Summary: Researchers have uncovered how the brain flexibly routes information by switching communication channels according to context, balancing recall of stored memories with processing of new sensory inputs. This capability depends on the interaction of slow (theta) and fast (gamma) rhythms and is regulated by two distinct inhibitory circuit motifs.
In familiar settings, neuronal activity favors reactivating stored representations; in novel contexts, the same circuits shift to integrate fresh sensory data and update memory. This dynamic routing mechanism may also apply to attention and offers a framework to better understand rhythm disruptions observed in disorders such as Alzheimer’s disease and epilepsy.
Key Facts
- Flexible switching: Brain rhythms reconfigure to prioritize either memory recall or novelty processing.
- Inhibitory balance: The relative strength of feedforward and feedback inhibition determines the dominant communication mode between regions.
- Clinical potential: Understanding these dynamics could inform new strategies for treating Alzheimer’s, epilepsy, and addiction.
Source: UMH
When recalling the familiar or encountering the new, the brain does not always use the same communication pathways.
An international team led by Claudio Mirasso at the Institute for Cross-Disciplinary Physics and Complex Systems (IFISC) and Santiago Canals at the Institute for Neurosciences (IN) of the Miguel Hernández University (UMH) has shown that the brain dynamically shifts its information routes by modulating the balance between two fundamental inhibitory mechanisms.
Published in PLoS Computational Biology, the study demonstrates that this flexible routing depends on the interplay between two types of inhibitory circuits that regulate cross-frequency coupling between slow theta oscillations and fast gamma activity. Through these interactions, the brain can select which information source—external sensory signals or internally stored representations—should dominate processing at any given moment.
To reach these conclusions, the researchers combined biologically grounded computational models with electrophysiological recordings from the hippocampus, a brain area central to memory and spatial navigation. Their observations indicate that in familiar environments, where sensory input is predictable, neurons favor a direct communication mode that promotes transmission from the entorhinal cortex to the hippocampus and supports memory reactivation.
Conversely, in novel environments the circuit shifts into a mode that better integrates ongoing sensory information with memory traces, supporting the updating of stored representations as new data arrive.
Previously it was widely assumed that the phase of slow oscillations simply gated the amplitude of faster rhythms. This work shows the relationship can be bidirectional: depending on circuit configuration, fast gamma dynamics can influence theta phase, and theta phase can modulate gamma amplitude.
“This study provides a mechanistic explanation of how the brain flexibly changes communication channels depending on context,” says Dimitrios Chalkiadakis, first author of the study. “By tuning the balance between different forms of inhibition, neural circuits determine which inputs to prioritize—those arising from memory-related pathways or from new sensory streams.”
Using a theoretical framework that integrates electrophysiological recordings from rats exploring familiar and novel environments, the team identified two main operational modes. In one mode, feedforward inhibition yields fast-to-slow (gamma-to-theta) directional interactions. In the other, feedback inhibition produces slow-to-fast (theta-to-gamma) interactions. Both motifs naturally coexist in brain circuits, and the study finds their relative influence is continuously graded by synaptic strengths within biologically realistic ranges.
A signature prediction of the model is that when feedforward motifs dominate—favoring fast-to-slow interactions—gamma oscillations appear at higher frequencies, whereas dominance of feedback motifs—favoring slow-to-fast interactions—is associated with lower gamma frequency. Empirical hippocampal data from freely navigating rats support this dynamic regulation of cross-frequency directionality.
Beyond memory
The authors suggest this flexible coordination of rhythms could generalize to other cognitive operations such as attention, where prioritization of external stimuli versus internal goals is essential. Recent human studies reveal patterns consistent with the model’s predictions, pointing to a broader organizing principle: the balance between inhibitory circuits steers information flow across the brain’s complex network.
“Our results help reconcile differing views about how rhythms at different frequencies interact,” explains Mirasso. “Rather than being solely local or merely inherited from upstream regions, these oscillations emerge from the interplay of external inputs and local inhibitory dynamics. This dual mechanism enables the brain to optimize processing under diverse conditions,” adds Canals.
Looking forward, the researchers plan to extend their model to include a wider diversity of neuronal types and region-specific architectures to better capture how these dynamics are altered in disorders such as epilepsy, addiction, or Alzheimer’s disease. Studying these mechanisms at the circuit level could ultimately inform new therapeutic approaches.
Funding: This research was supported by the Spanish Ministry of Science, Innovation, and Universities (R&D Project Program) and the Spanish State Research Agency through the Severo Ochoa and María de Maeztu Units of Excellence programs.
About this memory and neuroscience research news
Author: Angeles Gallar
Source: UMH
Contact: Angeles Gallar – UMH
Image: The image is credited to Neuroscience News
Original Research: Open access.
“The role of feedforward and feedback inhibition in modulating theta-gamma cross-frequency interactions in neural circuits” by Claudio Mirasso et al. PLoS Computational Biology
Abstract
The role of feedforward and feedback inhibition in modulating theta-gamma cross-frequency interactions in neural circuits
Cross-frequency interactions among brain rhythms organize neuronal firing sequences that support specific cognitive functions. In the hippocampus, coupling between the phase of theta oscillations and the amplitude of gamma activity has been extensively associated with memory processes. Traditional views emphasize that the phase of a slower rhythm modulates faster activity, but newer metrics indicate these electrophysiological interactions can be bidirectional.
Using computational models, the authors show that feedforward inhibition implemented as a theta-modulated interneuron network gamma (ING) mechanism produces fast-to-slow interactions, while feedback inhibition implemented as a theta-modulated pyramidal-interneuron network gamma (PING) mechanism drives slow-to-fast interactions. In circuits that combine both motifs, directionality is flexibly modulated by synaptic strength within biologically realistic ranges.
A characteristic of this interaction is that dominance of fast-to-slow coupling corresponds to higher-frequency gamma oscillations, and the reverse holds when slow-to-fast interactions dominate. Analysis of hippocampal electrophysiological recordings from rats navigating familiar and novel environments confirms that cross-frequency directionality is dynamically regulated and linked to gamma frequency, consistent with model predictions.
The model assigns each theta-gamma interaction regime—set by the balance between feedforward and feedback inhibition—to distinct modes of information transmission and integration, thereby adding computational flexibility. These findings provide a plausible neurobiological interpretation for measurements of cross-frequency directionality and for how different underlying circuit motifs support specific computational needs.