Brain Science Podcast discussion

The latest episode of the Brain Science Podcast is a discussion of Who's in Charge?: Free Will and the Science of the Brain by Michael S. Gazzaniga.

BSP 82 show notes
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Well presented summary. Tough stuff, and a lot to absorb without reading the book (yet). I especially like the idea that responsibility is a socially derived capacity; and the discussion of emergence is excellent.

But one thing that comes to mind is that I have heard that the pre-frontal cortex doesn't develop until age 21 -22. I understand that Gazzaniga doesn't like the idea of "executive function" but if the pre-frontal cortex is where a great deal of brain system integration goes on and where key responsibility factors, such as empathy, insight, attunment, emotional balance, and, according to some, "morality" are processed, how can someone who has no or a limited prefrontal cortex be considered as responsible as someone who has this area fully developed? We don't expect someone who has not yet developed the brain capacity for language to speak; how can we expect someone doesn't have the brain capacity to make the kind of decisions that are implied in responsibility to behave as responsibly as someone who has the full capacity? This obviously has implications for the legal system as well as many other aspects of social behavior (e.g., if a pre-22 year old can't be responsible for him/her self, who is? This would greatly expand the concept of parenting!).

Robert wrote: "Well presented summary. Tough stuff, and a lot to absorb without reading the book (yet). I especially like the idea that responsibility is a socially derived capacity; and the discussion of emergen..."

I didn't mean to suggest that Gazzaniga doesn't believe that frontal lobe function is essential to responsible behavior. (Actually this book doesn't talk much about the frontal lobes.) The key idea here is that we don't need fMRI scans to tell us if someone is capable of acting responsibly.

Consider the recent evidence that the frontal lobes mature last. Should that mean that we should strip responsible young people of their freedom? Surely behavior speaks for itself! Parents don't need brain scans to tell them when their children are ready for more freedom. But perhaps I should have said "parent shouldn't need" brain scans since in my work in the ER I do see parents that seem remarkably ignorant about what is age appropriate!

Historically young people have taken on adult roles much earlier in life, and while it might be argued that modern life if more complex, I tend to suspect that young people respond to cultural expectations, which means that if they are treated like adults most act more responsibly. The converse is also true!

It is empirically obvious that some children develop "a sense of responsibility" very early (evidently without benefit of the prefrontal cortex), but also that some don't. I would attribute that to socialization factors (family environment, culture, etc.) But if the prefrontal development really doesn't come on-line until the early 20's, who bears the responsibility? The individual or his/her environment?

I think every unconscious decision (aside from autonomic functions of the body) must have been conscious at some point before it becomes a pattern and therefore unconscious. Examples are many: like driving to a routine destination; the movements that become a reflex as a result of training, etc.

Robert wrote: "It is empirically obvious that some children develop "a sense of responsibility" very early (evidently without benefit of the prefrontal cortex), but also that some don't. I would attribute that t..."

I would argue that although the pre-frontal cortex is important; it is not the only part of the brain involved in decision-making. That's one reason why I think it is important not to exaggerate the implications of the late maturation of this region. Also, its not like the pre-frontal lobes are totally off-line, its just that their connections appear to continue to develop into early adulthood.

Who knows? One day we might discover that even older adults can make new connections between regions!

I may be mistaken but I have seen a lot of commentary that attributes the capacity of "moral reasoning" to the pre-frontal cortex, especially the ventromedial pre frontal cortex, and reference frequently made to Phineas Gage's experience of having a spike driven through his and the subsequent changes to his personality.

I also see that, as one writer puts it, "Total maturation of the prefrontal cortex occurs after all brain development is accomplished, with the VmPC being the absolute last part of the brain to finish developing." (Article on www.wiseGeek.com)

Perhaps a more credible source would be Anderson, S. W., A. Bechara, H. Damasio, D. Tranel and A. R. Damasio. 1999. Impairment of social and moral behavior related to early damage in human prefrontal cortex. Nat Neurosci 2:1032-7.

