Beta Rhythm (Music of the Mind)

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...

Overview From Sandra Ackerman's book Discovering the Brain : The actual signals transmitted throughout the brain come in two forms, electrical and chemical. The two forms are interdependent and meet at the synapse, where chemical substances can alter the electrical conditions within and outside the cell membrane. A nerve cell at rest holds a slight negative charge (about –70 millivolts, or thousandths of a volt, mV) with respect to the exterior; the cell membrane is said to be polarized. The negative charge, the resting potential of the membrane, arises from a very slight excess of negatively charged molecules inside the cell. A membrane at rest is more or less impermeable to positively charged sodium ions (Na + ), but when stimulated it is transiently open to their passage. The Na + ions thus flow in, attracted by the negative charge inside, and the membrane temporarily reverses its polarity, with a higher positive charge inside than out. This stage lasts less than a millisecond,...

Previous posts have covered a number of the low-level building blocks that are used by cells in the brain - things like ion channels, neurotransmitters, receptors, clathrin, vesicles, etc. This post focuses on some important pieces of infrastructure that are needed to enable the brain to do its thing.  Neurons operate in an aqueous medium - a kind of salt water bath, water that is full of postively charged ions (cations like sodium, potassium and calcium) and negatively charged ions (anions like chlorine).   Water molecules are V shaped and have a non-uniform distribution of charge - i.e. one end of the water molecule is more positively charged than the other end.  Like charges repel and unlike charges attract.  As a result, a sphere of these 'polar' water molecules tends to surround the ions (a 'sphere of hydration').   Complicating the picture further is the fact that charged particles like ions are influenced by both concentration gradient...

It's tempting to oversimplify things.  Like neurons.  It would be nice if there were one type of neuron, and all you needed to know about how neurons work could be clearly labelled on a diagram of that one type of neuron.  Well, nature LOVES to specialize.  So, before getting deeper into how neurons work, I thought it would be good to take a step back and get some vocabulary in place...   The Basics From University of Washington's 'Neuroscience for kids':   Neurons come in many different shapes and sizes. Some of the smallest neurons have cell bodies that are only 4 microns wide. Some of the biggest neurons have cell bodies that are 100 microns wide.  Neurons are similar to other cells in the body because: Neurons are surrounded by a cell membrane. Neurons have a nucleus that contains genes. Neurons contain cytoplasm, mitochondria and other "organelles" . Neurons carry out basic cellular processes such as protein synth...