MINICOLUMNAR ACTIVATION PATTERNS IN CAT AND MONKEY SI CORTEX

The distribution of stimulus-evoked C-14-2-deoxyglucose (2D6) labeling in primary somatosensory cortex (SI) of monkey (Macaca fascicularis) and cat was investigated. Reconstructions of the global pattern of lab eling reveal that discrete skin stimuli evoke activity within an exten sive region of SI, and that the activation pattern typically consists of multiple, elongated regions of above-background labeling (''modules ,'' typically 0.5-1.0 mm wide, and 1-4 mm long). Evidence obtained usi ng recently developed methods (Tommerdahl, 1989) for quantitative anal ysis of 2DG activity patterns is shown to be consistent with the idea (Whitsel et al., 1991) that SI modules typically are bounded by zones dominated by stimulus-evoked inhibition. The labeling pattern within i ndividual 2DG modules in SI of both cats and monkeys is analyzed quant itatively (in the frequency domain). Within-module spatial activation patterns are demonstrated to be periodic, consisting of radially orien ted profiles of above-background labeling separated from each other by less strongly labeled radial profiles. The spectral characteristics o f within-module 2DG labeling change systematically with location along the module's long axis: spatial frequencies between 18 and 35 cycles/ mm are prominent in the labeling that occupies both the middle and upp er layers at central locations in the module, but are a less obvious c omponent of the labeling in both the middle and upper layers at locati ons remote to the module center. Since the radially oriented periodic variation both (1) in 2DG labeling in regions of SI outside modules an d (2) in optical density in images of Nissl-stained sections of SI con sists predominantly of spatial frequencies in the range of 18-35 cycle s/mm, it is concluded that the radial profiles of labeling within indi vidual 2DG modules correspond to groupings of minicolumns distinguisha ble from their neighbors on the basis of labeling intensity. The findi ngs raise the possibility that highly structured, within-module spatia l patterns of SI minicolumnar activation encode information about the physical properties of tactile stimuli.