When touch elicits cold: functional imaging of an abnormal sensation

The authors report a 58-year-old man who presented with touch-induced cold sensations and loss of pain and normal temperature sensation in the left leg and trunk. He was found to have syringomyelia at the level of the third thoracic vertebrae. A functional magnetic resonance imaging (fMRI) study was performed to evaluate the underlying cortical processing of the touch-induced cold sensations. Blood oxygen level-dependent(BOLD) responses were measured in response to light tonic pressure stimuli and to cold stimuli applied to both the symptomatic area on the left leg and to the unaffected contralateral side. Tonic pressure applied on the unaffected right thigh and the left hand resulted in activations of contralateral primary (S1) and bilateral secondary somatosensory cortices (S2). In contrast, application of tonic pressure to the affected left thigh, ie, where touch stimuli elicited cold sensations, induced robust activations not only in contralateral S1 and bilateral S2, but also in bilateral insular cortices, which are cortical areas known to be pivotally involved in the central processing of cold. The fMRI data argue in favor of supraspinal cross-submodal plastic changes within the somatosensory system.