Changes to brain structure and function can lead to significant changes in personality and behavior.

Neurodegenerative disease can lead to changes in a person’s social interactions. These changes may occur because of structural and neurochemical changes in the brain that affect the person’s ability to process and act on information.


While people use the term personality to mean many different things, it has been very precisely defined over decades of modern psychometric research. There are different theoretical approaches to defining personality, but the predominant trait theory suggests that personality is the characteristic pattern of thoughts, feelings and behaviors habitually enacted by an individual. The main traits of personality are a continuum of behavior along five dimensions:

  1. Openness to new experiences
  2. Conscientiousness
  3. Extraversion
  4. Agreeableness
  5. Neuroticism

While temperament is biologically-based and is present before birth, rudimentary elements of personality begin to appear around the age of two and are very malleable and subject to dramatic shifts until they stabilize in early adulthood. Researchers generally agree that though personality does undergo gradual and mild developmental fluctuations after this point, it remains fairly consistent throughout the remainder of one’s life. It is of interest to caregivers, clinicians and researchers involved in the lives of patients with dementia because some types of neural degeneration and injury can lead to profound changes in personality.

The Anatomy of Personality

Neuroimaging studies in healthy individuals and those with brain diseases have revealed a relationship between personality traits and specific brain regions. Generally, the right hemisphere of the brain plays a more central role than the left in social and emotional behavior, thus many regions related to personality are primarily right-sided. Some of the main research findings involve traits related to extraversion and agreeableness:

  • Extraversion – Extraverted people tend to seek out social interactions and engage in them in an active, often highly verbal manner. Accordingly, extraversion mostly relates to dorsolateral frontal lobe regions associated with action planning, task management and goal setting. In addition, extraversion correlates with brain regions involved in emotion processing such as the insula and the anterior cingulate, reflecting the emotional aspects of social engagement.
  • Warmth – Warm-hearted people also seek social interactions, but desire to provide care and support to others, even to the extent of often putting others’ needs above their own. In line with this behavioral pattern, the personality trait warmth relates extensively to brain regions involved in emotion processing, including the amygdala, temporal pole, insula, anterior cingulate, and the most anterior parts of the frontal lobes.
  • Dominance/Assertiveness – Dominance reflects the tendency to negotiate with one’s environment to accomplish personal goals, regardless of whether those goals conflict with those of others. Thus, similarly to extraversion, dominance relates to brain regions involved in action planning and task management; however, in contrast to extraversion, dominance does not appear to involve brain regions that mediate emotion processing.

Though there is now considerable evidence for a structural basis for personality in the brain, other non-structural organic and environmental factors influence personality as well. For instance, depressed individuals likely have altered neurotransmitter and hormone levels in the brain and might become less extraverted, warm-hearted and assertive even without structural brain changes. Individuals with language problems severe enough to impair their communication with other people might become less extraverted and assertive because they can no longer accomplish their interpersonal goals verbally.


Emotional and behavioral symptoms are common in dementia and can be major sources of stress to patients and their caregivers. Some of the most common emotional and behavioral changes associated with dementia are:

  • Apathy & Indifference – lack of motivation to start new activities and continue old ones, reduced participation in household chores, loss of interest in talking to other people, becoming less affectionate and emotionally expressive.
  • Depression & Dysphoria – tearfulness and crying, consistently low mood, feelings of failure, despair about the future, suicidal thoughts and actions.
  • Disinhibition – acting impulsively without thinking, saying or doing things not usually done or said in public, doing things that are embarrassing to others.
  • Euphoria & Elation – inappropriate giggling and laughter, playing childish games, feeling excessively good for no apparent reason, making grandiose claims about one’s abilities or wealth.
  • Anxiety – being nervous or worried, avoiding situations that cause nervousness, tenseness or shortness of breath with no physiological explanation.
  • Irritability & Lability – increased temper, crankiness, rapid mood changes.
  • Agitation & Aggression – resisting those trying to help, refusing to cooperate, stubbornness, yelling, hitting.
  • Eating Disorders – changes in weight (gain or loss), changes in appetite, changes in appropriate eating behavior, preferences for only certain types of foods.
  • Sleep Disturbances – difficulty falling asleep or staying asleep, wandering or pacing in the middle of the night, getting up and getting dressed.
  • Stereotyped Motor Behaviors – repetitive behaviors such as opening and closing doors or drawers, repeatedly picking at things, pacing back and forth.
  • Hallucinations – seeing or hearing things that do not exist.
  • Delusions – holding false beliefs, such as thinking family members are not who they say they are, that others intend one harm, or that one’s home is not his/her home.

