The effects of restricting afferent input during early ontogenesis on evoked activity of projection neurons depend on the maturity of the sensory inputs.

Experiments were performed on 28 Wistar rats, of which 14 were subjected to unilateral denervation of the forelimb (by dissection of the median nerve) on day 13 of postnatal ontogenesis. The effects of restriction of sensory input on baseline and evoked somatosensory cortex neuron activity in the areas corresponding to the representation of the intact fore- and hindlimbs were studied. According to the proximal-distal rule of maturation, the sensory input from the forelimbs was completely formed by the moment at which deafferentation was performed, while the sensory input from the hindlimbs was still incompletely mature. Opposite changes were found to occur in areas receiving more or less mature afferent inputs. In the projection zone of the less mature input (from the hindlimbs), neurons showed a lower frequency of baseline activity and stimulation of the sciatic nerve evoked significantly more activatory responses and an increase in the duration of short-latency activatory responses. In the projection zone of the more mature sensory input (from the forelimb), stimulation of the intact median nerve evoked significantly more inhibitory responses and fewer complex responses. Thus, normal formation of normal brain neuron activity requires an adequate sensory input.