A persistence of responding in hyperstriatal chicks

Introduction: Various lesions in the dorsomedial hyperstriatum accessorium (DMHA) of chicks were investigated because a substrate with functions similar to the mammalian hippocampus has been proposed for this region (cf. Oades 1976). Methods: Operation: Chicks were given aspiration lesions or bilateral scalpel cuts to disconnect the DMHA on day 10 of life (4 types of lesion) and along with sham-operates first exposed to the the training regime 24h later. Training/testing: Birds were given a) a runway task with distraction at the focus of attention (black and white food dish) or peripherally (black and white panels on runway wallswith a grid to cross), b) operant conditioning for food reward on a DRL-10 schedule [differential learning at low rate of reinforcement - one response in 10 sec is rewarded] and c) a passive avoidance task (with the need to withold entering a compartment or receive an electric footshock). Results: 1/ DMHA lesioned animals were less distracted by all forms of novelty in the runway, except the presentation of differently coloured food). This feature was specific to DMHA damage and not seen with brain damage elsewhere or in sham-operates. 2/ After DMHA damage the animals had difficulty to learn to withold response on the passive avoidance task, and to learn to withold peck responses to achieve reward on the DRL schedule. Conclusions: The continuation of the characteristics associated with the trained response in DMHA-lesioned chicks (damage to the hyperstriatum accessorium) when experimental contingencies change is compared with the behaviour of mammals with lesions in the limbic system (the hippocampus and septum)