Short bursts of stress are useful. Cortisol and adrenaline sharpen attention and mobilise energy – then the system resets. The problem starts when stress never switches off .
Two small structures react in opposite ways. In animal studies, chronic stress made neurons in the amygdala – the brain's threat detector – grow extra branches, while neurons in the hippocampus, which handles memory, learning and context, lost theirs . In people, large imaging studies find a smaller hippocampus, on average, in recurrent depression . What that can feel like: more alarm, less context, weaker memory and focus.
The good news
The brain stays adaptable
In a one-year trial with 120 older adults, aerobic exercise enlarged the hippocampus by about 2 % – roughly reversing one to two years of age-related shrinkage – and improved memory . Regular meals, consistent sleep and daily movement are the inputs you control. They don't erase stress; they change how much buffer you have when it hits.
26: Schmaal L, Veltman DJ, van Erp TGM, et al. Subcortical brain alterations in major depressive disorder: findings from the ENIGMA Major Depressive Disorder working group. Mol Psychiatry. 2016;21(6):806-812.
27: Erickson KI, Voss MW, Prakash RS, et al. Exercise training increases size of hippocampus and improves memory. Proc Natl Acad Sci USA. 2011;108(7):3017-3022.