Unveiling the Brain's Hidden Networks: A Japanese Research Milestone

The world of neuroscience has witnessed a groundbreaking achievement as researchers from RIKEN's Center for Brain Science (CBS) and the University of Tokyo have successfully visualized how neural connections form functional networks in both conscious and unconscious brain states. This innovation sheds light on one of the enduring mysteries: why the brain responds to sensory stimuli during sleep but fails to perceive them consciously.

Led by Team Leader Masanori Murayama at RIKEN CBS's Haptic Perception Physiology Research Team, the study utilized cutting-edge imaging technology to observe over 10,000 neurons across more than 10 cortical regions in mice. The findings, published in Cell Reports (DOI: 10.1016/j.celrep.2026.116902), reveal that unconscious states like non-rapid eye movement (NREM) sleep and general anesthesia feature highly modular functional networks—segregated into subnetworks with strong internal connections but weak links between them. This segregation likely disrupts the global information integration necessary for perception.

Understanding Consciousness Through Functional Networks

Functional networks in the brain represent structures inferred from synchronized activity between neurons or brain regions. In conscious wakefulness, these networks are highly integrated, allowing seamless information flow across the cortex. Conversely, during unconsciousness, the networks fragment, a phenomenon now captured at the single-cell level for the first time.

This research bridges micro-scale (individual neuron) and macro-scale (region-level, as seen in functional magnetic resonance imaging or fMRI) observations. By applying spatial coarse-graining—averaging activity from nearby neurons—the team's data aligned with prior fMRI studies showing localized activity patterns in unconscious states.

The Pioneering Team Behind the Discovery

Masanori Murayama, Ph.D., directs the Haptic Perception Physiology Research Team at RIKEN CBS, focusing on neural bases of perception and action in the cerebral cortex. Collaborators include Ikumi Oomoto (RIKEN postdoctoral researcher), Masafumi Oizumi and PhD student Daiki Kiyooka from the University of Tokyo's Graduate School of Arts and Sciences, Jun Kitazono from Yokohama City University, and Kenta Kobayashi from the National Institute for Physiological Sciences (NIPS).

These institutions exemplify Japan's leadership in higher education and research. The University of Tokyo, a premier institution, fosters interdisciplinary neuroscience, while RIKEN serves as a national hub for advanced brain science. For aspiring researchers, opportunities abound in higher education research jobs at such centers.

Revolutionary Wide-Field Two-Photon Microscopy

Central to the study is the team's proprietary wide-field two-photon microscope, which scans a 3mm x 3mm field—covering multiple brain regions—with single-cell resolution. Traditional two-photon microscopy uses infrared lasers for deep-tissue imaging without damage, but the wide-field upgrade enables simultaneous calcium imaging of thousands of neurons expressing fluorescent calcium indicators.

Mice were head-fixed but free to move limbs, cycling naturally between awake, NREM sleep, and anesthesia states (REM excluded). This setup captured spontaneous activity and stimulus responses, revealing that while firing rates drop in unconsciousness, neurons remain responsive—just disconnected from perception.

Decoding Network Modularity Step-by-Step

The analysis began with computing correlation matrices from neuronal time-series data to construct functional networks. Modularity—a measure of subdivision into communities—was quantified using graph theory algorithms.

• Awake state: Low modularity, integrated network for conscious processing.
• NREM sleep/anesthesia: High modularity, segregated subnetworks persist temporally.

Subnetworks comprised intermixed neurons across regions, connected by both short-range (local) and long-range edges, challenging prior assumptions of purely local segregation.

The Unexpected Role of Mid-Degree Neurons

Hub neurons (high-degree, many connections) are network anchors, but surprisingly, they didn't drive state differences. Instead, mid-degree neurons—those with moderate connectivity—were key to modularity increases in unconsciousness. This highlights nuanced roles in network dynamics beyond hubs.

Coarse-graining transformed intermixed micro-networks into macro-localized patterns, reconciling with human fMRI data and suggesting scalable principles.

Solving the Sleep Perception Puzzle

During sleep, sensory stimuli evoke local neural responses, yet no awareness ensues. The segregated networks impair inter-subnetwork communication, blocking global integration theorized essential for consciousness (e.g., Integrated Information Theory). This provides a mechanistic hint: unconsciousness arises not from silence, but fragmented connectivity.Read the full RIKEN press release.

Implications for Brain Disorders and Treatments

Beyond sleep, findings illuminate disorders like coma, epilepsy, schizophrenia, and dementia, where network fragmentation correlates with symptoms. Cell-level visualization enables precise diagnostics and targeted therapies, such as neuromodulation for hubs or mid-degree cells.

In Japan, this advances precision neuroscience, with NIPS and Yokohama City University contributing virus vectors and data science expertise. Explore research assistant jobs in these fields.

Japan's Neuroscience Ecosystem and Higher Education

RIKEN CBS, under the National Institutes of Natural Sciences, collaborates seamlessly with universities like UTokyo—ranked globally top-tier. This synergy drives innovations, training PhD students like Daiki Kiyooka in advanced techniques.

Japan invests heavily in brain science via programs like Brain/MINDS, fostering careers. Check university jobs in Japan or career advice for academics.

Future Directions: From Mice to Humans

Next steps include human-scale imaging, causal interventions (e.g., optogenetics to desegregate networks), and links to disorders. The microscope's scalability promises in vivo studies during behavior.Access the Cell Reports paper.

For higher ed professionals, this underscores demand for neuroscientists; visit postdoc positions or professor jobs.

Photo by Pema G. Lama on Unsplash

Career Opportunities in Japanese Neuroscience Research

This breakthrough highlights vibrant opportunities at RIKEN, UTokyo, and affiliates. Roles span imaging specialists to data analysts. Platforms like Rate My Professor offer insights into mentors, while higher ed jobs list openings. Aspiring lecturers can prepare via lecturer career guides.

Japan's ecosystem supports international talent, with English programs at top unis.