Persistent Neuronal Firing in Primary Somatosensory Cortex in the Absence of Working Memory of Trial-specific Features of the Sample Stimuli in a Haptic Working Memory Task

摘要

Previous studies suggested that primary somatosensory (SI)nneurons in well-trainedmonkeys participated in the haptic–hapticnunimodal delayed matching-to-sample (DMS) task. In this study,n585 SI neurons were recorded in monkeys performing a task thatnwas identical to that in the previous studies but without requiringndiscrimination and active memorization of specific features of antactile or visualmemorandum. A substantial number of those cellsnsignificantly changed their firing rate in the delay compared withnthe baseline, and some of them showed differential delay activity.nThese firing changes are similar to those recorded from monkeysnengaged in active (working) memory. We conclude that the delaynactivity is not necessarily only observed as was generally thoughtnin the situation of active memorization of different features betweenmemorandanafter those features have been actively discriminated.nThe delay activity observed in this study appears to benan intrinsic property of SI neurons and suggests that there existsna neural network in SI (the primary sensory cortex) for hapticnworking memory no matter whether the difference in featuresnof memoranda needs to be memorized in the task or not. Overn400 SI neurons were also recorded in monkeys well-trained to discriminatentwo memoranda in the haptic–haptic DMS task forncomparison of delay firing of SI neurons between the two differentnworking memory tasks used in this study. The similarity observednin those two situations suggests that working memorynuses already-existing memory apparatus by activating it temporarily.nOur data also suggest that, through training (repetitive exposurento the stimulus), SI neurons may increase their involvementnin the working memory of the memorandum.