Illusory persistence of touch after right parietal damage: neural correlates of tactile awareness.

We studied a patient who experienced 'palinaesthesia', an illusion of persistent touch following tactile stimulation on the left hand, subsequent to a right parietal meningioma affecting primary somatosensory regions in the postcentral gyrus (SI) and superior parietal gyrus (Brodmann area 7), but preserving the secondary somatosensory cortex (SII) in the upper lateral sulcus. This subjective sensation was accompanied by transient increases in objective measures of tactile threshold. The patient had mild deficits in superficial tactile perception, but showed severe left-sided extinction for offsets of tactile stimuli during bilateral stimulation, but not for onsets of stimuli. Functional MRI revealed increased neural activity during palinaesthesia selectively arising within the ipsilesional-right SI cortex, but no abnormality within left SI and bilateral SII. Right SI responded to the onset of new tactile stimuli on the left hand but not to their offset. By contrast, any tactile events on either hand modulated activity in contralateral SII regions, even undetected left-sided offsets. These data demonstrate that illusory persistence of touch following stimulation on the hand may result from sustained neural activity in a restricted region of the SI cortex outlasting the offset of the actual tactile stimuli. These findings also provide direct evidence for a critical role of SI in mediating conscious somatosensory experience on contralateral parts of the body.