Mechanisms underlying somatosensory cortical dynamics: II. In vitro studies.

The response of the sensorimotor cortical slice to repetitive, single-site afferent drive is mapped using both evoked potential and metabolic mapping [2-deoxyglucose (2DG)] methods. Systematic changes (increases or decreases) in the evoked potential occur during repetitive 3-5 Hz stimulation. These resemble the changes in SI neuron response observed in the in vivo studies of the preceding companion article; they occur rapidly, recover within 1 min and are reproducible if stimulus parameters remain unchanged. Place, timing, and intensity of repetitive stimulation influence the amplitude and form of the response alterations observed at a given cortical locus. The neuron populations that exhibit different response modifications to the same repetitive stimulus are distributed nonrandomly in the slice: neurons occupying column-shaped aggregates undergo a common response alteration (either an increase or decrease) during repetitive stimulation, with sharp boundaries separating neighboring aggregates distinguishable on the basis of their dynamic behaviors. The distribution of stimulus-evoked 2DG uptake in the slice is "columnar," the dimensions of the 2DG columns corresponding to those mapped with neurophysiological methods. Taken together, the findings support the concept that repetitive stimulation causes the intrinsic network of somatosensory cortex to modify dynamically the network's response to extrinsic excitatory drive so that the local differences in the pattern of extrinsic excitatory drive to neighboring cortical columns are enhanced.