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    Getting Fired Up About Synapses
    By Kathy Murphy | July 11th 2010 07:46 PM | 6 comments | Print | E-mail | Track Comments
    About Kathy

    Kathy Murphy is a Neuroscientist studying the impact of early experience on neuroplasticity of the developing brain. Kathy is the Founder and Director...

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    You may have noticed that a lot of posts about neuroscience research on scientificblogging.com describe new discoveries about the synapse.  If you are not a neuroscientists you might wonder why we get so fired up about the synapse (pun intended). 

    Well the answer is simple -- understanding how synapses function is the most important question in the field of neuroscience research.  And we are getting close to the answer.
     
    For me what's so cool about the synapse is that they are constantly changing.

    But I want to know what you think -- why do you think the synapse is a cool thing to study?  If you could ask a neuroscientists about their synapse research what would you want to know?

    Let me know your questions then join us Wednesday July 14th at 8:30pm for a Fireside Chat about the Synapse that I will be moderating with 4 of the world's leading neuroscientists studying the synapse.  Go to livestream.com/minds  the free half hour discussion (Wed July 14 8:30pm EST).  You'll be able to watch the discussion live and even participate via the live chat window.

    If you are really into learning about the synapse then join us on the web for the full symposium -- The Synapse Symposium.

    Here's some background about the synapse.  A few factoids to fire up your synapses and get your synaptic plasticity mechanisms working.

    At its most basic level the nervous system has 2 fundamental parts -- neurons make up the nervous part and synapses link the neurons into a functioning system. 

    Synapses are the communication links between neurons, they build the neural circuits that ultimately support all of our thoughts, behaviours, actions and feelings.  A breakdown in the functioning of synapses is the source of many neurological and psychiatric diseases.  These diseases cause synaptic changes that lead to over or under production of synapses, abnormal synaptic function, abnormal synaptic structure, and many more changes that make the brain function abnormally.  Furthermore, most drugs for mental illness target synapses.


    All the red dots in the video above are synapses in a mouse cortex (the green branches are the dendrites of neurons).  It is an amazing video created by the group in the SmithLab at Stanford University that lets you fly through a piece of the mouse brain.

    The term synapse was coined over 100 years ago by the British physiologist Charles Sherrington.  It comes from the Greek word to clasp -- καρφίτσα -- and was first used by Sherrington in 1897 in his chapter in the Textbook of Physiology.

    A synapse is a very tiny structure, it is about 1 micron in diameter, which is 1000 times thinner than a piece of paper.  There are 2 parts to a synapse: a pre-synaptic side where the neurotransmitters are made, stored, and released; a post-synaptic side with receptors that receive the neurotransmitter and allow ions to flow into the post-synaptic neuron to change the electrical potential (depolarize), transmit the signal between neurons, and cause the neuron to fire.  The gap between the 2 sides of the synapse is extremely small, just 20 nanometers, which is 50,000 time thinner than a piece of paper.

    Each neuron has about 1,000-10,000 synapses. And the human brain has about 100 billion neurons.  For a total of 100-1000 trillion synapses in the human brain.  To put this into perspective there are more synapses in your brain than all of the cells in the body, more synapses than grains of sand on a beach, more synapses than the size of the US National Debt -- at least 10 times more!

    The Canadian Psychologist Donald O. Hebb and his colleague Jerzy Konorski were the first to use the term plasticity to describe how the brain change in response to a stimulus.  We now know that it is the synapses are the main site of plasticity in the brain. 

    Each of our synapses is like a tiny computer processor that can run many different programs depending on the situation.  They change in response to the firing patterns of neurons, leading to the strengthening of some synapses and weakening others.   Also synapses are not permanent, they come and go.  They are constantly being generated and lost, a process that can be watched with specialized high resolution imaging of neurons.

    During evolution the synapse has changed becoming more complex in mammals by increasing the number of proteins at each synapse.  There are about 1500 proteins and numerous molecular signaling pathways at work in each synapse.  These proteins and molecular signaling pathways work together to make the synapse function.

