Animals adapt to changing environmental conditions such as seasonal cycles to enhance their chances of survival. Although seasonal variation is associated with behavioral patterns such as hibernation, the effects of seasons on the brain are unclear.
The researchers examined seasonal changes in neural structure and activity in the smallest terrestrial mammal, the Etruscan shrew. The authors used MRI, microstructural analysis of cortical tissue sections, and two-photon calcium imaging, focusing on the somatosensory cortex, which plays a critical role in the sense of touch.
Layer 4, which is the most metabolically active layer of the somatosensory cortex, was 28% thinner in winter than in summer. Moreover, the fraction of layer 4 neurons suppressed upon whisker stimulation during spring and summer was 2.3-fold higher than that in autumn and winter.
In addition, there were fewer parvalbumin-positive interneurons, which are among the most metabolically active neuronal subtypes in layer 4 of the somatosensory cortex, in winter than in summer. These energy-conserving neural adaptations might allow shrews to reduce their metabolic demands during winter.
The findings suggest that lowering the threshold for detecting whisker stimulation could make shrews less selective about which prey to consume in winter.
According to the authors, the study illustrates how neural systems show adaptive plasticity in response to ecological demands.
How the mammalian brain adapts to seasons
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