Saturday, October 11, 2014

Review of The Selfish Gene by Richard Dawkins

I can't remember how but when I was 16 I came across this book and it changed my life. The title of Dawkins biography is "An appetite for wonder", and this appetite is no where more apparent than in this book (I have read most of his books). It is a wonderful introduction to the theory of evolution by natural (and sexual) selection, behavioral ecology, and the wonders of nature. At the same time it serves as a terrific example of first rate scientific reasoning. The writing is clear and fluid and extremely elegant. In his autobiography Dawkins admits that every sentence has been rewritten multiple times. Those that have survived this selection process really deliver. Every sentence seem to fill a purpose and yet, rarely does one feel that information is in some way lacking. This book, when it came out in the late seventies, influenced the general public and academics alike. It changed how academics thought about genes and evolution, and it introduced the meme, which has subsequently entered our dictionaries.

As I have said elsewhere, this book really is a literary masterpiece. The fact that it also teaches science to the reader is an added benefit that makes this book one of the best and most important ever written.

The book has a very good structure. At no point does it feel as if new concepts are introduced inappropriately. Dawkins begins by slowly and carefully introducing the replicator concept. In the widest sense a replicator is, as the name implies, something that replicates itself. This can be a mineral shape, a computer virus or a molecule such as RNA or DNA. It is inevitable that a replicator that produce more copies or copies that are more durable will become more prominent in the population. And so it is with our genes. The genes that exist in humans that are alive today are descendents of a very long series of genes that outperformed other genes. To achieve this success the genes have used many different tricks. Primary among these is cooperation with other genes to construct vehicles such as a plant or an animal that can both protect the genes and pass them on. Humans are thus "merely" vehicles created by genes for the benefit of genes (though in another sense we are of course much more than that).

Dawkins carefully builds from this starting point and reaches startling conclusions about many different aspects of nature and evolution. Why did sex evolve and why do the different sexes differ to a greater or a lesser extent in different species? Why are males in general more aggressive? Why do we cooperate? Does altruism exist? How did sterile ants evolve? Whatever he is discussing, Dawkins always provides illustrative examples from nature and when he use metaphors he is (unlike many others) always careful to translate those metaphors back into the language of replicators. The Selfish Gene also derives some of its fame from the fact that it introduced the meme concept. A meme, Dawkins suggested is like a gene in that it can replicate itself, typically via language or imitation. Successful memes (think viral youtube clips) will spread throughout population of less successful memes in the same way that successful genes spread, however, for memes the sexual reproduction of its host matters little. Rather, the success of a meme is determined by its ability to make its host share the idea with others. The meme concept is now in most dictionaries.

Throughout the book Dawkins is careful to point out that even though we are products of evolution and as a result have many instincts that are not always very noble, that does not mean that it is in anyway good or moral to follow ones evolutionary inclinations. Indeed if we understand human instincts we may be better able to construct societies that combat our caveman instincts.

Friday, October 3, 2014

New research from our lab shows that individual neurons can produce timed responses

Previously, when I have blogged I have mostly written about other people's research. Yet sometimes our research group in Lund also publishes first class, revolutionary research. This monday (sep 29th 2014), Fredrik Johansson and colleagues (of which I am one), published a study that I believe will have a huge impact, not only within our own field of research (we study the cellular mechanisms underlying classical conditioning), but for neuroscience at large.

To understand the findings a little background is necessary. Since the 80s we have known that the cerebellum is required for the acquisition of conditioned eye-blink responses. If a subject repeatedly hears a tone and then, right after the tone, is hit with an air-puff on the eye, then eventually that subject will learn to blink in response to the tone. However, if one removes the cerebellum, subjects can no longer acquire these conditioned blink responses. Removing the cortex as well as the mid brain, on the other hand, has little effect on this type of learning.

An important feature of the conditioned blink response is that it is adaptively timed. This means that even if a very long tone precedes the air-puff, the subject will still blink just before the air-puff arrives. This may not seem particularly interesting however, no one know how the brain can produce such delayed responses. Neurons communicate with each other using action potentials which propagate at certain speeds, however, they never slow down anywhere near as much as would be necessary to achieve the type of delay seen during eyeblink conditioning (>100 milliseconds). This means that somewhere within the brain there must be a delay or a memory trace that essentially keeps track of time, thus allowing the subject to execute a certain action at the appropriate time. Such delays are not only seen following eyeblink conditioning, but in pretty much any type of behavior. If you move your lips 10-20 milliseconds too early or too late then your speech will no longer be comprehensible, and when Cristiano Ronaldo runs up to score a free kick, even minor timing errors will cause the ball to hit the stands instead of the net...

Recent research have shown that during eye-blink conditioning, Purkinje cells in the cerebellum acquire conditioned pause responses which are directly linked to the conditioned blink responses. These pauses are, just like the eye-blinks, delayed with respect to the tone, meaning that if we can understand how the delayed pause responses are generated then we may also be able to understand how delays in general appear. The long standing assumption has been that there are so called "delay lines" somewhere along the signal pathway that transmit information about the tone to the Purkinje cells. The tone activates sensory cells in the cochlea which activates cells in the brainstem which in turn passes the signal on to the cerebellum. If one cell type along this pathway maintain a change in its firing rate following this input, then this could explain how the delayed responses arise. However, Fredrik have now shown that this cannot be the case...

Fredrik, instead of using a tone (or equivalent), for conditioning, used stimulation of parallel fibers. These tiny fibers project directly to the Purkinje cell dendrites meaning that there is no possibility of any delay lines. We wanted to see whether the Purkinje cells would still have a delayed response when using parallel fiber stimulation. The results convincingly showed that this was the case. That is, even when stimulating the fibers right next to the Purkinje cells, we still got delayed responses. The implications of this finding are huge. The results show that individual neurons can produce delayed responses to a certain input. In neuroscience this is represents a paradigm shift because previously it has been assumed that we can understand the brain if map all connections between cells as well as the strength of those connections. This study shows that there is much more to the story than this. Unknown processes within the cells evidently play a key role in determining the firing pattern... Johansson F, Jirenhed DA, Rasmussen A, Zucca R, & Hesslow G (2014). Memory trace and timing mechanism localized to cerebellar Purkinje cells. Proceedings of the National Academy of Sciences of the United States of America PMID: 25267641