Motor learning of compatible and incompatible visuomotor maps

Brain imaging studies demonstrate increasing activity in limb motor areas d uring early motor skill learning, consistent with functional reorganization occurring at the motor output level. Nevertheless, behavioral studies reve al that visually guided skills can also be learned with respect to target l ocation or possibly eye movements. The current experiments examined motor l earning under compatible and incompatible perceptual/motor conditions to id entify brain areas involved in different perceptual-motor transformations. Subjects tracked a continuously moving target with a joystick-controlled cu rsor. The target moved in a repeating sequence embedded within random movem ents to block sequence awareness. Psychophysical studies of behavioral tran sfer from incompatible (joystick and cursor moving in opposite directions) to compatible tracking established that incompatible learning was occurring with respect to target location. Positron emission tomography (PET) functi onal imaging of compatible learning identified increasing activity througho ut the precentral gyrus, maximal in the arm area. Incompatible learning als o led to increasing activity in the precentral gyrus, maximal in the putati ve frontal eye fields. When the incompatible task was switched to a compati ble response and the previously learned sequence was reintroduced, there wa s an increase in arm motor cortex. The results show that learning-related i ncreases of brain activity are dynamic, with recruitment of multiple motor output areas, contingent on task demands. Visually guided motor sequences c an be linked to either oculomotor or arm motor areas. Rather than identifyi ng changes of motor output maps, the data from imaging experiments may bett er reflect modulation of inputs to multiple motor areas.