When we recall something familiar or explore a new situation,the brain does not always use the same communication routes. An international study led by Claudio Mirasso at the Institute for Cross-Disciplinary Physics and Complex Systems (IFISC), a joint center of the Spanish National Research Council (CSIC) and the university of the Balearic Islands (UIB), and Santiago canals at the Institute for Neurosciences (IN), a joint center of the CSIC and the Miguel Hernández University (UMH) of Elche, has discovered how the brain flexibly changes its communication pathways by modulating the balance between two essential inhibitory circuits.

These results, recently published in PLoS Computational Biology on September 11, 2024, show that this flexibility depends on the balance between two types of inhibitory mechanisms, which regulate the interaction between slow (theta) and fast (gamma) rhythms. Thanks to this mechanism, the brain can select different sources of data, such as sensory stimuli from the external habitat or stored sensory experience from memory.

To reach these conclusions, the researchers combined computational models with experimental recordings in the hippocampus, a brain region crucial for memory and navigation. They observed that in familiar environments, where sensory experience is already stored, the brain relies more on fast gamma rhythms.Conversely, when exploring new environments, the brain prioritizes slower theta rhythms to process incoming sensory information.

“The brain doesn’t have a fixed map for everything,” explains Mirasso. “It adapts its communication strategy based on the situation. This dynamic balance between inhibition is what allows this flexibility.” Canals adds, “Understanding these dynamics at a mechanistic level could ultimately inspire new therapeutic intervention strategies.”

The Role of Theta and Gamma Rhythms

Brain activity isn’t random; it’s organized into rhythmic patterns. Theta rhythms (4-8 Hz) are associated with navigation, spatial memory, and the encoding of new information. Gamma rhythms (30-100 Hz), conversely, are linked to attention, perception, and the retrieval of existing memories.

The study reveals that the interplay between these rhythms, governed by inhibitory circuits, is key to the brain’s adaptability. Inhibitory circuits act like brakes, preventing overexcitation and allowing for precise signaling. The researchers found that the strength of these “brakes” shifts depending on whether the brain is recalling a memory or processing new information.