Development of the interhemispheric response in rats

In acute experiments on curarized rats, an interhemispheric response was observed for the first time at the age of 5 days. A stimulus of threshold intensity evoked both components of the response in the youngest animals, but only the negative phase of the evoked potential from the 9th day of age, with the initial positive phase appearing only after stimuli of high intensity. Upon using stimuli of double the value of threshold intensity, the responses had the same shape, i.e. positive-negative throughout the whole development. Marked changes in the latency of both components of the response were found during development. Up to 14 days latencies decreased rapidly; this was followed by a phase of relative stability and then, after the 19th day, by further, less pronounced decrease. An after-discharge, a late component of the response in adult animals, appeared for the first time in a mature form at 18 days. An after-discharge of a different shape was seen in young rats aged 7-14 days and none at all was observed in 5-day-old animals.