Quality of coding of whisker deflection by an ensemble of neurons in rat primary somatosensory cortex increases with postnatal development

Koji Ikezoe, Hiroshi Tamura, Fumitaka Kimura, and Ichiro Fujita

Sensory performance of animals gradually matures as they grow postnatally. This maturation should depend on developmental change of not only response properties of single neurons, but also relation among activities of an ensemble of neurons. Here we studied postnatal changes of pair-wise correlation of trial-to-trial fluctuation of responses between nearby neurons in rat primary somatosensory cortex, S1. Using a multi-probe single-shaft electrode, we recorded extracellular activities simultaneously from a group of single neurons that were vertically arrayed across the cortex in urethane-anesthetized rats (postnatal day 5, P5, to P31). Neurons in a rat on P9 showed the greatest positive trial-to-trial correlation (r = 0.78) in their responses to single whisker deflection. Correlation of responses gradually decreased with age and was 0.02 (p < 0.001) on P31. Nearby neurons thus respond to stimuli more independently from others as animals grow up. Because correlation of responses among neurons deteriorates the averaging effect of response fluctuation by pooling of their activities, the results suggest that quality of coding of whisker deflection by an ensemble of neurons increases with development. Correlated activity evoked by sensory inputs in earlier period, on the other hand, may play a role in formation of neural circuits.