Neurons exhibit rhythmic activity at different frequencies in an asynchronous state

at 17^th century, Dutch scientist Christiaan Huygens hung two of his newly invented pendulum clocks on a block of wood and observed that over time, the clocks synchronized their beats. He reported this finding, which he called ‘strange sympathy’, in 1665. Three and a half centuries later, neurons in the brain were found to synchronize their activity in the same way.

Neurons in the brain often synchronize in quasi-rhythmic activity, collectively producing ‘brain waves’ that can sometimes be detected even from outside the skull using electroencephalography. Synchronization in these rhythms helps neurons to exchange information efficiently, which is essential for performing important functions such as learning, memory, attention, perception, and movement. How these rhythms are generated, maintained, and abolished to suit the ever-changing needs for smooth brain operation is an active area of ​​research.

In a new study published today in Cell Reports, a team of neuroscientists led by Principal Investigator Balázs Hangya MD PhD at the Institute of Experimental Medicine, Budapest, Hungary found that a group of neurons in the brain exhibits rhythmic activity at different frequencies in desynchronization. states, like individual clocks, but they can align their rhythmic frequencies to produce a synchronized brain rhythm upon activation, similar to the pendulum clock in Huygens’ experiment.

To investigate brain synchronization mechanisms, the team recorded specialized neurons from a deep brain structure called the medial septum. These neurons form a ‘pacemaker network’, which produces a 4-12 Hz ‘theta’ rhythm in a structure called the hippocampus, which is responsible for encoding the episodic memory traces of the events we experience. It is well known that hippocampal theta oscillations are important for memory, but the exact mechanism by which they are generated is not well understood.

To understand how the cells in the medial septum synchronize, one must record the activity of several cells at once. In addition to this multichannel brain recording, parallel recording of hippocampal activity is also required to understand medial septal output signals. It’s still technically challenging, so this recording can only be done by a skilled experimenter.”

Balázs Hangya MD PhD, Principal Investigator, Institute of Experimental Medicine, Budapest, Hungary

To address this challenge, Hangya’s lab collaborated with another group led by professors István Ulbert, Viktor Varga and Szabolcs Káli to investigate the medial septal ‘pacemaker network’ in mice and rats, awake or under anesthesia. The Huygens synchronization mechanism was present under all conditions tested and could also be reproduced by a detailed computational model of the medial septal ‘pacemaker network’. The authors speculate that Huygens synchronization may be a common synchronization mechanism across brain circuits in different species, including humans.

“I think we have come up with a new idea about the origin of tissue synchronization. The fact that medial septal inhibitory cells synchronize their frequency upon activation by local excitatory input was previously unknown” says Barnabás Kocsis, first author of the article.

Brain synchronization mechanisms can go wrong in disease, cause problems with memory and attention, and even contribute to serious conditions such as schizophrenia, epilepsy, and Alzheimer’s disease. The researchers hope that a better understanding of how brain networks synchronize can eventually lead to better therapies for this disease.

The research described in this release was supported by grants from: European Commission, Hungarian Academy of Sciences, Hungarian National Office of Research, Development and Innovation, Hungarian Ministry of Innovation and Technology, Eotvos Lorand Research Network, Generalitat Valenciana and Kyoto University.

Source:

Experimental Medicine Institute

Journal reference:

Kosis, B., et al. (2022) Huygens synchronization of medial septal pacemaker neurons produces hippocampal theta oscillations. Cell Report. doi.org/10.1016/j.celrep.2022.111149.

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