Machine learning and human brain scans have revealed the regions of the brain behind how we form abstract concepts, like justice, ethics, and consciousness, researchers report.
“Humans have the unique ability to construct abstract concepts that have no anchor in the physical world, but we often take this ability for granted. In this study, we have shown that newly identified components of meaning used by the human brain [act] like an indexing system, similar to a library’s card catalog, to compose the meaning of abstract concepts,”
says senior author Marcel Just, professor of psychology at Carnegie Mellon University.
The ability of humans to think abstractly plays a central role in scientific and intellectual progress. Unlike concrete concepts, like “hammer,” abstract concepts, like “ethics,” have no obvious home in the parts of the brain that deal with perception or control of our bodies.
“Most of our understanding of how the brain processes objects and concepts is based on how our five senses take in information. It becomes difficult to describe the neural environment of abstract thoughts because many of the brain’s mental tools to process them are themselves abstract,”
says first author Robert Vargas, a graduate student in Just’s lab.
In the new study, Just and his team scanned the brains of nine participants using a functional MRI. The team sifted through the data using machine learning tools to identify patterns for each of the 28 abstract concepts.
They applied the machine learning algorithm to correctly identify each concept (with a mean rank accuracy of 0.82, where the chance level is 0.50).
Language, Reference, And Sociality
Just says three dimensions of meaning in the brain construct these abstract concepts.
The first dimension corresponds to regions associated with language. For example, the concept of “ethics” might be linked to other words like “rules” and “morals.” A person must first understand the words to construct the additional meaning of ethics.
The second dimension defines abstract concepts in terms of reference, either to self or an external source. For example, “spirituality” refers to “self,” while “causality” is external to the person.
The final dimension is rooted in social constructs. There is an inherent social component to the concepts of “pride” and “gossip.”
“For me, the most exciting result of this study was that we were able to predict the neural activation patterns for individual abstract concepts across people,” Vargas says. “It is wild to think that my concept of probability and spirituality is neurally similar to the next person’s, even if their experience of spirituality is different.”
During the scan, researchers presented each concept visually, and the participant was allowed to think about this idea for three seconds. The participants saw the set of words six times.
The 28 concepts covered in the study span seven categories:
mathematics (subtraction, equality, probability, and multiplication);
scientific (gravity, force, heat, and acceleration);
social (gossip, intimidation, forgiveness, and compliment);
emotional (happiness, sadness, anger, and pride);
legal (contract, ethics, crime, and exoneration);
metaphysical (causality, consciousness, truth, and necessity);
religious (deity, spirituality, sacrilege, and faith).
The researchers based their work on nine adult brain scans from a culturally homogenous community on the Carnegie Mellon campus.
“It’s flashy to call this work mind reading. For me, it is proof that we have identified some of the elements of the brain’s indexing system — verbal representation, externality/internality, and the social dimension — that our brains use to code concepts that have no physical manifestation in the world,”
 Robert Vargas, Marcel Adam Just. Neural Representations of Abstract Concepts: Identifying Underlying Neurosemantic Dimensions. Cerebral Cortex, bhz229, https://doi.org/10.1093/cercor/bhz229