− この都医学研セミナーは終了しました。 −
|会場||東京都医学総合研究所 2階 講堂|
|世話人||西村 幸男 （認知症・高次脳機能研究分野 脳機能再建プロジェクトリーダー）|
The goal of this study is to determine the role of basal ganglia for cerebellar dependent motor learning, namely saccade adaptation. Saccadic eye movements provide a valuable model to study the brain mechanisms underlying motor learning. If the target is displaced surreptitiously while a saccade is underway, the saccade appears to be in error. A persistent error induces gradual neuronal adjustments to cause the eye movement again to land on target. This saccade adaptation requires the oculomotor vermis of the cerebellum, and its complex spike activity reflects saccade error. Previous studies suggest that the complex spike originates in the rostral superior colliculus (SC). Furthermore, the visual activity of SC neurons, whose timing relative to the saccade error is similar to that of complex spikes, correlates with adaptation speed, suggesting that the error signal in the SC is modulated by sensitivity to error during saccade adaptation. How and where is this SC error signal modulated? In this study, we tested the Substantia Nigra pars reticulata (SNr), an output of the basal ganglia, as a possible source of the saccade error sensitivity signal because SNr inhibits the SC directly, and saccade adaptation speed is slowed in patients with Parkinson’s, a disease of the basal ganglia. Here, we will show our preliminary result that the SNr activity increased as adaptation speed decreased during adaptation. The inactivation of the SNr speeds the saccade adaptation. SC visual activity was increased after SNr inactivation. These results support our hypothesis that the SNr influence on the adaptation speed by modulating SC activity. In this scenario, the SNr weakens the error signal in the SC, and the weaker SC activity would produce less complex spike activity in oculomotor vermis. The weaker complex spike activity would reduce the speed of cerebellar plasticity, leading to the slower decrease in simple spike activity in the oculomotor vermis and consequently a slower saccade adaptation. Thus, this study revealed a previously undiscovered functional link between basal ganglia and cerebellum, i.e., the basal ganglia control the speed of cerebellar dependent motor learning by modulating the error sensitivity.