The brain is key to our existence, but there’s a long way to go before neuroscience can truly capture its staggering capacity. For now though, our Brain Control series explores what we do know about the brain’s command of six central functions: language, mood, memory, vision, motor skills and personality – and what happens when things go wrong.
Personality is a broad term describing how people habitually relate to the world and their inner self. After the developmental period through childhood and adolescence, these patterns of relating remain reasonably stable through life. They are then referred to as traits and influence behaviour, thinking, motivation and emotion.
Since everyone is different in their own way, psychologists have debated how to characterise personality. The most popular approach has so far been to use five dimensions: openness to experience (curious or cautious), conscientiousness (organised or careless), extraversion (outgoing or solitary), agreeableness (friendly or detached) and neuroticism (nervous or secure).
A self-report questionnaire is often used to give a score to each dimension, which then describes someone’s personality. These descriptions have been used to understand normal and abnormal behaviour, and to predict work success, academic achievement and interpersonal relationships.
Both genetic and environmental factors determine someone’s personality. Genes account for between 30-50% of the determination and the rest is made up largely of environmental experiences unique to the individual.
History of personalityWikimedia Commons
Understanding the neurological physiology of personality is sometimes seen as the holy grail of psychology, and was the topic of Sigmund Freud’s first paper, Project for a Scientific Psychology, in 1895.
Early developments in this field came from historical case descriptions.
The classical case is of Phineas Gage (1823-60), an American railroad worker who had a large iron rod driven completely through his head in an accident, which destroyed most of his left frontal lobe and resulted in a profound personality change.
After the accident, Gage was described as having become “fitful, irreverent, indulging at times in the grossest profanity (which was not previously his custom), manifesting… little deference for his fellows, impatient of restraint or advice when it conflicts with his desires.”
From this case, the frontal lobes, which occupy the front third of the brain, emerged as the seat of higher functions such as judgement, motivation, regulation of behaviour and social consciousness.
Later, in the early 20th century, neuroanatomists identified the limbic lobe – an arc-shaped part of the frontal, temporal and parietal lobes that sits in the middle of the brain – as the seat of emotion. It was recognised as making an important contribution to personality.
As our understanding evolved, personality has been regarded as a composite of character and temperament.
Temperament is understood as the way the body produces behaviour. It refers to certain biases an individual has when responding to external stimuli.
A well-established model proposes that whereas personality traits are based on habitual behaviour, temperamental traits are someone’s predispositions when it comes to four areas: harm avoidance, novelty seeking, reward dependence, and persistence. These are closely related to basic emotions such as fear, anger, attachment and ambition.
High harm-avoidance leads to avoiding behaviours that don’t produce reward or cause punishment; as in people who are shy, uncertain or socially inhibited.
Individuals with such traits have increased activity in the fear circuit of the brain, involving the amygdala and other structures of the limbic lobe.from shutterstock.com
This activity has been linked to abnormalities in two neurotransmitters: serotonin and γ-amino butyric acid (GABA). Modulating these with drugs – such as selective serotonin reuptake inhibitors (SSRIs that include Prozac) and benzodiazepines, including Valium – can help people with depressive, anxious and obsessive thoughts.
Novelty seeking leads to exploration and individuals high on this trait are curious, quick-tempered, impulsive and easily bored. They have increased activity in the basal ganglia, which are clumps of neurons sitting in the middle of the brain. This trait has also been linked to the so-called pleasure molecule dopamine, which acts on the basal ganglia, and changes in this pathway are associated with seeking novelty in different ways.
People with high reward dependence seek social rewards and are likely to be socially sensitive and reliant on social approval. Those low on this trait are tough-minded, cold and aloof.
The temporal lobes of the brain play a major role in how we process social cues, and increased activity in the anterior part of these lobes and in a brain structure called the thalamus has been related to higher levels of reward dependence.
Persistence leads to the maintenance of a behaviour despite fatigue, repetitiveness and frustration, and often results in such qualities as industriousness and determination. The regions of the brain particularly important for this include the inner and lower parts of the frontal lobes, especially those called the anterior cingulate and the orbitofrontal cortex, and their networks that involve the basal ganglia.
Persistence is loosely related to motivation. Emotion plays a major role in maintaining this drive, as basic emotions, such as happiness, tend to energise behaviour and lack of emotion has the opposite effect.
Authors: Perminder Sachdev, Scientia Professor of Neuropsychiatry, Centre for Healthy Brain Ageing (CHeBA), School of Psychiatry, UNSW Australia