SHORT-TERM BRAIN PLASTICITY IN HUMANS - TRANSIENT FINGER REPRESENTATION CHANGES IN SENSORY CORTEX SOMATOTOPY FOLLOWING ISCHEMIC ANESTHESIA

Transient rearrangements of finger representation in primary somatosen sory cortex induced by an anesthetic block of the sensory information from adjacent fingers have been shown invasively in animals. Such a ph enomenon has been now replicated in seven healthy human volunteers. So matosensory Evoked Fields (SEFs) have been recorded during separate el ectrical stimulation of the 1st, 3rd, or 5th finger. Recordings were o btained in control conditions (stage A), following complete ischemic a nesthesia of the 4 non-stimulated fingers (stage B), and after regaini ng sensation (stage C). SEFs were recorded using a 28-channel DC-SQUID magnetometer; a single position of the sensor was enough to identify the source of N20m, P30m and following components using the Equivalent Current Dipole (ECD) model. The amount of afferent input during stage s A through C was monitored with surface electrodes placed on the nerv e at wrist and elbow. No variation of the nerve compound potential was observed during stages A through C. In stage A, the localizing algori thm was able to discriminate the individual finger representation in a ccordance with the somatotopic organisation of the sensory homunculus. It was observed that the ECDs responsible for the cortical responses from the unanesthetized finger were significantly changing following a relatively brief period of sensory deprivation from the adjacent fing ers. Such changes of the ECDs with respect to the control conditions w ere characterized by an increase in strength and deepening for the mid dle finger, and by a shift on the coronal plane for the thumb and the little finger (medial for the former, lateral for the latter). Such ch anges became progressively evident in stage B, but were persisting in stage C.