Connectome Harmonic Signatures of Loss of Consciousness

Disorders of Consciousness: Harmonic Patterns at the Edge of Awareness

What distinguishes a brain that is conscious from one that is not? And how can we understand the subtle boundary between minimal awareness and its apparent absence? Using the connectome harmonic framework, we investigated these questions in patients with disorders of consciousness (DOC), such as the vegetative state and minimally conscious state, in collaboration with Andrea Luppi, Emmanuel Stamatakis, Jakub Vohryzek, Morten Kringelbach, and many others (Luppi et al., 2023, Communications Biology).

By applying connectome harmonic decomposition to fMRI data from DOC patients, we found a striking reversal of the harmonic signatures observed in psychedelic and meditative states. In contrast to the expansion of the harmonic repertoire seen in altered and enriched states of consciousness, the brains of patients in vegetative states showed:

• Amplification of the energy of low-frequency connectome harmonics, and

• Suppression of the energy of high-frequency conenctome harmonics.

This spectral shift suggests a collapse in the brain’s dynamical repertoire—a diminished ability to explore the full landscape of possible brain states. In other words, loss of consciousness is linked to a contraction in the repertoire of connectome harmonics, reducing the diversity and complexity of the brain’s harmonic expression.

Importantly, these harmonic signatures were not uniform across all DOC patients. Those in a minimally conscious state retained a richer connectome harmonic repertoire, more closely resembling healthy wakefulness, compared to those in a vegetative state, whose harmonic signatures reflected deeper suppression. This distinction points to a spectrum of residual awareness that can be captured by the brain’s harmonic language—often beyond what clinical behavior alone can reveal.

Even more remarkably, these harmonic patterns mirrored those seen in recovery from propofol-induced anesthesia: as individuals returned to consciousness, the suppression of high-frequency harmonics began to lift. This suggests a general principle: the re-emergence of consciousness—whether after anesthesia, brain injury, or deep unconscious states—may unfold through the reactivation of higher-frequency harmonic modes and a wider repertoire of harmonic brain states.

Together, these findings provide strong evidence that consciousness is linked to the breadth and balance of the brain’s harmonic activity. Whether due to brain injury or pharmacological intervention, unconsciousness appears to emerge when this harmonic richness collapses into a narrow, low-frequency regime.

This work continues to evolve through rich collaborations aiming to deepen our understanding of the neural correlates of consciousness and offers a powerful tool for identifying subtle forms of consciousness that might otherwise go undetected.

If you want to dive deeper, see the related publications below and watch the selected talks:

• Luppi, A. I., Vohryzek, J., Kringelbach, M. L., Mediano, P. A. M., Craig, M. M., Adapa, R., Carhart-Harris,R. L., Roseman, L., Pappas, I., Peattie, A. R. D., Manktelow, A. E., Sahakian, B. J., Finoia, P., Williams, G., B., Allanson, J., Pickard, J. D., Menon, D. K., Atasoy, S. & Stamatakis, E. A. (2021). Distributed harmonic patterns of structure-function dependence orchestrate human consciousness. Communications biology, 6(1), 117.

• Atasoy, S., Donnelly, I., & Pearson, J. (2016). Human brain networks function in connectome-specific harmonic waves. Nature communications, 7(1), 1-10. doi:10.1038/ncomms10340.

• Atasoy, S., Roseman, L., Kaelen, M., Kringelbach, M. L., Deco, G., & Carhart-Harris, R. L. (2017). Connectome-harmonic decomposition of human brain activity reveals dynamical repertoire re-organization under LSD. Scientific reports, 7(1), 1-18.

• Atasoy, S., Vohryzek, J., G. Deco, G., Carhart-Harris, R. L., Kringelbach, M. L. (2018). Common neural signatures of psychedelics: Frequency-specific energy changes and repertoire expansion revealed using connectome-harmonic decomposition. Progress in brain research, 242, 97-120.