FUNCTIONAL MAPPING OF SEQUENCE LEARNING IN NORMAL HUMANS

The brain localization of motor sequence learning was studied in norma l subjects with positron emission tomography. Subjects performed a ser ial reaction time (SRT) task by responding to a series of stimuli that occurred at four different spatial positions. The stimulus locations were either determined randomly or according to a 6-element sequence t hat cycled continuously The SRT task was performed under two condition s. With attentional interference from a secondary counting task there was no development of awareness of the sequence. Learning-related incr eases of cerebral blood flow were located in contralateral motor effec tor areas including motor cortex, supplementary motor area, and putame n, consistent with the hypothesis that nondeclarative motor learning o ccurs in cerebral areas that control limb movements. Additional cortic al sites included the rostral prefrontal cortex and parietal cortex. T he SRT learning task was then repeated with a new sequence and no atte ntional interference. In this condition, 7 of 12 subjects developed aw areness of the sequence. Learning-related blood flow increases were pr esent in right dorsolateral prefrontal cortex, right premotor cortex, right ventral putamen, and biparieto-occipital cortex. The right dorso lateral prefrontal and parietal areas have been previously implicated in spatial working memory and right prefrontal cortex is also implicat ed in retrieval tasks of verbal episodic memory. Awareness of the sequ ence at the end of learning was associated With greater activity in bi lateral parietal, superior temporal, and right premotor cortex. Motor learning can take place in different cerebral areas, contingent on the attentional demands of the task.