Neuroimaging of higher somatosensory processing in humans: Attention, space, and motion

Cerebrovascular accidents cause major morbidity in the United States, in many cases leading to somatosensory and attention deficits (i.e., neglect). The development of effective strategies for rehabilitation in such patients requires understanding the neural mechanisms involved in somatosensory processing. Perception of touch involves representations of stimulus location both on the skin and in space. However, the modulation of primary somatosensory cortex with attentional shifts to skin location remains controversial, and no imaging studies have addressed how such modulation codes for localization in three-dimensional, extrapersonal space. Converging evidence points to the involvement of the parietal cortex in coding and transforming spatial coordinate systems. This region likely participates in the localization of tactile stimuli in space utilizing a body-centered reference frame.; This research investigates the functional neuroanatomy of attention, spatial representation, and motion processing in the human somatosensory system. In five separate experiments involving a light tactile stimulus, using 15O-labeled water and positron emission tomography (PET) to measure relative regional cerebral blood flow (rCBF), this research addresses the following specific aims: (1) To characterize the neural system responsive to light tactile stimulation (LTS) by contrasting light touch at six separate skin locations with a baseline, control resting state; (2) To determine the regions modulated by attention to sensory modality in dually presented tactile and visual stimuli; (3) To determine whether cortical tuning (increased rCBF for the attended location) or sensory gating (decreased rCBF at unattended locations) modulates primary (SI) and secondary (SII) somatosensory cortices by measuring rCBF with the manipulation of attention in the presence or absence of stimulation; (4) To identify the location of body-centered representations of somatosensory stimulation by independently manipulating the site of the body stimulated (e.g., finger) and the location of the stimulation site in space (e.g., arm location); (5) To investigate the regions of the brain involved in processing a moving tactile stimulus and compare them with those stimulated by visual motion.