Spikes: Exploring the Neural Code (Computational Neuroscience)

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Summary: Quick thinking bat raises very large questions
Review: How fast can a bat make up its mind? With its refined sonar system, a speeding bat can detect an obstruction and swerve to avoid it in a split second. Experiments show the bat has time to process only one spike, or nerve impulse, in the available time window. This is remarkable, but it defies explanation in terms of the long established (circa 1926) idea that the nervous system encodes sensory information as a function of time intervals between spikes. It takes two spikes to open and close a time interval. For the hurrying bat, using just one spike to make its decision, there exists no interval to measure.

Somehow, a single spike is conveying information to the brain. This surprising news was revealed not only in bat studies, but also in other results. This book presents them and then asks anew: How does a nerve convey information about the world toward the brain? What's the real neural code?

The authors review several plausible neural codes and offer their own, but one possibility seems evident from inspection: There is no code. If a single spike conveys information, maybe no decipherment is required. The pulse cannot be amplitude modulated (this is absolute). But it can do various other clever things that would elude detection by ordinary lab instruments. The impulse could spin. Or wobble. It could travel up the axon membrane in one of many discrete longitudinal channels formed by linkage between adjacent ion channels. In such a nerve the information, or sensory increment level, would be inherent in the channel number. In any event, Spikes is a mildly written but altogether shocking book. It implies we have been wrong about the nerve since 1926. And we probably have been.

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Summary: Good book study for neural code
Review: i looked this book, some difficults. but study neural code...
this book help you study neural code, and good friends...

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Summary: An instant classic
Review: In this book RWSB explain in coherent terms, using basic statistical principles, how meaning is coded in the spike trains of neurons. A fascinating and fairly rigorous information-theoretic treatment of the phenomenon.

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Summary: Neuronal code -- it's all in the timing
Review: Neural coding has traditionally been assumed to be one of rate coding, ie, the stronger the stimulus, then the more action potentials per second that a sensory neuron transmits, and so on throughout the nervous system. However, this book begins by pointing out that in various sensory systems there appears to be sparse temporal neural coding, ie, the timing of action potentials transmits information, and in fact does so quite efficiently. A mathematical basis is built up throughout the reference in order to support these claims. However, the general reader who has prior reading of other neurobiological references listed above and below, will nonetheless find the descriptive portions of this reference informative and reasonable to read. If a neuron can fire 100 spikes (ie, action potentials) per second, then it would appear that many biological phenomena are coded by no more than one or two spikes. For example, bat echolocation occurs on a time scale of 5-20 milliseconds (enough time for coding by a maximum of one or two spikes). For example, in the fly, movements across its visual field can cause it to generate a flight torque in less than 30 milliseconds (ie, enough time for only a few spikes). For example, in the rat hippocampus signaling about position is performed on the order of one or two spikes per neuron. The fact that single spikes are carrying information in these examples indicates that at least in some parts of the nervous system, a temporal neural coding exists. As well, the issue of neuron reliability is considered in detail. Traditionally, it has been considered that individual neurons are unreliable (for example, repeated presentations of the same sensory stimulus does not cause a sensory neuron to generate the same spike train each time), and that it is only in the context of the large network of neurons of the nervous system that perception is reliable (for example, an animal running through the woods at a high speed does not collide with trees). However, it is not so clear how the different spike trains generated each time by the sensory neuron in response to the same stimulus should really be quantified, and there is much evidence showing individual neurons to be quite reliable. For example, in human vision in very dim light individual photosensitive sensory neurons are detecting single photons. The fact that the many neural circuits after the photosensitive sensory neuron add little noise to the sensory neuron output, indicates that the neural computation involved must be very reliable. The fact that hyperacuity (ability to detect sensory stimuli beyond, albeit generally just somewhat beyond before it is truly impossible to do so, the threshold of physical reliability) exists also indicates the existence of a very reliable neural computation. For example, echolocating bats resolving jitter in the echoes on an order of 10 nanoseconds, or weakly electric fish resolving signal shifts on the order of 100s of nanoseconds, or human observers with a theoretical visual acuity threshold of 0.01 degree able to discriminate 0.002 degrees. Most of this reference analyzes single trains of spikes (ie, the action potentials being generated by a single neuron), and shows clearly that very few spikes can represent very precise computations. The last chapter of this book considers briefly more recent research on spike trains of multiple neurons.

