Activity in dendrites critical in memory formation

Nov 7, 2014

Credit: © Mopic / Fotolia

By Science Daily

Why do we remember some things and not others? In a unique imaging study, two Northwestern University researchers have discovered how neurons in the brain might allow some experiences to be remembered while others are forgotten. It turns out, if you want to remember something about your environment, you better involve your dendrites.

Using a high-resolution, one-of-a-kind microscope, Daniel A. Dombeck and Mark E. J. Sheffield peered into the brain of a living animal and saw exactly what was happening in individual neurons called place cells as the animal navigated a virtual reality maze.

The scientists found that, contrary to current thought, the activity of a neuron’s cell body and its dendrites can be different. They observed that when cell bodies were activated but the dendrites were not activated during an animal’s experience, a lasting memory of that experience was not formed by the neurons. This suggests that the cell body seems to represent ongoing experience, while dendrites, the treelike branches of a neuron, help to store that experience as a memory.

“There are a lot of theories on memory but very little data as to how individual neurons actually store information in a behaving animal,” said Dombeck, assistant professor of neurobiology in the Weinberg College of Arts and Sciences and the study’s senior author. “Now we have uncovered signals in dendrites that we think are very important for learning and memory. Our findings could explain why some experiences are remembered and others are forgotten.”


 

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9 comments on “Activity in dendrites critical in memory formation

  • Here is neuronal structure research just starting to tease out the nature of conscious experience. Some have talked of being able to model or build brain like structures and run them. This work cannot properly begin until a deep understanding of all possible neuron cell functions is complete. Brain cells are very far from the logic gates we once might have imagined.



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  • It’s interesting how much we know and don’t know about neurons and their computer analog neural nets. When it comes to processing things like sense data: vision, audio information, communication between muscles and brain, etc. the progress has been phenomenal. So much so that they can now hook up artificial limbs directly to the CNS.

    And the same for neural nets. Back in the early days of AI people tried using non neural net systems to do things like process and analyze raw data. One of the first attempts (and dismal failures) at speech recognition used a traditional expert systems symbolic reasoning approach. Those results made people think that speaker independent speech recognition wasn’t going to be feasible for a long time. Then a few decades later and you can download apps that do a pretty decent job of it and those all use a neural net type of approach.

    But when it comes to things like “and gates”, symbolic logic, set theory, universal quantification,… neural nets (and how the brain does it with neurons) are still essentially a big unknown.

    I recommend the book The Myth of Mirror Neurons for a good discussion of these issues.



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  • I was talking with an optometrist. He said the visual field is an illusion. You actually can only see small region where the fovea is pointed. The rest is pretty much a blur. Yet somehow your brain looks at the input from the dancing eyeball to create the illusion of a continuous field.

    I will speculate you a have a 3D model of the outside world in your head, and you just tweak it with new optical input. Any time you need visual information, you have a complete model to “look” at, complete with fractal generators to concoct detail. You don’t have to remember the detail, just a generator for the detail.

    Perhaps the key to sports is avoiding looking at the model, and paying more direct attention to the incoming stream.



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  • Thanks for this, Red. Have just ordered it. I think it will be in the most part preaching to the converted. I have always (no! in the last couple of years) maintained that mirror neurons are simply motor skill related, but also that their significance is the more profound in training the young. That they are early conduits for a mass of Hebbian formalisations, that mostly come to an early pre-pubertal behavioural conclusion.

    The fact that they are still functional in later human life and can still influence behaviour and behaviour perception, may result in a disappointing assessment of their significance. The variability of behaviour perception abilities in teens and adults is nowhere near as devastating as it ought to be. It may be that such “intuiting” from say facial muscles as the highly perceptive might be is not that beneficial or accurate compared with other emotion reading or modelling skills acquired.

    I am in fact coming to a hypothesis that suggests that such “intuiting” that mirror neurons may engender (and whether they do or not is still unevidenced so far) may be in part like synaesthesia, a cognitional relic of early brain wiring processes. These may not be strictly functional (nor accurate!) per se, but may point to a devloped system of behaviours seeded in part by their early presence, the empathies and metaphorical thinking.



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  • Oh and logic gates…

    My favourite bit of non strict “digital behaviour” in neurons is ephaptic coupling. This is simply the cross-talk between (particularly) non myelinated fibres. This crosstalk is co-opted in neural processes as a means to synchronise (or at least phase relate) dissparate events. It may just underly our (neuronal) mechanism for defining the “window of simultaneity” to correlate events displaced slightly through external physics or internal processing or transmission delays. Ephaptic coupling is used by chickens (and possibly the rest of us) for stereophonic location.

    This is decidedly analogue stuff at the neuron level….



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  • It may be that such “intuiting” from say facial muscles as the more perceptive might have is not that beneficial or accurate compared with other emotion reading or modelling skills acquired.



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  • What I liked about the book was that it wasn’t just a refutation of the hype about Mirror Neurons but he went into some of the more philosophical issues. To be honest, I guess I also like it because it fit in with all my prejudices about what neurons can and can’t teach us about the brain. Many people (I would include Harris in this group; also Patricia Churchland) are still pushing what Pinker would call “mind blind” theories of cognition. Theories that try to explain everything in terms of neurons and chemicals and don’t think there is any need or legitimacy to higher order concepts such as intentions, rules, ontologies. It was nice to see someone who really understands the low level stuff talk about the need for higher order concepts.

    Also, one of the appendices is really good, it’s an overview of the physical areas of the brain and what we know so far about what happens where and how they communicate. It’s not long but it’s one of those things you can read several times and really packs a lot of info into a nice overview description.



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  • Vision is much better understood than general cognition. You don’t really need to speculate, we KNOW that people DO have 3D models built right into the vision system. Edge detectors for example are essential to define boundaries in 3D space and they are built right into the vision system and well before the brain, I think in the optic nerve but definitely somewhere before the brain.



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  • My view is I think that the transition from bottom up physics and chemistry to a potentialy-reachable-from-the-top “behaviour of systems” is the area of greatest interest. Whilst it won’t have any of the system detail predictions it will say something profound about the qualities processes will have in the system- just how memories are formed stored and accessed, their reliability or generative aspects; just how inferences are made and favoured; the fascinating implications on system behaviours with physics limited behavioural servo control in the ACC; the limits to the evolution of behaviour generation given the substrate of co-optable physics and chemistry and selectable processes. The operation of a wired adult brain is dullish for me compared with the mechanisms that guide the enormous levels of neural cell death in the infant brain. It is these processes that achieve inference generation and memory formation and use, etc., for the first time, that I see as the path to greatest insight.

    I am firmly of the view that brains exist to animate animals. They are movement first devices, and mirror neurons represented some sort of breakthrough in mamals enhancing the evolutionary rapidity of increasingly functional movements.



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