Neural mechanisms of motor adaptation for an internally driven movement

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Project Summary/Abstract The object of interest is not always visible at the time of movement. Visuospatial working memory plays an essential role in directing movements in such situations. This system stores the position of an object in the visual world and can be used to direct a movement to engage it. This is an internally driven movement. In contrast, we make so-called externally cued movement when the object is visible at the time of movement. To make movements accurate in both situations, visuospatial working memory and the visual signal need to be appropriately transformed to a motor command signal. The mechanism that maintains the motor accuracy is called motor adaptation. The behavioral characteristics and neural mechanisms of motor adaptation for an externally cued movement are well understood, however, little is known about motor adaptation of an internally driven movement. Do adaptations for both types of movement engage the same neural mechanism? If they are different, how are they different in their behavioral characteristics and neural mechanisms, and do they interact? We will use saccadic eye movements to study motor adaptation. Saccades, rapid eye movements that direct the gaze to targets of interest, can be induced by an external visual signal (visually-guided saccade, VGS) or by an internal visuospatial working memory (memory-guided saccade, MGS). Also, saccades are very precise. Because saccades remain accurate throughout life, despite the neural and muscular changes due to aging or injury, the saccadic system must be continually recalibrated through saccade adaptation. When we examined the VGS after MGS adaptation, VGS remained unchanged. Therefore, we hypothesize that the neural mechanism for MGS adaptation is distinct from that for VGS adaptation. In this project, we propose to investigate the adaptation of MGS and compare it with that of VGS. The main innovation of this study is that it could reveal a yet unknown motor adaptation mechanism for internally driven movement. The innovative concept is that the neural basis of motor adaptation for internally and externally driven movements could be separate but interact. Understanding the neuronal basis of motor adaptation for both externally and internally driven movements will provide a comprehensive picture of motor adaptation.