Fig. 4.

Energetically expensive layers of the somatosensory cortex, and cortex-specific reduction of brain volume induced by less food independent of season. (A) Cytochrome oxidase histochemistry indicates that layer 4 of the somatosensory cortex is the most metabolically active layer. (B) Immunohistochemical processing for PV⁺ neurons in summer (orange box) and winter (blue box) shows lower PV⁺ neurons in winter. (C) Columnar density of layer 4 PV⁺ neurons in winter compared to summer (n = 10 shrews). Error bars are mean ± SEM. (D) Superimposing the cortex of the same shrew imaged from a summer when it had abundant food (orange) to one with limited food (black) shows a decline in brain volume when having limited food (mostly orange is visible). (E) The brain and cortex of the same shrews (n = 7 shrews), but not other brain areas, reduce in volume when they have lesser food during the same seasonal period (summer). Black dots indicate means. For statistical information, see SI Appendix, Table S1.