Where in the brain consciousness resides remains unclear. Although scientists have not yet reached a conclusive answer, much empirical evidence has been accumulated in searching for the minimal mechanisms sufficient for conscious experience, called neural correlates of consciousness (NCC).

A new study shows the importance of certain types of neural connections in identifying consciousness.

The researchers searched for a particular characteristic of consciousness within the brain’s neural networks: bidirectional pathways to pinpoint the brain regions where consciousness resides.

Our brains process information when we see something or feel a sense. This is referred to as a feed-forward signal, although awareness of such signs alone is not enough for consciousness. Additionally, our brains must provide feedback or information that is sent back. 

Not all brain regions can receive feed-forward information and provide feedback in return. According to scientists, these connections in both directions are a crucial characteristic of the areas of the brain involved in consciousness.

mportance of bidirectionality for consciousness
It has been suggested that the part of the brain network supporting consciousness brain regions should be bidirectionally connected because both feed-forward and feedback processes are necessary for conscious experience. For example, previous studies examining visual perception have shown that conscious perception does not arise when there is only feed-forward processing, whereas it arises when there is feedback as well as feed-forward processing.
Credit: ©2022 Jun Kitazono

Jun Kitazono, a corresponding author and a project researcher in the Department of General Systems Studies at the University of Tokyo, said, “We found that the extracted complexes with the most bidirectionality were not evenly distributed among all major regions, but rather are concentrated in the cortical regions and thalamic regions. On the other hand, regions in the other major regions have low bi-directionality. In particular, regions in the cerebellum have much lower bidirectionality.”

These results are consistent with the region in the brain where scientists have long believed consciousness dwells.  The cerebral cortex, located on the brain’s surface, contains a sensory, motor, and association areas that are thought to be essential to consciousness experience.

The thalamus, a brain region in the center, has also been linked to consciousness. In particular, the thalamo-cortical loop, which mediates communication between the thalamus and cortical regions, is thought to be crucial for consciousness. According to these findings, identifying the place of consciousness can be determined by the brain network‘s bidirectionality.

Associate Professor Masafumi Oizumi, corresponding author and head of the lab conducting the study, said, “This study focuses only on ‘static’ anatomical connections between neurons or brain areas. However, consciousness is ‘dynamic,’ changing from moment to moment depending on neural activity. Although anatomical connections tell us how neural activity would propagate and how brain areas would interact, we need to directly investigate the dynamics of neural activity to identify the place of consciousness at any given moment.”

“As a next step, we will analyze activity-based networks of the brain in various types of neural recordings.”

“The ultimate goal of our lab is to find the mathematical relationship between consciousness and the brain. In this study, we have attempted to relate the network properties of the brain to the place of consciousness. We will further investigate the relationship between consciousness and the brain, toward what is our ultimate goal.”

Journal Reference:

  1. Jun Kitazono, Yuma Aoki, Masafumi Oizumi. Bidirectionally connected cores in a mouse connectome: extracting the brain subnetworks essential for consciousness. Cerebral Cortex, bhac143, DOI: 10.1093/cercor/bhac143