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Summary: The Neural Code (Variability & Meaning)
Review: Rieke et al. have written a great book exploring how single neurons and populations of cells code information sensitive spikes and patterns of spikes, i.e. single action potentials, clusters, repetitive bursts, or single bursts. There are quite a few equations in the book, but the authors have written the text so well, that an advanced undergraduate or graduate student in the Neurosciences can understand it. One of my favorate sections discusses the Entropy of information, and the entropy of neural code patterns. This concept will likely shape the future of many neurophysiological investigations.

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Summary: Wow. Comes the revolution!
Review: This book asks: How does a nerve convey information about the world toward the brain? It is a crucially important question - one of the most important questions in human history, in fact -- because before one can make realistic theories about how a brain works, one must know what sorts of signals it receives and acts upon.

We were all told, in basic biology, that this question was answered decisively in the 1920s: The nerve encodes and transmits information about the world in the form of frequency modulated pulse trains. The more intense the stimulus, the higher the pulse frequency, and the closer together the pulses in the train. In this system, a single impulse, or "spike", is trivial, in the sense that it is blank. It cannot convey any information alone. It takes at least two pulses to encode sensory meaning. The information that is read by the brain (meaning, say, a level of light, or the intensity of a musical tone) is encoded as the interval between pulses. And so as students we ate this FM story. And answered the inevitable, standardized questions about it on exams.

Now we learn that this familiar, ingrained bedrock idea is not actually true. Somehow, a single spike is - after all -- capable of conveying information to the brain. This news was not revealed in some single egregious experiment but, rather, by a substantial body of experimental results that have filtered into the literature recently. This book gathers and pivots around this unexpected (and probably very unpopular) body of research work, and I suggest that you initially skip all the introductory material and go straight to pages 54-60, where the experimental literature is summarized.

A nice example comes from studying the decision making time of bats. The animal uses echolocation to navigate in flight. An experimental question is this: How many nerve impulses can the creature's brain have decoded before it suddenly decides to swerve? The answer is on the order of one spike. One. Uno.

At this point in the book, the answer is already transparent. The secret of the neural encoding is that there is no code. A single spike conveys information. The information is explicit. No computation is required to extract it.

Ah, but not so fast. On page 4, the authors reiterate the all-or-none law, declaring that: "... incoming stimuli either produce action potentials, which propagate long distances along the cell's axon, or they do not. There are no intermediate signaling mechanisms. This means that a single neuron can provide information to the brain only through the arrival times of the spikes."

Evidently they still want to keep this absolute intact, and so they go on to recreate, in lieu of the familiar FM neural code, another more sophisticated code. This book is their proposal for a new code.

But it seems to me that having driven such wonderfully high piton (their assertion that the FM code isn't one) the authors proceed to rappel down the mountain very fast. Retreating, perhaps, into their alternative code theory.

Instead of following them to lower, safer ground, you might pause to consider this: There might exist, after all, "intermediate signaling mechanisms." The pulse cannot be amplitude modulated (this really is an absolute). But it can surely do many other clever things that would elude detection by the instruments used to study nerve impulses. (Voltage clamps, patch clamps, probes). Like what? It could spin. It could and probably does travel up the axon membrane in one of many discrete longitudinal channels, formed by protein links between adjacent ion channels. In such a nerve the information, or sensory increment level, is inherent in the channel number.

Neurobiology, as an industry, is somewhat at risk to ideas of the type that are let loose in this remarkable book. If one were to follow up on them, one might arrive at a theory of the brain that actually made sense. Well understood structures like the synapse would have to be explained in new ways, etc. There might be uproar.

Also take a look at Findings and Current Opinion in Cognitive Neuroscience, by Squire and Kosslyn. Chapter 25 reviews some the ideas presented in Spikes, and competing explanations offered by other authors in an effort to elucidate the so called "sparse code." One spike. Very sparse indeed. By all means get a copy of Spikes. It would be a shame to miss out on the scientific revolution it so strongly augers.

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Summary: Binary Brain
Review: This is a very interesting look deep into the binary nature of the human brain. It's nice to see the wet science guys taking information theory seriously. And it's also very interesting to see how digital the brain is when you look at interneuronal communication; how every perception you have, is in the end just a string of 1's and 0's.

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Summary: a lot of interesting information
Review: This is one of the best books on brain's neuronal system. Very self-contained, and without a lot of those overstatements you normally find in similar books. The basic points are discussed while many of the classical (but not very useful) points are ignored. The math is clear and the discussion of the real important question always very sharp.