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Scientific Understanding of Consciousness |
Synchronized Brain Interactions for Memory and Decision-Making
PLoS Biology Synchronized Brain Interactions Associated with Memory and Decision-Making Liza Gross Citation: (2005) Synchronized Brain Interactions Associated with Memory and Decision-Making. PLoS Biol 3(12): e432. doi:10.1371/journal.pbio.0030432 Published: November 15, 2005 (paraphrase) In the laboratory, rats learning maze tasks also rely on hippocampal spatial information, which the prefrontal cortex integrates with memory of the route, task rules, and other relevant cues to direct navigational decisions. How the brain coordinates this activity is an active area of research. When neuron populations fire in sync, they produce oscillations in brain wave patterns (measured as local field potentials) that operate at many different frequencies. Brain wave frequencies called theta rhythms, which are prevalent in the rat hippocampus, are associated with working memory and decision-making in both animals and humans. Theta rhythms—which oscillate at about eight cycles per second—appear to act like a metronome for individual neurons that “phase lock” their firing in time with the theta rhythm. Whether the synchronized activity of neuron populations across different brain structures correlates with functions like decision-making, and whether phase-locking somehow coordinates these diverse structures has remained an open question. But now, by training rats on a spatial working memory task—navigating a maze to a food reward—researchers demonstrate a clear correlation between coordinated hippocampal and prefrontal cortex activity and memory or decision-making processes. Firing rates of individual neurons in both CA1 and mPFC were indeed task-related: they distinguished between the directions of runs across the central arm, and between the different routes between reward points during the choice stages. The firing rates of CA1–mPFC neuron pairs coactivated during central arm crossings showed the highest correlations as rats ran toward the decision point. This correlated activity between the neuron pairs was significantly reduced when rats made mistakes and chose the wrong direction. Such synchronized activity may represent the transfer of spatial information from the hippocampus to a working memory system in the mPFC. Many CA1 and mPFC neurons were phase-locked to theta rhythms, with enhanced phase-locking during trials requiring working memory and decision-making. This effectively means that the firing of neurons in both structures was aligned to the same theta rhythm “metronome.” This, in turn, means that CA1–mPFC activities became correlated during distinct portions of the task. These correlations suggest that, as expected, the coordination and function of different brain regions depends on the task at hand. Additionally, this study shows that theta rhythms can be used as a reference against which to coordinate hippocampal and mPFC activity in accordance with behavioral demands of this maze task. Beyond shedding light on the neurobiology of behavior, these findings suggest that theta rhythms may contribute to diseases that involve disruptions in prefrontal cortex connectivity, such as schizophrenia—which, interestingly, can impair the spatial working memory of patients. (end of paraphrase)
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