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The headline seems to be somewhat at odds with explanation of this "phase precession" is the body of the article: "The phenomenon is called phase precession. I
by HarHarVeryFunny 5y ago
The headline seems to be somewhat at odds with explanation of this "phase precession" is the body of the article:
"The phenomenon is called phase precession. 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. A theta brain wave, for instance, rises and falls in a consistent pattern over time, but neurons fire inconsistently, at different points on the wave’s trajectory. In this way, brain waves act like a clock, said one of the study’s coauthors, Salman Qasim, also of Columbia. They let neurons time their firings precisely so that they’ll land in range of other neurons’ firing — thereby forging connections between neurons."
My understanding of what they're saying is that it's related to "neurons that fire together wire together". Given different signal travel distances, it's necessary for neurons to fire at different times if they're to arrive at a given destination at the same time (in order to "wire together"). They achieve this timing by firing in synchrony with the theta brain waves that travel across regions.
So, with this understanding, I guess you could say the timing is encoding information, but really in essence it's only the relative spatial position - within the cortex - of the firing neuron that's being "encoded". A more useful way to view it is just that firing times are synchronized to theta waves in order to achieve larger scale coordination that compensates for signal travel distances.
- sdwr 5y agoFire together, wire together refers to the connection between two neurons strengthening. Firing just before the recipient neuron fires strengthens the bond, and firing afterwards/off tempo weakens the bond. It's an elegant concept, because it handles neural weights, a non-linear activation function, and clock speed with a simple, distributed rule.
- HarHarVeryFunny 5y agoRight, but first the "recipient" neuron needs to fire, which requires integrated synaptic inputs to cross some threshold, which requires input spikes to arrive close to the same time. This phase precession mechanism being discussed is what allows inputs arriving from different distances (i.e. with different signal travel times) to arrive close to the same time such that the recipient fires. Once it fires, then "fire together, wire together" can strengthen/weaken the synapses as appropriate.
- sdwr 5y agoAfter reading the article, I don't think that's what they're saying. My understanding is that place cells stand in for a literal location in space, and fire when they detect that location. The phase precession is how place cell A overlaps firing with place cell B when the individual is moving from location A to B, strengthening the connection (to create a mental link/memory between the two?)
- HarHarVeryFunny 5y agoThe article does discuss the place cell example (observed in rats), but basically as old news. What seems to be new (at least going by the Quanta article - I don't have access to Cell) is seeing phase precession in humans, and hints of it being a more universal mechanism also used for sequence learning, etc. In the place cell instance, it seems one effect of this mechanism might be for place cell firing to act as a predictive input for adjacent place cells (a pretty solid real-word prior - you can't be "here" unless you just came from somewhere adjacent!), and another might be to make prior-and-current place simultaneously available which could be used to learn direction of travel. If this is a general (or at least widespread) mechanism, not limited to place cell firing, then it opens up all sort of learning possibilities by bringing together (in time) inputs that would otherwise be asynchronous.