On mud and blog titles

I was away this past weekend doing Tough Mudder in Scotland. It was fun, but I could barely move afterwards. We ran on Saturday and I’m still aching on Tuesday. Then again, I am very unfit. I would recommend it if you fancy a nice long run but find the thought of a marathon tedious, or if you are a masochist.

I’ll have something to post on our wonderful EURO 2012 league soon, complete with analysis of the non-linear complex scoring function, but I still need to make some graphs. In the mean-time, here’s a little something about autapses:  Massive Autaptic Self-Innervation of GABAergic Neurons in Cat Visual Cortex. It’s an oldish paper quantifying the number of connections that different types of neurons make back onto themselves (background: most current brain theories consider the brain to generate and process information in networks of neurons, which communicate by sending electrical and chemical signals to each other – more here. In most of the brain, neurons can be divided into two categories, excitatory and inhibitory, depending on whether they send signals that make other neurons more or less likely to send on signals of their own). The authors found that, in cat visual cortex at least, inhibitory (GABAergic) neurons made substantially more self-connections than excitatory neurons, meaning that when they “spike” and send inhibitory signals to other neurons, they also inhibit their own spiking, thus stopping themselves from sending out more signals. This provides another mechanism for inhibitory neurons to control their output, in addition to the inhibition provided to them by the many connections from other inhibitory neurons in the network, that is separate from the inhibition provided by these other neurons.

I’m unaware of how much work has been done on the functional significance of autapses, but they are a rather interesting concept and usually ignored in the kind of neuronal network research that I am involved in. More digging required.

  • Interesting stuff! Neural coding seems to be amazingly complex, do you know of any nervous sytem/brain-containing organisms that don’t employ neural coding as a signalling mechanism? Or does every nervous system have some sort of intrinsic coding?

  • Hi Piv! Well there are neurons that don’t spike and instead release neurotransmitters in a graded continuous way, like rod and cone cells in the eye, though this transmitter release is then interpreted by other retinal neurons which transmit the information to the brain as spikes. Also electrical signals are transmitted between neurons through gap junctions in cell membranes, which complicates matters, but we tend to assume the network is coding things in terms of spikes. Certainly spikes are necessary as soon as you try to transmit rapid signals beyond a certain distance; other forms of transmission aren’t fast or reliable enough. My knowledge is very much mammal and cortex-centric though, so I’ll have a look around for other mechanisms.

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