Beta Rhythm (Music of the Mind)

As I've learned more about bio-systems, starting from water molecules and working up to synapses and networks of neurons, I've come to appreciate how incredibly powerful and compact the molecular computing substrate that life is built on top of is. Our most powerful supercomputers take days to calculate how one protein molecule folds, when the simplest bacteria can perform millions of these operations in parallel in seconds. What these simulations give us, however, is insight into exactly what special characteristics each of the proteins has in all of the various shapes it can assume. Building up from this low level understanding, hopefully we will be able to understand what the larger-scale purpose is for each of the various signaling chains and genetic transcriptions that are taking place, and perhaps we may one day be able to model these complex molecular interactions using state machines and logic that allows us to achieve a functionally equivalent set of operations without...

The more I read about "Cognitive Computing", the more disenchanted I get with most of the work being done under this banner. There is an awful lot of hype going on here: everything from university researchers that claim how simple it is to create a silicon chip that accurately emulates millions of neurons and projects to create silicon prosthetics for some of the major centers in the brain to overly ambitious claims stating how close we are to getting computers to 'think' and thus to the resulting 'singularity'. Most 'cognitive computing' efforts seem to miss the point that there is more happening here than simple electrical signaling over a network. So coming across the following articles and podcast was like a breath of fresh spring air: Complex Synapses Drove Brain Evolution : ScienceDaily (June 9, 2008) — One of the great scientific challenges is to understand the design principles and origins of the human brain. New research has shed light on t...

From "Modeling the Mind: From Circuits to Systems: section 1.2 "Sensory Coding" by Suzanna Becker. "Several classes of computational models have been influential in guiding current thinking about self-organization in sensory systems. These models share the general feature of modeling the brain as a communication channel and applying concepts from information theory. The underlying assumption of these models is that the goal of sensory coding is to map the high-dimensional sensory signal into another (usually lower-dimensional) code that is somehow optimal with respect to information content. Four information-theoretic coding principles will be considered here: 1) Linsker's Infomax principle, 2) Barlow's redundancy reduction principle, 3) Becker and Hinton's Imax principle, and 4) Risannen's minimum description length (MDL) principle. Each of these principles has been used to derive models of learning and has inspired further research into relate...

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...