Inactivation of the ventral lateral geniculate and nucleus of the optic tract impairs retention of visual eyeblink conditioning.

Reversible inactivation was used to examine the conditioned stimulus (CS) pathway for visual eyeblink conditioning (EBC). Previous research has shown that the ventral lateral geniculate (LGNv) and nucleus of the optic tract (NOT) could play a role in visual EBC through ipsilateral projections to the medial pontine nuclei. Rats were given visual EBC followed by inactivation of the ventral lateral geniculate (LGNv), nucleus of the optic tract (NOT), or both nuclei contralateral to the conditioned eye. Muscimol infusions into the NOT or LGNv impaired retention. Combined inactivation of LGNv/NOT produced the most severe impairment. Rats given inactivation of these visual nuclei after training with a vibration CS showed no impairment. The findings indicate that a parallel pathway of visual CS information projects from the LGNv and NOT to the medial pontine nuclei.