HIPPOCAMPAL NEURONAL-ACTIVITY AND IMPRINTING IN THE BEHAVING DOMESTICCHICK

The hippocampus of the chick projects to the intermediate and medial p art of the hyperstriatum ventrale (IMHV) which stores information acqu ired through the learning process of imprinting. We have investigated whether the response properties of hippocampal neurons are similar to those of IMHV neurons. Chicks were imprinted by exposure, one group (n = 7) to a rotating red box (RB), the other (n = 5) to a rotating blue cylinder (BC). Four chicks were untrained. The following day, when th e chicks were similar to 48 h old, neuronal activity was recorded in t he left hippocampus. The proportion of neurons responding to the RE an d that to the BC in untrained chicks were compared with the proportion s in trained birds. (i) In RE-trained chicks both the proportion respo nding to the RE and that to the EC were significantly increased. (ii) In EC-trained chicks no significant effect on these proportions was fo und. Of the responsive neurons some were colour (red or blue) sensitiv e and others were shape (box or cylinder) sensitive; the proportions s o responsive were not influenced by training condition. Certain neuron s responded significantly differently when a stimulus was 0.5 m or 2 m from the chick (35%; d-sensitive); very few neurons were equivalently responsive to a stimulus at both distances (3%; d-invariant). These p roportions were not significantly affected by training condition. Hipp ocampal responses are compared with those in the left IMHV. It is conc luded that IMHV responses do not passively reflect those of hippocampa l neurons.