Skip to main content

Verified by Psychology Today


Why Does Behavior Deteriorate in Dementia?

Depression, anxiety, irritability, and agitation are common in dementia.

We all have needs, drives, and cravings—such as hunger, territoriality, and sexuality—which stem from the ancient part of our brain that we share with reptiles. Why don’t we constantly act upon these desires? As discussed in a prior article, mammals developed new parts of the brain to keep these primitive impulses in check.

With these new brain regions, we are able to mentally put ourselves in other people’s shoes and imagine what they might feel if we were to steal their food, for example. We understand that we live in a community and must abide by the rules. The new brain regions also enable us to envision and plan for the future, which includes not stealing someone’s food because they might retaliate, not eating all the food today so there will be some for tomorrow, and planning how we are going to obtain food in the future, whether that means hunting game, planting crops, or visiting the supermarket.

In this and the next few articles, we’ll discuss what happens when these brain regions break down in dementia, leading to behavioral problems, including apathy, irritability, agitation, and aggression.

Irritability, along with frustration, depression, anxiety, and not participating, may be due to declining abilities

Although much undesirable behavior in dementia is due to the deterioration of the brain, some behaviors—particularly early in the disease—are due to the normal reaction that any of us would have if it became difficult to carry out daily or enjoyable activities. Frustration at not being able to complete a task can lead to irritability. The mood can also be affected. Worry about how you will be able to manage in the future can lead to depression and anxiety.

And the combination of all these emotions plus the impairments can lead our loved ones to stop participating because the activities are too difficult, too frustrating, or too depressing—because failing at the activity emphasizes how impaired they really are.

Depression and anxiety may be caused by dementia

In addition to the loss of abilities and worry about the future, depression and anxiety can, of course, be caused by external life events, such as retirement, the death of a friend, or leaving a home one has been in for 50 years. However, injury caused by dementia to the brain can also directly affect your loved one’s emotions. Whether caused by life changes, loss of abilities, or damage to the brain directly, anxiety and depression are quite common in dementia, particularly when the dementia is mild, and there is some insight into one’s difficulties.

In addition to feelings of nervousness and worry, anxiety can produce many physical symptoms, such as an increased heart rate, breathing rapidly, sweating, nausea, and even diarrhea. Understandably, sometimes the symptoms of anxiety are attributed to medical problems. On the other hand, many of these symptoms could indicate a very serious medical problem, such as a heart attack.

If your loved one is having any of these symptoms, it is important that they see their doctor to look for medical causes, such as heart disease. But if the doctor has “ruled out” all of the medical problems that could be causing their symptoms, it may be that they have anxiety.

Common symptoms of anxiety

  • Feeling nervous, restless, or tense
  • A sense of impending danger, panic, or doom
  • Increased heart rate
  • Breathing rapidly
  • Sweating
  • Trembling
  • Feeling weak or tired
  • Trouble concentrating
  • Trouble thinking about other things
  • Stomach or bowel problems
  • Difficulty controlling anxious feelings
  • Avoiding things that trigger the anxiety

In addition to feeling anxious about memory loss, many people also feel sad, especially when they receive the diagnosis of Alzheimer’s disease or another dementia. Often these feelings of sadness are temporary and resolve on their own. If the sadness lasts for an extended period of time (two weeks or longer) and impairs functioning, we typically call it depression. Depression is not normal and is not to be expected just because your loved one is older.

Common symptoms of depression are sleep difficulties, daytime fatigue, physical slowing, loss of interest in living, and hopelessness about the future in addition to sadness, worthlessness, and guilt. Depression can sometimes be difficult to differentiate from dementia. An evaluation by a physician or neuropsychologist may be needed to know, for example, whether dementia has caused depression, or it is the other way around.

Common symptoms of depression in older adults

  • Feelings of sadness
  • Feelings of worthlessness or guilt
  • Fixating on past failures
  • Being tearful
  • Irritability or frustration, even over small matters
  • Memory difficulties
  • Trouble concentrating
  • Sleep difficulties
  • Daytime fatigue and lack of energy
  • Changes in appetite
  • Often wanting to stay at home
  • Physical slowing
  • Physical aches or pain
  • Loss of interest in activities
  • Loss of interest in sex
  • Loss of interest in living
  • Hopelessness about the future
  • Frequent thoughts of death

We’ll continue our discussion of behavior issues in dementia in our next article.

© Andrew E. Budson, M.D., 2020, all rights reserved.


Budson AE, O’Connor MK. Seven Steps to Managing Your Memory: What’s Normal, What’s Not, and What to Do About It, New York: Oxford University Press, 2017.

Budson AE, Solomon PR. Memory Loss, Alzheimer’s Disease, & Dementia: A Practical Guide for Clinicians, 2nd Edition, Philadelphia: Elsevier Inc., 2016.

More from Andrew E. Budson M.D.
More from Psychology Today