How does the brain activity change during repetitive behaviours?
“Civilization advances by extending the number of important operations which we can perform without thinking of them.” In this quote, the philosopher A. Whitehead underlines the importance of automated low-level tasks when performing a complex and repetitive task. Tying shoelaces, writing, walking… our mind is relieved from the elementary actions that constitute these behaviours. To understand what is happening in the brain during repetitive behaviours, our team at the Physics for Medicine Paris lab has recorded the brain activity of rats while they were performing stereotypes episodes of running along a track, using a new neuroimaging technique coined “functional ultrasound” (fUS). fUS imaging has been developed by our lab to visualize the cerebral activity across the entire brain at unprecedented resolution. Moreover, this lightweight technique does not affect the natural behaviour of the animal, enabling the observation of the brain activity during subtle behaviour such as locomotion.
In a study published this week in Nature Communications, we have recorded simultaneously, during locomotion episodes, the animal’s behaviour, the electrical activity in the hippocampus – a region known for hosting spatial memory in rodents, particularly the “place cells” which act as a brain GPS – and the brain vascular activity using fUS. This approach reveals all the regions activated when the animal moves and positions itself in its environment. We have found that locomotion involves a vast network including the hippocampus, the dorsal thalamus and the retrosplenial cortex in a very precise sequence, even though the motor cortex is completely deactivated!
Besides, we were surprised to observe that two locomotion episodes which look similar in terms of displacement speed and duration can drastically differ from the vascular point of view. In the beginning of the recording session, the cortex has a strong response while the hippocampus remains quiet. But then, as the animal accumulates locomotion episodes, the cortex seems to hand over the power to the hippocampus which gets more and more intensively active. Yet, from an external point of view, both trials are similar and the electrical activity of the hippocampus is not much altered! This shows that the link between vascular activity, electrical activity and behaviour is complex, and that the repetition of a routine task can create largely variable activation pattern across the whole brain.
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A Bergel, E Tiran, T Deffieux, C Demené, M Tanter, I Cohen, Adaptive modulation of brain hemodynamics across stereotyped running episodes, Nature Communications 2020, https://doi.org/10.1038/s41467-020-19948-7