Perceptual illusion of "paradoxical heat" engages the insular cortex.

Paradoxical heat (PH), the illusion of skin heat, accompanies many neurological disorders. Using the technique of percept-related functional MRI, we found a region of the right insular cortex specifically activated when subjects perceive a heat sensation in their right hand even though their skin temperature is cool or at neutral. This region was suppressed during mild skin cooling. We propose that this differential response is a manifestation of the role of the insula in signaling temperature perceptions regardless of the actual temperature of the skin. These findings suggest that a region within the insula has a complex role in heat perception, perhaps contributing to a specific, rather than general, thermosensory perception. These data provide insight to our basic understanding of normal and pathological thermosensory perceptions.

Neural correlates of prickle sensation: a percept-related fMRI study.

The painful sensations produced by a laceration, freeze, burn, muscle strain or internal injury are readily distinguishable because each is characterized by a particular sensory quality such as sharp, aching, burning or prickling. We propose that there are specific neural correlates of each pain quality, and here we used a new functional magnetic resonance imaging (fMRI) method to identify time-locked responses to prickle sensations that were evoked by noxious cold stimuli. With percept-related fMRI, we identified prickle-related brain activations in the anterior cingulate cortex (ACC), insula, secondary somatosensory cortex (S2), prefrontal cortex (PFC), premotor cortex (PMC), caudate nucleus and dorsomedial thalamus, indicating that multiple pain, sensory and motor areas act together to produce the prickle sensation.