Got Gray Matter? High Moral Reasoning Links To Larger Regions Related To Social Behavior, Conflict Processing

brain imaging
People with a higher level of moral reasoning skills showed increased gray matter in areas of the brain involved in social behavior, decision-making, and conflict-processing. Photo courtesy of Shutterstock.

Gray matter includes areas of the brain involved in sensory perception, memory, muscle control, emotions, and speech. A new study investigates whether any relationship exists between gray matter volume and moral development. Compared to others, people with a higher level of moral reasoning skill showed increased gray matter volume in the ventromedial prefrontal cortex and subgenual anterior cingulate cortex — areas of the brain involved in social behavior, decision-making, and conflict-processing.

Neuroscientists theorize the size of a brain region is influenced by its use — since neurons that regularly “fire together, wire together,” greater plasticity occurs in the brain areas we use most frequently.

To investigate whether brain architecture is influenced by flexing our ethical judgment muscles, Dr. Hengyi Rao, an assistant professor of cognitive neuroimaging at the Perelman School of Medicine, and his colleagues enlisted the help of Master of Business Administration students between the ages of 24 and 33, safely past the age of brain structural maturation.

Mental Architecture

First, the participants completed a test of moral reasoning, the Defining Issues Test (DIT2). Psychologist Lawrence Kohlberg’s work from the last century indicated that people progress through different stages of moral reasoning as their cognitive abilities mature. The DIT2 is based on Kohlberg’s work and so stratifies moral development into separate schema. After categorizing the ethical abilities of participants, the researchers looked at the levels of gray matter in their brains using voxel-based morphometry, a type of imaging technique.

The team observed increased gray matter in the prefrontal cortex for those participants who scored at the highest level of moral reasoning. Gray matter volume, then, correlated with participant's level of ethical reasoning abilities.

Interestingly, the participants also underwent personality testing. The participants at more advanced levels of moral development generally scored higher on openness to experience and generally scored lower on neuroticism. Meanwhile, the women scored lower with regard to self-esteem and sense of control, “including lower perceived control, mastery, and more perceived constraints,” as described in the study.

The voxel-based morphometry revealed increased gray matter volume for women compared with men in a number of brain regions: the left inferior frontal gyrus, bilateral superior temporal gyri, bilateral hippocampi, left postcentral gyrus, left posterior cingulate cortex, and the left occipital lobe. A number of studies show that, relative to brain size, females exhibit greater cortical gray matter volume than males with larger volumes in language-related brain regions.

Source: Prehn K, Korczykowski M, Rao H, et al. Neural Correlates of Post-conventional Moral Reasoning: A Voxel-based Morphometry Study. PLOS ONE. 2015.

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