This region also came up at a recent presentation I attended on schizophrenia by Dr. David Habif (http://www.mhcci.com/habiflectureseri...). He described the prefrontal cortex as a integrator of many different brain functions and told us that damage to this area accounts many of the symptoms of schizophrenia.

I have a personal interest in this subject especially as it relates to schizophrenia as I have a daughter with this disease and am writing a book on our current understanding and treatment of it. If you have any good resources on the neurobiology of schizophrenia, I would appreciate references.

Thanks for your work.

BTW, I hope your last comment was tongue in cheek -- otherwise I am wasting a lot of time exercising my brain along the lines proposed in Norman Doidge's wonderful book!

Ginger,
Thanks very much for this episode. A few years ago I read Gazzaniga's big textbook on Neuroscience which was a very colourful and exciting read.
So hearing your summary of what he considers to be hot current research areas is fascinating, although the question of free-will and ethics leaves me a bit cold.
To my mind as an Artificial Intelligence worker, a more fundamental question relates to how our neural nets are trained. Synapses are unidirectional devices, and computer models of neural-net learning always assume the ability to "back-propagate" from conclusions that are verified by real-world knowledge, to the stimuli that provoked them.

If a synapse can't work backwards, we should not be able to learn. I can think of two solutions:

1) There are backward synaptic mechanisms that we are not yet aware of, which seems unlikely.

2) The stimuli, together with matching responses are recorded and sorted into "accepted" and "rejected" bins depending on the verification against real-world knowledge (or operant conditioning) for play-back later (maybe during sleep).

During playback, the recorded stimuli are re-applied in a training mode where synapses adjust their "gain" so as to maximise the matching metric of the responses that were accepted, and minimise those that were rejected.

The cerebellum would seem an ideal candidate for such recording. Its general architecture is uncannily like that of the programmable-sequential-MSI circuits that are used in electronics to build devices that sequence through an arbitrary set of states. A familiar example is the automatic clothes washer that adjusts water and soap input, pumped water output and drum speed and direction at various stages of the wash cycle.

Given the very large number of neurons available, it would be easy to build a general-purpose recorder where stimulus-response pairs were recorded by changes in neuro-transmitter concentration that persisted for less than 24 hours.

That is one reason why I found the arguments against dead-reckoning by desert ants presented in Gallistel and King to be rather unconvincing. All the components for a digital-differential-analyser are present in the cerebellum, and these devices used to be used in planes for navigation by dead-reckoning.

But perhaps I am simply currently obsessed with my cerebellum since I have just taken up cycling again after a 45-year interval, and it has taken nearly 3 months to learn to balance as effectively as I remember doing back then.

Are these sorts of questions coming up in neuroscience, and what useful books might we be missing?

John wrote: "Ginger,
Thanks very much for this episode. A few years ago I read Gazzaniga's big textbook on Neuroscience which was a very colourful and exciting read.
So hearing your summary of w..."

John,

You bring up some very interesting questions and based on your comments I assume you have read Memory and the Computational Brain: Why Cognitive Science will Transform Neuroscience by C. R. Gallistel, and Adam Philip King. I am not sure how something like scrub jay caching can be explained by the mechanism you suggest.

I am sure there are people working on these questions, but as a person outside the field I can barely sample the books being produced, which unfortunately means there is a certain amount of chance involved in which books reach my attention. Naturally I try to keep an eye out for books by scientists like Gazzaniga because not only is he a pioneer in cognitive neuroscience, he is very good at explaining it to the rest of us.

Ginger,
Thanks. I had forgotten about the scrub jays and will think about it.

John

Hi John,

re: "If a synapse cannot work backwards," see Feb. 2011 issue of Nature Neuroscience where a team from Northwestern U publishes a paper with evidence of two-way activity. Fascinating stuff.

Kcuhcttenneb


John wrote: "Ginger,
Thanks very much for this episode. A few years ago I read Gazzaniga's big textbook on Neuroscience which was a very colourful and exciting read.
So hearing your summary of w..."

