| Sensory testing offers sensitive means of assessing brain health. In particular, spatiotemporal patterns of vibrotactile stimulation of fingertips have been shown in to be highly effective in probing cerebral cortical machinery involved in perception and detecting its abnormalities in a variety of neurological disorders.;In this study, extracellular spike discharge activity was recorded in microelectrode penetrations of primary somatosensory cortex (SI) in 12 rats while stimulating tips of contralateral index and middle fingers. These data were collected at 42 recording sites in the two macrocolumns responsible for processing tactile information from the stimulated fingertips. Two computer-controlled vibrotactile stimulators delivered 15 different patterns of sinusoidal skin vibrations of amplitudes and time courses previously found effective in human sensory studies in detecting various neurological disorders. Simultaneous responses of the two macrocolumns to the same stimulus were reconstructed from the responses recorded in one macrocolumn to finger-reversed stimuli. These recordings show that a single-digit stimulus initially evokes a response in multiple macrocolumns and its amplitude is best reflected in their net mean firing rate. Next, two-digit stimulation differentially affects their macrocolumns based on relative amplitudes of the stimuli applied, with the more weakly stimulated macrocolumn being suppressed by contrast-enhancing lateral inhibition. Application of a high-amplitude conditioning stimulus to a single digit prior to two-digit stimulation greatly reduces activity at the macrocolumn corresponding to that digit through adaptation, decreasing the relative difference between the adjacent macrocolumns despite contrast-enhancing inhibition. Meanwhile, application of a low-amplitude conditioning stimulus to both digits prior to two-digit test stimulation increases the relative difference in the responses of the two macrocolumns. Finally, a slowly ramping stimulus from subthreshold to suprathreshold amplitudes evokes slow feed-forward inhibition and decreases the overall activity of the responding macrocolumn. All these cortical behaviors well parallel perceptual effects of the same stimulus permutations reported by human subjects.;In conclusion, this study identifies and quantitatively characterizes a number of dynamic features of the neurotypical SI cortical response to standardized vibrotactile stimulation, which are expected to show significant variability in different neurological disorders, thus guiding the study of their underlying mechanisms. |
