torn. 
<img src="/files/ftp_upload/2562/2562fig1.jpg" alt="Figure 1" /> 
Figure 1. (Left) A PBM-array on the mouse skull. The anterio-posterior axis of PBM-array matches the line between bregma (BP) and lambda points (LP). (Right) The putative electrode positions on the mouse brain surface. The anatomy of the mouse are segmented from the 3-D MRI digital atlas database of an adult C57BL/6J mouse brain produced in Brookhaven national lab and the electrode locations are marked according to the stereotaxic measurement. Ground (G) and reference (Ref) electrodes are marked in the right figure.</li>
<li>Mark at least three positions on the open area of the skull, and then make holes in those locations using a dental drill for the positioning of the supporting microscrews. These microscrews have a role of stanchion and mechanically support the dental cement on the skull. Extra caution is needed during drilling. Since the mouse skull consists of thin layers, hemorrhage can occur easily during drilling. When bleeding happens, stop drilling and apply small amount of hemostatic powder into the hole.</li>
<li>Apply the dental acrylic cement (Vertex-Dental, Vertex Self-Curing, The Netherlands) to cover the PBM-array, anchor screws, and the rest of the skull. Prepare the dental cement in a gluey and viscous condition.</li>
<li>Position a rigid stick as a strut on the middle of the head using strong glue (for example, Loctite, Henkel Loctite Corp, Dublin, Ireland). Put double-sided adhesive tape on the back of the connector plane. Manipulate the PBM-array connector position to connect with the tip of the strut. The vertical distance between the skull and the connector should be more than 5 mm. Stick the connector plane and the tip of the stick using strong glue for better adhesion.</li>
<li>Make sure that the dental cement is completely cured. Then apply the dental acrylic cement over the skull and the backside of the connector plane to secure the connector to the skull.</li>
<li>Remove the micro clamps. Suture incised skin with sterilized stitching fiber. Remove the mouse from the apparatus. You may apply extra dental acrylic cement to shield the exposed skull. Apply an antibiotic (fucidin ointment, Dong Wha Pharmacy, South Korea) around the cement and sutured skin.</li>
<li>Place the mouse in a sterilized cage until it recovers its original body weight (approximately 5 to 7 days). It is recommended not to introduce any cage mates.</li>
<li>After recovery, connect the mouse by a light-weight printed circuit board (PCB) connector to the headbox of a multichannel EEG amplifier system (Synamps2, North Carolina, USA) in its own cage. The connecting lines should be treated carefully so it does not get tangled.</li>
<li>After 1 hour of habituation, perform EEG recording. Scan 4.4. (North Carolina, USA) acquisition software was used in this experiment. A typical time trace set of mouse EEG is shown in Figure 2. It is recommended to log the video to relate the behavior of the mouse.</li>
<li>Obtained signal can be analyzed by MATLAB (MathWorks, Natick, MA, USA) to produce the topographical brain map. Sample topographies of EEG power map of mouse brain are shown in Figure 3.</li>
</ol>
3. 	Representative Results
If above surgical procedures are correctly conducted, 40 channels mouse EEG recording will be successfully performed without bad channels. Following figures show the representative raw EEG traces and topographic maps.
<img src="/files/ftp_upload/2562/2562fig2.jpg" alt="Figure 2" /> 
Figure 2. A sample trace of EEG experiencing absence seizure induced by injection &gamma;-butyrolactone (GBL, 50mg/kg, i.p.). Red bar indicates spike-wave and discharges (SWDs) during absence seizure. The horizontal and vertical axes indicate time and voltage, respectively. The number follows the channel montage defined in Figure. 1 (right).
<img src="/files/ftp_upload/2562/2562fig3.jpg" alt="Figure 3" /> 
Figure 3. The topographic maps indicate the 2-6 Hz power distribution. The value in the colorbar represents the color scale of power map. During spike-wave and discharges (SWDs) induced by &gamma;-butyrolactone (GBL, 50mg/kg, i.p.), the power in the large frontoparietal cortical regions significantly increase compared with the power before GBL injection (Baseline).

