Dynamical Neuroscience: Wiki Article Entry - Input Needed

[rhody]

I thought this was interesting and worth sharing. TED: Antonio Damasio: The quest to understand consciousness. Here is a nice view of real axional connections in the brain and the directionality of their pathways. His talk is geared toward "what" the brain does as he best understands it. The how the brain does it is what the three of you have been discussing here. I thought it is useful to put into context.

http://img833.imageshack.us/img833/2078/connectionsinthebrain.jpg

http://img859.imageshack.us/img859/4840/axionalconnections.jpg

Backing up a bit to my post and the responses:

Thanks for your explanation of dopamine and acetycholine, atty, now I understand, and for the links.

Dopamine and acetylcholine are "non-classical" neurotransmitters and are called neuromodulators, because they act on different time scales from the fast "classical" neurotransmitters.

aperion, you said.

It is only surprising if you presume the brain must be constructed bottom-up out of definite hardware components. And given neurons are built out molecular components like microtubles with a half-life of about 10 minutes, this seems a silly presumption indeed.

You mention a time component of a half life of about ten minutes for microtubules, and I was referring to a distance of about one half of an inch of change observed in the experiment of the nerves on a monkey's deafferentiated arm. What does the half life of a microtubule have to do with the distances, up to one half of an inch in the measurement of activity in an up to that time unused brain region ?

See excerpt of https://www.physicsforums.com/showpost.php?p=2925375&postcount=25 below:

They performed the procedure in four hours, which normally took a whole day to complete. They removed part of the monkey's skull, and inserted 124 electrodes in different spots of the sensory cortex map for the arm, then stroked the deafferentiated arm. As expected, the arm sent no impulses to the electrodes. Then, Pons stroked the monkey's face, knowing that the brain map for the face is right next to the one for the arm. The neurons in the monkey's deafferentiated arm map began to fire, confirming that the facial map had taken over the arm map. As Merzenich had seen in his experiments, when a brain map is unused, the brain can organize itself so another mental function can take over the processing space. Most surprising was the scope of the organization, over a half of an inch ! Holy crap... that to this humble observer is freaking amazing. The monkey was then euthanized. Over the next six months, this experiment was repeated with three more monkeys, with the same results. Taub had proved that reorganization in damaged brains could occur in very large sectors giving hope to those suffering from severe brain injury.

Rhody...

 

[apeiron]

You mention a time component of a half life of about ten minutes for microtubules, and I was referring to a distance of about one half of an inch of change observed in the experiment of the nerves on a monkey's deafferentiated arm. What does the half life of a microtubule have to do with the distances, up to one half of an inch in the measurement of activity in an up to that time unused brain region ?

You are framing this as a "problem of plasticity", whereas I am pointing out the contrary issue - the difficulty in creating organisational stabiliity. If all the parts are fluid, how do you ever get anything to stand still?

So the puzzle from a biological point of view is stasis rather than flux. How come the cortical maps don't just change all the time and it takes fairly radical surgery, growth and relearning to make a significant change in them?

In fact from memory, the likely story in the case of this particular experiment is that the wider neural connections (from finger to facial maps) already existed. They just would have been very weak. So nothing new would have to grow over that half-inch in fact. There would just have to be upregulation of dendrites and synapses, which happens in hours.

 

[rhody]

So the puzzle from a biological point of view is stasis rather than flux. How come the cortical maps don't just change all the time and it takes fairly radical surgery, growth and relearning to make a significant change in them?

Fast forward the link to the TED talk for 12:00 and listen to what Antonio Damasio has to say about this, at 14:00 minutes discusses how the structures, he calls them modules in the diagram "create brain maps that are exquisitely topographic, and exquisitely interconnected in a recursive pattern." He also goes onto what brain areas give rise to "the self" (14:20 - 14:50). Give it a look and see what you think. I understand that you, atty and pythagorean are trying to cover all the bases. A noble but difficult endeavor. It takes persistence, going down false paths, even failure at times to discover the truth about what happens inside of our noggins.

Rhody...

