The study of empathy, altruism, and other behaviors that help another at one's own expense has long been a topic of interest and debate. Altruism was believed to be an evolutionary disadvantage, and for a while theories focusing on a biological understanding of it were sidelined. In recent years, evolutionary evidence has pushed the study of altruism into the realm of evolutionary biology: a recent study found evidence for the evolution of indiscriminate altruism [1] in meerkats [1]. Individual meerkats would instinctually take on a sentry role and put their own lives at risk by alerting their peers to the presence of predators, indiscriminately putting their lives at risk for their mob. [NN2] Similarly to altruism, the study of empathy has also been expanded to account for the influence of evolution. Biologists theorized that in social animals like humans, empathy likely emerged as a way to support one's social group and contribute to their collective well-being. This partly drove the field's shift towards a model for cognitive empathy, which was held back by an assumption that upper-level empathy was limited to only a few intelligent species. This assumption was challenged when animal studies in the mid-20th century found that cognitive empathy is present at a limited capacity in rodents [2]. In recent decades a more focused neurobiological model has started to take shape, with an emphasis on understanding empathy's roots in neurobiology and its functional aspects.
Human brain structure correlates with inter-individual differences in empathy [4][NN3] . Studying the physiological effects of routine substance use provides a reliable strategy to map the functions of certain brain regions. Since different drugs take different pathways through the brain to reach different regions, researchers can link affected regions to affected functions. For example, alcohol use is correlated with a reduction in balance and motor function [3]. By analyzing the parts of the brain that alcohol affects, such as the cerebellum, researchers found that alcohol users suffered from impaired motor coordination due to alcohol-related cerebellar damage, thus providing further evidence of the role of the cerebellum in balance and motor function [5].
To further develop a functional model of empathy, it is important to understand the consequences of differences in substance and dependence levels. To this end, researchers compared emotional empathy (measured with a self-reported survey) and grey matter volume in three groups of individuals: a control group with no history of substance use, a group of users dependent on smoked cocaine (also known as ‘crack cocaine’), and a group of users dependent on insufflated cocaine (the ‘snorted’ form of cocaine). Grey matter refers to brain tissue with a high concentration of neuron cell bodies, and lower than normal grey matter volume negatively affects a brain region’s function[4] [NN5] . As smoked cocaine has been linked to an increased rate of treatment difficulty and withdrawal symptom severity relative to intranasally ingested (insufflated) cocaine [6], the researchers hypothesized that empathy would differ between users of different forms of cocaine. The researchers primarily focused on monitoring grey matter volume in brain regions such as the inferior parietal lobe, which is linked with empathy and social cognition [7]. Prior research regarding empathy and addiction was behaviorally unspecific and omitted brain structural or functional correlates, so this study aimed to fill that gap and provide both qualitative and neurological evidence.
The study found that smoked cocaine had a significantly larger impact on empathy scores and gray matter volume relative to insufflated cocaine. The affective empathy scores were assessed as a synthesis of self-reported comprehension, intentionality, and concern judgements when participants were exposed to a series of images showcasing pre-selected scenarios. In parallel to assessing affective empathy, the researchers also measured gray matter volume in the left postcentral gyrus, left fusiform gyrus, right angular gyrus, and other regions of the brain linked with pro-social cognition. Notably, lower empathic concern for the intentionality subcategory had a positive association with lower gray matter volumes in the left postcentral gyrus, left fusiform gyrus, and right angular gyrus. For both groups, lower empathic concern was correlated with reduced gray matter volume, but both empathy score and gray matter volume were lower for smoked cocaine users [8].
It is important to note that the study's results could be influenced by the socioeconomic factors that influence substance abuse. To screen for this potential confound, the studies' control group was selected to have a similar socioeconomic background to that of the experimental group. To minimize validity issues, the researchers ensured that participants were screened for potential confounding variables, and individuals with a history of other substance use, psychiatric disorders, and neurological disease were not included in the study. The empathy scores themselves were the product of a behavioral assessment that noted response to visual stimuli, a methodological approach that still relies on self-reported empathy scores. Self-reported surveys will always have reliability concerns. To minimize this, researchers operationalized empathy as the product of three separate assessments, but the use of self-report scores is nonetheless a limitation for the study's findings. Finally, it is important to acknowledge that research on drug dependency in humans is limited to observational studies involving the naturally existing pool of drug users and that almost all experiments with substance use in humans are limited in their options to suggest causality.
This study paves the way for more quantitative research by integrating new models for experimental empathy tasks with neuroanatomical analysis. By finding which substances have greater impact on empathy, it is possible to trace that impact to the regions and nuclei that experience greater effects from a specific drug. For example, alcohol might negatively impact motor function, but a drug like Tramadol can have no negative or positive effect on motor function [9]. In a similar light, an expanded understanding of what other drugs affect gray matter volumes in the left postcentral gyrus, left fusiform gyrus, right angular gyrus, and other regions linked with social cognition (correlates) could then contribute to a proper comparison of the difference in drug effect on neuroanatomy. This would help shed light on the functional role of each correlate in empathy cognition. A promising direction for research in the field lies in direct animal studies. The existence of cognitive empathy in rodents mentioned earlier, opens the door for research with an established research species. A future direction for research in the field lies in lesion studies, which impair function in certain brain regions and link it to the loss of a certain function, to showcase the neural mechanisms behind empathy and further explore the link between neural mechanisms and perceived emotional experience. Expanding our understanding of empathy and addiction may help improve rehabilitation and recovery programs and methodology and further our understanding of the neurological basis of empathy.
References
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