A dementia patient's unexpected changes in behavior can cause the most difficulty for her family. Emotion processing in Alzheimer's disease or dementia changes the way a family member reacts. In the most fundamental ways, your family member cannot handle stress. While we often focus on memory loss as the main challenge of dementia, an equal and sometimes greater challenge is loss of judgment and the inability to reason.

... which then influences the emotional reaction? You mean that loss of the ability to judge reasonably causes more extreme affective reactions, i.e. it is the evaluation of the experienced situation that is changing with the progress of dementia?

Alzheimer disease is known to progress from medial regions of brain, first damaging nucleus basalis of Meynert (the source of acetylcholine and GABAergic gamma coupling in cortex) and hippocampus. I guess that the anger might be caused by damage to ventral ACC (anterior cingulate cortex) later on, when disease progresses through brain.

The vACC signals well-being state (when things go well for us = when we reach safety, rewards, resources, goals and comfort zone of homeostasis, when we are liked and accepted, and when we do something well, i.e. make someone laugh, make a song, build a house... ) to other regions of the brain. vACC is known to inhibit central amygdala nucleus by glutamatergic projections to intercalated GABAergic neurons, and to be activated by learning about safety for example during extinction learning of stimuli that no longer predict the punishment.

So damage to vACC will disinhibit the threat processing in central amygdala and aggressive response in parts of BNST. As the vACC stimulates serotonin release in DRN, the low vACC activation will cause less serotonin in ventral striatum and thus disinhibit the impulsive behavior, via stronger D1 loop output, leading to less inhibitory avoidance and self-control. In addition to direct suppression of amygdala output by vACC projections, the vACC inhibits amygdala indirectly via serotonin. Dopamine in contrary stimulates threat response, anger and self-defense by stimulating amygdala.

https://www.scienceopen.com/document/vid/13e62385-1fb0-4a49-9a5d-e435baa5b95e?1

vACC function is explained in section: Serotonin Signaling. page 10

if you have more questions just ask :)

Thanks a lot, Karin! A very good explanation of often observed behavior change in AD patients!