Plasticity in human somatosensory thalamus as a result of deafferentation

Experimental studies indicate that deafferentation results in reorganization of the somatosensory map at various levels of the CNS, such that the representation of a body part adjacent to a region that is denervated expands into the deafferented area. Recent data suggest that in the human this occurs at the cortical level, but subcortical structures have not been systematically investigated. To test the hypothesis that the human thalamus is capable of significant reorganization as a result of changes in afferent input, microelectrode recording and stimulating techniques were used to define thalamic somatotopy in 61 patients undergoing stereotactic procedures. Five groups were compared: those with pain in the deafferented body part, face (n = 9), arm/hand (n = 4), leg/foot (n = 8) and hemibody (n = 5) and those with neither pain nor deafferentation, i.e., movement disorder (n = 24). Trunk representation, as determined from receptive fields, was significantly larger in patients with leg/foot deafferentation than in patients without deafferentation (1.8 +/- 0.7 vs. 0.5 +/- 0.2 mm; p < 0.01). Also, microstimulation induced paraesthesiae in the face from a significantly larger region of thalamus in the facially denervated group compared to the movement disorder group (13.8 +/- 2.8 vs. 3.7 +/- 0.6 mm; p < 0.001). There were no significant differences in the representation of other body parts in the five groups. The results in the leg-deafferented group agree with conclusions reached from animal studies; however, the human situation is more complex. There appear to be different patterns and degrees of somatotopic reorganization in the human, all of which may be associated with pain syndromes.