The electrical signals traveling the along neurons create a surrounding electrical field which adds to the fields created by the activity of other neurons. The EEG trace is the result of these combined fields. Scientists have been attempting to obtain more and more information on the processes of the brain by studying these fields. But what about the opposite effect do electrical fields affect the activity of neurons?
Scientific American has a article by F. Jabr (here) on research by D. McCormick showing that this is a feedback loop.
A few neurons are like individuals talking to each other and having small conversations. But when they all fire in unison, it’s like the roar of a crowd at a sports game… They surrounded the cortical sample with an electric field that approximated the size and polarity of the fields produced by an intact ferret brain during slow-wave sleep to create an exaggerated version of the exact feedback loop they were investigating. Essentially, they enveloped the brain slice in an echo of itself.
When the team applied this electric field echo, they found it amplified and synchronized the neural activity in the brain slice. The field didn’t create disorderit increased harmony. The “roar” of the brain slice became louder and more regular. “Its kind of like if you were cheering at a football game and someone played over the speaker the sound of the crowd cheering and you started responding to that, too, cheering along with both the real crowd and the speaker playback,” McCormick explains. “It’s a kind of reinforcing feedback.”
Not only did the researchers show that this positive feedback facilitated the synchronous slow waves of electrical activity in the slice of ferret brain, they also showed that an electric field of the same strength, but opposite polarity, disrupted its synchronous neural activity.
This is not a surprising result; it is to be expected that an electrical field would affect an electrical current. It also appears that the brain responds to magnetic fields and I presume also produces them. It is also clear that neuron activity is affected by various chemical gradients. This should put paid to the idea that the brain is digital. Many aspects of communication in the brain vary continuously (like an electrical field does) and everything is not ‘fire or don’t fire’ (like a digital computer’s 1 or 0 and nothing in between). Computers are a very, very limited analogy for biological brains.