Role Of The Primate Prefrontal Cortex On Numerosity Based Decision And Its Neural Encoding Mechanism

Quantity perception is a manifestation of the brain’s processing of complex perceptual information,allowing it to transition from concrete to abstract processes,and is an important foundation for various behavioral decision-making processes in both humans and animals.Research has shown that the parietal cortex and prefrontal cortex are the core brain regions involved in quantity perception in both humans and non-human primates.The posterior parietal cortex of macaques contains a large number of neurons that exhibit specific responses to quantity stimuli,and it plays an important role in quantity discrimination tasks.As a higher-order information integration center,the prefrontal cortex has extensive reciprocal projections with the parietal cortex,but its role in quantity perception and decision-making is not well understood,particularly with respect to its neural encoding mechanisms.In this study,we trained two rhesus macaques to perform relative quantity and color comparison tasks in order to investigate the role of the prefrontal cortex in quantity perception.We studied the role of the prefrontal cortex in quantity perception and decision-making by conducting in vivo electrophysiological recordings and reversible inactivation in the prefrontal area.Behavioral results showed that both monkeys learned the relative quantity and color comparison tasks,achieving an overall correct response rate of over 85%.Furthermore,the correct response rates in both tasks were inversely proportional to task difficulty.We set the total area of two quantity matrices in half of the relative quantity comparison tasks to be equal,and the monkeys’ performance was similar to that when the area of the matrices was not controlled,which ruled out the possibility that the monkeys used area information to perform the task.We conducted acute single-electrode extracellular spike signal recording in the monkeys’ prefrontal area.The results showed that there were more neurons with signal selectivity during the cue period in the ventral prefrontal cortex,and their selectivity was modulated by task difficulty.In the quantity discrimination task,more neurons exhibited selectivity at low difficulty levels or exhibited selectivity earlier,while in the color discrimination task,more neurons exhibited signal selectivity under conditions of high difficulty or did not show differences in difficulty levels.This result suggests that as the difficulty of the quantity discrimination task increases,the prefrontal cortex needs more time to decode quantity,indicating that the prefrontal cortex is involved in quantity decoding."In the color discrimination task,the prefrontal cortex may not actively participate in signal recognition,but instead only load the recognition results as working memory information.