ELECTROPHYSIOLOGICAL CORRELATES OF PRIOR TRAINING - AN IN-VITRO STUDYOF AN AREA OF THE AVIAN BRAIN WHICH IS ESSENTIAL FOR EARLY LEARNING

Day-old domestic chicks will peck at any small, distinct object, such as a metal bead. One-trial passive avoidance learning can be establish ed by coating the metal bead with methyl anthranilate (MeA) and allowi ng the birds to peck it once, after which they conspicuously avoid it. We have used birds successfully trained not to peck metal beads, and a control set of chicks where the training beads were innocuously dipp ed in water. Brain slices were prepared from both groups, containing t he left, intermediate, medial part of the hyperstriatum ventrale (IMHV ) - a region essential for this form of early learning. The electrophy siological properties of neurones in the IMHV were examined in vitro. Neurones recorded intracellularly in slices taken from MeA-trained bir ds had higher membrane resistances than did cells from water-trained c ontrols. MeA training was also associated with an increased incidence of spontaneous, large EPSPs. Field responses to local electrical stimu lation appeared to be somewhat greater in MeA-trained birds than in wa ter-trained controls. In contrast, field potentials proved harder to p otentiate with a burst of relatively high frequency stimulation in MeA -trained birds: the change in amplitude was less in MeA-trained birds, and there was less variability than in slices from water-trained cont rols.