Anomalous double sensations after damage to the cortical somatosensory representation of the hand in humans

Hand amputees may report that a tactile stimulus delivered to the stump region or the face ipsilateral to the amputation induces the sensation of being touched on the phantom. Given the representational contiguity between hand and face, this phenomenon has been related to electrophysiologically demonstrated orderly remappings occurring in deafferented somatosensory areas. Here we report, for the first time, double sensations evoked by tactile stimuli delivered to the contralesional hypoaesthesic hand in a patient with a lesion involving the hand representation in the primary somatosensory cortex. These double sensations were very precise and consistent over a 4-month period, and were clustered on the contralesional scalp and bilaterally on the nape. The distribution of the referred sensations did not conform to any orderly topographic relationship with the known somatosensory hand representation. Since in our patient the lesion left the nervous pathway from the skin to the thalamus unaffected, the selective cortical perturbation may have induced a thalamic reactivity eventually leading to the expression of latent thalamic inputs to intact cortical targets. The non-topographic distribution of the areas inducing double sensations is likely to reflect a noisy rearrangement process.