For decades, neuroscientists have treated the brain somewhat like a Geiger counter: The rate at which neurons fire is taken as a measure of activity, just as a Geiger counter’s click rate indicates the strength of radiation. But new research suggests the brain may be more like a musical instrument. When you play the piano, how often you hit the keys matters, but the precise timing of the notes is also essential to the melody.

Neurons save information in timing of their firing

Some researchers think the discovery of importance of neurone firing timing might help solve a major mystery: how brains can learn so quickly.

It’s a relationship between the continuous rhythm of a brain wave — the overall ebb and flow of electrical signaling in an area of the brain — and the specific moments that neurons in that brain area activate. In this way, brain waves act like a clock.

Phase precession phenomenon

Researchers began noticing phase precession decades ago among the neurons in rat brains that encode information about spatial position. Human brains and rat brains both contain place cells, each of which is tuned to a specific region or “place field.” Our brains seem to scale these place fields to cover our current surroundings. As you leave one place field and enter another, the firing of the first place cell peters out, while that of the second picks up.

Place cells in brain allow for coding spatial position

What about timing? As the rat passes through a place field, the associated place cell fires earlier and earlier with respect to the cycle of the background theta wave. As the rat crosses from one place field into another, the very early firing of the first place cell occurs close in time with the late firing of the next place cell. Their near-coincident firings cause the synapse between them to strengthen, and this coupling of the place cells ingrains the rat’s trajectory into the brain (strengthening of synapses occurs only when two neurons fire within tens of milliseconds of each other.)

Learning new routes based on neuron firing time

Pulling out signals from human brains required sophisticated statistical analysis, because humans exhibit a more complicated pattern of overlapping brain waves than rodents do — and because less of our neural activity is devoted to navigation. But the researchers could say definitively that phase precession is there.

Rats? But what about humans?

Other research suggests that phase precession may be crucial beyond navigation. In animals, the phenomenon has been tied to non-spatial perceptions, including processing sounds and smell.

Not just navigation

Phase precession organizes the timing so that learning happens more often than it could otherwise. It arranges for neurons activated by related information to fire in quick-enough succession for the synapse between them to strengthen. “It would point to this notion that the brain is basically computing faster than you would imagine from rate coding alone,” Diba said.

Phase procession might play a role in learning in general

A temporal pattern of activity observed in human brains for the first time may explain how we can learn so quickly.

Neurons Unexpectedly Encode Information in the Timing of Their Firing | Quanta Magazine

Kasia Radziwon