Neuronal activity related to memory in the intermediate and medial part of the hyperstriatum ventrale of the chick brain.

The intermediate and medial part of the hyperstriatum ventrale (IMHV) in the forebrain of the domestic chick Gallus gallus domesticus has been shown in previous studies to be critically involved in the learning process of imprinting. In the present study, 1-day-old chicks were imprinted by exposing them to one of two artificial stimuli. 24 h later each chick was given a preference test in which the two stimuli were presented in sequence. A preference score, an index of the strength of imprinting (i.e., of learning), was calculated from approach activity during the preference test. The chicks were divided into groups with low, medium and high preference scores (corresponding to weak, medium and strong learning respectively) and coded so that all subsequent procedures were performed blind. Each chick was then anaesthetized and spontaneous action potentials recorded extracellularly from groups of neurones in the left IMHV. The mean neuronal firing rate in chicks with medium and high preference scores was significantly greater than that in chicks with low preference scores. This relation between neuronal activity and preference score was not attributable to the chicks' locomotor activity per se. The results demonstrate an association between spontaneous electrical activity in the left IMHV and a measure of learning 1 day after the learning occurred.