Experience-dependent changes in the hippocampus of domestic chicks: a model for spatial memory.

In the domestic chicken, providing visual barriers for a brief period early in life has been found to improve spatial memory [R. Freire et al. (2004)Animal Behaviour, 67, 141-150]. In the present study we compared the structure of neurons in the hippocampus and neostriatum in chicks reared with or without visual barriers. From 8 to 16 days of age, chicks were reared in pens either with two wooden screens (Treatment E) or with no screens (Treatment C). At 16 days of age, chicks were anaesthetized, perfused intracardially and brain samples collected and stained using a Golgi-Cox technique. Morphometric analysis revealed that the multipolar projection neurons of Treatment E chicks had longer dendrites (ANOVA, F(1,14) = 7.4, P < 0.05) and had more spines per 20 micro m of dendrite (SLD; ANOVA, F(1,14) = 10.6, P < 0.01) than those of Treatment C chicks. By contrast, no evidence was found that rearing treatment differentially influences dendrite length or SLD in the neostriatum, suggesting that the above environment-induced changes may be specific to the hippocampus. Multipolar projection neuron dendrites of the right hemisphere were longer (ANOVA, F(1,14) = 36.4, P < 0.0001) and had more spines (ANOVA, F(1,14) = 8.8, P < 0.05) than dendrites of the left hemisphere, supporting previous findings that the right hemisphere of chickens is predominantly involved in spatial processing. We conclude that the chicken provides a useful model for the study of developmental plasticity in brain and behaviour, partly because the possibility of rearing chicks in isolation and imprinting them on an artificial object provides a means of accurately manipulating early experience.