Personality neuroscience uses neuroscientific methods to study the neurobiological mechanisms underlying individual differences in stable psychological attributes. Specifically, personality neuroscience aims to investigate the relationships between inter-individual variation in brain structures as well as functions and behavioral measures of persistent psychological traits, broadly defined as "predispositions and average tendencies to be in particular states", including but are not limited to personality traits, sociobehavioral tendencies, and psychopathological risk factors. [1] Personality neuroscience is considered as an interdisciplinary field integrating research questions and methodologies from social psychology, personality psychology, and neuroscience. It is closely related to other interdisciplinary fields, such as social, cognitive, and affective neuroscience.
Personality neuroscience is a field built upon the study of personality, which has been a central theme in psychology and evolving through various theoretical perspectives as well as methodological approaches over many years. Specifically, personality neuroscience aims to understand what neurobiological mechanisms underlie and contribute to personality, and therefore, is primarily based on theories that attribute individual differences to physiological and biological systems of the human body or brain. These theories can be traced back to many theories proposed by early physicians, philosophers, and psychologists. [2] Ancient Greek physician Hippocrates developed the theories of Humorism by identifying four vital bodily "humors" or fluids (i.e., blood, phlegm, black bile, and yellow bile) to be associated with temperaments (i.e., sanguine, phlegmatic, melancholic, and choleric, respectively) as well as physical health outcomes. [3] In the early 20th century, the psychoanalytic theories put forth by Austrian neurologist Sigmund Freud was anchored on the unconscious mental processes. [4] Influenced by the psychoanalytic theories, American psychologist Henry A. Murray proposed five principles of personology, his term for the study and system of personality, in which the first principle states that "personality is rooted in the brain. The individual's cerebral physiology guides and govern every aspect of personality". Relatedly, Murray also suggested that "needs", which is the motivation that drive behaviors, arose as a result of "a physiochemical force in the brain". [5] American psychologist William Sheldon was known for his work on defining three "somatotypes" (i.e., body types: endomorphs, mesomorphs, and ectomorphs) to personality attributes. [6]
As early as the late 19th century, the case study of Phineas Gage, a railroad worker who survived a severe brain injury from an accident and underwent a significant personality change, was the first to suggest a causal link between the brain and personality. [7] In the 1940s, there were studies investigating the association between brain wave patterns and individual differences using twin study paradigms, demonstrating that identical twins showed remarkably similar brain wave patterns measured by electroencephalography (EEG) when compared to fraternal twins. [8] [9] However, results from these studies were deemed hard to interpret "in the absence of any satisfactory theory linking brain-wave patterns to personality". [10] Building off these studies and other studies that investigated the genetic inheritance of psychological attributes, in 1951, Hans J. Eysenck and D.B. Prell experimentally tested the heredity of neuroticism using a twin study paradigm and concluded that "the factor of neuroticism is not a statistical [artifact], but constitutes a biological unit which is inherited as a whole" and "the neurotic predisposition is to a large extent hereditarily determined". [10] Following this work, Eysenck continued to investigate psychological traits in relation to neurobiological systems, including the nervous systems, arousal, and brain structures (e.g., reticular formation and the limbic system). [11] [12] [13] In 1961, American psychologist Gordon W. Allport defined personality as "the dynamic organization within the individual of those psychophysical systems that determine his characteristic behavior and thought", localizing personality within "psychophysical systems". [14]
Extending from Eysenck's theory on the biological basis of personality, Jeffrey A. Gray's reinforcement sensitivity theory of personality and his work that studied the neural mechanisms underlying personality traits set the foundation for the contemporary field in personality neuroscience. [15] [16] For example, Gray's work suggested that introversion involved both the ascending reticular activating system and an inhibitory system of brain areas including the orbital frontal cortex, medial septal area, and. the hippocampus. [15] In 1999, a chapter titled "The neuroscience of personality" written by Alan D. Pickering and Jeffrey A. Gray was published in the Handbook of personality: Theory and research, in which it introduced ways to "build a modern, integrated neuroscience of personality". [17]