Anatomy of Emotion & Behavior

Emotional and behavioral symptoms are thought to be caused by damage to specific areas of the brain that are responsible for directing our attention, motivating our behavior, and learning the significance of what is going on around us. Pioneering work by Papez (1937) originally suggested that emotion is related to a ring of structures in the center of the brain called the limbic system. This ring includes the hypothalamus, anterior thalamic nuclei, cingulate cortex and hippocampus. More recent research has shown that some of these structures are not as directly related to emotion as others, while additional structures have also been added to the list. The following brain structures are currently thought to be most involved in emotion and behavior:

  • Amygdala – The amygdalae are two small round structures located near the anterior (front) end of the temporal lobes. The amygdalae are involved in detecting and learning what parts of our surroundings are important and have emotional significance. They are critical for the production of emotion and may be particularly important for the generation of negative emotions, especially fear.
  • Prefrontal Cortex – The term prefrontal cortex refers to the very front part of the brain located behind the forehead and above the eyes. It appears to play a critical role in the regulation of emotion and behavior by anticipating the consequences of our actions and inhibiting behaviors. The prefrontal cortex may play an important role in delayed gratification by maintaining emotions over time and organizing our behavior toward specific goals.
  • Anterior Cingulate – The anterior cingulate cortex (ACC) is located in the middle of the brain just behind the prefrontal cortex. The ACC is thought to play a central role in attention and may be particularly important with regard to one’s conscious subjective emotional awareness. This region of the brain may also play an important role in the initiation of motivated behavior.
  • Ventral Striatum – The ventral striatum refers to a group of subcortical structures thought to play an important role in emotion and behavior. One part of the ventral striatum called the nucleus accumbens is thought to be involved in the experience of goal-directed positive emotion. Individuals with addictions, for example, experience increased activity in this area when they encounter the object of their addiction.
  • Insula – The insular cortex is thought to play a critical role in the bodily experience of emotion, as it is connected to other brain structures that regulate the body’s autonomic functions (heart rate, breathing, digestion, etc.). This region also processes taste information and is thought to play an important role in experiencing the emotion of disgust.

Impact of Neurologic Illness on Emotion & Behavior

Neurologic disorders result in different patterns of emotional and behavioral changes depending on what parts of the brain are affected. In frontotemporal dementia, behavioral and emotional changes are often dramatic and form the core clinical features of the disorder. In other disorders, behavioral and emotional changes may occur but are often less common or less severe.

  • Behavioral Variant Frontotemporal Dementia (bvFTD) – bvFTD is associated with atrophy of the prefrontal cortex, anterior cingulate, insula and ventral striatum. When this atrophy is predominantly right-sided, bvFTD is almost always associated with changes in behavioral and emotional function. The changes most commonly associated with bvFTD are apathy, disinhibition, stereotyped motor behaviors and eating disorders (specifically increases in appetite and strong preferences for sweets or other particular foods). Other behavioral changes in bvFTD include elation and euphoria, aggression, irritability, sleep disturbances, depression and anxiety. Sometimes patients with bvFTD also develop addictive behaviors late in life.
  • Semantic Variant PPA (svPPA) – svPPA results from atrophy of the anterior temporal lobes (including the amygdala), insula, prefrontal cortex and anterior cingulate. Though more commonly thought of as a language disorder, svPPA is often associated with dramatic changes in behavioral and emotional function& as well. Disinhibition and compulsive behaviors are the most common changes in svPPA. Other common changes include apathy, eating disorders, sleep disturbances, elation and euphoria, as well as depression, anxiety, irritability and aggression.
  • Alzheimer’s Disease (AD) – The behavioral and emotional changes seen in AD, on average, are less severe than those that occur in bvFTD and svPPA particularly in the early stages. The most common behavioral change associated with AD is apathy. Also common in AD are irritability, agitation, depression, anxiety, sleep disturbances, and eating disorders (especially a decreased appetite and loss of weight).
  • Dementia with Lewy Bodies (DLB) – DLB may be associated with many of the same changes seen in AD. DLB is often associated with vivid hallucinations (such as small children or animals).
  • Other Disorders – Behavioral and emotional changes are less common or less severe in disorders such as corticobasal syndrome (CBS), progressive supranuclear palsy (PSP) and nonfluent variant primary progressive aphasia (nfvPPA).

Social Skills

Neurodegenerative disease can lead to changes in a loved one’s social interactions. These changes may occur because of structural and neurochemical changes in the brain that affect a person’s ability to process and act on information. Common functional areas affected by dementia are:

  • Self-awareness – Being able to reflect on one’s actions, how these actions may be interpreted by others, and the ability to modify one’s behavior accordingly.
  • Other-awareness – Being able to both recognize and interpret another’s emotions and intentions and to respond to them appropriately.
  • Adherence to social norms – An understanding and adherence to social norms and situation-appropriate behavior, an avoidance of punishment, ostracism, ridicule or making others uncomfortable.
  • Interpretation of social behavior – The ability to understand situations, to follow conversations, to distinguish between what is said and what is implied.
  • Interpretation of emotional cues – The ability to understand facial expressions, emotions in a person’s voice, body posture and gesticulations.

The Anatomy of Social Function

The neuroanatomy of social function is not well understood. Structures throughout the brain are thought to be involved, including the frontal lobes and the right temporal lobe. Alterations in neurochemistry may also be responsible for changes in personality and social interaction. Though until recently, very little direct study of social interactions in individuals with a neurodegenerative disease has been performed.