Functional MRI of the primary somatosensory cortex in extinction to simultaneous bilateral tactile stimuli due to right temporal lobe stroke

Abstract

Patients with right posterior temporoparietal cortical lesions often exhibit extinction to tactile double simultaneous stimuli (EDSS). It is not known whether sensory unawareness-extinction results from suppression of sensory input into the somatosensory cortex (SI), inhibition of SI, or interference which prevents SI output from activating and being fully processed by association areas. A patient with EDSS due to a right temporal stroke sparing SI and posterior parietal cortex and eight age-matched healthy controls were studied with fMRI during tactile stimulation. The volume of activation of SI during tactile stimulation of the right hand, the left hand and both hands was measured and the patient's volume of activation was compared to that of the control subjects in each of these stimulus conditions. Although the patient demonstrated behavioral EDSS, during fMRI the patient's activation of SI on both sides was within the range of the control participants' volumes of activation. These findings suggest that EDSS in patients with a right temporal lobe stroke results from processing abnormalities that occur after these afferent tactile stimuli are processed by SI.