Wednesday, March 19, 2008

Oscillations Part III: Why write a book?

(This is a continuation of notes taken from Ginger Campbell's podcast #31 with György Buzsáki, and a continuation of Part I and Part II):


Scientific reasons

- debate, exaggeration, denial, and misunderstanding exist regarding the brain rhythms and brain oscillations

- oscillations were considered a mere byproduct in physics, engineering, architecture and neuroscience

- many questioned how the brain can perform despite the fact that there are these oscillators at all levels of neuron organization.

- Buzsáki began to look at what kind of advantages oscillators provide to the nervous system - lots of fundamental things that can be solved very effectively with oscillators:

1. Codification

- messages in the brain from one place to another must first be coded

- information coding entails that every message that is transmitted from one place to another must have a beginning and an end;
"It's the same with coding for DNA; you have to have a beginning code and an ending one."

- this is not trivial in a brain which is interconnected and continuously active:
"For example, if you are looking at events at the periphery, such as the cochlea, then the beginning of the sound and the end of the sound perfectly signals the messages because these are coded or signaled by extrinsic physical stimuli. But these stimuli are not available in the brain especially during cognitive processes when there are no external timers, so the brain has to come up with these internal timers. So, oscillations are perhaps the best solutions for marking the beginning and the end of the messages, because, as we may be talking about a little bit later, every single oscillation reflects or is associated with the fluctuation of excitability. There is always the period or phase of the oscillator when the activity is maximum and when it is minimum. So, when you go from minimum to minimum, then these time periods can beautifully mark the beginning and the end of a message. So this is one attractive feature."

2. Existence of Oscillator systems

- people acknowledge that there are oscillators in the brain - e.g., sleep spindles, alpha oscillations, Parkinsonian tremor

- not only are there a few oscillators with different frequencies in the brain but there is a system of oscillators:
"What I mean by that, is that several orders of magnitude of time starting let's say with the high frequencies - 3, 4, 500 Hz, which is only a few milliseconds of time window - all the way to tens of seconds, or minutes, are covered by neuronal oscillators. And there is no gap. And if you look at the mean frequencies, and the variability of the range of these oscillation generators, they are overlapping in a regular way, and their mean frequencies happen to coincide with a number of life's natural logarithms. And that was an interesting revelation.. that oscillators exist together, or can exist together; they don't have an integer relationship - in other words one oscillator cannot entrain the other one permanently - but because they are related to each other through irrational relationships, irrational numbers, they can never sustain some permanent activities. For the interference between oscillators, between natural brain oscillators, is always transitional. And this was an attractive feature for many, because it's led to the recognition that this is probably the way how you can generate pictures that look like noise, as well as this is a force that keeps the brain going permanently, and it never comes back to the same state. These are the scientific arguments behind trying to write a book."

Practical reason

- different departments: biomedical engineering, physics departments, neurosciences departments, molecular biology - much of the knowledge about oscillators is available only in various specific publications

- people in various disciplines are exploiting information about oscillators; physics, mathematics, engineering, and membrane physiology, systems neuroscience, even clinical neuroscience, but such information has never been bound together into a coherent whole

- discussion about a specific oscillator is assumed to be very specific to a favorite structure, or to a favorite species, but there was no comprehensive overview:
"to present a coherent synthesized picture, all this scattered information should come together in a single brain, and cross reference across the information, and somehow simplify it. So my goal was to simplify the existing knowledge and to explain it not necessarily to the layman but to those people who have some background in neuroscience or some serious interest in neuroscience and see how a neglected area of dynamics can represent something very important and fundamentally in the brain."


Further reading:
1. Information on sleep cycles, including sleep spindles.
2. Memory and Brain Dynamics: Oscillations, Integrating Attention, Perception, Learning and Memory, by Erol Basar (large portions of this book can be read online)

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