S106

THE ACTIVITY OF NEURONS IN THE ROSTRAL PART OF THE PUTAMEN DURING VOLUNTARY LIMB MOVEMENT IN THE MONKEY

MINORU KIMURA and MA~OTO KATO *#, Dept. of Physiology, Jichi Medical School, Minamikawachi-machi, Tochigi-ken, 329-04, ~ Dept. of Physiology, School of Medicine, University of Tokyo, Japan.

Electrical microstimulation of the monkey putamen can evoke discrete movements of contralateral distal muscles. The latency of the evoked EMG in forearm muscles is 20-25 ms (stimulation, 300 Hz, 5-40 pulses, 0.2 ms duration). The microexcitability (excitable sites with threshold currents less than 50 ~A/total stimulation sites) is 20-35 % in the caudal putamen (AI3-AI8), while less than 6 % in the rostral putamen (AI9-A26). The purpose of the present investigation is to examine the neuronal activity of the rostral part of the putamen during learned movements in the monkey, and reveal the role of the rostral putamen in the mechanism of voluntary movement. Two movement tasks were used in three monkeys (Macaca fuscata): (i) 3 repetitive flexion-extensions of the right elbow across the target for a juice reward triggered by a lamp command (AMI), and (2) the same as (AMI) except that the instruction lamp was presented preceding the trigger lamp to inform the animal of the direction of the initial movement (AM2). The reaction time of the movement after the visual trigger stimulus was about 30 msec shorter in AM2 than in AM1, and this revealed that monkeys used the instruction stimulus to prepare for the proper movement. Fifty-five out of 92 task-related cells increased discharges tonically during the instruction delay period. The selectivity of the activity to the direction of the initial movement was examined in 34 cells out of the 55 cells. Eighteen cells showed the selectivity. Twenty-four out of these 55 cells showed a building up of activity toward the trigger visual stimulus in AM1 as well as tonic activity during instruction delay period in AM2, but none of them showed directional selectivity. Fifty-three cells showed responses to the visual trigger stimulus with a short fixed latency (80-100 msec). The reponses of 40 out of 53 cells were greatly enhanced when the trigger stimulus was anticipated by the preceding instruction stimulus in AM2. Previously, we reported that neurons in the caudal putamen exhibit sensory responses to the trigger stimulus and activity time-locked to the movement, but almost no change of activity during instruction delay period (Neurosci. Res. 3:436-443, 1986). Therefore, the characteristic features of the neuronal activity suggested that the neurons in the rostral part of the putamen are specifically related to preparation and anticipation of the forthcoming trigger stimulus and of performing the proper movement.

TOPOGRAPHICAL ARRANGEMENT OF THE THALAMIC NEURONS RPOJECTING TO THE STRIATUM IN THE MACACA MONKEY

KATSUMA NAKANO I , YASUO HASEGAWA *2, AKINORI TOKUSHIGE *2, and SHIRO NAKAGAWA *2, IDepartment of Anatomy, School of Medicine, Mie Univers i ty , Tsu, Mie 514, Japan, 2Department of Anatomy, Faculty of Medicine, Kagoshima Univers i ty , Kagoshima 890, Japan

In order to c l a r i f y the topographic arrangement of the s t r i a t a l a f ferents, the thalamostr iata l connections of the macaca monkey were invest igated by the placement of smal l - to- large in ject ions of the retrograde t racer wheat germ agglut in in conjugated to horseradish peroxidase into various port ions of the str iatum. The main f indings are as fo l lows: Neurons in the do rsa l - to - la te ra l parts of the parafascicular nucleus (Pf) pro ject to the la te ra l port ions of the caudate nucleus (CN) and the rost ra l part of the pQtamen (Put). Neurons in the media l - to-ventra l parts of the Pf pro ject to the medial port ions of the CN and of the ros t ra l part of the Put. Most medial ly located Pf neurons pro ject to the fundus s t r i a t i . Neurons in the dorsomedial part of the centro- median nucleus (CM) project to the dorsolateral part of the Put, corresponding to the leg area of KUnzle ('76). Neurons in the lateral part of the CM project to the intermediate zone of the Put, corresponding to the arm area, and neurons in the ventromedial CM project to the ventromedial part of the Put, corresponding to the face area of KUnzle ('76). Our findings also indicated that neurons in the VAmc and the medial part of the subthalamic nucleus (STN) project mainly to the medial part of the CN and the fundus s t r i a t i ; neurons in the VLo and lateral part of the STN project to the Put, and neurons in the medial part of the STN project to the lateral part of the CN. Other thalamic neurons projecting to the striatum were observed in the midline thalamic nuclei (paraventricular and rhomboidal nuclei), intralaminar nuclei (central la tera l , paracentral and central medial nuclei), and only rarely in the anterior thalamic nuclei and the dorsomedial nucleus (MD). No labeled neurons were observed in the suprageniculate, lateral posterior nuclei, or magnocellular part of the medial geniculate nucleus. From the results presented here, and the well developed CM in the monkey, i t is suggested that the CM plays an important role in movement control.