    The tiny size, large number, and molecular complexity of the synapses is truly mind boggling.  
    Despite all that complexity neuroscientists are breaking through and making significant steps to understanding the synapse.  Recent advances in molecular biology techniques that let us label and manipulate synaptic synaptic proteins, along with ultra-high resolution imaging that can record synapses in action, have revolutionized studying the synapse.   We are on the brink of being able to translate our understanding about the synapse into new more effective treatments for mental illness, neurodevelopmental disorders, and neurological disease.

    Studying these dynamic little engines in our brains still has a lot of challenges but the potential payoff is well worth the investment that neuroscientists are making to unlock the secrets of the synapse.
     
    So put your synapses to work and let me know what questions you would like to ask the experts.   Then join us on the web to learn more about the synapse.

    Comments

    jenwong
    Your article really illustrated the elegant complexity of the synaptic network in the nervous system.  An enjoyable read! I particularly liked the images that you've included in the text.

    You've described the mind-boggling number proteins and signaling pathways that regulate synapses. I wonder if we would also see even a greater number of epigenetic and microRNA codes at the nucleotide level. (http://www.science20.com/quotsciencequotstruck_bookworm/brains_molecular...)

    I also wonder whether the synaptic structure only shows a part of the picture of how neurological disorders occur, and whether most of the story lies in the biochemical changes in the synapse.
    Is it possibe to hear one's actual synapses "firing" in the brain? Like multi mini-firecrackers going off?

    Here's my question as a cognitive psychologist: although there are very good computer simulations of the synapse and other parts of a neuron AND there are excellent computer simulations of brain structure (IBM has modeled a human brain) none, to my reading, exhibit BEHAVIOR -- even simple behavior. Neural nets work very well for recognition (classification) so they seem ideal for perception. But:

    1) classification is always "taught" to the neural net and feedback sent via a separate path to every synapse so that it's weighting values are modified appropriately--yet I never see a comparable path in brain structure or synapse operation. So, how does a synapse establish its firing level?

    2) it's one thing for a neural net to classify a stimulus -- this has been shown to be possible since the 70s -- but HOW is an integrated chain of behavior produced? Early psychologists imagined that behavior was nothing more than a a chain of Responses to a series of Stimuli. That concept died long ago, especially in language and it never handled "novel" behavior. Yet, it seems that neuroscience is still based on this mid-20th Century concept. Somehow it seems they see behavior as nothing more than a brain recognizing an infinite number of stimuli patterns, with each pattern generating an infinite series of correct responses. By assuming this is how behavior is produced they can focus on chemical and structural changes occurring during really simple learning tasks, just like the early rat psychologists. So my second question, has any of these brain in a computer simulations actually generated correct behavior based upon exposure to simulated situations? (No "training" allowed.)

    My feeling is that neuroscience is modeling the hardware of cognition thinking the hardware directly drives behavior. While this is true of reflexes and instinct -- think firmware -- they are totally missing the "software" that is required to implement cognition which is necessary for complex learned behavior. I suspect that is why IBM's brain although claimed to be a perfect model of a rat and cat brain, never does anything. Only when the cat brain chases the rat drain through a building, will it demonstrate that the current brain function and structure models are even close to being correct. And, it will take working math models. Right now neuroscience describes a very simple, even trivial, example of brain function and then claims that the sheer number of neurons explains how complex behavior is possible. To me it is like demonstrating a computer can do math and then pointing out it gas 100GB of RAM and saying this explains how a payroll is produced. Nope. Nothing happens until the software is loaded and run by the hardware. It is the software that embodies the algorithms and logic that generates complex output from complex input.

    So, "where's the software" and how is it self generated by the brain?

