most adults experience a gradual reduction in brain volume after the age of thirty-five of about 5 percent per decade through age sixty, with the decline speeding up after age seventy. All of these factors lead to a general slowing of cognitive function. Much of this volume and weight reduction comes from shrinkage of the prefrontal cortex and hippocampus. The prefrontal cortex is what we use to set goals, make plans, divide a large project up into smaller pieces, exercise impulse control, and decide what we’re going to pay attention
