Finger somatotopy in human motor cortex

Although qualitative reports about somatotopic representation of fingers in the human motor cortex exist, up to now no study could provide clear stati stical evidence. The goal of the present study was to reinvestigate finger motor somatotopy by means of a thorough investigation of standardized movem ents of the index and little finger of the right hand. Using high resolutio n fMRI at 3 Tesla, blood oxygenation level-dependent (BOLD) responses in a group of 26 subjects were repeatedly measured to achieve reliable statistic al results. The center of mass of all activated voxels within the primary m otor cortex was calculated for each finger and each run. Results of all run s were averaged to yield an individual index and little finger representati on for each subject. The mean center of mass localizations for all subjects were then submitted to a paired t test. Results show a highly significant though small scale somatotopy of fingerspecific activation patterns in the order indicated by Penfields motor homunculus, In addition, considerable ov erlap of finger specific BOLD responses was found. Comparing various method s of analysis, the mean center of mass distance for the two fingers was 2-3 mm with overlapping voxels included and 4-5 mm with overlapping voxels exc luded. Our data may be best understood in the context of the work of Schieb er (1999) who recently described overlapping somatotopic gradients in lesio n studies with humans. (C) 2001 Academic Press.