In my previous blog, I described “temperament” as one’s constitutionally determined way of responding emotionally to the world and introduced Akiskal’s five affective temperaments: Depressive, Hyperthymic, Cyclothymic, Irritable, and Anxious (1). Akiskal’s conceptualization of temperament begins with endophenotypes; that is, the outward expression of a gene or trait. These descriptive endophenotypes provide the scaffolding from which one learns about the underlying processes involved in their formation and evolution. This approach to studying personality and temperament can best be described as “top-down” – start with what you observe and go from there, from macro to micro. Another example of the “top-down” view includes the work of Eysenck, who described three “dimensions” of human personality: Neuroticism (N), Psychoticism(P), and Extroversion (E) (2). Still another example is that of Cloninger, who described temperament using the following terms: novelty seeking, harm avoidance, reward dependence, persistence, self-directedness, cooperativeness, and self-transcendence (3).
While the “top-down” approach plays an important role in identifying and describing the wide range of temperament, others have used brain circuitry as their starting point. This would be a “bottom-up” approach, in which what is learned at the level of neurons, neurotransmitters and neural networks lays the groundwork for observed endophenotypes. I will now attempt to summarize what we know to date about this circuitry, as well as how it can help us understand approach/avoidance patterns of behavior that underlie personality traits as well as anxiety, depression and mania.
In 1991, Jeffrey Gray, a British psychologist, proposed that temperament is formed on the basis of three neurologically based systems: the Behavioral Approach System (BAS), the Behavioral Inhibition System (BIS) and the Fight/Flight System (FFLS) (4). This later became known as the Reinforcement Sensitivity Theory (RST), based on the observation that reinforcement is a prominent feature of the BAS, BIS and FFLS. Briefly, reinforcers are responses from the environment that increase the probability of a behavior being repeated. Reinforcers can be positive (reward) or negative (removal of an adverse stimulus)(5). For example, Gray defined the Behavioral Approach System (BAS) as activated by signals of reward and/or removal of punishment. Both the Behavioral Inhibition System (BIS) and Fight/Flight System (FFLS) would be activated by nonreward and/or punishment; however, in the BIS, all behavior would be inhibited, while in the FFLS, the subject would engage in active escape (flight) or defensive aggression (fight).(4)
Assuming that different neurocircuitry is involved for each component of the Reinforcement Sensitivity Theory (RST) – for the BAS, BIS and FFLS – how exactly does this translate into the formation of temperament? According to Gray, “Temperament reflects individual differences in predispositions towards particular types of emotions” (4). One way of interpreting this idea is an individual comes into the world with his or her own pre-programmed way of behaving in response to the environment. This “programming” sets the individual up to respond with specific behaviors (approach, avoidance, or fight/flight) to “reinforcing” environmental stimuli. Repeated interactions with reinforcers establishes the outward manifestation (endophenotype) of temperament. For example, a person who has several close relatives with severe anxiety may come into the world “primed” for fearful reactions to the environment. In this person, the Fight or Flight System (FFLS) might be triggered by seemingly harmless stimuli that are associated with what caused the initial fear response (flight). Or the Behavioral Inhibition System (BIS) may be overactive, causing the person to feel paralyzed in multiple situations. The pattern becomes “reinforced,” over time, solidifying his or her affective temperament.
Gray’s work has been expanded and supported by Depue and Collins, who in 1999 proposed a neurobiological model of incentive reward and extraversion (6). They began with Eysenck’s concept of extraversion, focusing on components of interpersonal engagement and impulsivity, and created a model of “positive incentive motivation. ” This model is thought to be triggered by signals of reward and is based on the Behavioral Approach System (BAS). Communication throughout the reward circuit (which includes such brain structures as the nucleus accumbens, ventral tegmental nucleus, medial orbital prefrontal cortex, hippocampus and amygdala) is maintained by the neurotransmitter dopamine. In this circuit, there is an emphasis on “appetitive stimuli” that creates a situation of “incentive motivation” (i.e. the feeling of “I’ve got to have this now!!!”) and results in approach towards the desired object. Individual differences in dopamine functioning are thought to underlie one’s sensitivity to reward and triggering of the BAS. One can see how dysregulation of the BAS can get a person into trouble. Indeed, BAS sensitivity has been implicated in mania, substance abuse, compulsive gambling and ADHD (7).
The idea of Gray’s Reinforcement Sensitivity Theory (RST) being applied to modern research on mood disorders offers intriguing possibilities according to Gonen et. al. Based on neuroimaging and other data, they propose an “integrative model” of bipolar disorder in which “dysregulated interactions of both punishment and reward related processes… account for the psychological and neural abnormalities observed in (bipolar disorder) (8).” Interactions between motivational systems (BAS and BIS) determine mood state – mania or depression. For example, BAS over-activation (enhanced reward sensitivity and approach behavior) with BIS under-activation (reduced punishment sensitivity and avoidance) would result in a manic state. Conversely, BIS over-activation (enhanced punishment sensitivity and avoidance) with BAS underactivation (reduced reward-driven approach behavior) would result in depression (8).
Gray’s Reinforcement Sensitivity Theory (RST) proposes a model of temperament that starts at the level of neural circuitry. These circuits reflect an inborn susceptibility to signals of reward (high BAS sensitivity) or punishment (high BIS sensitivity). Interactions between the individual and the environment reinforce such sensitivities and result in longstanding patterns of behavior. Depue and Collins use the RST as a starting point in describing a model of positive incentive motivation fueled by dopamine. Finally, Gonen et. al. apply the RST to their integrative model of bipolar disorder, which explains mood states in terms of inbalances between BAS and BIS. While our understanding of these processes is far from complete, each of these contributions offers a means by which we can translate brain circuitry into an outward manifestation of mood or temperament.
Susan Stern, M.D.