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Why Do People with Dementia Suddenly Become Aggressive?

The thoughtful pause between stimulus and response may deteriorate in dementia.

In the last post, we discussed how and why frustration, depression, anxiety, and not participating in activities are common in dementia. In this article we’ll tackle the thorny issues of apathy, irritability, agitation, aggression, combativeness, inappropriate behavior, willfulness, and sundowning.

Apathy is common in dementia. When dementia damages the front of the brain or some of its connections, apathy can result. The normal drive to plan for the future is lost. Sometimes this loss can manifest by letting house repairs go, neglecting to pay bills, or not going to the grocery store until every scrap of food in the house is gone. When more severe, the desire to do anything at all may be gone, and the individual with dementia can sit passively for hours staring at a blank wall or a television that is not turned on.

Irritability, agitation, aggression, combativeness, and inappropriate behavior are common in dementia. Has something ever upset you and you felt like breaking something or hitting someone? What would have happened if the part of the brain that stopped you from acting on those feelings was not working? Because the front part of the brain provides the pause between stimulus and response, when it or its connections are damaged, a person may react without thinking. Vascular dementia frequently damages the connections to and from this part of the brain. Other causes of dementia damage it directly. Because of this damage, a person with dementia may act on their feelings without pausing to think whether the action is appropriate or not. They may steal food or other items. They may gamble excessively or engage in other risky behavior. And they may say or do sexually inappropriate things, use more profanity, or make racists or sexists comments.

Disinhibited behavior can lead to safety issues. When your loved one has behavior problems it can be distressing, physically exhausting, and heart-breaking. Behavior problems can also lead to safety issues. Dementia may lead individuals to act precipitously without thinking of the consequences. If they are feeling angry, they could strike out with their fists or any available item, including knives, guns, and baseball bats. If they feel like getting out of the car they may do so—despite the fact that the car is moving! In later posts, we’ll discuss ways of managing these safety issues.

Willfulness: Resisting doing activities that they need to do.

One does not need to have dementia to exhibit willfulness. You’ve likely encountered a child (or stubborn individual or any age) who refuses to do something which obviously needs to be done, such as change their clothes after a urinary accident. In situations where someone is acting willfully, simply making your point rationally will not win the argument. Many individuals with dementia have both apathy and difficulty controlling impulses. They may be completely content sitting in a chair for hours, but if you want them to do something different—such as go to the bathroom to prevent an accident, get dressed to go to an appointment, brush their teeth, bathe, or get out of the car after it is parked—not only can they willfully resist but they may suddenly become violent with little warning.

Sundowning: Behavior and cognition may worsen at the end of the day.

For most older adults, cognition worsens at the end of the day, including memory, language, vision, and reasoning. In healthy individuals, the difference is typically small, such that only pencil and paper testing can detect the subtle changes. In an individual whose brain is impaired by dementia, the decline in cognition is often marked, and behavioral changes are usually prominent as well. There are many theories as to why this decline occurs, and there is probably some truth in all of them. Older adults may be tired at the end of the day, and no one’s thinking and memory are sharp when they are tired. There is less light after sunset, and because we depend upon vision to make sense of the world, sight may be diminished in the evening, leading to confusion and disorientation. Lastly, either due to a sleep cycle disturbance or simply because sleep cycles are not clearly separated in individuals with dementia, parts of the brain may become drowsy and dysfunctional while other parts of the brain are fully awake.

Key Questions

I don’t mind cleaning up when she doesn’t make it to the bathroom in time and soils herself, but why is she fighting me when I try to get her washed up?

  • Willfulness is common once dementia reaches the moderate to severe stage. Individuals may be happy and content but suddenly become obstinate when asked to do something they don’t want to—even when is reasonable or necessary.

He’s good in the morning, fine at lunch, confused in the afternoon, and a terror in the evening. What’s going on?

  • Sundowning is the term used when cognition or behavior declines in the afternoon and evening in dementia. Theories as to why it happens include fatigue, poor vision in waning light, and a disrupted sleep cycle such that part of the brain is drowsy while another part is wide awake.

© Andrew E. Budson, MD, 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.

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