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Characterization of low-frequency neuronal oscillations in human magnetoencephalography

​In a study published in Scientific Reports, researchers at UNICOG (NeuroSpin) show that spontaneous neuronal oscillations in the 'delta' frequency band (0.5-3 Hz), the wave of unconscious states, can be observed in awake human volunteers using magnetoencephalography. A step towards characterizing underlying physiological signals?

Published on 18 October 2023

​It has long been recognized that rhythmic brain dynamics play an important functional role in perception and cognition. Rhythmic activity in the delta frequency range (0.5-3 Hz) is one of the features of brain dynamics that could play a role in these domains, as its biophysical properties allow the synchronization of large networks of brain areas to a common temporal regime. In particular, the question is how temporal regularities in sensory inputs are extracted and translated into temporal predictions by our brains.

In this study, the authors investigated whether spontaneous delta oscillations, which have been shown in awake animals to play an important functional role in auditory perception and attention orientation, could be measured non-invasively in humans by magnetoencephalography (MEG). The researchers analyzed MEG data from 22 participants at rest with their eyes open (no rhythmic behavior), which they compared with data acquired when the participants tapped their fingers spontaneously (overt rhythmic behavior) and counted silently (covert rhythmic behavior). They did indeed observe neuronal oscillations in the 'delta' frequency band (0.5-3 Hz) at rest and during overt and covert rhythmic activity. Further analysis shows that only the resting condition corresponds to endogenous periodic neuronal dynamics.

This work shows that, using advanced signal processing techniques, it is possible to observe endogenous delta oscillations in non-invasive recordings of the dynamics of the awake human brain at rest. By analyzing these spontaneous oscillations in even greater detail, the authors hope to improve the characterization of underlying physiological signals and their possible functional roles.

Contact : Sophie Herbst

- Magnetoencephalography (MEG) is a non-invasive neuroimaging method that records the electromagnetic activity of the brain in real time. On a large scale, the magnetic fields recorded with MEG, in the femtotesla range (1 fT = 10-15 T), derive from the synchronous electrical activity of a few tens of thousands of neurons.
- The Delta brain wave is the predominant wave when a person is in deep sleep or in a sometimes unconscious state of letting go (hypnosis).​

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