Although there had long been theoretically driven interests and experimental endeavors to understand the neurobiological basis of personality, it wasn't until recent years that, with the advancement in neuroscientific methodologies (e.g., non-invasive neuroimaging methods), the focus of personality psychology began to shift from observing, describing, and categorizing the phenomenon of individual differences towards discovering what may contribute to these observed individual differences. [18] In 2010, the name "personality neuroscience" was coined by Colin G. DeYoung, [19] [20] who is a psychology professor and the director of the DeYoung Personality Lab at the University of Minnesota. [21] [22] In 2018, the Personality Neuroscience journal was established to "[publish] papers in the neuroscience of personality (including cognitive abilities, emotionality, and other individual differences) concerned with understanding causal bases" with "its focus on the equal importance of personality and neuroscience". [23]
As personality neuroscience seeks to understand the link between personality and its underlying neurobiological mechanisms, generating testable hypotheses involve both the measurements of personality attributes and neurobiological structures and/or functions. [19]
In the field of personality psychology, there have been two main approaches to define personality traits: [2]
In personality neuroscience, personality is often defined using the nomothetic approach. Personality trait is typically measured using scales developed for the personality attributes of interests and administered through self-report surveys and questionnaires. One of the most commonly used ways to measure personality attributes in personality neuroscience research is the Big-Five personality traits. In addition to the criticism by proponents of the idiographic approach as mentioned above, self-report measures on personality traits in general are susceptible to response biases (e.g., social desirability bias, acquiescent response bias, etc.) and inaccurate introspection of mental states. Therefore, it is important to establish construct validity of the self-report measures of personality by using other scales of the same construct or other modalities of measures, such as behavioral data or aggregated ratings from other knowledgeable informants. [33]
Another common nomothetic approach is the Affective Neuroscience Personality Scales (ANPS). The ANPS was originally published in 2003 and was used by neuroscientists to evaluate the primary emotional systems that underlie mental well-being and affective brain disorders. [34] This scale was created by Jaak Panksepp so that researchers could use this self-report test to measure differences in the primary emotions, SEEKING, LUST, CARE, PLAY (the positive emotions) and FEAR, SADNESS, ANGER (the negative emotions). These differences in the emotions were then compared to the Big Five personality to look at the scale from an evolutionary perspective as the primary emotions were seen as a survival mechanism of inherited behavioral patterns by humans interacting with their environment. [35] Each of these primary emotions have “been evolutionarily shaped in terms of inherited tools for survival and, more generally, for fitness” and are seen to regulate human nature. [36] The SEEKING energy is used to seek valuable resources for survival, such as food, a mate, or shelter. The LUST energy is used to sustain the human species through reproductive means. The CARE system is significant in order to protect offspring so that they can grow into adults and the species is sustained once again. PLAY is important in order to foster social bonding between humans, to learn social and motor skills, and to regulate emotions. On the other hand with negative emotions, the FEAR energy is used for safety and to keep away from danger through means such as the flight or fight response. The SADNESS system, from an evolutionary perspective, is used to maintain socialness of an individual, as being isolated often evokes this emotion. The ANGER energy is important to protect resources from others or the environment. [37]
However, since the late 2010s, researchers have begun to question the relevancy of ANPS and have identified areas of improvement. The primary emotional systems in psychopathologies often fluctuate. The assessment is also only found in one long version, and patients with depression who suffer from fatigue would benefit from a shorter version. Furthermore, the FEAR and SADNESS emotions exhibit high correlation because they are closely related, and it would be useful to find a method to disentangle them to better study them. Another concern is that the original ANPS does not assess individual differences in LUST. [38]
To study the neurobiological mechanisms, or the structures and functions of the brain, underlying personality, personality neuroscience research employs established methods from neuroscience research. Some of the available neuroscientific methods are listed below with brief descriptions and how they can be incorporated in personality neuroscience research. [18]