<ol>
	<li>Choi, J. H., Koch, K. P., Poppendieck, W., Lee, M., Shin, H. S. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=High+resolution+Electroencephalography+in+Freely+Moving+Mice.">High resolution Electroencephalography in Freely Moving Mice.</a> J Neurophysiol. , .</li><li>Lee, M., Shin, H. S., Choi, J. H. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Simultaneous+recording+of+brain+activity+and+functional+connectivity+in+the+mouse+brain.">Simultaneous recording of brain activity and functional connectivity in the mouse brain.</a> Conf Proc IEEE Eng Med Biol Soc. , 2934-2936 (2009).</li></ol>

No conflicts of interest declared.

Here we report surgical and recording procedures to acquire high-density EEG in freely moving mice. This method enables us to obtain functional brain maps from mouse model to study molecular mechanisms of spontaneous rhythmic1,2 or event related brain activities.
Acquisition of all the channels in the PBM-array is a necessary condition to obtain whole brain mapping, however making a secure contact for every channel is very challenging. To maintain consistent contact of the channel to the skull, the following procedures are found to be important. First of all, any tissue debris on the skull may set apart the electrode from the skull. Hence it is very important to remove all the tissue debris with sterilized cotton swabs and dry up the skull surface. Secondly, the ability of PBM-array which can stick to the skull surface is van der Waals force. It is suggested to apply a drop of tap water on the skull to build water layer before one apply PBM-array to the skull. Thirdly, the right viscosity of dental cement is very important. If it is too runny, it may build an insulating layer under the PBM-array. If it is too dense, the dental cement will easily fall apart from the skull due to its own weight. Lastly, at least three supporting microscrews should be implanted on the skull to make the dental cement tightly bound to the skull. The supporting microscrews hold up the dental cement and secure the headstage, which is essential for long-term study.
The application of PBM-array will be limited to chronic study with adult mice due to its size and weight. Based on our experience, mice heavier than 25 g are adequate to use. As further applications, through the null space between branches in our PBM-array, one may introduce secondary electrodes for recording or stimulation purpose.

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high-density eeg recordings of the freely moving mice using polyimide-based microelectrode

Electroencephalogram (EEG) indicates the averaged electrical activity of the neuronal populations on a large-scale level. It is widely utilized as a noninvasive brain monitoring tool in cognitive neuroscience as well as a diagnostic tool for epilepsy and sleep disorders in neurology. However, the underlying mechanism of EEG rhythm generation is still under the veil. Recently introduced polyimide-based microelectrode (PBM-array) for high resolution mouse EEG1 is one of the trials to answer the neurophysiological questions on EEG signals based on a rich genetic resource that the mouse model contains for the analysis of complex EEG generation process. This application of nanofabricated PBM-array to mouse skull is an efficient tool for collecting large-scale brain activity of transgenic mice and accommodates to identify the neural correlates to certain EEG rhythms in conjunction with behavior. However its ultra-thin thickness and bifurcated structure cause a trouble in handling and implantation of PBM-array. In the presented video, the preparation and surgery steps for the implantation of PBM-array on a mouse skull are described step by step. Handling and surgery tips to help researchers succeed in implantation are also provided.

Watch this Scientific Journal Video about High-density EEG Recordings of the Freely Moving Mice using Polyimide-based Microelectrode at JoVE.com

High-density EEG Recordings of the Freely Moving Mice using Polyimide-based Microelectrode

In this article, we described the surgery procedure and handling tips for implantation of ultra-thin polyimide-based microelectrode array (PBM-array) on the mouse skull for acquisition of high-density encephalography (EEG) in a mouse model.

Electroencephalogram (EEG) indicates the averaged electrical activity of the neuronal populations on a large-scale level. It is widely utilized as a ...

high-density-eeg-recordings-freely-moving-mice-using-polyimide-based

Research

JoVE Journal

Neuroscience

36.9K Views.  Korea Institute of Science and Technology (KIST). In this article, we described the surgery procedure and handling tips for implantation of ultra-thin polyimide-based microelectrode array (PBM-array) on the mouse skull for acquisition of high-density encephalography (EEG) in a mouse model.

