The heart as the brain’s metronome in coma

The brain’s ability to integrate internal bodily signals with external stimuli is essential for our survival. A recent study led by Marzia De Lucia at the Department of Clinical Neurosciences at CHUV in collaboration with Sophie Schwartz, Professor in the Department of Basic Neuroscience at the UNIGE Faculty of Medicine, reveals that this mechanism remains active even in a state of coma. These astonishing results can be read in PNAS.

The connection between the heart and the brain plays an essential role in interpreting sounds from the environment, even in a coma (© DNC/CHUV - image created by AI)

Our body and brain are in constant interaction. This dialogue is vital not only to answer to signals from our internal organs, but also for interpreting stimuli from the outside world. But how does this vital connection function, and how is it preserved in the absence of consciousness? These questions remain largely unanswered.

New research shows that the heartbeat plays a key role: it guides the brain of comatose people by processing sounds coming from outside. The study was led by Marzia De Lucia of the Department of Clinical Neurosciences at CHUV and the Biomedical Imaging Centre, MER and private doctor in the Faculty of Biology and Medicine at UNIL, in collaboration with Sophie Schwartz, full professor in the Department of Fundamental Neurosciences in the Faculty of Medicine at UNIGE, and several Swiss hospitals.

Using electroencephalography (EEG), the scientists recorded the brain responses of patients in a comatose state who were exposed to sequences of simple sounds - beeps. These sounds were either synchronised with the heartbeat or delivered independently. The results: even without consciousness, the brain continues to rely on the heartbeat to better process external sounds. "The heartbeats act as an internal clock, helping the brain to anticipate auditory sensory information", explains Marzia De Lucia. This integration helps the brain to interpret environmental sounds, which is essential for detecting potential threats. "It's an integrated surveillance system, capable of detecting changes and threats, even in the absence of consciousness".

Moreover, the degree of synchronisation between the heart and the brain may predict comatose patient’s likelihood of recovery: the stronger the link between the heartbeat and sound processing, the greater the chances of awakening. "Our findings not only enhance our understanding of consciousness and perception, they also open up new avenues for diagnosing and treating patients in a coma", says  de Lucia.

Same mechanism during sleep

"These results reflect a very fruitful collaboration between our teams at the UNIGE and the CHUV," adds Sophie Schwartz. "We also tested the impact of the body's internal signals - heartbeat or breathing - on the processing of sounds coming from outside during sleep. In this way, we were able to demonstrate that the same mechanisms at work in people in a coma are also at work in each and every one of us, when our brain is in an altered but normal state such as sleep. Find out more about this research in Communications Biology.

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