 

[atyy]

As apeiron points out the brain plastic is both good and bad. The plastic brain is what allows sound localization in some animals to remain accurate even though their heads change as they age. It allows us to learn new things and recover from brain injury. However, severe tinnitus due to brain plasticity is "maladaptive". So the brain should have some means of regulating its plasticity according to age, as it does by the critical period; and according to behavioural necessity, which involve rhody's neuromodulators. Zhou et al summarize this in their introduction of this paper (free!).

When one sees change in the brain, the synapse that changed is not necessarily near by. To provide a naive example, if one neuron connects to ten, and each of those connect to another ten, then a change in one synapse at the first layer would change the 100 neurons in the last layer, without additional synapses changing. Apeiron mentions that the inputs were probably already there but weak, so that not much neurite lengthening would be needed, just more anatomically local changes. The experimental papers I linked to in post #92 (abstracts only, unfortunately) try to look at weak inputs using intracellular recording. Work that shows that some of the changes are non-local enough to be visible by light microscopy includes Antonini et al and Xu et al.

I remember an interview of Alfred Brendel about trying to learning new fingerings for a piece of music, and how in a moment of stress one reverts to the old fingerings. Most have probably had similar experiences. Zheng and Knudsen did an interesting study that shows the old maps are still there in some sense. Vogels et al's new modelling study, which I hope has enough continuous time evolution for Pythagorean to consider dynamical:) "can accommodate synaptic memories with activity patterns that become indiscernible from the background state but can be reactivated by external stimuli." The background state is a state that is experimentally probabilistically described, and theoretically thought to represent chaos, stable chaos, or transient chaos (Pythagorean, did I get your attention ).

He also goes onto what brain areas give rise to "the self" (14:20 - 14:50).

rhody, thanks for that terrific link. Damasio's talk is wonderfully argued as usual! I'd be interested to know what you think of Holland and Goodman's proposal. What is common to Damasio's and Holland and Goodman's proposals is that there is a part of the brain that makes a model of itself and its interaction with the environment. Probably the difference is that Holland and Goodman's internal models are inspired by work on motor control, and I had myself similarly guessed that the cerebellum is the seat of consciousness. In contrast, Damasio proposes brainstem areas, focussing in particular on the midbrain periaquaductal gray. Most curiously, Wikipedia's article on the PAG explicitly addresses its role in consciousness, and links to comments by Patricia Churchland (about 20 minutes in).

 

[apeiron]

Fast forward the link to the TED talk for 12:00 and listen to what Antonio Damasio has to say about this, at 14:00 minutes discusses how the structures, he calls them modules in the diagram "create brain maps that are exquisitely topographic, and exquisitely interconnected in a recursive pattern." He also goes onto what brain areas give rise to "the self" (14:20 - 14:50). Give it a look and see what you think. I understand that you, atty and pythagorean are trying to cover all the bases. A noble but difficult endeavor. It takes persistence, going down false paths, even failure at times to discover the truth about what happens inside of our noggins.

Rhody...

I don't really get the point you are trying to make. The brainstem has very little developmental plasticity, the cortex a tremendous amount.

And there are no surprises in Damasio's talk - except where he says the optic nerve apparently exits throught the foveal pit.

 

[rhody]

And there are no surprises in Damasio's talk - except where he says the optic nerve apparently exits throught the foveal pit.

You are a stickler for the smallest slip or detail, aperion, I imagine Damasio would not like to work for you.

Rhody...

 

[Pythagorean]

chaos, stable chaos, or transient chaos[/B] (Pythagorean, did I get your attention ).

The interesting thing I read in the abstract of that paper, just in general (ignoring for a moment the brain and "focusing" on the whole universe) is that irregularity can arise from a system that is not either chaotic or stochastic. (you had me at "free!").

 

[rhody]

I'd be interested to know what you think of Holland and Goodman's proposal.

Thanks atty, concerning the topic of "self", I scanned sections of Holland's and Goodman's proposal. I think this section pretty much sums it up, my interpretation, from page 14. In 1999, Damasio proposed a neurologically based theory of consciousness, summarized by Churchland in 2002 in a paper examining self-representation in nervous systems:

...that the self/nonself distinction, originally designed to support coherencing, it ultimately responsible for consciousness. Simply put, a brain whose wiring enables it to distinguish between inner-world and outer-world representations and to build a metarepresentational model of the relation between out and and inner entities is a brain enjoying some degree of consciousness.