Video: High-density EEG Recordings of the Freely Moving Mice using Polyimide-based Microelectrode

Combining Computer Game-Based Behavioural Experiments With High-Density EEG and Infrared Gaze Tracking

Experimental paradigms are valuable insofar as the timing and other parameters of their stimuli are well specified and controlled, and insofar as they yield data relevant to the cognitive processing that occurs under ecologically valid conditions. These two goals often are at odds, since well controlled stimuli often are too repetitive to sustain subjects' motivation. Studies employing electroencephalography (EEG) are often especially sensitive to this dilemma between ecological validity and experimental control: attaining sufficient signal-to-noise in physiological averages demands large numbers of repeated trials within lengthy recording sessions, limiting the subject pool to individuals with the ability and patience to perform a set task over and over again. This constraint severely limits researchers' ability to investigate younger populations as well as clinical populations associated with heightened anxiety or attentional abnormalities. Even adult, non-clinical subjects may not be able to achieve their typical levels of performance or cognitive engagement: an unmotivated subject for whom an experimental task is little more than a chore is not the same, behaviourally, cognitively, or neurally, as a subject who is intrinsically motivated and engaged with the task. A growing body of literature demonstrates that embedding experiments within video games may provide a way between the horns of this dilemma between experimental control and ecological validity. The narrative of a game provides a more realistic context in which tasks occur, enhancing their ecological validity (Chaytor &amp; Schmitter-Edgecombe, 2003). Moreover, this context provides motivation to complete tasks. In our game, subjects perform various missions to collect resources, fend off pirates, intercept communications or facilitate diplomatic relations. In so doing, they also perform an array of cognitive tasks, including a Posner attention-shifting paradigm (Posner, 1980), a go/no-go test of motor inhibition, a psychophysical motion coherence threshold task, the Embedded Figures Test (Witkin, 1950, 1954) and a theory-of-mind (Wimmer &amp; Perner, 1983) task. The game software automatically registers game stimuli and subjects' actions and responses in a log file, and sends event codes to synchronise with physiological data recorders. Thus the game can be combined with physiological measures such as EEG or fMRI, and with moment-to-moment tracking of gaze. Gaze tracking can verify subjects' compliance with behavioural tasks (e.g. fixation) and overt attention to experimental stimuli, and also physiological arousal as reflected in pupil dilation (Bradley et al., 2008). At great enough sampling frequencies, gaze tracking may also help assess covert attention as reflected in microsaccades - eye movements that are too small to foveate a new object, but are as rapid in onset and have the same relationship between angular distance and peak velocity as do saccades that traverse greater distances. The distribution of directions of microsaccades correlates with the (otherwise) covert direction of attention (Hafed &amp; Clark, 2002).

Procedures for recording high-density EEG and gaze data during computer game-based cognitive tasks are described. Using a video game to present cognitive tasks enhances ecological validity without sacrificing experimental control.

Experimental paradigms are valuable insofar as the timing and other parameters of their stimuli are well specified and controlled, and insofar as they ...

Recording Single Neurons' Action Potentials from Freely Moving Pigeons Across Three Stages of Learning

While the subject of learning has attracted immense interest from both behavioral and neural scientists, only relatively few investigators have observed single-neuron activity while animals are acquiring an operantly conditioned response, or when that response is extinguished. But even in these cases, observation periods usually encompass only a single stage of learning, i.e. acquisition or extinction, but not both (exceptions include protocols employing reversal learning; see Bingman&#160;et al.1 for an example). However, acquisition and extinction entail different learning mechanisms and are therefore expected to be accompanied by different types and/or loci of neural plasticity.
Accordingly, we developed a behavioral paradigm which institutes three stages of learning in a single behavioral session and which is well suited for the simultaneous recording of single neurons&#39; action potentials. Animals are trained on a single-interval forced choice task which requires mapping each of two possible choice responses to the presentation of different novel visual stimuli (acquisition). After having reached a predefined performance criterion, one of the two choice responses is no longer reinforced (extinction). Following a certain decrement in performance level, correct responses are reinforced again (reacquisition). By using a new set of stimuli in every session, animals can undergo the acquisition-extinction-reacquisition process repeatedly. Because all three stages of learning occur in a single behavioral session, the paradigm is ideal for the simultaneous observation of the spiking output of multiple single neurons. We use pigeons as model systems, but the task can easily be adapted to any other species capable of conditioned discrimination learning.

