The role of the inferior collicular cortex in the neonatal rat: sensorimotor modulation.

A tail pinch in rats up to 10 days of age produces a spectrum of motor behaviors characterized by forelimb paddling, hindlimb treading and occasional curling and rolling of the torso, a behavioral pattern similar to the seizure behaviors electrically-elicited from the inferior collicular cortex of 5- or 10-day-old rats. In 5-day-old rats, these tail pinch-induced paddling and treading behaviors coincided with afterdischarge-like EEG activity recorded from the seizure-sensitive site in the inferior collicular cortex. In contrast, no change in the EEG activity occurred in an adjacent seizure-insensitive site during these tail pinch-induced behaviors. Similar electrographic-behavioral synchrony was found in 10-day-old rats, but by 16 days of age, as in the adult rat, a tail pinch stimulus did not induce post-stimulus behavioral changes or afterdischarge-like EEG activity. Since auditory function does not develop until 12-14 days of age in the rat, we propose that the inferior collicular cortex modulates sensorimotor integration in the neonatal rat, prior to assumption of this function by the cerebral cortex.