Persistence of the pattern of feeding in chicks with hyperstriatal lesions
Introduction: Strategies for coloured food pellet selection (response sequences to one or another colour) were studied after training for a red (vs. yellow) preference on a board with/without distracting coloured pebbles. Various lesions in the dorsomedial hyperstriatum accessorium (DMHA) of chicks were investigated because a) a substrate with functions similar to the mammalian hippocampus has been proposed for this region (Oades 1976), b) perseveration of choice based on persistent stimulus representations is a feature of selective attention after hippocampal brain-damage, and c) treatment with testosterone, with uptake sites in the hippocampus (i.a) also induced persistence in this task Rogers, 1971; Andrew, 1972). Methods: Operation: Chicks were given aspiration lesions or bilateral scalpel cuts to disconnect the DMHA on day 10 of life and along with sham-operates first exposed to the the training regime 24h later. Training/testing: Birds were given red-dyed food for 10 days, (but would accept normal yellow grains). On test they were presented with 200 red, 200 yellow grains spread on either a plain perspex floor or one with pebbles coloured like the food glued to the floor, and the identity of the first 100 pecks scored. The influence of priming with 50 pecks on one or the other colour vs. overnight experience of the non-preferred colour of food was also tested over 2 days. Results: 1/ Colour choice in terms of mean run length (MRL) or first 10 pecks was more stable in the lesioned birds and varied more with the test (and prior experience) in intact animals. 2/ On the plain floor - controls decreased their non-preferred food intake on day 1, but with overnight experience increased it markedly on day 2. 3/ On the pebble floor - controls were more distracted and pecked more pebbles. By comparison the DMHA group retained longer MRL for the trained colour preference. 4/ Chicks with lesions more lateral to the DMHA differed by showing a disruption of the trained preference 5/ Chicks with more ventral or more posterior brain-damage showed a food choice pattern that was indistinguishable from intact controls. Conclusions: The lack of lability of the trained feeding preferences of the DMHA animals (whether primed for short or long periods) and in the face of distracting stimuli is interpreted as consistent with the functions of the mammalian hippocampus in tests of selective attention. Different behaviour following damage to the DMHA periphery point to the specificity of the role attributed to the hyperstriatum accessorium.