Evidence for fusion and segregation induced by 21 Hz multiple-digit stimulation in humans

Subjects were trained to detect changes in the frequency of 21 Hz tactile s timulation applied to digits 2+3+4 (fusion group) or 2+4 (segregation group ) of the right hand. The 21 Hz steady-state response for digit 3 was measur ed by 64 channel EEG on mapping trials before and after training. Discrimin ation improved over 3 days, confirming that subjects attended to the traini ng stimuli. The 21 Hz response was larger on training than on mapping trial s, indicating sensitivity of the response to the strength of cortical activ ation. Under these conditions the 21 Hz response for digit 3 decreased afte r training in both groups on day 1. On day 3 this effect reversed in a subs et of fusion subjects while segregation continued to yield decreases. The f indings suggest that somatosensory representations are dynamically modified by the sensory input experienced on a task. NeuroReport 11:2313-2318 (C) 2 000 Lippincott Williams & Wilkins.