Changes of local synaptic activity during acquisition of a visuomotor skill were examined with positron emission tomography (PET) imaging of regional cerebral blood flow (rCBF). Eight subject learned the pursuit rotor task, a predictable tracking task, during three sequential PET scans (day 1). Subjects returned 2 days later and repeated the three pursuit trials and PET scans (day 2) after completing an extensive practice session. Control scans without movement bracketed the pursuit trials on both days to rule out time effects unrelated to motor skill learning. PET images were transformed to a common stereotaxic space using matched magnetic resonance imaging (MRI) scans. Group learning effects were determined by a repeated measures multivariate analysis of variance (ANOVA). During motor skill acquisition (day l), increases of synaptic activity were identified in cortical motor areas and cerebellum, supporting the hypothesis that procedural motor learning occurs in motor execution areas. During long-term practice (day 2), changes were limited to the bilateral putamen, bilateral parietal cortex, and left premotor cortex. To characterize differences in the rate of learning between subjects, each subject's performance data from day 1 was fit with a power function. The exponents were correlated with rCBF data on a pixel-by-pixel basis. Rapid skill acquisition was associated with increasing rCBF in premotor, prefrontal, and cingulate areas, and decreasing rCBF in visual processing areas located in the temporal and occipital cortex. This pattern in fast learners may reflect a more rapid shift from a visually guided strategy (accessing perceptual areas) to an internally generated model (accessing premotor and prefrontal areas).

1. The somatotopic representation of the human primary motor cortex was examined noninvasively with estimates of cerebral blood flow (CBF) obtained with positron emission tomography. Twelve normal subjects performed a motor tracking task with the arm, first finger, tongue, and great toe commensurate with the bolus injection of radioactive H215O. Images of the relative percent increase of blood flow, compared with control studies, demonstrated reproducible foci of CBF increases in the motor cortex in every subject. Each motor task could be localized to a predictable site on a coronal section containing the precentral gyrus. 2. In reproducibility experiments of repeated measures, it was determined that two foci of activation in the primary motor cortex could be discriminated with a 95% confidence if they were separated by 5.4 mm. 3. In five subjects with matched magnetic resonance imaging studies, the sites of activation were variable with respect to surface anatomy and could be found at the depth of sulci or the surface of gyri. The findings were similar to previously reported electrophysiological studies using direct cortical stimulation. 4. The method may be applied to the in vivo functional mapping of the primary motor cortex in patients with cerebral disorders.

VNS causes activation of several central areas including contralateral thalamus. Localization to the thalamus suggests a possible mechanism to explain the therapeutic benefit, consistent with the role of the thalamus as a generator and modulator of cerebral activity.

Finger movement-related responses were identified in three discrete sites of mesial frontal cortex in 7 normal subjects using high resolution functional magnetic resonance imaging. During imagination of the same movements there was a differential response with rostral areas more active than caudal areas. Humans have multiple motor areas in mesial frontal cortex that subserve different functions in motor planning and execution.