Cortical Computing

A study shows that dendrites not only transmit information between neurons, but also process some of that information.

By | October 28, 2013

Pipette attached to a dendriteEUREKALERT, SPENCER SMITHDendrites—the branches that cover a neuron’s cell body—were once believed to function primarily as signal conductors, relaying information between nerve cells. Recent evidence has suggested that dendrites can also respond to stimuli, but it was unknown whether action potentials generated by dendrites were integrated into the signals that the neuron sent to receiving cells. Researchers have demonstrated that dendrites had electrical responses, or dendritic spikes, to visual stimuli in vivo and that these spikes enhanced the output of the neuron. Their work was published this week (October 27) in Nature.

“Imagine you’re reverse engineering a piece of alien technology, and what you thought was simple wiring turns out to be transistors that compute information,” study coauthor Spencer Smith of the University of North Carolina at Chapel Hill said in a statement. “That’s what this finding is like. The implications are exciting to think about.”

The research team exposed mice to visual stimuli and made electrophysiological recordings from single dendrites of pyramidal cells in the rodents’ visual cortices. The researchers then compared the dendritic recordings to recordings from the cell body. They also made recordings at dendrites while simultaneously measuring fluctuations of calcium ions in the cell body. Because the activity in the soma and at the dendrites differed, the researchers concluded that the spikes they observed in the dendrites originated there.

The team also treated cells with a drug that blocked NMDA receptors—candidates for the integration of dendritic spikes with neuronal output—and showed that visual processing was disrupted, suggesting that dendritic activity is necessary for neurons to compute information.

“This work shows that dendrites, long thought to simply ‘funnel’ incoming signals towards the soma, instead play a key role in sorting and interpreting the enormous barrage of inputs received by the neuron,” said study coauthor Michael Häusser of University College London in a press release. “Dendrites thus act as miniature computing devices for detecting and amplifying specific types of input.”

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Avatar of: James V. Kohl

James V. Kohl

Posts: 476

October 28, 2013

GnRH Neurons Elaborate a Long-Range Projection with Shared Axonal and Dendritic Functions

Excerpt: "We report here a highly unexpected scenario in which GnRH neurons elaborate long distance projections with blended dendritic and axonal properties to control GnRH secretion into the median eminence."

My comment: "Dendrons" appear capable of sorting and interpreting the epigenetic effects of olfactory/pheromonal input that control the nutrient-dependent physiology of  GnRH-directed reproduction in organisms with or without eyes, and whether or not an individual organism is congenitally blind. This suggests to me that the dendrites acting as miniature computing devices in the context of visual input are acting as secondary sources of information that is largely irrelevant without its classically conditioned association with olfactory/pheromonal input.

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