Sustained attention modulates the immediate effect of de-afferentation on the cortical representation of the digits: source localization of somatosensory evoked potentials in humans

Long-term cortical reorganization of the somatotopic arrangement of the dig its after alterations of the peripheral input is well established. Studies on the immediate effects of manipulating peripheral input have shown confli cting results indicating that additional factors might modulate cortical re organization. We present a source localization study using somatosensory ev oked potentials (SEP) following electric stimulation of digits one and five before and during anaesthesia of digits two, three and four in 10 normal v olunteers. When attention was directed to a stimulus at the dorsal hand, th e 3D-distance between digits one and five decreased during as compared to b efore anaesthesia. In Contrast, this distance enlarged when subjects were n ot attending a particular stimulus. In this condition most subjects focused their attention on the clear sensation of the de-afferented hand region. T hese results indicate that attention modulates the effect of immediate cort ical reorganization of the hand area during partial deafferentation, As an hypothesis: it may be speculated that the sensation of the de-afferentation results in increased synchronized activity of the de-afferented somatosens ory cortex and, thus, to its enlarged representation. Conversely, if attent ion is directed to a different hand region, the representations of the neig hboring digits may expand into the de-afferented cortex. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.