Functional reorganization of barrel cortex following atypical sensory rearing experiences: the effect on cortical spike synchrony

Abstract

Functional reorganization of primary sensory cortex following peripheral sensory deprivation and other atypical sensory experience typically focused on changes in single neuron deficits till date. This dissertation studies the effect of manipulating sensory experience during development, on the neuronal population measure of cortical spike synchrony. Spike synchrony, which can be defined as correlated responses of a pair of neuron, were studied in anesthetized barrel cortex in normal as well as unilaterally and bilaterally whisker trimmed rats. Bilateral deprivation of whisker sensation led to severe reduction in neuronal synchrony but trimming whiskers in only side of the rat’s face led to an increase in spike synchrony in areas rich in inputs from the non-deprived hemisphere. This strongly indicates that cortical spike synchrony is highly activity dependent and can also be affected following altered postnatal sensory experience. Moreover, the results in this dissertation show that responses in normal barrel cortex, which is part of the primary somatosensory cortex in rats, can be modulated by auditory inputs as well. Such modulations were observed in the firing rate, onset-latency as well as the spike synchrony of whisker driven neuronal responses, when an auditory stimulus was presented in conjunction with a whisker stimulus. In addition, an auditory stimulus alone strongly modulated cortical spike synchrony of barrel cortex neurons without changing its firing rate. Interestingly, these ‘cross-sensory’ influences were also dependent on early sensory experience. Thus, postnatal bilateral whisker deprivation and simultaneous click rearing of rats exaggerated the cross-sensory influences in barrel cortex. All of the above results indicate the emergence of cortical spike synchrony as an important contributor to the formation of a neural code of objects in barrel cortex. Also, the fact that it can be manipulated independently of firing rate by an auditory stimulus reveals a novel mechanism by which a non-dominant stimulus can affect the neural code formation in primary sensory cortex.