Preparation for reaching: a PET study of the participating structures in the human brain.

The regional cerebral blood flow (rCBF) was measured as an indicator of regional metabolic activity with positron emission tomography (PET) in eight subjects who, after seeing a screen with seven targets prepared themselves with their eyes closed to reach these targets. The preparation phase was associated with increases of rCBF in the prefrontal cortex, several remote visual association areas in the parietal lobe, the supramarginal gyrus, the ventrolateral thalamus and the cerebellar vermis. During the course of learning the activations in the parietal visual areas, the supramarginal gyrus and the prefrontal cortex prevailed as a sign of the visual spatial information; its transformation being kept in working memory. The other activations vanished. No activations were seen in the motor cortices, indicating that reaching is a task which does not require substantial preparatory activity of motor cortices prior to the go signal.