SOMATOTOPY IN THE HUMAN MOTOR CORTEX HAND AREA - A HIGH-RESOLUTION FUNCTIONAL MRI STUDY

Fine-scale somatotopic encoding in brain areas devoted to sensorimotor processing has recently been questioned by functional neuroimaging st udies which suggested its absence within the hand area of the human pr imary motor cortex, We re-examined this issue by addressing somatotopy both in terms of functional segregation and of cortical response pref erence using oxygenation-sensitive magnetic resonance imaging at high spatial resolution, in a first step, spatial representations of self-p aced isolated finger movements were mapped by using motor rest as a co ntrol state. A subsequent experimental design studied the predominance of individual finger movements by using contrasting finger movements as the control task. White the first approach confirmed previous repor ts of extensive overlap in spatial representations, the second approac h revealed foci of differential activation which displayed an orderly mediolateral progression in accordance with the classical cortical mot or homunculus, We conclude that somatotopy within the hand area of the primary motor cortex does not present as qualitative functional segre gation but: as quantitative predominance of certain movement or digit representation embedded in an overall joint hand area.