What is temperament?

Temperament begins biologically through the genes one inherits. The DNA of one’s genome determines each person’s traits. The genome formulates how the fetal brain structures its neural circuits to establish a wide range of trait expressions [24]. Our traits are with us for life. However, they are continually shaped by environmental influences. Once traits are genetically coded, environmental influences begin to impact trait expression during fetal development and continues during infancy, childhood and throughout one’s adult life.

Overall, both biological and environmental processes establish one’s personality. Following Cloninger’s personality model, temperament has been viewed as the biological or nature side of personality, and character has been described as the nurture side that shapes a person’s responses through environmental influences [17, 25]. Currently researchers describe these two entities as intertwined, with temperament continuously affecting character and vice versa [26]. Temperament traits continuously trigger responses from the inside while the environment shapes a person’s character from the outside. Extreme environmental stimuli significantly impact behavioural responses, such as times of trauma and other adverse events. Trauma can significantly alters one’s character. Acute starvation, severe binge eating and purging episodes are ED traumatic examples that could cause epigenetic changes [27,28,29,30]. This means that the environment and one’s behaviours impact neurobiological and trait responses through alterations in gene expressions [29, 31, 32]. Gene expressions can be turned “on or off” throughout life based on influences from e.g., biological, dietary, environmental, and interpersonal experiences.

For example the environmental pressures to be thinner coupled with specific traits such as perfectionism, anxiety, and obsessiveness increase vulnerability to develop extreme dieting patterns that trigger gene expressions to alter [31, 33, 34]. However, the actual genes that code the identified traits remain constant. The environment can shape trait expressions, but it cannot change one’s traits. An example from nature is an oak tree. It is genetically coded to be an oak. That cannot change. It cannot become a maple or pine tree. But the way the tree grows, the extent of its branches, the height and breadth are all shaped in part by the environment. It remains that traits are the precursors to how a person responds, whether in calm to extreme environmental situations. When treatment focuses solely on ED symptoms and trauma, a major part of the problem and solution is ignored, one’s traits.

The relationships among traits, symptoms, and habit formation

Temperament consists of the biological ingredients that define us and is neurobiologically expressed through our traits [22, 35]. Traits influence actions. Symptoms are approached therapeutically as problematic or destructive responses or actions [36,37,38]. However, this does not mean that a person simply chooses to do destructive actions. Research has found that traits influence the development of ED symptoms [22, 39]. Symptoms are in part outward actions triggered in part by internal traits, which are in turn influenced by abnormal neural circuits that fire differently from those who do not have ED [40]. Externally, ED symptoms include excessive food restriction, binge eating, or purging behaviours [34, 41, 42]. Internally, ED symptoms look like significant dysfunctional neural circuits within the brain.

Habits occur when actions, healthy or unhealthy, become automatic through repetition [43]. From a neurobiological perspective, habits are unconscious learned responses established through repetition [2]. They are predisposed by a person’s temperament [19, 44]. Habits are neurobiologically efficient ways of expressing one’s temperament and coping with environmental stimuli [2]. There are compelling behavioural and neural data that suggests habitual responses may underlie the persistence of ED, such as those with severe-and-enduring anorexia nervosa (SE-AN) [45, 46]. Eating disorder habits become stronger the longer the illness persists [47]. Overall, traits influence which habits develop. Treatment can help shape whether habitual actions remain symptomatic or become healthy/productive. Traits, symptoms, and habits are important targets in clinical treatment because one’s traits biologically influence which actions that one expresses productively to destructively.

Figure 1 illustrates the relationships among temperament, symptoms, and habit formation. It visually describes that genes identify or code neural structures to develop trait expressions. Neural circuits continuously initiate and influence trait expressions and vice versa. The interactive process impacts trait expressions via neural circuit alterations which, in turn, impact habit formation. Environmental stimuli have an ongoing role in shaping trait expressions to become productive to destructive. Habitual behaviours strengthen brain circuit responses which in essence strengthens habits [48]. The paradox is that while genes and traits remain constant throughout life, trait expressions and their neurobiological rewiring continuously change. Clinicians could enhance their ongoing therapies with temperament-based, structured interventions that could help clients rewire their trait-syntonic ED symptoms into trait-syntonic productive habits.

Fig. 1

Temperament impact on eating disorder symptoms and habit formation

Preventatively, the same traits expressed destructively through ED symptoms could be rerouted to be trait-aligned or trait-syntonic productive actions contributing to the persistence of productive habits. Productive habits become stronger the longer they are practiced in the same way ED behaviours become persistent [49]. Early childhood is a prime time to identify and structure trait expressions in productive ways. One child may be fearless, while another holds back and is shy. A preventative intervention could include teaching parents how to identify their child’s traits and offering tools to structure and shape opportunities for their child to express their traits as strengths. This could encourage the child to be more comfortable with themselves as they play, learn, and interact with others.

