Neuropsychology researchers at LMU have discovered a rhythm in the midbrain that could serve as a bio-physiological signature for specific states of consciousness.

The thalamus is a deep-lying structure in the center of the brain which gathers and relays signals from many different areas of the brain. It functions like a gate for perception and attention and is thought to play a key role in supporting conscious states. In a study published recently in the journal Nature Human Behaviour, Professor Tobias Staudigl (Psychology, LMU) and his team, in collaboration with PD Dr. Elisabeth Kaufmann (Neurology, LMU), have discovered a previously unknown rapid activity pattern in the human thalamus.

This rapid oscillation, in the frequency range of 20 to 45 Hertz, occurs exclusively during waking hours and REM sleep, the phase of sleep with rapid eye movements and intensive dreams. It is entirely absent in non-REM sleep, when eye movements are absent and consciousness is strongly reduced. In this sleep phase, the brain activity is dominated instead by slower oscillations.

Measurements with implanted electrodes

In this study, the researchers investigated patients undergoing deep brain stimulation therapy, a form of treatment for epilepsy. The therapy involves implanting electrodes in the thalamus of the patients to reduce the number of epileptic seizures. From a scientific perspective, this offers an exciting and very rare opportunity to directly record neural activity in the human thalamus. Recording neural activity from such deep brain structures is notoriously difficult using common methods such as surface EEG. The researcher’s findings were based on direct field potential recordings in the central thalamus, combined with surface EEG measurements, eye movement analyses, and the classification of sleep patterns in individual patients. This allowed them to precisely track how thalamic oscillation patterns change when the subjects were awake or in various sleep phases.

“Our results show that the central thalamus plays an important role in regulating brain states. In the context of existing research, our results show that this small deep-lying brain structure could actively influence our states of consciousness,” explains Dr. Aditya Chowdhury, lead author of the study. Tobias Staudigl adds: “These characteristic rhythm patterns can be reliably attributed to specific states and thus have the potential to serve as a measurable biological signature of states of consciousness.”

A deeper understanding of the signal discovered in the thalamus would also be of much interest from a clinical perspective. The signal could be used to optimize existing therapeutic approaches and, in the long run, lead to new approaches for the treatment of other neurological diseases. Staudigl was recently awarded funding by the European Research Council to further explore the clinical potential of the discovery.