When dementia progresses, communication becomes increasingly difficult. The ability to translate thoughts and needs to meaningful language deteriorates, for example, because of word finding problems. Also, people may have difficulty to translate their feelings and bodily sensations (e.g., hunger or pain) into concrete needs. The unmet needs model (Cohen-Mansfield et al. 2015) states that because of these communication problems and because of a decreased ability to be self-supporting in fulfilling one’s own needs, many needs of people with dementia are unmet. Challenging behavior subsequently arises as an outcome of frustration, as a means of fulfilling needs or as a means of communicating needs.

The unmet needs that lead to the challenging behavior may have various causes. In the unmet needs model, needs are categorized as “environmental,” “current condition,” and “lifelong habits and personality.” Environmental needs can refer to physical or psychosocial environment. The physical environment may create an unmet need for a person who wants to wander around, when there is no space to do so. The psychosocial environment can be the interaction with other people, for example, caregivers may create an unmet need when a person with dementia wants to be independent and autonomous while all tasks are taken over by nursing staff. The current physical or mental condition of a person with dementia may create an unmet need, for example, pain that arises when he or she is unable to communicate pain. Lastly, lifelong habits and personality may not attune with the current way that one’s life is arranged, which can result in an unmet need (Cohen-Mansfield et al. 2015).

When a person exhibits challenging behavior, it is therefore very important to make an objective description and to analyze which needs this person may have and which of those needs may be unmet. Together with disciplines like a physician, dietician, and/or occupational therapist, nursing staff can examine physical needs such as the possibility of a person being hungry, in pain, or sitting uncomfortably. The psychologist may help with analyzing psychological and psychosocial needs. It can be helpful to use the Camberwell Assessment of Needs for the Elderly (CANE) to structure the process of analyzing unmet needs (Cohen-Mansfield et al. 2015).

The progressively lowered stress threshold (PLST) model (Hall and Buckwalter 1987; Smith et al. 2004) starts with the assumption that every person had a threshold for the amount of stress he can cope with before he becomes upset. This threshold is more or less stable once it is set in adulthood, although it can be temporarily lowered by circumstances such as feeling ill or going through a major life event. The basic principle of the PLST model is that due to brain damage, the stress threshold of people with dementia lowers during the disease. Also because of brain damage, people with dementia experience stimulants that are not particularly distressing for healthy people as stressors (e.g., the noise of a television or people walking by), and due to cognitive impairment, many stressful situations arise (e.g., not knowing where you are or not recognizing family or friends). Because of these disadvantages, the chance of a person with dementia to cross the stress threshold and become upset is heightened. The third disadvantage a person with dementia has to deal with is that he or she is often unable to recognize the feeling of crossing the threshold and/or is unable to independently undertake action to lower the stress. The behavior that follows is a result of coping with stress, for example, by shouting out or becoming agitated.

The model helps caregivers in analyzing behavior and adapting the environment so that it becomes less stressful. It also explains the pattern of behavior that is often seen in residential settings. Often, in the afternoon or the early evening, challenging behavior is most apparent. The PLST model might explain this phenomenon, because stressors accumulate during the day while the stress threshold decreases during the day because of the lowered amount of energy most people with dementia have. When a clear behavioral pattern is recognizable throughout the day, it is thus helpful to analyze the amount of stressors and the possibility of adapting the environment and the daily activity plans.

With functional analysis, factors that cause behavior or that cause behavior to continue are analyzed (Moniz et al. 2012). Usually, the ABC approach is used in which A stands for “antecedent,” B for “behavior,” and C for “consequences.” Antecedents of behavior can be found by observing the situation before the challenging behavior starts. For example, you can observe a person sitting quietly in a chair while nurses are passing by (“A”). In “B,” the behavior is described objectively and detailed, for example, “Mr. Smith begins to move in his chair and makes a clicking sound with is tongue. After 2 min, he stands up and calls out ‘help help’ to the nurses.” Finally, the consequences following the behavior are described. Often, immediate and prolonged consequences are described, for the immediate consequences can cause behavior to continue while prolonged consequences are often the reason for consulting a physician or psychologist. An immediate consequence could be that a nurse speaks with Mr. Smith, calms him down, and helps him back into his chair. A prolonged consequence could be that nurses become frustrated, avoid or ignore Mr. Smith. Preferably, the interventions that are drawn up after making a functional analysis aim at the antecedent, for this might prevent the behavior from happening. However, this is not always possible, for example, when encountering a specific fellow resident is an antecedent. Also, an antecedent might also be a consequence, for example, when calling out of one resident (A) leads to another resident shouting back (C) which triggers (A) agitation (B) in the first resident. If, for whatever reason, treating the antecedent is not possible, treatment will focus on diminishing the consequences that cause the behavior to continue.

The models that are described above do not exclude each other and can be used together when analyzing challenging behavior. The models overlap in that they are based on the principle that challenging behavior is a symptom that something is upsetting the person with dementia. Because the reason why a person with dementia becomes upset can lie on different levels and on different areas of expertise, multidisciplinary collaboration is crucial for the analysis and treatment of challenging behavior. It is important to combine the analysis of biological factors, psychological factors, and social factors into one biopsychosocial model in which all aspects of the behavior are joined together (Cohen-Mansfield 2000; Zwijsen et al. 2016).