Chemosensory input and lateralization of brain function in the domestic chick

One-day old domestic chicks (Gallus gallus domesticus) show concentration-dependent behavioural responses to olfactory cues. In the present study we investigated the lateralized olfactory responses of 1-day-old chicks to the odours of eugenol and iso-amyl acetate. In experiment 1 different concentrations of each odour were presented in repeated trials to chicks housed individually. The odours were presented together with a small coloured bead at which the chick pecked. When tested with the highest concentration of eugenol (100% v/v), the chicks demonstrated more head shaking when their left nostril was occluded (RN; right nostril in use) than when their right nostril was occluded (LN; left nostril in use). No such lateralization occurred in response to iso-amyl acetate. This result was confirmed in a second experiment in which the chicks were tested with unscented stimuli, 100% eugenol and 100% isoamyl acetate. In experiment 3 we found that occluding both the chicks' nostrils abolished the head shaking response to eugenol and to iso-amyl acetate. Thus, the chicks' head shaking responses to the odorants eugenol and iso-amyl acetate are mediated primarily by inputs from within the nasal cavity, and not by oral or occular inputs. The present results are consistent with the hypothesis that there is lateralization to olfactory cues and that it is dependent on the involvement of receptors inside the nasal cavity. We suggest that differences in lateralized olfactory responses to different odours are affected by the relative involvement of intranasal olfactory and trigeminal chemoreceptors.