Beta Rhythm (Music of the Mind)

In 2006, IBM Research hosted a series of lectures on Cognitive Computing, featuring presentations from some well-known researchers in neuroscience and cognitive computing. Videos of the lectures and the presentations that were given are available at http://www.almaden.ibm.com/institute/2006/agenda.shtml . A word of caution, however: as one person in the audience commented in a Q&A session after a panel presentation, a number of the presentations were more 'neuromythology' (i.e. bravado, marketing, speculation and wishful thinking) than neuroscience. I did learn a number of things from a few of the presentations, however, and will try to summarize the good stuff and ignore the rest in the next few posts. The presentation by Henry Markram , EPFL/BlueBrain: The Emergence of Intelligence in the Neocortical Microcircuit ( video ) describes the Blue Brain project that Markram was director of at the time, which aimed to create a computer model of the neurons in a cortical colu...

The previous post began with a slogan pertaining to Hebbian learning that was coined by Donald Hebb: "Cells that fire together, wire together". A number of papers have been appearing in recent years that extend this idea further - that pulses that coincide are actually one of the most important ways that the brain transmits information. This concept appears to be a natural consequence of Hebbian learning: the brain adapts its network of synaptic connections by pruning those connections where the incoming signals are not correlated with other signals coming into the neuron and reinforces those where this type of coincidence does occur. It is doing this for a reason - to establish the 'right' set of connections and synaptic weights in order to associate one input or one set of inputs with another. This type of correlation between events has been proposed as being what knowledge itself is made of and as the basis for some of the key aspects of cognition and symbolic thou...

In 1949, Canadian psychologist Donald Hebb proposed that "When an axon of cell A is near enough to excite cell b or repeatedly and consistently takes part in firing it, some growth process or metabolic changes take place in one or both cells such that A's efficiency, as one of the cells firing B, is increased". ( ref. ) This idea is captured in the slogan 'Cells that fire together wire together'. A special set of molecules called neurotrophins play an important role in this. From Joseph LeDoux's book The Synaptic Self : When an action potential occurs in a postsynaptic cell, neurotrophins are released from the cell and diffuse backward across the synapse, where they are taken up by presynaptic terminals. Under the influence of neurotrophins, the terminals begin to branch and sprout new synaptic connections. Since only those presynaptic cells that were just active (that just released transmitter) take up the molecules, only they sprout new connections. a...

One of the reasons that neuroscience has taken off over the last decade is the emergence of functional Magnetic Resonance Imaging as a tool to non-invasively watch the living human brain in action. But fMRI scans can't directly detect neurons firing - instead, they monitor where blood is flowing in the brain. The brain somehow directs the body's vascular system to bring blood to just those regions of the brain that need it, a "Just In Time" marshalling of resources. And this happens not just in the brain but throughout the body, under direction from the nervous system. Basically, in order to get blood to flow to a specific region of the body, the diameter of the blood vessels in this region need to increase ("vasodilation"). This reduces the blood pressure and, since liquids always flow from regions of high pressure to regions of low pressure, blood moves into the area of the brain that has dilated blood capilleries. The fMRI detects the fact that there...

I'm currently reading Joseph LeDoux's excellent book "Synaptic Self" - I highly recommend it. Chapter 3 of the book - "The Most Unaccountable Machinery" - does a splendid job of covering the basic working mechanisms of neurons, axons, dendrites and synapses, as well as the history behind some of the most important discoveries in neurobiology. The section covering inhibition was particularly enlightening for me, so I'd like to use this post to capture the key points on inhibition and the roles of Glutamate and GABA. In a previous post (Neurotransmitters - molecular messages) , the following definition of GABA was quoted from another excellent (and free!) book: " Discovering the Brain " by Sandra Ackerman: GABA (gamma-aminobutyric acid) often acts as a fast synaptic transmission inhibitor. Unlike dopamine or serotonin, which have diverse roles, GABA consistently acts as an “off” signal; the cerebellum, retina, and spinal cord all use this...

The picture at right is truly amazing. It overlays three color-coded images of dendritic spines in a living mouse's brain, collected 45 minutes apart. White regions indicate stable dendritic segments. Green shows spines that retracted and red shows spines that sprouted during the observation period. From A New Window to View How Experiences Rewire the Brain : Howard Hughes Medical Institute researchers have developed sophisticated microscopy techniques that permit them to watch how the brains of live mice are rewired as the mice learn to adapt to new experiences. Their studies show that rewiring of the brain involves the formation and elimination of synapses, the connections between neurons. The technique offers a new way to examine how learning can spur changes in the organization of neuronal connections in the brain. ... “Our first observations of the large-scale structure of neurons, their axons and dendrites, revealed that they were remarkably stable over a month.” Dendrites...

Recall from the previous post, that when a neuron's axon fires repeatedly the relevant genes (in that neuron) turn on, and the synapses that are holding the short-term memory when the synapse strengthening proteins find them, become, in effect, tattooed (from Making Memories Stick by R. Douglas Fields) It appears that this 'tattooing' process involves enzymes that cause actin to change the shape of the synapse, broadening it so that more receptors can be brought into play. Much progress has been made in the past 10 years or so to understand the details of what is going on. From ScienceDaily (Jun. 14, 2004) : Neuroscientists at the Picower Center for Learning and Memory at MIT show for the first time that storage of long-term memories depends on the size and shape of synapses among neurons in the outer part of the brain, the cerebral cortex. ... When an experience or a fact is repeated enough or elicits a powerful emotional response, it shifts from short- to long-term m...

If there was one experience that pushed my interest in neurobiology beyond the activation threshold and kick-started the process that led to the creation of this blog, it was reading Dr. R. Douglas Fields' article "Making Memories Stick" in the Feb. 2005 issue of Scientific American ( ref. ). I'd long been interested in molecular biology but had been intimidated by the level of jargon and assumed knowledge that filled most articles. Dr. Fields' article explained the inner workings of a neuron so clearly and lucidly that I was able to get a basic understanding of what was happening, and was motivated to try to learn more about molecular biology and neurobiology in particular. This blog is essentially the notes I've been making as I try to learn more about the details of how biology works at a molecular, cellular and neuronal level. So, things have finally come full circle. Let's take a deeper look at what makes memories stick... From Making Memories Sti...

I happened to stumble upon Martin Rodbell's 1994 Nobel Lecture paper : "Signal Transduction: Evolution of an Idea" again recently. I really enjoy reading these Lecture papers as they are a) written by the scientists that did the breakthrough research, b) contain a lot of insights into the creative process behind their discoveries and c) are intended for a general audience. Rodbell's paper is a good example. The following excerpt from his lecture paper bridges two areas I had no idea were related: G-protein receptors and the cytoskeleton. (The picture at right is from the web page for Andres Lebensohn of the Kirschner Lab at Harvard. It shows the assembly of an actin network.) G-PROTEINS ARE SIMILAR IN STRUCTURE AND REGULATION TO CYTOSKELETAL PROTEINS. by Martin Rodbell During these studies, my attention was drawn to the striking similarities in the properties of G-proteins with those of tubulin and actin, the major cytoskeletal elements in cells. For example, G...