Magnetic resonance imaging (MRI) is a non-invasive imaging technique that uses the physical properties of magnetic fields and injection of radio-frequency pulses to examine the brain structure and functions with high spatial resolution. [39] Both sMRI and fMRI have been used widely in both clinical and research settings to establish associations between the brain and a wide range of human socio-cognitive and psychological processes, [40] [41] [42] as well as individual differences. [43] Structural MRI (sMRI) of the brain provides the information on the neuroanatomical properties of the brain, such as the volumes of the gray and white matter. [44] Functional MRI (fMRI) of the brain maps the functional organization of the brain by monitoring the localized brain activation through the change in blood oxygenation level as a result of the cerebral blood flow (CBF), either when participants are engaging in tasks (i.e., task-based fMRI) or at rest (i.e., resting-state fMRI). [45] In addition to examine brain structure and function within localized brain regions, topological network analyses, such as graph theory in network neuroscience, can be conducted across brain regions to map out structural and functional connectivity patterns that vary with inter-individual variation in cognition and behaviors. [46] [47] In recent years, large MRI datasets, such as the Human Connectome Project (HCP), were collected with the aim to investigate the individual differences in structural and functional connectivity of the brain networks underlying a wide range of cognitive processes elicited by fMRI tasks. [48]
Positron emission tomography (PET) is an imaging technique that uses radiotracers to spatially localize and track the distribution of changes in metabolic processes. [49] Specifically, PET neuroimaging scans have been widely used in pre-clinical and clinical settings in relation to epilepsy, dementia, Parkinson's disease, and traumatic brain injuries. [50] [51]
Electroencephalography (EEG) is a tool that directly measures and records the electrical activity generated in the brain with high temporal resolution but relatively low spatial resolution. [52] The EEG signal can be obtained non-invasively by placing electrodes on the scalp to capture the electrical impulses produced by neurons in the brain. It is commonly used in clinical settings to assess and detect neurological abnormalities in brain functions, such as epilepsy, sleep disorder, and brain injuries; in research, it has been used in couple with tasks to probe brain activities underlying various cognitive and emotional processes. [53]
Molecular genetics is a sub-field in biology that investigates the structure, expression, and functions of genes, informing brain development and functions at the level of the genome. [54] In the context of personality neuroscience, methods in molecular genetics have been used to establish genetic underpinnings of personality traits. [55]
Assay measures biological processes by detecting signals produced by reagents. [56] It can be used to quantify "endogenous psychoactive substances or their byproducts" (e.g., levels of dopamine, oxytocin, serotonin, etc.) that have been associated with psychological processes which may contribute to personality trait development or psychopathology. [18]
Neuropharmocological manipulation involves the use of medication to induce changes in neurochemical processes and has been primarily studied for neurological or psychiatric drug treatments. [57] Personality neuroscience can incorporate neuropsychopharmocological manipulation to establish causal link between personality traits and specific neurochemical processes (e.g., induced manipulation on levels of dopamine). [19]
In the past two decades, research in the field of personality neuroscience, utilizing neuroscientific methods outlined in the previous section, has identified neural mechanisms underlying a wide range of trait variables. This section reviews some of the major research findings in the field. [1] [19]
Empathy, in the discussion here as a stable trait as in empathetic ability or capacity, can be defined as an affective response that "is similar to one’s perception (directly experienced or imagined) and understanding (cognitive empathy) of the stimulus emotion, with recognition that the source of the emotion is not one’s own", although there is still ongoing debate in the field on how to best define empathy. [70] One sMRI study has demonstrated that inter subject variability in different facets of empathy is linked to neuroanatomical variation across different brain regions, such that (1) affective empathic abilities towards others were negatively correlated with the gray matter volumes of the precuneus, inferior frontal gyrus, and anterior cingulate, (2) cognitive perspective taking abilities were positively correlated with the gray matter volume of the anterior cingulate, and (3) the ability to empathize with fictional characters was positively linked to gray matter changes in the right dorsolateral prefrontal cortex. [71] A meta-analysis of a series of fMRI studies have revealed that, when humans engage in empathetic processes, a network of brain regions are engaged, encompassing the insula, inferior frontal gyrus, medial frontal regions around the cingulate cortex, amygdala, thalamus, putamen, caudate, and primary somatosensory area SI. [72] In addition to MRI studies, neuromodulation on mice and monkeys have shown that interference with oxytocin signaling causally influences empathy-related phenomena. [73]
