INVESTIGATING WAITING IMPULSIVITY USING A FOUR-CHOICE SERIAL REACTION TIME TASK IN MACAQUE MONKEYS

Impulsivity is a tendency to act quickly, without adequate consideration of consequences. Waiting impulsivity, also known as premature or anticipatory responses, is the inability to restrain an action before an appropriate moment. Here, we aimed to investigate the timing of premature or anticipatory responses in monkeys.
Data was collected from two 5-year old male Macaca fascicularis monkeys that were trained in a four-choice serial reaction time eye-movement task. The task was run on EventIDE software (OkazoLab Ltd), saccades were recorded on EyeLink (1k, SR-Research Ltd) and data was collected with Plexon software. Saccadic latency was calculated as the time interval between target onset and the initiation of the saccade following central fixation, with negative values reflecting anticipatory or premature saccadic responses.
The timing of premature/anticipatory responses was determined by pooling data of 8604 trials and fitting Gaussian curves. Data from six sessions with monkey H (1988 trials) and five sessions with monkey D (2433 trials) were analyzed. Monkey H had 28% premature (latency < -404 ms), 58% anticipatory (latency between –404 and 42 ms) and 14% visually guided (latency > 42 ms) responses. Monkey D had 16% premature, 46% anticipatory and 37% visually guided responses.
Both monkeys had significant variability in saccadic latency, indicating inconsistent response timing across trials. Notably, most of the saccades were initiated before the target was presented, suggesting impulsive behavior. Our ongoing research investigates the use of transcranial ultrasound stimulation to explore whether different types of impulsive behavior can be modified by targeting the nucleus accumbens.