|Budget Amount *help
¥2,200,000 (Direct Cost : ¥2,200,000)
Fiscal Year 1996 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1995 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1994 : ¥1,400,000 (Direct Cost : ¥1,400,000)
The parietal cortex is well known to be involved in perception of space. However, recent neurophysiological studies in awake monkeys indicated that neurons in the parietal cortex were involved in the control of reaching and manipulation. In this project, first we identified the responsible areas for control of reaching and hand manipulation by micro injection of muscimol into several areas of the lateral bank of intraparietal sulcus, then recorded reaching neurons in these areas to investigate the neural mechanisms of reaching.
We injected muscimol into two areas : 1) Anterior part of the lateral bank of the intraparietal sulcus (Area AIP), 2) Most anterior part of lateral intraparietal area (area LIP). The injection of muscimol into area AIP caused sever deficit of hand manipulation. Before the injection the monkey preshaped its fingers to pick up a small piece of food, however, after the injection the monkey extended its finger until they touched the food. The injection of muscimol in
to anterior part of area LIP caused miss-reaching without any deficits in preshaping of the hand. The distance of error was small ; the monkey tried to pick up a small piece of food again and again until it touched finger tip. These results seem to indicated that the neural control mechanisms for reaching and hand manipulation are segregated into different areas in the lateral bank of the intraparietal sulcus.
Neurons related to reaching movements were also identified in almost same area. We trained the monkey to perform the hand manipulation task and the reaching task. We identified sixty four neurons as reaching neurons because these were activated vigorously during reaching period of the task. Almost 60% of these neurons were preferentially activated when the monkey reached to a particular shape of object, however, the rest were activated whenever the monkey reached out. We also classified the reaching neurons into three types by predominant component of activity. In preferentially activated reaching neurons, "visual dominant" type of neurons were significantly higher parentage than in non-selectively activated reaching neurons. Preferentially activated reaching neurons are likely involved in preshaping movement rather than reaching movement. We tested the selectivity in movement direction of 24 neurons, however, most of them (19 of 24) were not selective in movement direction. Only five neurons were selective in movement direction, however, their selectivity was not so sharp. We also investigated the effect of gaze direction in some neurons and found about half of them (5 of 11) were more active when the monkey reached toward the fixation point. We found some other neurons which were very active during the fixation task in which the monkey put its hand on the fixation point quietly but not active when the view of the hand was covered. These results suggest that this type of reaching neurons in this area may play a crucial role in fine adjustment of reaching movement such as pointing rather than ballistic movement. Less