A preventative example could be a child who has high achieving, perfectionistic, competitive, and detailed traits. These traits are associated with both highly impactful accomplishments and also with AN. The parents could explore if the child naturally enjoys and has a propensity to focus on words. They could help their child enter a local spelling bee. The attention to detail, the need to compete and to get every word spelled correctly reroutes a potential to focus from counting calories to letters. Letters could be less burdened with social pressures around body size and ED symptoms. A spelling bee provides structure for attention and actions to focus on new words each day with friends and family. Upon winning the local spelling bee, the child may have the drive to achieve more by going to the regional spelling bee. The child’s traits become strengthened and habitualized productively.

Traits are considered healthy until problems begin to occur biologically, interpersonally, or psychologically. Could the obsessive tendency to spell each word correctly coupled with high achievement and perfectionism traits become problematic? Yes. What begins as a fun challenge with traits expressed within healthy limits for the child’s developmental abilities, could become a dreadful experience when problems develop. The same traits that influence the best in the child’s performance could also bring out the worst if actions become too extreme. Warning signs such as increased isolation from friends and acute anxiety when failing to spell each word perfectly may arise. Treatment providers could help parents identify external structures that align with the child’s traits and within the child’s tolerance levels.

Hypothetically, rerouting anxiety and obsessions could mean that a plan that the regional spelling bee is enough for achievement this year. Then the parents and teachers could help the child refocus interests onto a new project to give the same traits a new outlet of expression within healthy limits. The project could have criteria that the child temperamentally relates to, such as a science project that requires attention to detail. Ongoing projects provide opportunities for the child’s traits to be expressed in fun and productive ways. They are non-food and dietary focused to reroute and reduce the potential for the child to develop problems with calories and body size. This does not guarantee that an ED will not develop. It offers a trait-based reroute to prevent the possibility from triggering a cascade of biologically harmful symptoms, such as ED. Shifting trait expressions to more productive and healthier levels of expression is referred to as sublimation. Overall, the child could experience opportunities that celebrate their traits as strengths.

How new decisions develop into productive or ED destructive responses/symptoms

Temperament is the neurobiological platform that defines and refines who a person is [50,51,52]. Overall, the brain is a global city containing millions of neural superhighway networks. They have intersections of communication that manage every aspect of the body in relation to environmental stimuli. While the brain remains the least understood of all body organs, advancing technology is zooming in with greater detail to observe what pathways are firing and how accurately or abnormally they are transmitting signals throughout the brain among those with ED [36].

New decisions are required when facing new interoceptive (internal), and environmental (external) experiences. The brain needs to assess and identify a new response. For example, “What do you want to do tonight?” is a new stimulus that requires a new decision and behavioural response. The brain directs cognitive attention to the new experience. The brain sorts through expansive amounts of neural data received from the physical senses and environmental stimuli. It also incorporates internal sensations, thoughts, and feelings. A high level of accuracy of the vast number of neurocircuit responses is fundamental in order for a person to make a well-informed decision.

How circuits respond to situations moment by moment contributes to one’s health as well as one’s ED. Brain research has compared neural responses of persons with ED, with those who have recovered from ED, and with those who have never had ED [53,54,55]. Findings have identified brain circuits that fire differently from those who do not have ED during and after the remission of ED [33, 54, 56, 57]. These findings indicate that some traits appear to increase the risk of developing and maintaining ED. For example, abnormal insular function appears to contribute to the inability to process gustatory, satiety and other interoceptive sensations causing errors in decision making [58,59,60]. Eating disorders in part consist of an overabundance of abnormally firing neurocircuits that contribute to habitual symptoms and relapses among those with AN and other ED [61,62,63].

If some to all of a person’s neural circuit responses are abnormally firing, judgement is skewed and clarity in decision-making is impaired. A simple parallel is one’s sight. If an individual is farsighted, it means that one’s eyes see objects clearly that are far away while they experience problems, or blurred vision, when seeing objects that are close. The blurring is caused by refraction errors in the eye influenced by genetic and environmental factors [64]. Decision-making involves a wide variety of neural circuits throughout the brain, with vision being but one area. Accurate neural circuit responses from one’s five senses and interoceptive cues are necessary to provide accurate neural information to navigate “clearly” through new personal and interpersonal decisions. In addition to trait influences, overall accuracy in neurocircuit responses is impacted when poorly supplied or well supplied with energy/glucose [65, 66]. Regardless, the brain makes decisions based on the neural signals it has at any given moment in time, accurate or inaccurate.

