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Brain-viscera interactions underlie subjectivity

Periodic Reporting for period 4 - BRAVIUS (Brain-viscera interactions underlie subjectivity)

Reporting period: 2020-06-01 to 2021-11-30

What is the problem/issue being addressed?

The core defining feature of consciousness is the ability to have subjective experiences: when I feel cold, when I appreciate the softness of a fabric, or when I find a movie boring. Where do subjective experiences come from? The overall aim of BRAVIUS is to develop and test a novel hypothesis on the biological implementation of subjectivity.

Why is it important for society?

Understanding how biological processes generate consciousness is not only one the most intellectually challenging issue in science, it has also profound implications for society. Indeed, having consciousness is what defines a sentient being, and a sentient being should be granted rights. For instance, in modern societies voting rights are granted to adults not because of intelligence or wealth, but to each adult as a conscious person. The need to determine who - or what - is conscious or not is becoming more and more pressing: are fetuses, flies, cows, or artificial agents conscious? A first step in answering such questions is to identify the biological mechanisms generating subjective experiences in humans.

What are the overall objectives?

The hypothesis developed and tested in BRAVIUS is that subjectivity stems from brain-body interactions. In particular, we are interested in how the brain monitors two vital organs, the stomach and the heart. Each of these organs that generates its own rhythmic electrical activity, a bit like a battery, and is wired to the brain. In this project we investigate to which extent the activity of the heart and the stomach explain brain dynamics in humans, and whether and how neural responses to visceral signals are involved in subjective experiences in various domains, from perception to imagination, from spontaneous thoughts to decisions and emotions.
We showed that brain-viscera interactions are pervasive in humans. So far, brain-heart coupling was thought to be confined to a rather small subset of evolutionary ancient areas, and nothing was known on the coupling between the brain and the stomach electrical activity. We found that many brain regions respond to heartbeats, and that many neurons contribute to the regulation of heart rate. We revealed that brain-stomach coupling occurs in large portions of the brain, notably and unexpectedly in all brain regions that extract information from the outside world through senses like vision, touch or audition, as well as in brain regions used for motor control of arms, legs and hands. More specifically, we showed that the neural monitoring of cardiac inputs is related to the self and subjectivity, in many different situations: when explicitly thinking about oneself, but also in many case where the self is less obvious. Indeed, the mere fact of having a subjective experience – such as when seeing consciously, feeling an emotion or simply deciding which movie you prefer - implies the existence of a subject of experience. How the brain listens to internal, bodily signals, thus captures an essential component of our mental life.

Most of the results have already been presented to the scientific community at international meetings, and are accessible in peer-reviewed scientific articles. They are also presented in conferences and articles intended for a more general public.
BRAVIUS went beyond state-of-the-art mostly in two directions.
First, we show that brain-viscera interactions engage large portions of the human neocortex. Sensing and regulating heart and stomach is not confined to specialized areas: the anatomical substrate for tight interactions between the perception of internal organs and externally-oriented perception, cognition or emotion is present.
Second, we show that subjectivity is a core component, explicitly or implicitly present in many different domains of human perception, cognition and emotion. We obtained experimental evidence that subjectivity is related to the neural monitoring of visceral inputs, and argue that the basic functions of the human mind could be reorganized along an subjective/objective/ axis.
Some of the brain regions highly coupled with the gastric rhythm in humans