Brain Cells Can Switch Their Rhythm Up to Ten Times a Second

The human brain is extremely dynamic. The connections between nerve cells change when we learn or forget. But our brain’s computations change even faster than its structure: in a heartbeat, we shift our focus from what we see to what we hear or smell. The coffee aroma might have been there all the time, but as we attend to it, circuits in our brain shift their activity rhythms and we actively perceive the aroma. A transdisciplinary research team at the Göttingen Campus has now combined experimental and mathematical approaches and found a new perspective on the rhythmic processes in the brain. The results were published in the journal Proceedings of the National Academy of Science (PNAS).

Scientists at the Göttingen Campus Institute for Dynamics of Biological Networks (CIDBN) have investigated the cellular mechanisms behind these processes. Cells that are involved in brain functions such as the processing of sensory information, as well as in the consolidation of memory, exhibit collective rhythmic activity. "Typically, nerve cells are studied using artificial stimuli, such as brief pulses or oscillations," explains Dr Andreas Neef, head of the Laboratory for Neurophysics at the CIDBN. "But we wanted to study these cells using more natural, irregular stimuli."

Previous research that characterised cells using conventional methods seemed to paint a straightforward picture: some nerve cell types are specialised to participate in fast activity rhythms, while another cell type – the “adapting interneuron” – participates mainly in slow rhythms. However, when the Göttingen team analysed the responses of nerve cells to the novel, more natural stimuli, a very different picture emerged. The adapting interneurons did not simply follow the slow rhythms, as was expected, instead they were able to switch between very slow rhythms and very fast rhythms.

During certain sleep phases or during inactive daydreaming, the adaptive interneurons can contribute to brain rhythms of up to 200 cycles per second, according to these new findings. This is more than 20 times faster than thought possible for these cells. "We were surprised at how differently these cells could respond," says first author Dr Ricardo Martins Merino. "But what is even more astonishing to me is the speed of their ‘re-tuning’. One moment they are contributing to the fast oscillations, the next they are not. They can switch back and forth ten times a second!"

The scientists assume that this ability to switch quickly is the solution to the long-standing puzzle of how the different rhythms in the brain interact with each other and how we can shift our attention so quickly from one aspect to the next. "The next goal is to study the role of switching in both the computer and the living brain. The CIDBN offers the ideal space for this because here theoretical and experimental research approaches are combined under one roof," says co-author Professor Fred Wolf, founding director of the CIDBN.

Reference: Merino RM, Leon-Pinzon C, Stühmer W, et al. Theta activity paradoxically boosts gamma and ripple frequency sensitivity in prefrontal interneurons. PNAS. 2021;118(51). doi: 10.1073/pnas.2114549118

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