Learning new stimulus-response associations engages a wide range of neural processes which are ultimately reflected in changing spike output of individual neurons. Here we describe a behavioral protocol allowing for the continuous registration of single-neuron activity while animals acquire, extinguish, and reacquire a conditioned response within a single experimental session.

While the subject of learning has attracted immense interest from both behavioral and neural scientists, only relatively few investigators have observed ...

Recording EEG in Freely Moving Neonatal Rats Using a Novel Method

EEG is a useful method to detect electrical activity in the brain. Moreover, it is a widely used diagnostic tool for various neurological conditions, such as epilepsy and neurodegenerative disorders. However, it is technically difficult to obtain EEG recordings in neonates as it requires specialized handling and great care. Here, we present a novel method to record EEG in neonatal rat pups (P8-P15). We designed a simple and reliable electrode using computer pin loci; it can be easily implanted into the skull of a rat pup to record high-quality EEG signals in the normal and epileptic brain. Pups were given an intraperitoneal (i.p.) injection of the neurotoxin kainic acid (KA) to induce epileptic seizures. The surgical implantation performed in this procedure is less expensive than other EEG procedures for neonates. This method allows one to record high-quality and stable EEG signals for more than 1 week. Furthermore, this procedure can also be applied to adult rats and mice to study epilepsy or other neurological disorders.

Here, we introduce a novel technique designed to record electroencephalography (EEG) in freely moving neonatal epileptic pups and describe its procedures, features, and applications. This method allows one to record EEG for more than 1 week.

EEG is a useful method to detect electrical activity in the brain. Moreover, it is a widely used diagnostic tool for various neurological conditions, such ...

Visual Evoked Potential Recordings in Mice Using a Dry Non-invasive Multi-channel Scalp EEG Sensor

For scalp EEG research environments with laboratory mice, we designed a dry-type 16 channel EEG sensor which is non-invasive, deformable, and re-usable because of the plunger-spring-barrel structural facet and mechanical strengths resulting from metal materials. The whole process for acquiring the VEP responses in vivo from a mouse consists of four steps: (1) sensor assembly, (2) animal preparation, (3) VEP measurement, and (4) signal processing. This paper presents representative measurements of VEP responses from multiple mice with a submicro-voltage signal resolution and sub-hundred millisecond temporal resolution. Although the proposed method is safer and more convenient compared to other previously reported animal EEG acquiring methods, there are remaining issues including how to enhance the signal-to-noise ratio and how to apply this technique with freely moving animals. The proposed method utilizes easily available resources and shows a repetitive VEP response with a satisfactory signal quality. Therefore, this method could be utilized for longitudinal experimental studies and reliable translational research exploiting non-invasive paradigms.

We designed a dry-type 16 channel EEG sensor which is non-invasive, deformable, and re-usable. This paper describes the whole process from manufacturing the proposed EEG electrode to signal processing of visual evoked potential (VEP) signals measured on a mouse scalp using a dry non-invasive multi-channel EEG sensor.

For scalp EEG research environments with laboratory mice, we designed a dry-type 16 channel EEG sensor which is non-invasive, deformable, and re-usable ...

