Neuroscientists discover new 'mini-neural computer' in the brain

October 27, 2013, University of North Carolina Health Care
This is a dendrite, the branch-like structure of a single neuron in the brain. The bright object from the top is a pipette attached to a dendrite in the brain of a mouse. The pipette allows researchers to measure electrical activity, such as a dendritic spike, the bright spot in the middle of the image. Credit: Spencer Smith

Dendrites, the branch-like projections of neurons, were once thought to be passive wiring in the brain. But now researchers at the University of North Carolina at Chapel Hill have shown that these dendrites do more than relay information from one neuron to the next. They actively process information, multiplying the brain's computing power.

"Suddenly, it's as if the processing power of the brain is much greater than we had originally thought," said Spencer Smith, PhD, an assistant professor in the UNC School of Medicine.

His team's findings, published October 27 in the journal Nature, could change the way scientists think about long-standing scientific models of how neural circuitry functions in the brain, while also helping researchers better understand neurological disorders.

"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," Smith said. "That's what this finding is like. The implications are exciting to think about."

Axons are where conventionally generate electrical spikes, but many of the same molecules that support axonal spikes are also present in the dendrites. Previous research using dissected brain tissue had demonstrated that dendrites can use those molecules to generate electrical spikes themselves, but it was unclear whether normal brain activity involved those dendritic spikes. For example, could dendritic spikes be involved in how we see?

The answer, Smith's team found, is yes. Dendrites effectively act as mini-neural computers, actively processing neuronal input signals themselves.

Directly demonstrating this required a series of intricate experiments that took years and spanned two continents, beginning in senior author Michael Hausser's lab at University College London, and being completed after Smith and Ikuko Smith, PhD, DVM, set up their own lab at the University of North Carolina. They used patch-clamp electrophysiology to attach a microscopic glass pipette electrode, filled with a physiological solution, to a neuronal in the brain of a mouse. The idea was to directly "listen" in on the electrical signaling process.

"Attaching the pipette to a dendrite is tremendously technically challenging," Smith said. "You can't approach the dendrite from any direction. And you can't see the dendrite. So you have to do this blind. It's like fishing if all you can see is the electrical trace of a fish." And you can't use bait. "You just go for it and see if you can hit a dendrite," he said. "Most of the time you can't."

But Smith built his own two-photon microscope system to make things easier.

A network of pyramidal cells in the cerebral cortex. These neurons have been simulated using a computer program which captures the beautiful dendritic architecture of real pyramidal cells. These dendrites have now been shown to carry out sophisticated computations on their inputs. Credit: UCL

Once the pipette was attached to a dendrite, Smith's team took electrical recordings from individual dendrites within the brains of anesthetized and awake mice. As the mice viewed visual stimuli on a computer screen, the researchers saw an unusual pattern of electrical signals – bursts of spikes – in the dendrite.

Smith's team then found that the dendritic spikes occurred selectively, depending on the visual stimulus, indicating that the dendrites processed information about what the animal was seeing.

To provide visual evidence of their finding, Smith's team filled neurons with calcium dye, which provided an optical readout of spiking. This revealed that dendrites fired spikes while other parts of the neuron did not, meaning that the spikes were the result of local processing within the dendrites.

Study co-author Tiago Branco, PhD, created a biophysical, mathematical model of neurons and found that known mechanisms could support the dendritic spiking recorded electrically, further validating the interpretation of the data.

"All the data pointed to the same conclusion," Smith said. "The dendrites are not passive integrators of sensory-driven input; they seem to be a computational unit as well."

His team plans to explore what this newly discovered dendritic role may play in circuitry and particularly in conditions like Timothy syndrome, in which the integration of dendritic signals may go awry.

Explore further: Control of brain waves from the brain surface

More information: Dendritic spikes enhance stimulus selectivity in cortical neurons in vivo, DOI: 10.1038/nature12600

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1 / 5 (10) Oct 27, 2013
I was under the impression the pyramidal tracts were a housing development outside Cairo.
1 / 5 (14) Oct 27, 2013
"...GnRH neurons elaborate a previously uncharacterized neuronal projection that functions simultaneously as an axon and dendrite. This structure, termed a "dendron," greatly expands the dynamic control of GnRH secretion into the pituitary portal system to regulate fertility." http://www.jneuro...abstract

In mammals, the dynamic control of GnRH secretion involves the nutrient-dependent molecular mechanisms involved in self-assembly of the brain and its self-organization. The self-organization is a function of feedback loops that link nutrient uptake and the metabolism of nutrients to species-specific pheromones. Their epigenetic effects on GnRH mimic the epigenetic effects of glucose (associated with food odors).

What's missing from evolutionary theory is any evidence that mutation-initiated natural selection could result in any aspect of self assembly or self-organization.

