The prevailing understanding of the brain as a network of interconnected circuits has been challenged by new research indicating that electric fields play a crucial role in coordinating the activity of these circuits. A study published in Cerebral Cortex reveals that as animals engage in working memory tasks, the information they remember is coordinated across crucial brain regions by electric fields generated from the underlying electrical activity of all participating neurons. These fields drive neural activity by influencing the fluctuations of voltage observed across the cells’ membranes.
The researchers compare the electric field to a conductor in an orchestra. If neurons are the musicians, brain regions are the sections, and memory is the music produced, the electric field acts as the conductor. This phenomenon, known as “ephaptic coupling,” occurs when the prevailing electric field influences the membrane voltage of neurons, which is fundamental to brain activity. When membrane voltages reach a certain threshold, neurons generate electrical signals, or spikes, that are transmitted to other neurons via synapses.
According to the study’s senior author, Earl K. Miller, a Picower Professor in the Department of Brain and Cognitive Sciences at MIT, even small amounts of electrical activity can contribute to the prevailing electric field and influence neural spiking. This suggests that evolution has likely exploited this mechanism to shape brain activity.
The study demonstrated that electric fields drove the electrical activity of networks of neurons, leading to a shared representation of the information stored in working memory. This finding has implications for developing brain-computer interface (BCI) devices, which can read information from the brain and assist in designing brain-controlled prosthetics for individuals with paralysis. By understanding how electric fields guide neural activity and memory formation, scientists and engineers can improve the accuracy and effectiveness of BCI devices.
In a previous study, the researchers developed a biophysical model of the electric fields produced by neural electrical activity. They found that the overall fields emerging from groups of neurons in a brain region provided more reliable and stable representations of information than the electrical activity of individual neurons. Neurons can exhibit representational drift, causing inconsistencies in information processing. The researchers proposed that electric fields influence the brain’s molecular infrastructure, fine-tuning its processing efficiency.
In the new study, the researchers investigated whether ephaptic coupling spreads the governing electric field across multiple brain regions to form a memory network, or “engram.” They focused on two relevant brain regions: the frontal eye fields (FEF) and the supplementary eye fields (SEF), which control voluntary eye movement. Animals playing a working memory game were observed, and the researchers recorded the local field potentials (LFPs) produced by neurons in each region. They used mathematical models to predict neural activity and electric fields based on the recorded LFP data.
The researchers used mathematical methods such as Granger Causality and representation similarity analysis to determine the causal relationships between electric fields, neural activity, and information transfer between brain regions. The results showed that the fields exerted a robust causal influence on neural activity, not vice versa. The influence of electric fields remained more stable and reliable than neural activity, supporting the notion that fields are essential for information processing.
Furthermore, the researchers found that the electric fields reliably represented the transfer of information between the FEF and SEF regions, unifying them into an engram memory network. The transfer of information typically flowed from FEF to SEF, consistent with previous studies on the interaction between these regions. The researchers used representation similarity analysis to confirm that the electric fields, but not the LFPs or neural activity, represented the same memory information across both regions.
The findings suggest a bidirectional relationship between electrical activity and electric fields in the brain. While neuronal spiking and synapses are essential foundations for brain function, electric fields can also influence spiking. This insight has potential implications for mental health treatments, as neuronal spiking influences the strength of connections and the function of circuits through synaptic plasticity.
Clinical techniques like transcranial electrical stimulation (TES), which alters brain electrical fields, could be used to modulate circuits. By manipulating electrical fields, it may be possible to help patients rewire faulty circuits in the future.
In summary, this research challenges the traditional view of the brain as solely composed of interconnected circuits. It highlights the significant role of electric fields in coordinating neural activity and memory formation. Understanding the influence of electric fields on brain function can advance the development of BCI devices and potentially lead to innovative therapeutic interventions for neurological disorders.