Simultaneous Recordings of Cortical Local Field Potentials, Electrocardiogram, Electromyogram, and Breathing Rhythm from a Freely Moving Rat

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls body functions and internal organ rhythms when animals are exposed to emotional challenges and changes in their living environments. In general experiments, signals from different organs, such as the brain and the heart, are recorded by independent recording systems that require multiple recording devices and different procedures for processing the data files. This study describes a new method that can simultaneously monitor electrical biosignals, including tens of local field potentials in multiple brain regions, electrocardiograms that represent the cardiac rhythm, electromyograms that represent awake/sleep-related muscle contraction, and breathing signals, in a freely moving rat. The recording configuration of this method is based on a conventional micro-drive array for cortical local field potential recordings in which tens of electrodes are accommodated, and the signals obtained from these electrodes are integrated into a single electrical board mounted on the animal's head. Here, this recording system was improved so that signals from the peripheral organs are also transferred to an electrical interface board. In a single surgery, electrodes are first separately implanted into the appropriate body parts and the target brain areas. The open ends of all of these electrodes are then soldered to individual channels of the electrical board above the animal's head so that all of the signals can be integrated into the single electrical board. Connecting this board to a recording device allows for the collection of all of the signals into a single device, which reduces experimental costs and simplifies data processing, because all data can be handled in the same data file. This technique will aid the understanding of the neurophysiological correlates of the associations between central and peripheral organs.

This study introduces a method for the simultaneous recording of local field potentials in the brain, electrocardiograms, electromyograms, and breathing signals of a freely moving rat. This technique, which reduces experimental costs and simplifies data analysis, will contribute to the understanding of the interactions between the brain and peripheral organs.

Monitoring the physiological dynamics of the brain and peripheral tissues is necessary for addressing a number of questions about how the brain controls ...

Noninvasive EEG Recordings from Freely Moving Piglets

The method allows the recording of high-quality electroencephalograms (EEGs) from freely moving piglets directly in the pigpen. We use a one-channel telemetric electroencephalography system in combination with standard self-adhesive hydrogel electrodes. The piglets are calmed down without the use of sedatives. After their release into the pigpen, the piglets behave normally&#8212;they drink and sleep in the same cycle as their siblings. Their sleep phases are used for the EEG recordings.

Here, we present a protocol to record telemetric electroencephalograms (EEGs) from freely moving piglets directly in the pigpen without the use of a sedative, making it possible to record typical EEG patterns during non-REM sleep, like spindle bursts.

The method allows the recording of high-quality electroencephalograms (EEGs) from freely moving piglets directly in the pigpen. We use a one-channel ...

Microdialysis of Excitatory Amino Acids During EEG Recordings in Freely Moving Rats

Microdialysis is a well-established neuroscience technique that correlates the changes of neurologically active substances diffusing into the brain interstitial space with the behavior and/or with the specific outcome of a pathology (e.g., seizures for epilepsy). When studying epilepsy, the microdialysis technique is often combined with short-term or even long-term video-electroencephalography (EEG) monitoring to assess spontaneous seizure frequency, severity, progression and clustering. The combined microdialysis-EEG is based on the use of several methods and instruments. Here, we performed in vivo microdialysis and continuous video-EEG recording to monitor glutamate and aspartate outflow over time, in different phases of the natural history of epilepsy in a rat model. This combined approach allows the pairing of changes in the neurotransmitter release with specific stages of the disease development and progression. The amino acid concentration in the dialysate was determined by liquid chromatography. Here, we describe the methods and outline the principal precautionary measures one should take during in vivo microdialysis-EEG, with particular attention to the stereotaxic surgery, basal and high potassium stimulation during microdialysis, depth electrode EEG recording and high-performance liquid chromatography analysis of aspartate and glutamate in the dialysate. This approach may be adapted to test a variety of drug or disease induced changes of the physiological concentrations of aspartate and glutamate in the brain. Depending on the availability of an appropriate analytical assay, it may be further used to test different soluble molecules when employing EEG recording at the same time.

Here, we describe a method for in vivo microdialysis to analyze aspartate and glutamate release in the ventral hippocampus of epileptic and non-epileptic rats, in combination with EEG recordings. Extracellular concentrations of aspartate and glutamate may be correlated with the different phases of the disease.

Microdialysis is a well-established neuroscience technique that correlates the changes of neurologically active substances diffusing into the brain ...

