https://gizmodo.com/darpa-s-brain-chips-could-be-the-next-big-mental-health-1791549701

quick quote from article:

Doctors observed that increasing the amount of electrical stimulation in his brain resulted in him “anxiously crouching in a corner, covering his face with his hands” and speaking “with a childish high-pitched voice.

another:

Stimulating a part of the human brain’s limbic region could invoke euphoria strong enough to counteract depression, and even pain.

and another:

In some cases, DBS seems to bring on side effects like a decline in word fluency and verbal memory, depression, increased suicide tendencies, anxiety and mania. In other cases, like Murphy’s, though, there seem to be really no changes in personality at all.