Stress and depression lead to long-term memory loss. How?
Hippocampus is an area in the brain that turns our short-term explicit memories into long-term explicit memories.
Stress, depression and childhood trauma all release glucocorticoids, which kill cells in the hippocampus leading to memory loss.
The longer people are depressed, the small their hippocampus gets.
After recovery from stress or depression, neurons can grow back in the hippocampus.
Physical exercise helps re-generate new neurons in the hippocampus while learning helps keeping those new neurons alive.
Source: The Brain That Changes Itself By Dr. Norman Doidge