Thaler1995_Article_TheFunctionsOfTheMedialPremoto.pdf - Exp Brain Res(1995 102:445~460 9 Springer-Verlag 1995 D Thaler 9Y-C Chen 9P.D Nixon 9C.E Stern

Thaler1995_Article_TheFunctionsOfTheMedialPremoto.pdf - Exp...

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Exp Brain Res (1995) 102:445~460 9 Springer-Verlag 1995 D. Thaler 9 Y.-C. Chen 9 P.D. Nixon 9 C.E. Stern R.E. Passingham The functions of the medial premotor cortex I. Simple learned movements Received: 6 January 1994 / Accepted: 23 June 1994 Abstract We report several studies on the effects of re- moving the medial premotor cortex (supplementary motor area) in monkeys. The removal of this area alone does not cause either paralysis or akinesia. However, the animals were poor at performing a simple learned task in which they had to carry out an arbitrary action: they were taught to raise their arm in order to obtain food in a foodwell below. They were impaired whether they worked in the light or the dark. They were impaired when they had to perform the movements at their own pace, but much less impaired when a tone paced perfor- mance. Monkeys with lesions in the anterior cingulate cortex were as impaired as monkeys with medial premotor le- sions at performing this task at their own pace. Howev- er, monkeys with lateral premotor lesions were less im- paired. We conclude that the medial premotor areas play a crucial role in the performance of learned move- ments when there is no external stimulus to prompt performance. Introduction The premotor cortex (area 6) forms a strip in front of the motor cortex (area 4), divided into a medial and a lateral D. Thaler . Y.-C. Chen. P.D. Nixon 9 C.E. Stern R.E. Passingham (Nil) Department of Experimental Psychology, University of Oxford, South Parks Rd, Oxford OX1 3UD, UK Y.-C. Chen Shanghai Brain Research Institute, Shanghai 200031, China C. E. Stern MGH-NMR Center, Charlestown, MA 02129, USA D. Thaler Department of Neurology, Brigham and Women's Hospital, 75 Francis Street, Boston, MA 02115, USA portion. It is usually termed the "supplementary motor area" (SMA). By electrical stimulation of this region Woolsey et al. (1952) were able to evoke movements of the body, and to delineate a somatotopic map that was independent of the map in motor cortex. However, more recent studies using microstimula- tion have revealed independent somatotopic maps in the lateral and medial parts of area 6 (Kurata and Wise 1988; Godschalk et al. 1990; Luppino et al. 1991). Fur- thermore both the lateral and medial parts of area 6 send projections to area 4 (Muakkasa and Strick 1979) and have outputs through the pyramidal tract (Dum and Strick 1991; He et al. 1993). The descriptive terms "medial premotor cortex" (MPC) and "lateral premotor cortex" (LPC) will therefore be used here. The term "supplementary motor cortex" is avoided, because it suggests some hierarchical difference between the medi- al and lateral premotor areas. Whereas removal of motor cortex (area 4) causes a temporary paralysis, removal of the the MPC does not do so (Coxe and Landau 1965). Furthermore, whereas removal of the MPC and anterior cingulate gyrus pro- duces akinesia in patients (Laplane et al. 1977), the bi- lateral removal of the MPC alone does not produce akinesia in monkeys (D. Thaler, unpublished D. Phil.
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