Neuronal electrical activity varies during repetitions of the same task, even with identical outcomes. A new study shows that many fluctuations in brain activity can be attributed to the influence of local electric fields on neurons, a phenomenon known as "ephaptic coupling." Published in Cerebral Cortex, this finding adds evidence that electric fields serve as critical control signals for brain function. Co-author Earl K. Miller states, "The brain is a rollicking sea of electrical influences, but the traditional view of brain function focuses only on spiking and synaptic connections among individual neurons. Growing evidence supports the significance of electric field effects."
In 2022 and 2023, Miller and co-author Dimitris Pinotsis published studies showing that local electric fields in the cortex not only reflected the information processed by neurons better than any individual neuron but also organized the underlying neural spiking. Like an orchestra conductor, electric waves can synchronize groups of neurons to "play the same tune." They theorize that these fields exert physical influence on brain structure through cytoelectric coupling, altering the cytoskeleton of neurons to optimize synchronous oscillation.
Since electric fields are manipulable, Miller and Pinotsis argue that understanding their influence on momentary brain function could lead to therapeutic interventions for impaired conditions. They suggest that "properly devised electric field manipulations could help patients rewire faulty circuits." In prior studies, they averaged signals over time, documenting that while local electric fields arise from individual neuronal activity, they ultimately coordinate the function of these neurons.
In the new study, the team investigated whether mesoscale electric fields provide ephaptic influence during working memory tasks, trial by trial. They reanalyzed data from animals playing a simple video game where they had to remember the position of a dot. The researchers recorded neural electrical spiking and local field potentials, calculating the prevailing local electric field at each moment.
Their statistical analysis revealed significant variability in neural activity during tasks. Using a mathematical technique called Granger Causality, they found that the influence direction between the electric field and neural activity favored the field, indicating its dominance. The researchers stated, "We found that electric fields emerging from neural activity, captured with LFPs [local field potentials], turn around and influence this activity in a top-down fashion (ephaptic coupling)." Moreover, their modeling showed that the strength of ephaptic coupling was proportional to variations in LFP power, indicating that fields influence neural activity. "The larger the variability, the more evident the top-down organizing effects," they noted. "The emerging picture is that electric fields serve as control parameters."
The study was funded by the UK Medical Council, the U.S. Army Research Office, the U.S. Office of Naval Research, the Freedom Together Foundation, and the Picower Institute.
Blogger's Review: This research unveils the significant role of electric fields in neural activity, challenging traditional neuron connection perspectives. Ephaptic coupling opens new avenues for regulating brain function, potentially offering novel approaches for treating neurological disorders in the future.