Prior research focused primarily on the causes of specific traits like extraversion, but 2018 research indicated that these individual traits do not alone determine personality. Researchers looked into the genes that are related to human personality. They identified the genes that interact with each other and one’s environment to create personality. Around 1000 of such genes that affect temperament and character were found. This was further studied by looking at 1000 people in Germany and a 1000 people in Korea, and they found that in both countries and cultures, the genes for personality were all expressed in the brain. Around 33% of the genes were involved in the expression of temperament and character, while 67% of the genes were involved in either one or the other. These genes for character were expressed primarily in the brain circuits that regulate complex cognitive processes, such as goal seeking, conflict solving, and self-awareness. The genes were found to affect temperament and were expressed primarily in the habit learning pathways. Through these studies, these researchers were able to determine that the components of personality are numerous complex profiles. They also found that many molecular pathways can cause the exact same personality trait. Furthermore, environmental influences had small interactions with the genes for temperament and character but still had significant influence. [74]
As an interdisciplinary field that lie between personality psychology and neuroscience, personality neuroscience research may benefit both fields by informing the formation of neuroscience hypotheses and helping interpret findings through theoretical framework developed in personality psychology, and in turn, developing and refining personality models and theories with an enhanced understanding of underlying neurobiological mechanisms. [19] Nonetheless, in the meantime, the interdisciplinary nature aggregates paradigmatic and methodological challenges from both fields. [19] [46]
One prominent challenge for neuroimaging studies that aim to investigate individual differences is the low statistical power as a result of small sample sizes due to the high cost of data collection. [75] [76] Personality neuroscience research can thus benefit from data-sharing among studies and collective efforts to aggregate large neuroimaging datasets that include personality measures, such as the Human Connectome Project (HCP) and the Adolescent Brain and Cognitive Development (ABCD) Study. [1] [77] [65] Ongoing effort to collect data from more diverse sample is also recommended to allow for generalization of study results to a larger population or investigation of similarities/differences among diverse communities. [19]
Another challenge is to establish reliable, systematic, and high-quality measurement of personality traits. [78] Unlike intelligence tests that are performance-based, personality questionnaires are susceptible to biases as mentioned in earlier sections. As the theories of personality psychology continues to evolve and develop, extensive psychometric research may need to be conducted on various types of scales or assessments that are used to measure psychological traits to ensure that they produce reliable measures of personality variables of interest. [1]
One other challenge is that personality neuroscience is a relatively young field. Because of this, many of the previously published studies may be proven to be false positives due to under-powered studies that use small samples. Larger sample sizes are needed to detect smaller effects, which are common in personality neuroscience. A sample size of around 200 is needed to have 80% power and detect a correlation .2, which is often the average effect size in personality neuroscience. Thus, larger sample sizes are a needed change for this field. [79]
The complexity of both the brain and personality traits poses additional challenge to the interdisciplinary field of personality neuroscience which studies the relationship between these two complex systems. [19] Current research suggests that there exists no one-to-one mapping between neurobiological and personality variables: multiple brain regions or neurochemical processes may underlie one trait variable, while in turn, one brain region or neurochemical processes may be instrumental for several cognitive and affective processes that may influence multiple traits. As a result, personality network neuroscience approaches, integrating quantitative methodologies from network analysis, have been proposed to encode the complex nature of both neural mechanisms and personality variables as networks to facilitate the investigation the brain-personality relationship. [46] [78] [80]
Personality is any person's collection of interrelated behavioral, cognitive and emotional patterns that comprise a person’s unique adjustment to life. These interrelated patterns are relatively stable, but can change over long time periods.