Long-term Sensory Conflict in Freely Behaving Mice

Long-term sensory conflict protocols are a valuable means of studying motor learning. The presented protocol produces a persistent sensory conflict for experiments aimed at studying long-term learning in mice. By permanently wearing a device fixed on their heads, mice are continuously exposed to a sensory mismatch between visual and vestibular inputs while freely moving in home cages. Therefore, this protocol readily enables the study of the visual system and multisensory interactions over an extended timeframe that would not be accessible otherwise. In addition to lowering the experimental costs of long-term sensory learning in naturally behaving mice, this approach accommodates the combination of in vivo and in vitro experiments. In the reported example, video-oculography is performed to quantify the vestibulo-ocular reflex (VOR) and optokinetic reflex (OKR) before and after learning. Mice exposed to this long-term sensory conflict between visual and vestibular inputs presented a strong VOR gain decrease but exhibited few OKR changes. Detailed steps of device assembly, animal care, and reflex measurements are hereby reported.

The presented protocol produces a persistent sensory conflict for experiments aimed at studying long-term learning. By permanently wearing a fixed device on their heads, mice are continuously exposed to a sensory mismatch between visual and vestibular inputs while freely moving in home cages.

Long-term sensory conflict protocols are a valuable means of studying motor learning. The presented protocol produces a persistent sensory conflict for ...

Hybrid Microdrive System with Recoverable Opto-Silicon Probe and Tetrode for Dual-Site High Density Recording in Freely Moving Mice

Multi-regional neural recordings can provide crucial information to understanding fine-timescale interactions between multiple brain regions. However, conventional microdrive designs often only allow use of one type of electrode to record from single or multiple regions, limiting the yield of single-unit or depth profile recordings. It also often limits the ability to combine electrode recordings with optogenetic tools to target pathway and/or cell type specific activity. Presented here is a hybrid microdrive array for freely moving mice to optimize yield and a description of its fabrication and reuse of the microdrive array. The current design employs nine tetrodes and one opto-silicon probe implanted in two different brain areas simultaneously in freely moving mice. The tetrodes and the opto-silicon probe are independently adjustable along the dorsoventral axis in the brain to maximize the yield of unit and oscillatory activities. This microdrive array also incorporates a set-up for light, mediating optogenetic manipulation to investigate the regional- or cell type-specific responses and functions of long-range neural circuits. In addition, the opto-silicon probe can be safely recovered and reused after each experiment. Because the microdrive array consists of 3D-printed parts, the design of microdrives can be easily modified to accommodate various settings. First described is the design of the microdrive array and how to attach the optical fiber to a silicon probe for optogenetics experiments, followed by fabrication of the tetrode bundle and implantation of the array into a mouse brain. The recording of local field potentials and unit spiking combined with optogenetic stimulation also demonstrate feasibility of the microdrive array system in freely moving mice.

This protocol describes the construction of a hybrid microdrive array that allows implantation of nine independently adjustable tetrodes and one adjustable opto-silicon probe in two brain regions in freely moving mice. Also demonstrated is a method for safely recovering and reusing the opto-silicon probe for multiple purposes.

Multi-regional neural recordings can provide crucial information to understanding fine-timescale interactions between multiple brain regions. However, ...

Multi-Fiber Photometry to Record Neural Activity in Freely-Moving Animals

Recording the activity of a group of neurons in a freely-moving animal is a challenging undertaking. Moreover, as the brain is dissected into smaller and smaller functional subgroups, it becomes paramount to record from projections and/or genetically-defined subpopulations of neurons. Fiber photometry is an accessible and powerful approach that can overcome these challenges. By combining optical and genetic methodologies, neural activity can be measured in deep brain structures by expressing genetically-encoded calcium indicators, which translate neural activity into an optical signal that can be easily measured. The current protocol details the components of a multi-fiber photometry system, how to access deep brain structures to deliver and collect light, a method to account for motion artifacts, and how to process and analyze fluorescent signals. The protocol details experimental considerations when performing single and dual color imaging, from either single or multiple implanted optic fibers.

This protocol details how to implement and perform multi-fiber photometry recordings, how to correct for calcium-independent artifacts, and important considerations for dual-color photometry imaging.

Recording the activity of a group of neurons in a freely-moving animal is a challenging undertaking. Moreover, as the brain is dissected into smaller and ...