The brain’s «circuit» metaphor is as indisputable as it is familiar: Neurons make direct physical connections to create functional networks, such as to store memories. or create thoughts. But the metaphor is also incomplete. What drives these circuits and networks to come together? New evidence suggests that at least some of this coordination comes from the electric field.
New research in Cortical showed that when animals played a working memory game, the information about what they were remembering was coordinated between two major brain regions by electric fields emerging from the basic electrical activity of all the neurons involved. family. The field, in turn, appears to control neuronal activity, or fluctuations of apparent voltage across cell membranes.
If neurons are the musicians in an orchestra, the brain regions are their parts, and memory is the music they make, then the electric field is the conductor, the study’s authors say.
The physical mechanism by which this common electric field affects the membrane potentials of the constitutive neurons is called «entity splicing». These membrane voltages are fundamental to brain activity. When they cross a threshold, neurons «spike,» sending an electrical pathway that signals other neurons across connections called synapses. Any level of electrical activity can contribute to a common electric field, says study lead author Earl K. Miller, Professor Picower in the Department of Brain and Cognitive Sciences at MIT. This also affects the spike.
Many cortical neurons spend a lot of time oscillating on the verge of a spike. Changes in the electric field around them can repel them one way or another. It’s hard to imagine evolution not exploiting that.»
Earl K. Miller, Professor Picower, Department of Brain and Cognitive Sciences at MIT
In particular, the new study shows that electric fields manipulate the electrical activity of neural networks to produce a general representation of information stored in working memory, said lead author Dimitris Pinotsis, Associate Professor at City -; University of London and a study said. branch in the Picower Institute. He noted that the findings could improve scientists and engineers’ ability to read information from the brain, which could help design brain-controlled prostheses for people with paralysis.
«Using complex systems theory and mathematical calculations, we predicted that the brain’s electric field guides neurons to create memories,» says Pinotsis. «Our experimental data and statistical analysis support this prediction. This is an example of how math and physics unravel the fields of the brain and how they can yield insights to building brain-computer interface (BCI) devices.»
Dominant fields
In a 2022 study, Miller and Pinotsis developed a biophysical model of the electric field generated by neuroelectrical activity. They showed that the overall fields emerging from groups of neurons in a brain region were a more stable and reliable representation of the information animals used to play memory games. rather than the electrical activity of individual neurons. Neurons are somewhat fickle devices whose erratic changes create information inconsistencies known as «representative drift». In a paper earlier this year, scientists also showed that in addition to neurons, electric fields affect the brain’s molecular infrastructure and its regulation of how the brain processes information. fruit.
In the new study, Pinotsis and Miller extended their investigation to ask whether ephaptic coupling propagates a controlled electric field across multiple brain regions to form memory networks or «engrams.»
They therefore extended their analyzes to consider two regions in the brain: the frontal eye field (FEF) and the supplementary eye field (SEF). These two regions, which govern voluntary eye movements, were involved in the working memory game the animals were playing because during each round the animal saw an image on the screen placed at any angle. around the center (like numbers on a clock). After a short period of time, they had to glance in the direction the object had come.
As the animals played, the scientists recorded the local field potential (LFP, a measure of local electrical activity) generated by the neuronal scores in each region. The scientists fed this recorded LFP data into mathematical models that predicted individual neural activity and the overall electric field.
The models then allowed Pinotsis and Miller to calculate whether changes in the field predict changes in membrane voltage, or whether changes in such activity predict changes in the field. To perform this analysis, they used a mathematical method called Granger Causality. It is clear from this analysis that within each region the fields have a strong causal effect on neural activity and not vice versa. Consistent with last year’s study, the analysis also shows that measurements of effect strength for fields remain much more stable than neural activity, suggesting that fields are more reliable.
The researchers then examined causality between the two brain regions and found that the electric field, but not neural activity, reliably represented the transmission of information between the FEF and the SEF. More specifically, they found that the transfer process usually takes place from the FEF to the SEF, which is consistent with previous studies on how the two regions interact. FEF tends to take the lead in initiating eye movement.
Finally, Pinotsis and Miller used another mathematical technique called representation similarity analysis to determine whether two regions are, in fact, processing the same memory. They found that electric fields, not LFP or neural activity, represent the same information across both regions, unifying them into an engram memory network.
Other clinical significance
Considering the evidence that electric fields emerge from neuronal electrical activity but then lead to neural activity representing information, Miller speculates that perhaps a function of electrical activity in individual neurons is create fields to then govern them.
«It’s a two-way street,» Miller said. «The spike and the synapse are important. That’s the background. But then the fields come back and affect the spike process.»
That could have important implications for mental health treatments, he said, because whether neurons spike, affect the strength of their connections, and hence the function of the circuits they form, a phenomenon called synaptic plasticity.
Miller notes that clinical technologies such as transcranial electrical stimulation (TES) alter the electrical field of the brain. If the electric field not only reflects neural activity but actively shapes it, then TES technologies could be used to alter electrical circuits. Properly invented electric field manipulations, he said, could one day help patients reconnect faulty electrical circuits.
Funding for the research came from UK Research and Innovation, the US Office of Naval Research, the JPB Foundation and the Picower Institute for Learning and Memory.
Source:
Reference magazine:
Pinotsis, D. A & Miller, EK, (2023) In vivo ephaptic coupling enables memory network formation. Cortical. doi.org/10.1093/cercor/bhad251.
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