The overall goal of the following experiment is to introduce an automated behavioral framework for operant conditioning of rodents to test complex cognitive tasks. The behavioral task is a five hole nose poke design that is conventionally used for five choice serial reaction time task studies. The subjects are required to maintain their snout inside a fixation hole until the presentation of a go queue after a short delay period.
An auditory instruction queue is presented during the fixation epic to guide the subject to choose a future motor target to receive a reward. The use of an auditory queue enables well-defined transitions between different task epics and permits, studying multiple aspects of behavior, as well as neuronal mechanisms of working memory, decision making, and motor planning. The main advantage of this technique over existing methods, such as maze navigation experiments, is that overt motor behavior that may be confounded by systematic variations in the subject's trajectory is minimized during critical epoch of the task.
Though this method can provide insight into motor control, studies can also be used to investigate other high level cognitive processes, such as perception, attention, and memory formation. Demonstrating the procedure will be Dylan Miller, an undergraduate student from my lab. The following study is performed in an opera conditioning box consisting of a five hole nose poke wall on one side and a food delivery trough on the opposite side.
The center nose poke hole is considered a fixation hole, and the four other holes, two on each side of the fixation hole are considered motor target holes. Each hole is equipped with a tricolor LED and an infrared beam emitter detector system that detects when the animal enters and retracts from the fixation hole. A programmable tone generator creates a single frequency tone with millisecond precision and disconnected to a speaker mounted inside the opera box.
The tone generator and nose poke holes are controlled through the behavioral tracking system. Using specialized software during the habituation period, handle the animals daily and allow them to explore the operant conditioning chamber and food hopper gradually restrict their food intake over a three day period to reach 85 to 90%of their original body weight. The first step is to familiarize the subject with the nose poke holes, food delivery port, and the association between the flashing holes and reward.
To do this, select one out of the two targets on a random schedule and play the go queue, a white auditory noise while the LED inside the hole is flashing. Set the software to reward the subject upon visits to the hole. Time out the trial after 30 seconds if the hole is not visited, and start a new trial to aid in target selection.
Punish visits to incorrect holes by terminating the trial followed by five seconds of blackout. Next, select a new hole and start a new trial until the desired level of performance is reached. To train the subject to poke inside the fixation hole.
To start a trial, a yellow LED is flashed inside the fixation hole. Upon visiting the fixation hole immediately play the go queue And start a new trial. Once the subject learns to visit the fixation hole, teach it to maintain their nose inside the hole for a set period of time.
To do this, wait for the subject to visit the fixation hole and terminate the trial. If the subject retracts within 500 milliseconds, penalize premature retractions by a blackout period for seven seconds. Otherwise, play the go queue and reward the correct visits by delivering a food pellet.
The next step is to introduce the auditory instruction queue as a single frequency auditory tone, pulsed and triplets with a pulse duration of 150 milliseconds and interpulse interval of 100 milliseconds. In addition, increase the length of the delay period to an average of 1.5 seconds. Choose a random delay period length at each trial based on a uniform density between 1.3 to 1.8 seconds.
Play the instruction cue immediately after the subject enters the fixation hole. Assign two instruction cues to each of the targets. However, only use one cue associated for each target at this stage until the subjects become more familiar with the task.
Let the subject use both auditory and visual cues to select the target hole until the desired performance level is reached. To train the subject to only use auditory cues, turn off the flashing LEDs inside the target hole so that the subject can only use auditory instruction cues. Introduce the two other cues to the sequence of randomly presented instruction cues when the desired performance is reached, and repeat the training steps.
Make sure that at the end of each step, the subject maintains greater than 75%behavioral performance for at least three consecutive sessions before progressing to the next stage. Once the final stage is reached, keep the subject on the protocol for a week to ensure the performance is maintained at the desirable level. Define the success rate as the percentage of correct visits to the targets divided by the total number of trials.
The success rate should be measured at each stage of training. The different error types include premature retraction, the percentage of trials timed out due to early retractions from the fixation hole commission error, the percentage of failed trials when the subject visits an unconstructed target and a mission error. The percentage of errors when the subject does not visit any of the targets after trial initiation.
For each trial measure the reaction time defined as the delay between the onset of the go queue and the subject retracting from the fixation hole. The time to target is also measured as the duration between the subject retracting from the fixation hole and entering the target hole. This example shows the success rate for a single subject across 14 recording sessions.
Error types are dominated by premature retractions with commission errors and omission errors occurring less frequently. This histogram shows the distribution of the reaction time across different trials. Here, the distribution of the time to target across different trials is shown.
Once the subject acquired the task, it was implanted with a 32 channel micro electrode array. In the pre limbic area, a sample trace is shown aligned with a raster plot of 22. Simultaneously recorded units, markers for behavioral events are plotted on top of the traces.
While attempting this procedure, it is important to remember to check the Perus prior to each training session and monitor the subject's performance afterwards. Significant decline in the behavioral scores may be caused by equipment malfunction After its development. This technique should pave the way for researchers in the field of cognitive neuroscience to explore top-down control of goal-directed behavior.
