Animal associations

New study identifies brain network cores with strong bidirectional connections

Science could be a step closer to understanding the location of consciousness in the brain. A new study shows the importance of certain types of neural connections in identifying consciousness.

The research, published in Cerebral cortexwas led by Jun Kitazono, corresponding author and project researcher at the Department of General Systems Studies, University of Tokyo.

“Where consciousness resides in the brain has been one of the biggest questions in science,” said Associate Professor Masafumi Oizumi, corresponding author and head of the lab conducting the study. “Although we have not come to a conclusive answer, a great deal of empirical evidence has accumulated during the search for the minimum sufficient mechanisms for conscious experience, or the neural correlates of consciousness.”

For this study, the team took a step toward identifying minimally sufficient subnets in the brain that support conscious experience.

To identify areas of the brain where consciousness resides, the researchers looked for a specific feature of consciousness in the neural networks of the brain: bidirectional pathways. When we see something or experience a sensation, our brain absorbs information. This is called an anticipatory signal, but receiving such anticipatory signals is not enough for consciousness. Our brain also needs to send information back, in what is called feedback. Not all parts of the brain can receive feedback and feedback at the same time. Researchers have hypothesized that these two-way connections are an essential feature of the parts of the brain responsible for consciousness.

“Anticipatory processing alone is insufficient for subjects to consciously perceive stimuli; on the contrary, feedback is also necessary, indicating the need for bidirectional processing. The feedback component disappears not only upon loss of specific contents of consciousness in waking states, but also during unconscious states where conscious experiences are usually lost, such as general anesthesia, sleep, and vegetative states,” Kitazono said. He also explained that it doesn’t matter whether you’re looking at a human , a monkey, a mouse, a bird or a fly; the bidirectionality of the treatments remains essential.

The 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 parts of the brain with strong bidirectional connections, called complexes. Next, they applied the algorithm to the mouse connectome.

“We found that the extracted complexes with the most bidirectionality were not evenly distributed across all major regions, but rather concentrated in cortical regions and thalamic regions,” Kitazono said. “On the other hand, regions of other major regions have weak bidirectionality. In particular, regions of the cerebellum have much weaker bidirectionality.”

These findings align with where scientists have long believed consciousness resides in the brain. The cerebral cortex, located on the surface of the brain, contains sensory areas, motor areas, and association areas that are considered essential for the experience of consciousness. The thalamus, located in the middle of the brain, has also been thought to be related to consciousness, and in particular, the interaction between the thalamus and cortical regions, called the thalamo-cortical loop, is thought to be important for consciousness. These results support the idea that bidirectionality in the brain network is a key to identifying the place of consciousness.

The researchers emphasized that they were still working to identify the location of consciousness.

“This study focuses only on ‘static’ anatomical connections between neurons or brain areas. However, consciousness is ‘dynamic’, changing from moment to moment based on neural activity,” Oizumi said. “Although anatomical connections tell us how neural activity would spread and how brain areas would interact, we need to directly investigate the dynamics of neural activity to identify the location of consciousness at any given time.”

As a next step, he said the team is currently analyzing activity-based brain networks in various types of neural recordings.

“The ultimate goal of our lab is to find the mathematical relationship between consciousness and the brain,” Oizumi said. “In this study, we 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, towards which is our ultimate goal.”