Somatosensory: Imaging tactile perception

Optical imaging of intrinsic signals has extended our understanding of the functional organization of primary somatosensory cortex (SI) in primates. This chapter describes the findings which show that somatotopy, long a staple of somatosensory cortical functional organization, may not be as precise as the maps drawn from single and multiunit recordings. Optical maps of the tactile funneling illusion, which demonstrates a map of how tactile stimuli are perceived in SI rather than a map of skin topography, support the topographic representation in SI which is not a physical body map, but a perceptual map. Optical images of vibrotactile pressure, flutter, and vibration submodality domains overlaying the somatotopy reveal striking similarities and differences between other modality maps in somatosensory as revealed through electrophysiological methods and visual cortices as revealed through optical imaging methods. In an effort to extend these findings to functional MRI studies and somatic perception in humans, we compared in the same animal the maps acquired with high spatial resolution optical imaging in monkey SI with positive BOLD maps acquired at high filed (9.4T). We demonstrated that the positive BOLD fMRI maps were comparable to the fine scale OI maps in revealing both somatotopy and funneling. With the addition of high field human fMRI studies at 7 Tesla, this combination of approaches can investigate the relationship between somatotopic representation and sensory perception from the human to the modular domain and single unit level in primates.