Empathy is generally described as the ability to take on another's perspective, to understand, feel, and possibly share and respond to their experience. There are more definitions of empathy that include but is not limited to social, cognitive, and emotional processes primarily concerned with understanding others. Often times, empathy is considered to be a broad term, and broken down into more specific concepts and types that include cognitive empathy, emotional empathy, somatic empathy, and spiritual empathy.
In psychology, trait theory is an approach to the study of human personality. Trait theorists are primarily interested in the measurement of traits, which can be defined as habitual patterns of behavior, thought, and emotion. According to this perspective, traits are aspects of personality that are relatively stable over time, differ across individuals, are relatively consistent over situations, and influence behaviour. Traits are in contrast to states, which are more transitory dispositions.
Arousal is the physiological and psychological state of being awoken or of sense organs stimulated to a point of perception. It involves activation of the ascending reticular activating system (ARAS) in the brain, which mediates wakefulness, the autonomic nervous system, and the endocrine system, leading to increased heart rate and blood pressure and a condition of sensory alertness, desire, mobility, and reactivity.
The study of personality has long been a cornerstone of psychology, seeking to unravel the mysteries of what makes individuals unique. Among the myriad of approaches to understanding personality, one framework stands out for its simplicity and robustness: the Big Five personality traits. These traits, often referred to as the Five Factor Model (FFM), provide a comprehensive framework for describing and understanding human personality. In this article, we delve into the Big Five model, exploring its origins, dimensions, and implications for understanding human behavior and individual differences. The Big Five personality traits, sometimes known as "the five-factor model of personality" or "OCEAN model", is a grouping of five unique characteristics used to study personality. It has been developed from the 1980s onward in psychological trait theory.
Affective neuroscience is the study of how the brain processes emotions. This field combines neuroscience with the psychological study of personality, emotion, and mood. The basis of emotions and what emotions are remains an issue of debate within the field of affective neuroscience.
In psychology, the Eysenck Personality Questionnaire (EPQ) is a questionnaire to assess the personality traits of a person. It was devised by psychologists Hans Jürgen Eysenck and Sybil B. G. Eysenck.
Social neuroscience is an interdisciplinary field devoted to understanding the relationship between social experiences and biological systems. Humans are fundamentally a social species, rather than solitary. As such, Homo sapiens create emergent organizations beyond the individual—structures that range from dyads, families, and groups to cities, civilizations, and cultures. In this regard, studies indicate that various social influences, including life events, poverty, unemployment and loneliness can influence health related biomarkers. The term "social neuroscience" can be traced to a publication entitled "Social Neuroscience Bulletin" which was published quarterly between 1988 and 1994. The term was subsequently popularized in an article by John Cacioppo and Gary Berntson, published in the American Psychologist in 1992. Cacioppo and Berntson are considered as the legitimate fathers of social neuroscience. Still a young field, social neuroscience is closely related to personality neuroscience, affective neuroscience and cognitive neuroscience, focusing on how the brain mediates social interactions. The biological underpinnings of social cognition are investigated in social cognitive neuroscience.
Neuroticism is a personality trait associated with negative emotions. It is one of the Big Five traits. Individuals with high scores on neuroticism are more likely than average to experience such feelings as anxiety, worry, fear, anger, frustration, envy, jealousy, pessimism, guilt, depressed mood, and loneliness. Such people are thought to respond worse to stressors and are more likely to interpret ordinary situations, such as minor frustrations, as appearing hopelessly difficult. Their behavioral responses may include procrastination, substance use, and other maladaptive behaviors, which may aid in relieving negative emotions and generating positive ones.
The Temperament and Character Inventory (TCI) is an inventory for personality traits devised by Cloninger et al. It is closely related to and an outgrowth of the Tridimensional Personality Questionnaire (TPQ), and it has also been related to the dimensions of personality in Zuckerman's alternative five and Eysenck's models and those of the five factor model.
