Overview: Brain mapping research identifies key neural networks and their connections that appear to enhance conscious experience.
Source: University of Tokyo
Science may be one step closer to understanding where consciousness resides in the brain. A new study demonstrates the importance of certain types of neural connections in identifying consciousness.
The research, published in cerebral cortexwas led by Jun Kitazono, a corresponding author and a project researcher in the Department of General Systems Studies at the University of Tokyo.
“Where in the brain consciousness resides has been one of the biggest questions in science,” said associate professor Masafumi Oizumi, corresponding author and head of the lab conducting the study.
“While we haven’t gotten a conclusive answer, a lot of empirical evidence has been accumulated while looking for the minimal mechanisms sufficient for conscious experience, or the neural correlates of consciousness.”
For this study, the team took a step toward identifying the minimally sufficient subnetworks in the brain that support conscious experience.
To identify the brain regions where consciousness resides, the researchers looked for one specific feature of consciousness within the brain’s neural networks: bidirectional pathways. When we see something or experience a sensation, our brain takes in information.
This is called a feed-forward signal, but receiving such feed-forward signals is not enough for consciousness. Our brains also need to send information back, in what is called feedback. Not every part of the brain can receive both feedforward and return feedback information.
Researchers hypothesized that these bidirectional connections are an essential feature of the parts of the brain responsible for consciousness.
“Feed-forward processing alone is insufficient for subjects to consciously perceive stimuli; instead, feedback is also required, indicating the need for bi-directional processing.
“The feedback component disappears not only during the loss of specific contents of consciousness in waking states, but also during unconscious states in which conscious experiences are generally lost, such as general anesthesia, sleep and vegetative states,” Kitazono said.
He also explained that it doesn’t matter if you’re looking at a human, monkey, mouse, bird or fly; bidirectional processing remains essential.
Researchers used a mouse connectome and computer techniques to test their idea. A connectome is a detailed map of the connections in the brain.
First, they developed an efficient algorithm to extract the parts of the brain with strong bidirectional connections called complexes. They then applied the algorithm to the mouse connectome.
“We found that the extracted complexes with the most bidirectional properties were not evenly distributed across all major regions, but rather concentrated in the cortical regions and thalamic regions,” Kitazono said. “On the other hand, regions in the other major regions have low bidirectionality. Regions in the cerebellum in particular have much lower bidirectionality.”
These findings are in line with where scientists have long thought consciousness resides in the brain. The cerebral cortex, which is located on the surface of the brain, contains sensory areas, motor areas, and association areas that are thought to be essential for experiencing consciousness.
The thalamus, which is located in the center of the brain, is also thought to be related to consciousness, and in particular, the interaction between the thalamus and its cortical regions, called the thalamo-cortical loop, is thought to be important for the conscience.
These results support the idea that the bidirectionality in the brain network is a key to identifying the location of consciousness.
Researchers stressed that they are still working on identifying the place of consciousness.
“This research focuses only on ‘static’ anatomical connections between neurons or brain regions. However, consciousness is ‘dynamic’ and changes from moment to moment depending on neural activity,” Oizumi said.
“While anatomical connections tell us how neural activity would propagate and how brain regions would interact, we need to directly examine the dynamics of neural activity to identify the place of consciousness at any given time.”
As a next step, he said, the team is currently analyzing activity-based networks of the brain in different types of neural recordings.
“The ultimate goal of our lab is to find the mathematical relationship between consciousness and the brain,” says Oizumi.
“In this study, we tried to relate the network properties of the brain to the location of consciousness. We will further explore the relationship between consciousness and the brain, towards what our ultimate goal is.”
Financing: Japan Science and Technology Agency ACT-X (Grant Number JPMJAX20A6), Japan Science and Technology Agency CREST (Grant Numbers JPMJCR1864 and JPMJCR15E2), AIP challenge program, Japan Science and Technology Agency Moonshot R&D (Grant Number JPMJMS2012), and Japan Society for the Promotion of Science KAKENHI (Grant Numbers 18H02713 and 20H05712) supported this research.
About this consciousness research news
Author: Joseph Krisher
Source: University of Tokyo
Contact: Joseph Krisher – University of Tokyo
Image: The image is attributed to Jun Kitazono
Original research: Open access.
“Bidirectionally connected nuclei in a mouse connectome: towards extracting the brain subnetworks essential for consciousness” by Jun Kitazono et al. cerebral cortex
Bidirectionally connected nuclei in a mouse connectome: towards extracting the brain subnetworks essential to consciousness
Where in the brain consciousness is located remains unclear. It has been suggested that the subnetworks that support consciousness must be bidirectionally (repeatedly) connected, as both feed-forward and feedback processing are required for conscious experience.
Accordingly, evaluating which subnetworks are bidirectionally connected and the strength of these connections would likely help identify regions essential to consciousness.
Here we propose a method to hierarchically decompose a network into nuclei with different strengths of bidirectional connection, as a way to reveal the structure of the complex brain network. We applied the method to a whole-brain mouse connectome.
We found that nuclei with strong bidirectional connections consisted of regions believed to be essential for consciousness (e.g., the isocortical and thalamic regions, and claustrum) and did not contain regions believed to be irrelevant to consciousness (e.g., cerebellum).
On the contrary, we could not find such a match between cores and consciousness when we applied other simple methods that ignored the two-way street.
These findings suggest that our method provides a new insight into the relationship between bidirectional brain network structures and consciousness.