    Bonny Bonobo alias Brat
    The IBM brain is probably sitting there all day just thinking 'I think IBM therefore I am IBM".
    My latest forum article 'Australian Researchers Discover Potential Blue Green Algae Cause & Treatment of Motor Neuron Disease (MND)&(ALS)' Parkinsons's and Alzheimer's can be found at http://www.science20.com/forums/medicine
    Since few have submitted question or comments, let me expand. My cat, sitting on my bed, sees a bird or rabbit moving outside the window and leaps to the window to watch it. This behavior is simple to explain in terms of a series of stimuli each of which has a response. You can assume either the SR links are built into the brain (instinct) or is learned.

    As the object gets near to going out of view, she looks away from the window and then leaps away from the window and runs through the house directly to the window where the bird or rabbit can be best seen.

    Neuroscience would have you believe that every step in this process is a response to a stimulus pattern that leads to another stimulus pattern which is linked to a correct response. And, all the SR links for all behavior are stored for all situations (patterns) in the vastness of the brain's neural net. The problem is, what led to the first instance of my cat running AWAY from a moving object. Saying that this response is "generalized" from other instances is the solution claimed by early psychologists, but it sets up an infinite appeal to earlier events. They always claimed the initial (novel) response was developed through trial and error. In other words, the cat made lots of errors in either this or similar situations.

    A cognitive view would say that the brain has developed and executes a set of "processes" that handle situations. The moving object is handled by a mental skill called object constancy. It generates a prediction that the object will soon move out of view and it's motion vector. This information is used in conjunction with a mental map of the house and a path plotted that takes the cat to the correct window. This path is sent to the motor system to be executed.

    The argument against the cognitive view is that it would take too long to execute complex cognition AND we have no examples of processes being developed by machines -- they need to be programmed by humans. Moreover, since the brain itself seems to run on an SR model, it would mean the processes would need to be developed using an SR-based operation. Unless, of course, they are pre-wired by genetics and as an animal develops they are simply checking out their set of processes and getting them running. In short, they do not learn a process, they merely get it working. What they learn and store are cognitive maps of the world so they have information on things not within their direct vision.

    It would seem the experiments now being done would enable us to check which view is correct. They don't. The fact chemicals flow during learning only tells us that STORAGE is chemical. It tells us nothing about HOW storage is used.

    The fact blood flows to various regions does not tell us what is actually being done in the region. When a computer is doing different tasks, more current flows to the circuits doing the task and more heat is generated by these circuits. And the recording of neural spikes and patterns. Nothing here either. Everyone who brings a radio near a large computer will hear all sorts of patterns. In the olden days we learned to tell what part of our code was being executed by the tone patterns.

    So while it is correct to say "mind is brain," it seems to me that rather than linking neural activity directly to behavior, it would useful to also see IF the "behavior" that the brain generates is, in fact, COGNITION. Cognition is inherently a system of processes and rules that are GENERAL in nature. (Think of the DARPA self-driving cars.) And, the key to this type of cognition is to obtain speed by using parallel processing. So, when a neuroscientist talks about multiple brain area, each with a neural network, imagine multi-processing.

    Unless the brain performs cognition, language will be impossible to explain using an SR approach as psychologists figured out 50 years ago. Activities such as programming would be absurd to see in terms of SR being passed through neural networks.

    Therefore, while the work being done on the brain is interesting, I think it is fundamentally misleading to say this work explains behavior. Until neuroscientists see the brain as the mechanism that performs cognition that uses sensory data to generate motor command data, they will see themselves as solving a puzzle they are not really solving. Complex behavior will never be explained at the neural level.

    Equally, there is no reason to assume that the brain operates like a computer nor that cognition works like a computer program. We know enough about the brain to guess the cognitive software isn't written in C++. Cognitive psychologists need to consider what kind of processes explain behavior and the nature of processes that ARE POTENTIALLY COMPATIBLE WITH BRAIN ACTIVITY while neuo research needs to consider how the brain might be USE an "abstraction" layer (cognition).

    What is it when a person actually "hears" synapses firing in their brain.