Usage of the middle finger shapes reorganization of the primary somatosensory cortex in patients with index finger amputation

PURPOSE: The primary somatosensory cortex (S1) is somatotopically reorganized after limb amputation. The duration of the amputation, the intensity of phantom limb pain but also a multifactoral model of altered cerebral input have been discussed to be associated with cortical changes. Patients with finger amputation rarely show phantom limb pain, the deafferented cortical area is small but other fingers might well overtake function. METHOD: We selected a group of index finger amputated patients and performed a high resolution (in plane: 1.5 mm2) S1-mapping during tactile stimulation of finger tips. RESULT: We found an interhemispheric imbalance of the distance between the thumb and middle finger only for the patient-group. When patients used their middle finger more they showed less interhemispheric imbalance, increased spatial tactile discrimination and increased fMRI-activation in response to stimulation. Phantom limb pain was not associated with somatotopic representation parameters in S1. CONCLUSIONS: Overall, our fMRI-data point to a usage dependent plasticity of Brodmann's area 3b in man.