You have made a convincing case to your father's doctor that your father just isn't thinking as clearly as he used to. The doctor has concluded that your father is not depressed, and tests have ruled out other common problems such as infection and various metabolic disorders. You want to ask for some kind of test of mental functioning, and you don't want it to be just a five-minute test that you suspect your father, who was at the top of his class in graduate school many decades ago, will pass with flying colors.

Lurking in the back of your mind is the concern that perhaps your father is in the early stages of some sort of dementia. Dementia, such as Alzheimer's disease, involves damage to -- or death of -- nerve cells in the brain, according to the Mayo Clinic. Describing Alzheimer's, the most common type of dementia, they report, "Your cognitive abilities slowly decline. Eventually, the affected areas of your brain don't work properly, including parts of your brain that control memory, language, judgment and spatial abilities."

But how do you find out if the problem really is dementia or not?

The gold standard is a consultation with a board-certified clinical neuropsychologist. Clinical neuropsychology, according to the American Academy of Clinical Neuropsychology, focuses on "understanding the relationship between the brain and behavior." Clinical neuropsychologists specialize in "evaluating an individual's thinking skills (cognitive functioning), mood, and behavior, diagnosing brain disorders, and treating these disorders."

Since there's no blood test or other easy marker for dementia, how is it diagnosed? Dr. Chris Morrison, clinical neuropsychologist, Department of Neurology, NYU Langone Medical Center in New York City, explained, "No clinical neuropsychologist will diagnose - or rule out - dementia with just one test. They will consider four separate types of information. The first is the history that a family member may provide. What happened that led them to ask for an evaluation? Specific information is very, very helpful here."

Hearing that I had suggested that people keep a log of incidents that reveal decline in mental functioning, Dr. Morrison commented, "That's outstanding. When family members can bring that kind of information, I am very happy to get it. It makes a big difference."

She continued, "The second type of information comes from the individuals who are being evaluated. Do they have any concerns about their mental functioning? What observations do they have? The third piece is their medical history. And the fourth is a series of tests. All of the pieces of the puzzle have to be considered together."

Tests can identify problems with different types of mental processes; examples include planning and organizing, understanding language, visualizing how objects would look if rotated, and remembering facts and experiences. Different types of brain disorders result in different patterns of problems and gaps, so thorough testing is important to get an accurate diagnosis.

Dr. Morrison also explained, "If people are in their late 60s or in their 70s, they are generally healthy and their life is stable, declines in cognitive functioning may be more likely to be due to some kind of dementia than is the case for people in their early 50s who are severely stressed due to some big disruption in their lives - divorce, moving, downsizing, job loss and so forth - or people who have some major health problems that could account for lapses. So one might be quicker to refer someone for an evaluation if they are older, stable and generally healthy, because they fall into the higher-risk group. For younger people or people with other major medical problems or lives that are chaotic, it might be reasonable to first try to figure out if their mental lapses are due to those issues, and address the stress and other issues first."

Dr. Morrison noted that people can search for board-certified clinical neuropsychologists at this site: When I searched, I did not find any locally but did find 17 in the Phoenix area. If you are looking for help in an area not served by any board-certified clinical neuropsychologists, Dr. Morrison recommends asking about the specific advanced training in neuropsychology that any professionals who are not board-certified but who describe themselves as neuropsychologists have.