This blog will often be about synapses - the tiny structures that connect nerve cells (henceforth "neurons") together and that are largely responsible for storing and processing information in the brain. The synapse is the central subject of modern neuroscience, much in the way that the atom is the center of physics and chemistry, and DNA of biology.
Let's start with a simplified diagram of a "typical" synapse (while noting that no synapse is typical, just as no image of a human being can be).
Why do I call the blog "Hebbery" rather than for example "Synapse"? First, that name is already taken (by a blog that has no relation to synapses). Second, and more importantly, while the blog will mostly talk about synapses in general, it will often focus on perhaps the most intriguing aspect of these fascinating little devices, their plasticity, or ability to change (and thus store information). Donald Hebb was a famous Canadian psychologist and neuroscientist who was one of the first to propose the seminal idea that a neural connection might strengthen in response to "successful"1 electrical activity at that connection. It's only a slight exaggeration to say that this idea explains how the brain generates the mind - a mystery that has vexed philosophers and scientists for millenia and is still far from a generally accepted solution. But this notion of a "Hebbian synapse", a synapse that is malleable in strength in response to the electrical signals that it transmits between neurons, occupies a central role, perhaps analogous to the idea of base-pairing in DNA. Indeed we will see that synaptic plasticity is triggered by "spike-pairing", where "spikes" are brief electrical signals. "Hebbery' is my general word for everything to do with plastic synapses, especially aspects (such as neural computation) that has to do with the 2 main functions of synapses, storing and transmitting information.
So let's jump right in and explain what is going on in the above diagram of a synapse. The 2 horizontal black tubes are neural "wires", which carry electrical signals. The synapse has 2 components: an input component, marked "pre" and an output component, marked "post". These labels stand for "presynaptic" and "postsynaptic" respectively. The synapse itself is made from a presynaptic bulge (the "bouton") in the input wire (which is called an axon) and a postsynaptic protuberance, the "spine", which ends in a rounded swelling called the spine head. In addition you can see 2 key parts of the synapse: the blue "vesicles" which contain the chemical "transmitter" and the red "receptors" which receive the chemical signal. In a nutshell, the arrival of an electrical signal, conducted along the axon, at the presynaptic bouton releases the transmitter (blue) which acts on the receptors (red) to generate a postsynaptic electrical signal. However, this barebones sketch hardly even hints at the rich phenomena that synapses enable, just as describing a hydrogen atom as an electron circling a proton misses the richness of physics and chemistry.
The blog will describe progress (much of it ongoing) in understanding the synapse, and relating it to the overall function of the brain (i.e. the generation of the mind and overt behavior). My target audience is roughly an upper level undergraduate studying neuroscience, but I will try to make most of the ideas accessible to any ambitious layperson, and sometimes I will try to explain highly technical issues that I barely understand myself. To help a reader choose apropriate posts that are at these different levels, I will use a star system: each post starts with 1, 2 or 3 stars, indicating the overall level. This introductory post gets 1 star.
I'll end up with another image of a synapse, this time a detailed picture obtained with the electron microscope. This will act as an initial test of the extent to which I'm allowed to post images which others have created.
I don't know what type of synapse this is, but it shows the basic features I described, although in this case the bouton, unusually is at the end of the axon. You can see the neurochemical-containing vesicles in the bouton, and the central thickening (where the receptors are located) at the top of the spine head though there are other, less important, structures as well.
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In the section below this dotted line I will provide the footnotes beloved by academics such as myself (I'm a professor of Neurobiology at Stony Brook University).
