Tonic activity during visuo-oculomotor behavior in the monkey superior colliculus

The purpose of this study was to examine whether the superior colliculus is involved in intermediary cognitive processes such as memory, movement preparation, and peripheral attention. To answer this question, we recorded single cell activities in the superior colliculus of monkeys trained to perform a series of visuo-oculomotor tasks: delayed saccade task (SACD), saccade task with overlap target (SACO), and attention task (ATT). We recorded 141 neurons showing tonic activities related to the tasks. Depending on the predominance of the activities among the three tasks, we classified the tonic neurons into four types: (1) visuomotor (greater activity in SACO), (2) mnemonic motor (SACD dominant), (3) attention (ATT), and (4) nonspecific. Among 108 neurons recorded in the intermediate layer, 13 were of a visuomotor type, 15 were of a mnemonic motor type, and 13 were of an attention type. The other 67 neurons were of a non-specific type. Of the 33 neurons in the superficial layer, many neurons were of the non-specific type. These results suggested that the tonic activities in the superior colliculus are related to memory of the target location, preparation of saccades and peripheral attention.