Hippocampal plasticity predicts behavioral lateralization and stress resilience in laying hen chicks

Perinatal environmental conditions can shape neural and cognitive development in poultry, yet the combined effects of lighted-incubation and immediate post-hatch feed and water access remain unknown. In this exploratory study, layer chick embryos were exposed to continuous light during embryonic days 18-21 and provided with immediate post-hatch access to feed and water, as exemplified in on-farm hatching systems. Hippocampal expression of neural plasticity markers (i.e., BDNF, DCX, PCNA) was measured in left and right hemispheres at eight weeks of age to assess structural plasticity and lateralization, and its relationship to lateralized visuomotor responses within the same individual chicks. The different plasticity markers correlated highly with each other and were combined in a hippocampal plasticity index. Neither lighted incubation nor immediate feed and water access altered hippocampal plasticity or lateralization, suggesting that these traits may reflect intrinsic hemispheric organization rather than early-life modulatory effect by environmental conditions. We did, however, find a pronounced left-right asymmetry, particularly in the caudal hippocampus (p=0.04). Behavioral observations from a multitasking and step detour test revealed potential hemisphere-specific associations in these exploratory analyses. Right-hemispheric plasticity negatively correlated with latency to detect a predator, consistent with right-hemispheric dominance in threat detection. Higher overall hippocampal plasticity was associated with faster return to foraging after predator exposure (p=0.01), hinting at a link between hippocampal plasticity and stress resilience, as has been found in mice. Detouring behavior also correlated with opposite patterns of hippocampal plasticity (p=0.002), suggesting interactions between structural asymmetrical plasticity and lateralized cognitive processing. These findings suggest that hippocampal plasticity may primarily reflect intrinsic developmental trajectories, with early-life environmental factors exerting only modest effects, if any. These preliminary findings highlight the potential importance of considering intrinsic neural organization alongside perinatal environmental conditions in shaping cognitive and behavioral traits.