Figure 2 identifies the home base, or executive site, where decisions are formulated. It is located at the front of the brain, the dorsolateral prefrontal cortex (DLPFC). This cognitive brain area draws upon a vast amount of neural circuit input to make decisions regarding what to do or not to do in novel experiences. If neural circuits inform the DLPFC with accurate information, the neural information consolidates with clear information to make accurate decisions. If one or more of the neural circuit pathways from various brain areas offer erroneous cues, then thoughts, feelings, perceptions, and sensations tend to “blur” decisions [67]. Behavioural ED symptoms are, in part, consequences of trait-based abnormal neural circuit input that “blur” decisions [33, 38, 54, 68, 69].

Fig. 2

Brain areas and functions involved in decision making

Figure 2 demonstrates the large number of brain areas and massive number of neurocircuit networks required throughout the brain each time a new decision is made. It is overwhelming to comprehend. Yet the brain incorporates the immense neural data moment by moment every day. Overall, the more accurate the neural responses, the greater the potential for clear, productive responses, and vice versa. Decisions are skewed when input consists of a wide range of abnormal neurocircuit responses.

Neuroscience has identified differences in neurocircuit responses among those with ED compared to those without ED, in areas related to anxiety, interoception, and reward/punishment. This implicates neurocircuit involvement in symptom expression [33]. These neural alterations culminate at the DLPFC, skewing, and in some cases “blinding” decision-making for those with ED [69]. ED neurocircuit dysfunction includes errors in reward circuits that impact motivation and habit formation [38, 70, 71]. These dopamine neurocircuit responses are significantly lower in AN causing decreased motivation [72, 73], and vacillate between significantly low and excessively high dopamine responses among those with bulimia nervosa and binge eating disorder. This extreme vacillation increases one’s desire to eat significantly more compared to healthy controls [27, 74, 75]. Errors in interoception, one’s ability to experience physical sensations such as taste, satiety, hunger, or pain, highly impact decision-making [76, 77]. For example, a client cannot make an accurate decision to eat or to stop eating if they are unable to correctly assess if they are hungry or full. This does not appear to be due to one’s awareness or degree of mindfulness, but due in part to abnormal insular neurocircuit responses [78, 79].

In addition, there are neurocircuit errors in body image perception that contribute to body shape disturbances [79]. Neurocircuit errors in anticipation [80], contribute to increased anxiety [78, 81, 82], and to prediction errors among those with ED [70, 83]. Cognitive neurocircuit abnormal responses could contribute to increased inflexibility in decision-making [84, 85]. Reduced neural myelin across many neurocircuits, from reduced food intake, contributes to inflexible and rigid decisions [72, 86, 87]. Neural responses clarify if it is safe to respond or not to respond to new stimuli. Learned abnormal responses from former experiences continue to fold into current abnormal circuit responses compounding the repetitious development of symptomatic behaviours [38].

Dysfunctional neural circuit responses establish an increased inability to trust new decisions for those with AN [17]. Open-ended questions such as, “What do you want to do?” tend to trigger anxiety for those with AN, compared to persons without ED [46]. Open-ended questions imply unending options. For those with AN, this creates a problem in one’s expectation to sort through endless options to make a decision. Input from decreased insular and reward neurocircuits blurs input to the DLPFC causing doubt in decision-making. Offering two or three options recognizes the underlying inability to decide. Limited choices help the client compensate for skewed neural input and reason through each option to better trust their decision and reduce anxiety [17]. Is deliberate cognitive reasoning or over-thinking an act of “over control” as social media, families and some therapies indicate [16]? Or might it be the need to cognitively compensate by thinking intentionally about each option due to aberrant neural input transmitted to the DLPFC? This model points to the later.

Taken together, ED behavioural symptoms are triggered by a plethora of abnormal neurocircuit responses. Decisions are made based on skewed neural input. An assessment is made by the DLPFC drawing upon past and present neural circuit calculations and miscalculations [88]. The decision is transmitted, accurate or inaccurate, to the motor cortex areas to plan a new action for a response. The new action may range from productive to destructive depending upon neural and trait input and environmental influences.

The brain wires destructive symptoms into habits in the same way that it wires productive behaviours into habits

What does the brain look like neurobiologically when habits form? While it is evident that behavioural habituation is caused by different mechanisms depending on the time frame when the new responses are initiated, the sensory pathways involved, and the hierarchical level of signal processing, the brain remains highly conservative in reducing habitual responses for the sake of survival. [89]. The brain efficiently shifts neural responses from multiple brain areas needed when making decisions, illustrated in Fig. 2, to the central area of the brain [90,91,92]. This area in part transmits the refinement of habitual actions. As habits form, roles in the brain shift.

Cognition, attention, planning, and reward responses, which hold primary roles in decision-making, shift to secondary and even tertiary roles as habits form. The amount of input needed from each brain area appears to depend on fine-tuning factors such as the novelty of circumstances each time the habitual action is repeated [91, 93]. The prefrontal brain areas have already assessed if the action offers reward, satisfaction, or reduced punishment. One habi