Effects of passive tactile co-activation on median ulnar nerve representation in human SI

In animals simple passive co-activation causes a fusion and expansion of th e involved cortical representations. We used passive tactile finger co-acti vation for 40 min to investigate cortical representational changes in the h uman somatosensory cortex. Magnetic source imaging revealed that the euclid ean distance between median and ulnar nerve somatosensory evoked fields (SE F) was significantly reduced after application of 600 synchronous airpuff s timuli to the fingertips of four fingers. In the control experiment without co-activation no significant change in distance was observed. Perception t hreshold and spatial two-point discrimination were not affected by the sync hronous stimulation. This is in contrast to blind three-finger Braille read ers who frequently mislocalize stimuli applied to the reading fingers. This points to a lack of behavioural relevance or the short duration of co-acti vation. NeuroReport 11:1285-1288 (C) 2000 Lippincott Williams & Wilkins.