Thus, evidence reported here is another refutation of mutation-driven evolution.
2 / 5 (8) Oct 28, 2013
JVK lumbered with
"What's missing from evolutionary theory is any evidence that mutation-initiated natural selection could result in any aspect of self assembly or self-organization."

There is plenty of evidence that structures can 'self-assemble', you need time & a vast number of permutations. As atoms can result from self assembly of protons and neutrons to form stable elements, one can extrapolate the same paradigm easily.

There is obviously an underlying pattern that allows atoms to be stable, well ie.long enough to form compounds but, this pattern of underlying physics is not consistent with the claims made of any deity & especially so that all ever claimed are so impotent & woefully incompetent communicators.

JVK, with flawed logic
"Thus, evidence reported here is another refutation of mutation-driven evolution."

These are primarily observations, the interpretations of which can't necessarily be stated with much certainty as 'evidence' to ally with your odd ambit claim.
1 / 5 (4) Oct 28, 2013
Mike Massen attempts to link physics to biology outside any context whatsoever. No evidence from physics enters the big picture of biology until it is viewed from the perspective of biological replication, which is obviously nutrient-dependent and pheromone-controlled in species from microbes to man.

The inability of physicists and mathematicians to explain how the stability of hydrogen bonds required for biological life to exist is regulated during life's self-assembly without introducing mutation-initiated natural selection, attests to MM's nonsensical view of life where self assembly and self organization automagically occur and somehow lead to the plasticity required during development of individuals.

But how does that plasticity lend itself to mutation-driven evolution?

The "all you need is time & permutations" is nonsense typical of those who have no understanding of biologically-based cause and effect, which is unequivocally nutrient-dependent & pheromone-controlled.
not rated yet Oct 28, 2013
Since the dendrite has a new function, why not assign it a new name to distinguish it further from dendritic cells. Since axons fire as well, why not name it denaxite?
1 / 5 (5) Oct 28, 2013
Thanks Brenda,

It was named a "dendron" in the context of GnRH by Herde et al. It's as if they knew that every interaction with sensory input would come down to its association with epigenetic effects on hyDROgen bonds. DenDROn and hyDROgen... get it?
not rated yet Oct 29, 2013
Why does
"dendrites fired spikes while other parts of the neuron did not"
imply that
"the spikes were the result of local processing within the dendrites"?
1 / 5 (3) Nov 19, 2013
JVK doesnt get it, blurting-
"No evidence from physics enters the big picture of biology until it is viewed from the perspective of biological replication.."

Physics is foundation for chemistry & is the foundation for all biological processes.

You have forgotten/ignored all life processes occur above absolute zero, therefore constant (brownian) motion, therefore physics & the collisions between atoms are the basis of chemistry & we know that is also subject to dynamic equilibria therefore outcomes are not necessarily 100% all or any of the time therefore opportunity for many incomplete/intermediate interactions which lead to potential for mutation.

My comment stands "time & permutation", stable compounds will be favoured by virtue of natural selection & on a continual basis.

Early earth's atmosphere ammonia, water, hydrogen etc
Given it time & heat you get formamide
Give that time & heat you get Guanine - a DNA amino acid...

Physics ! (Oh & imagination/intellect)

1 / 5 (3) Nov 19, 2013
Thanks MM: You regurgitated what I wrote.

I didn't forget physics, I placed it into the context of biological replication. If you have the expertise to link physics to protein biosynthesis, you can tell us more about the thermodynamics of intercellular signalling that enable the de novo creation of olfactory receptor genes or another means of receptor-mediated ingestion of DNA from long dead organisms, which facilitates nutrient-dependent pheromone-controlled adaptive evolution in my model.

Therein lies the problem. People like you want to tell me I'm not considering what they have not detailed in the context of what should be considered: the link from physics to chemistry to the basis principles of biology and levels of biological organization that link the sensory environment to behavior via, for example, GnRH neurons.

Please try to make more sense if you wish to contribute to discussion of biological facts. See for example the question by 'machinephilosophy' and my answer.
1 / 5 (3) Nov 19, 2013
Why does
"dendrites fired spikes while other parts of the neuron did not"
imply that
"the spikes were the result of local processing within the dendrites"?

Thanks for asking: This has to do with "Mosaic Copy Number Variation in Human Neurons" and the likelihood that "...neurons with different genomes will have distinct molecular phenotypes because of altered transcriptional or epigenetic landscapes." http://www.scienc...abstract

The epigenetic 'landscape' is incorporated into the DNA of organized genomes in species from microbes to man. Olfactory/pheromonal input alters transcription and thus the construction of individual neurons during neurogenic niche construction in species with even the most primitive of nervous systems, like nematodes. Organismal complexity then becomes tractable to the complexity of 'dendrons' in the human brain via RNA-binding proteins and alternative splicings. MM will tell us about the physics of that! Won't you MM?

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