What's Happening in the Brain
Judgment arises from circuits that include the frontal lobes (areas in the front part of the brain). We know this because people who have localized damage to their frontal lobes (say from a car accident, bullet, tumor or blood vessel problem) characteristically have impaired judgment, and become more self-centred. In the past, frontal lobe impairment was seen as a late sign of Alzheimer's disease , but thinking about this has changed in two ways.
Now that there is better testing of the frontal lobes, we see that this area of the brain is involved much earlier. Also, brain imaging studies suggest that early on, the brain is able to compensate for damage in the frontal lobes. However, the ability to compensate becomes less as the disease progresses. This is an important insight, because it suggests that strategies to treat Alzheimer's disease should not just focus on countering the disease process, but also should enhance the repair process.
This issue is explored in considerable detail in the chapter on 'Executive Function' by Sarah Voss and Roger Bullock, of the book Trial Designs and Outcomes in Dementia Therapeutic Research, published in London by Taylor & Francis, 2005, and edited by Kenneth Rockwood and Serge Gauthier.