Neurons communicate with each other and with other cells by sending molecular signals across a synapse or gap junction. But now researchers at Case Western Reserve University have identified what they call a new kind of neuronal communication.
Electricity is an integral part of neuronal signaling, and scientists have known that when lots of neurons are firing at once, it can generate a weak electric field, but one that can be measured with an electroencephalogram (EEG). These fields were thought to be too weak to act on neurons. This work, which has been reported in the Journal of Physiology, shows that not only can these weak electrical fields excite cells, they can propagate a wave of activity by generating electrical fields of their own.
“We don’t know yet the ‘So what?’ part of this discovery entirely,” admitted lead researcher Dominique Durand, the Elmer Lincoln Lindseth Professor in Biomedical Engineering and director of the Neural Engineering Center at the Case School of Engineering. “But we do know that this seems to be an entirely new form of communication in the brain, so we are very excited about this.”
The researchers had set out to study a phenomenon called ephaptic (or electric) coupling - the propagation of rapid brain waves that are akin to those generated during sleep. “We’ve known about these waves for a long time, but no one knows their exact function, and no one believed they could spontaneously propagate,” Durand said. “I’ve been studying the hippocampus, itself just one small part of the brain, for 40 years and it keeps surprising me.”
During their work, the scientists observed that a brain wave could cross a gap the researchers had made in a slice of brain tissue. After repeating the experiment many times, and watching the wave jump the gap over and over, the researchers hypothesized that electric field coupling was the explanation for what they saw. Just as a wave of people in a stadium crowd can continue even if there is a chunk of empty bleachers, the brain wave kept going.
The researchers found that without a synapse, and without gap junctions, slow periodic activity can move through the hippocampus, and is able to create an electric field that can stimulate nearby cells.
The research team was stunned by their findings. Their collaborators did not believe the results. After submitting their paper for peer-review, they were asked to double- and triple-check their research.
“It was a jaw-dropping moment, for us and for every scientist we told about this so far. But every experiment we’ve done since to test it has confirmed it so far,” Durand said.
While there may not be immediate applications for this work, it will help us learn more about the brain, an organ that still holds many mysteries. Learn more about what we know from the video below, which outlines neuronal synapses.