Essentially that the self-representation's relations to representation of things in the world lead's to consciousness.

I like efficient, pithy language to describe human consciousness, and the concept of "self". Whether or not this theory lives up to testable/repeatable experiment(s) is another matter. I for one would like to see a "test for consciousness" and "test for self" created. It may not be possible, because it challenges my notion of what is possible, and that cannot be a bad thing.

P.S. I am listening to Patricia Churchland's talk now...

Rhody...

 

[rhody]

atty,

Thanks for The Science Network link, circa 2009. Churchland's talk was interesting as was the follow on speaker's. A whole new sandbox of characters to consider, I loved the hosts comment's at one point during question and answer, "Another addition to our mound of bafflement's". Pretty much sums up my thoughts. I did learn one thing, the thought process into what attributes that collectively contribute to what we recognize as "consciousness" is farther outside of the box by these researcher's than I ever imagined.

Example, a certain species of fly sleeps, and has been shown to twitch it's lower legs during sleep. The implication here is that REM sleep is necessary for consciousness and that this species of fly shares that with human's. Suggesting that REM sleep and insect leg twitching are somehow related. I would say that is outside the box, wouldn't you ?

Rhody...

 

[atyy]

rhody, my own view is that consciousness is essentially solved - I'll buy the Damasio, and Holland and Goodman approach. Maybe high tc superconductivity is more mysterious.

I would like to know how I am a strange loop fits in though. It seems closely related, but I am not sure whether inifinity is needed - perhaps as some sort of limit, analogous to phase transitions in which the thermodynamic limit exists in theory, but not exactly in real life - or the reflections in a pair of mirrors where true infinity is spoilt by atomic structure.

 

[Pythagorean]

A Good Grounding paper:

The Complex Systems Approach: Rhetoric or Revolution
Chris Eliasmith
Department of Philosophy, University of Waterloo
Received 4 February 2011; accepted 14 February 2011

http://onlinelibrary.wiley.com/doi/10.1111/j.1756-8765.2011.01169.x/pdf

rhody, my own view is that consciousness is essentially solved - I'll buy the Damasio, and Holland and Goodman approach.

Would you mind posting some references and your own summary of the solution? Due next Friday. : )

 

[rhody]

Would you mind posting some references and your own summary of the solution? Due next Friday. : )

Cute Pythagorean, I like it.

Rhody...

 

[PPagan]

Hello All,
I am a newbie here--happened to be passing through and got interested. Apologies in advance if this is not the right venue for this question, but I was struck by the claim that the problem of consciousness is solved. Do you distinguish between the question of how self-representation is achieved by the brain, and the question of how actual conscious experience ("qualia", if you like) arises out of brain function?
Thanks

 

[atyy]

Good lord, do people have no sense of humour?

 

[Pythagorean]

Good lord, do people have no sense of humour?

You mean that watery fluid in the eye between the lens and the cornea?

 

[Pythagorean]

I don't really have a sense for it, but I memorized the humorism table

 

[PPagan]

OK extremely embarrassed...

 

[Pythagorean]

"Is There Chaos in the Brain?", parts I and II:

http://www.ncbi.nlm.nih.gov/pubmed/11558325

http://www.ncbi.nlm.nih.gov/pubmed/14694754

 

[Pythagorean]

Currently, the top featured paper this month for Nature Neuroscience is:

Bump attractor dynamics in prefrontal cortex explains behavioral precision in spatial working memory
http://www.nature.com/neuro/journal/v17/n3/full/nn.3645.html

 

[AgentSmith]

Consciousness

atty,

Example, a certain species of fly sleeps, and has been shown to twitch it's lower legs during sleep. The implication here is that REM sleep is necessary for consciousness and that this species of fly shares that with human's. Suggesting that REM sleep and insect leg twitching are somehow related. I would say that is outside the box, wouldn't you ?

Rhody...

The implication makes at least two, perhaps three assumptions. Further, the use of the word consciousness in this discussion as if there was only one kind and of one degree is unwarranted.