26 October 2010

How Do Your Sparks Spray? How Do Your Dominos Fall?

A human brain works very much like a chain of small explosions -- tiny sprays of spark strung together in chains of rising and falling energy potentials. Like falling dominos, the chain reactions trace tracks that were pre-determined years ago by unique combinations of novel experience working within a novel genetic substrate.
...the "synfire chain" model, in which neurons fire in a chain reaction -- each one triggering the next in the sequence, like a cascade of falling dominos.

In a new study, which appears in the October 24 online issue of Nature, Fee and colleagues have now tested this idea using intracellular recordings, an approach that can record tiny voltage fluctuations in individual HVC neurons. In a technical tour-de-force, they developed a method in which these recordings could be made while the bird was freely moving around his cage and engage in natural behaviors such as singing.

Their results support the chain of dominoes model. When individual HVC neurons fire, they do so suddenly, as if hit by the preceding domino. There was no prior build-up of activity; instead, each neuron remained silent until its turn came to fire, at which point it showed a sudden burst of activity, presumably caused by excitatory input from the previous neuron in the chain. In further experiments, the authors showed that this burst of activity is triggered suddenly by an all-or-none influx of calcium through specialized membrane channels that open in response to this excitatory input. _SD (MIT study)

But those chains of dominos had to be set up "just so." How were these patterns of chain-reaction set up to begin with?
When rats and human beings create a new memory, they are effectively forming a representation, or “mapping” that location or moment and encoding it in their brains. Using advanced monitoring technologies, Markus has been able to actually “hear” place cells in a rat’s mind firing as the animal creates a memory and encodes its route through a maze. The burst of place cell activity the rat experiences when it searches for a food source is conveyed as a staccato series of “pops,” like tiny firecrackers, when picked up by the high-tech monitors in the lab. _PO (U. of Connecticut)
The intermediate details of cascading memory formation depend upon the particular type of memory that is being laid down -- sensorial, spatial, experiential, conceptual etc. -- but the underlying neuronal process is the same, and intriguingly complex.

A human's brain becomes very much like a dynamic sculpture over time, revealing intricate sprays of light and dark, as circumstances inevitably vary in its environment. Circumstances change, but they often vary in cycles. As the cycles of circumstance repeat, so do the dynamic chain reactions of spraying sparks and falling dominos. For example: How do we know what someone close to us is going to say before they say it? How do we often anticipate the exact words an author will use to describe a character or a scene?

We are attracted to other brains both for their ability to surprise us, and for their ability to create a comforting stability around us. In that sense we are really not that different from children.

The differences in our genes place each of us in a different starting point on the path to a well-sculpted brain. Our brain dominos will fall differently -- and will form different chains of falling -- depending upon how our genes (and epigenetics) are laid out in the beginning. Take one simple example: sleep.

Simple gene variations determine how well a person can function on limited sleep. This difference in function can easily determine the fate of an individual in a highly competitive society.
...The people with the DQB1*0602 gene variant were sleepier and more fatigued while both fully rested and sleep deprived. Their sleep was more fragmented. For example, those with the gene variant woke up on average almost four times during the fifth night of sleep deprivation, compared to those without the gene variant, who woke up on average twice. Those with the gene variant also had a lower sleep drive, or desire to sleep, during the fully rested nights....“This gene may be a biomarker for predicting how people will respond to sleep deprivation, which has significant health consequences and affects millions of people around the world. It may be particularly important to those who work on the night shift, travel frequently across multiple time zones, or just lose sleep due to their multiple work and family obligations. However, more research and replication of our findings are needed,” said lead study author Namni Goel, PhD, of the University of Pennsylvania School of Medicine in Philadelphia. _AAN (U.Penn, NIH)

Sleep is a complex phenomenon which determines much of a person's trajectory through life. There are certain moments in time where an alert mind makes the difference between life and death, success and failure. One tick of the clock and that moment has passed. If sleep -- and the ability to function optimally on limited sleep -- is genetically determined, then how many other determinants of a person's quality and quantity of life are hidden in the molecules?
We are learning more about how the human brain is re-charged and re-built during sleep. A person's memories -- the "lay of the land" in a person's brain -- is re-built and re-furbished on a regular basis, with slight modifications over time. Sleep is a critical part of that ongoing program of maintenance.

And so we humans, we slightly advanced apes, blunder into the future riding a cresting trajectory of saccadic memories. It is a bit like riding a surfboard, except that we are the surf, the board, and the rider. The environment is the storm hundreds of miles offshore, and our genes are the shallowing seabottom and the reefs and kelp. Always a balancing act, never exactly the same wave twice. Learning to let go is the hardest part.

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Blogger Embrace Learning said...

interesting article. I find it interesting because I'm involved in e-learning and it suggests alot about how the human mind works and develops.

Wednesday, 27 October, 2010  

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