Extraversion and introversion are a central trait dimension in human personality theory. The terms were introduced into psychology by Carl Jung, though both the popular understanding and current psychological usage are not the same as Jung's original concept. Extraversion tends to be manifested in outgoing, talkative, energetic behavior, whereas introversion is manifested in more reflective and reserved behavior. Jung defined introversion as an "attitude-type characterised by orientation in life through subjective psychic contents", and extraversion as "an attitude-type characterised by concentration of interest on the external object".
Cultural neuroscience is a field of research that focuses on the interrelation between a human's cultural environment and neurobiological systems. The field particularly incorporates ideas and perspectives from related domains like anthropology, psychology, and cognitive neuroscience to study sociocultural influences on human behaviors. Such impacts on behavior are often measured using various neuroimaging methods, through which cross-cultural variability in neural activity can be examined.
The biopsychological theory of personality is a model of the general biological processes relevant for human psychology, behavior, and personality. The model, proposed by research psychologist Jeffrey Alan Gray in 1970, is well-supported by subsequent research and has general acceptance among professionals.
Reinforcement sensitivity theory (RST) proposes three brain-behavioral systems that underlie individual differences in sensitivity to reward, punishment, and motivation. While not originally defined as a theory of personality, the RST has been used to study and predict anxiety, impulsivity, and extraversion. The theory evolved from Gray's biopsychological theory of personality to incorporate findings from a number of areas in psychology and neuroscience, culminating in a major revision in 2000. The revised theory distinguishes between fear and anxiety and proposes functionally related subsystems. Measures of RST have not been widely adapted to reflect the revised theory due to disagreement over related versus independent subsystems. Despite this controversy, RST informed the study of anxiety disorders in clinical settings and continues to be used today to study and predict work performance. RST, built upon Gray's behavioral inhibition system (BIS) and behavioral activation system (BAS) understanding, also may help to suggest predispositions to and predict alcohol and drug abuse. RST, a continuously evolving paradigm, is the subject of multiple areas of contemporary psychological enquiry.
Personality change refers to the different forms of change in various aspects of personality. These changes include how we experience things, how our perception of experiences changes, and how we react in situations. An individual's personality may stay somewhat consistent throughout their life. Still, more often than not, everyone undergoes some form of change to their personality in their lifetime.
The biological basis of personality is a collection of brain systems and mechanisms that underlie human personality. Human neurobiology, especially as it relates to complex traits and behaviors, is not well understood, but research into the neuroanatomical and functional underpinnings of personality are an active field of research. Animal models of behavior, molecular biology, and brain imaging techniques have provided some insight into human personality, especially trait theories.
Activity-specific approach in temperament research is the theory related to a structure of temperament, i.e. how temperament traits can be classified and organized. This approach suggests:
Intelligence and personality have traditionally been studied as separate entities in psychology, but more recent work has increasingly challenged this view. An increasing number of studies have recently explored the relationship between intelligence and personality, in particular the Big Five personality traits.
Social cognitive neuroscience is the scientific study of the biological processes underpinning social cognition. Specifically, it uses the tools of neuroscience to study "the mental mechanisms that create, frame, regulate, and respond to our experience of the social world". Social cognitive neuroscience uses the epistemological foundations of cognitive neuroscience, and is closely related to social neuroscience. Social cognitive neuroscience employs human neuroimaging, typically using functional magnetic resonance imaging (fMRI). Human brain stimulation techniques such as transcranial magnetic stimulation and transcranial direct-current stimulation are also used. In nonhuman animals, direct electrophysiological recordings and electrical stimulation of single cells and neuronal populations are utilized for investigating lower-level social cognitive processes.
Network neuroscience is an approach to understanding the structure and function of the human brain through an approach of network science, through the paradigm of graph theory. A network is a connection of many brain regions that interact with each other to give rise to a particular function. Network Neuroscience is a broad field that studies the brain in an integrative way by recording, analyzing, and mapping the brain in various ways. The field studies the brain at multiple scales of analysis to ultimately explain brain systems, behavior, and dysfunction of behavior in psychiatric and neurological diseases. Network neuroscience provides an important theoretical base for understanding neurobiological systems at multiple scales of analysis.
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