Mechanisms of Dynamic Peri- and Intra-columnar Interactions in Somatosensory Cortex: Stimulus-specific Contrast Enhancement by NMDA Receptor Activation

The available experimental evidence convinces us that the response of somatosensory cortex to environmental stimulation can undergo substantial, moment-to-moment modification with stimulus repetition. Our view of the mechanisms which underlie this appreciable functional plasticity of the adult somatosensory cortex has been shaped by the findings obtained in a series of studies that used the 14C-2-deoxyglucose (2DG) metabolic mapping method, either alone, or in combination with other methods. Crucial to those studies was the development of experimental strategies, apparatus, and data analysis procedures allowing the generation of high-resolution, quantitative “maps” of the 2DG uptake evoked by repetitive peripheral stimulation (Juliano et al., 1981, 1983; Tommerdahl et al., 1985; Tommerdahl et al., 1987; Tommerdahl, 1989; Whitsel et al., 1989). These developments have made it possible to generate high resolution 2DG maps of somatosensory cortical activity for a variety of stimulus conditions (brushing, vibrotactile, electrocutaneous, and joint rotation). For all species (rat, cat and monkey), and for all conditions of stimulation employed to date, the 2DG maps which have been generated exhibit much in common: i.e., they all consist of strip-like patterns of responding and non-responding cortical columns. In addition, they are highly reproducible when the same stimulus is used in different subjects (Juliano and Whitsel, 1985; Whitsel et al., 1989), and maps generated using different modes of tactile stimulation applied to the same body site typically exhibit prominent differences in the orientation, number, and configuration of strips (Tommerdahl, 1989).