Today, researchers They spend so many hours in the lab doing difficult experiments, they might listen to music or podcasts to get them going all day. But in the early years of neuroscience, hearing was an essential part of the process. To find out what the neurons are interested in, the researchers translate the near-instant signals they send, called “sound waves,” into sound. And the louder the sound, the more often the neuron fires — and the faster it fires.
“You can just hear the number of pops coming out of the speaker, and whether it’s really loud or quiet,” says Joshua Jacobs, assistant professor of biomedical engineering at Columbia University. “And this is a really intuitive way to see how active a cell is.”
Neuroscientists no longer rely on sound. They can accurately record nails using implanted electrodes and computer software. To describe a neuron’s firing rate, a neuroscientist would choose a time window – say 100 milliseconds – to see how often they fire. Through firing rates, scientists have discovered a lot of what we know about how the brain works. Examining her in a deep area of the brain called the hippocampus, for example, led to the discovery of place cells — cells that become active when an animal is in a particular place. This 1971 discovery earned neuroscientist John O’Keefe the 2014 Nobel Prize.
Fire rates are a handy simplification; They show the cell’s overall activity level, although they sacrifice accurate information about the timing of the spike. But the individual sequences of spikes are so complex and variable that it can be difficult to know what they mean. So the focus on firing rates often comes down to pragmatism, says Peter Latham, a professor in the Gatsby Unit of Computational Neurosciences at University College London. “We never have enough data,” Latham says. “Every experience is completely different.”
But this does not mean that studying the timing of the rise is useless. Although the interpretation of neuron mutations is difficult, finding meaning in these patterns is possible, if you know what to look for.
That’s what O’Keefe was able to do in 1993, more than two decades after he discovered place cells. By comparing the timing of these cells’ firing to local vibrations – overall waveform patterns in a brain region – he discovered a phenomenon called The proactive phase. When a rat is in a particular location, that neuron will fire at the same time that other nearby neurons are more active. But as the rat continues to move, that neuron will fire a little before or shortly after its neighbors’ peak activity. As neurons become increasingly out of sync with their neighbors over time, they show a pre-phase. Eventually, as the background brain activity follows a repeating up-and-down pattern, it will get back in sync with it, before the cycle starts again.
Since O’Keefe’s discovery, the anticipatory phase has been extensively studied in mice. But no one knew for sure if it occurred in humans until May, when Jacobs’ team published in the journal cell The The first evidence of this is in the human hippocampus. “This is good news, because things fall into place across different types, different experimental conditions,” says Mayank Mehta, a lead researcher in the anticipatory phase at UCLA, who was not involved in the study.
The Columbia University team made their discovery through ten-year-old recordings from the brains of epilepsy patients that tracked neural activity while the patients navigated a virtual environment on a computer. Epilepsy patients are often recruited for neuroscience research because their treatment can include surgically implanted deep electrodes, giving scientists a unique opportunity to eavesdrop on the firing of individual neurons in real time.