CHANGING DIRECTIONS OF FORTHCOMING ARM MOVEMENTS: NEURONAL ACTIVITY IN THE PRESUPPLEMENTARY AND SUPPLEMENTARY MOTOR AREA OF MONKEY CEREBRAL CORTEX. MATSUZAKA, YOSHIYA and JUN TANJI. Department of Physiology, Tohoku University School of Medicine, Sendai, Japan.
APStracts 3:0124N, 1996.
SUMMARY AND CONCLUSIONS
1. To understand roles played by two cortical motor areas, the presupplementary motor area (pre-SMA) and supplementary motor area (SMA), in changing planned movements voluntarily, cellular activity was examined from two monkeys (Macaca fuscata) trained to perform an arm- reaching task in which they were asked to press one of two target buttons (right or left) in three different task modes. 2. In the first mode (VISUAL), monkeys were visually instructed to reach and press either a right or left key in response to a forthcoming trigger signal. In the second mode (STAY), they were required to wait for the trigger signal and press the same target key as pressed in preceding trials. In the third mode (SHIFT), a 50-Hz auditory cue instructed them to shift the target of the future reach from the previous target to the previous nontarget. 3. While the monkeys were performing this task, we recorded 399 task- related cellular activities from the SMA and pre-SMA. Among them, we found a group of neurons that exhibited activity changes related specifically to SHIFT trials (SHIFT-related cells). The following properties characterized these 112 neurons. First, they exhibited activity changes after the onset of the 50-Hz auditory cue and before the movement execution when the monkeys were required to change the direction of forthcoming movement. Second, they were not active when the monkeys pressed the same key without changing the direction of the movements. Third, they were not active when the monkeys received the 50-Hz auditory cue but failed to change the direction of the movements by mistake. These observations indicate that the activity of SHIFT- related cells is related to the redirection of the forthcoming movements, but not to the auditory instruction itself, nor to the location of the target key or the direction of the forthcoming movements. 4. Although infrequently, monkeys made errors in the STAY trials, and changed directions of the reach voluntarily. In that case, a considerably high proportion of SHIFT-related neurons (12/19) exhibited significant activity changes long before initiation of the reach movement. These long- lasting activities were not observed during the preparatory period in correct STAY trials, but resembled the SHIFT-related activity observed when the target shift was made toward the same direction. Thus, these activity changes were considered to be also related to the process of changing the intended movements voluntarily. 5. We found another population of neurons that showed activity modulation when the target shift was induced by the visual instruction in VISUAL trials (visually guided SHIFT-related neurons). These neurons were active when the LED guided the forthcoming reach to the previous nontarget but not to the previous target. Therefore, their activity was not a simple visual response to the LED per se. A majority of them also showed SHIFT-related activity in SHIFT trials (19/22 in monkey no. 2). 6. Neurons exhibiting the SHIFT-related activity were distributed differentially among the two areas. In the pre-SMA, 31% of the neurons recorded showed the SHIFT-related activity, whereas in the SMA, only 7 % showed such an activity. These results suggest that pre-SMA and SMA play differential roles in updating the motor plans in accordance with current requirements.

Received 12 February 1996; accepted in final form 29 May 1996.
APS Manuscript Number J109-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 17 June 96