Seasonal cycles govern life on earth, from setting the time for the mating season to influencing migrations and governing physiological conditions like hibernation. The effect of such changing conditions on behavior is well-appreciated, but their impact on the brain remains virtually unknown. We investigate long-term seasonal changes in the mammalian brain, known as Dehnel’s effect, where animals exhibit plasticity in body and brain sizes to counter metabolic demands in winter. We find large seasonal variation in cellular architecture and neuronal activity in the smallest terrestrial mammal, the Etruscan shrew, Suncus etruscus. Their brain, and specifically their neocortex, shrinks in winter. Shrews are tactile hunters, and information from whiskers first reaches the somatosensory cortex layer 4, which exhibits a reduced width (−28%) in winter. Layer 4 width (+29%) and neuron number (+42%) increase the following summer. Activity patterns in the somatosensory cortex show a prominent reduction of touch-suppressed neurons in layer 4 (−55%), the most metabolically active layer. Loss of inhibitory gating occurs with a reduction in parvalbumin-positive interneurons, one of the most active neuronal subtypes and the main regulators of inhibition in layer 4. Thus, a reduction in neurons in layer 4 and particularly parvalbumin-positive interneurons may incur direct metabolic benefits. However, changes in cortical balance can also affect the threshold for detecting sensory stimuli and impact prey choice, as observed in wild shrews. Thus, seasonal neural adaptation can offer synergistic metabolic and behavioral benefits to the organism and offer insights on how neural systems show adaptive plasticity in response to ecological demands.

季节性周期控制着地球的生命，从设定交配季节的时间到影响迁徙并控制诸如冬眠之类的生理条件。这种变化的条件对行为的影响已广为人知，但实际上它们对大脑的影响仍然未知。我们调查了哺乳动物大脑的长期季节性变化，这种变化称为Dehnel效应，其中动物表现出身体和大脑大小的可塑性，以应对冬季的代谢需求。我们发现最小的陆地哺乳动物伊特鲁里亚sh，Suncus etruscus在细胞结构和神经元活动方面存在较大的季节性变化。他们的大脑，特别是它们的新皮层，在冬天萎缩。rew是触觉猎手，来自胡须的信息首先到达体感皮质层4，该层在冬季的宽度减小了（-28％）。第二年夏天，第4层宽度（+ 29％）和神经元数量（+ 42％）增加。体感皮层的活动模式显示出第4层（最活跃的代谢层）中受触摸抑制的神经元显着减少（-55％）。抑制性门控的丧失发生在小白蛋白阳性中间神经元减少时，这是最活跃的神经元亚型之一，是第4层抑制的主要调节因子。因此，第4层神经元的减少，尤其是小白蛋白阳性中间神经元的减少可能导致直接代谢好处。然而，正如在野生observed中所观察到的那样，皮层平衡的变化也可能影响检测感觉刺激的阈值并影响猎物的选择。因此，季节性的神经适应可以为有机体提供协同的代谢和行为益处，并提供有关神经系统如何根据生态需求显示适应性可塑性的见解。