Kcuhcttenneb,
Thanks.
John Brown

Kcuhcttenneb wrote: "Hi John,

re: "If a synapse cannot work backwards," see Feb. 2011 issue of Nature Neuroscience where a team from Northwestern U publishes a paper with evidence of two-way activity. Fascinating stu..."

I was unable to find that reference in the Feb 2011 edition of Nature Neuroscience. Can you give a more specific reference? Thanks.

I believe Kcuhcttenneb was referring to this article: http://www.ncbi.nlm.nih.gov/pmc/artic... (Nature Neurscience: Slow integration leads to persistent action potential firing in distal axons of coupled interneurons)

Iva wrote: "I believe Kcuhcttenneb was referring to this article: http://www.ncbi.nlm.nih.gov/pmc/artic... (Nature Neurscience: Slow integration leads to persistent action potential firing in dista..."

Hmmm. Very interesting article (and thanks for the source link), but unless I missed it (or just don't understand it) I don't see anything about "two-way activity" or "backward firing." Unless "persistent firing" implies two-way firing? But it doesn't seem that this is involved.

Iva,

You are correct, that's the one.

Thanks for locating it--I've been up against a hard deadline at work and hadn't had a chance to hunt it down.

kcuhcttenneb

Iva wrote: "I believe Kcuhcttenneb was referring to this article: http://www.ncbi.nlm.nih.gov/pmc/artic... (Nature Neurscience: Slow integration leads to persistent action potential firing in dista..."

Hi Robert,

From the introduction,

"... in the mammalian central nervous system, the evidence for spike initiation in axon terminals is mostly limited to pathological conditions such as epilepsy9. Here we present direct evidence that action potentials can be initiated in the distal axon under normal conditions and in response to natural firing patterns."

http://www.ncbi.nlm.nih.gov/pmc/artic...

Also, see http://machineslikeus.com/news/rewrit..., where Spruston is much more plainspoken: "Signals can travel from the end of the axon toward the cell body, when it typically is the other way around. We were amazed to see this."

Thanks,


kcuhcttenneb

Robert wrote: "Iva wrote: "I believe Kcuhcttenneb was referring to this article: http://www.ncbi.nlm.nih.gov/pmc/artic... (Nature Neurscience: Slow integration leads to persistent action potential fir..."

Kcuhcttenneb wrote: "Hi Robert,

From the introduction,

"... in the mammalian central nervous system, the evidence for spike initiation in axon terminals is mostly limited to pathological conditions such as epile..."


OK - got it! Thanks to Iva and you for this reference. This IS news.

Is it possible that this "molecular" action is the source of the missing read/write memory that appears to be necessary to account for dead reckoning (among other things!)? (Just listened to Brain Science Episode 66, interview with Randy Gallistel on his book Memory and the Computational Brain where he argues that the current model of memory just isn't sufficient.)

I'd be hesitant to go that far with it. Although Spruston implies at the end of the second article that this isn't uncommon, I'm not sure how likely his technique of stimulating a neuron over time is to occur in nature. It might be common, I just honestly don't know.

Perhaps someone with a more neurobiological background can comment (my background is in computer science, although I've been following neuroscience for some 20 yrs).

Iva wrote: "I believe Kcuhcttenneb was referring to this article: http://www.ncbi.nlm.nih.gov/pmc/artic... (Nature Neurscience: Slow integration leads to persistent action potential firing in dista..."

Perhaps one of you could start a thread about this paper in our Neuroscience News section.

Kcuhcttenneb wrote: "I'd be hesitant to go that far with it. Although Spruston implies at the end of the second article that this isn't uncommon, I'm not sure how likely his technique of stimulating a neuron over time..."

Unfortunately your link to Spurston doesn't seem to work, but I would like to remind you that there is an area for posting Neuroscience News within this Group.

Regarding jays and food-caching, there is a very nice videod talk on how rats remember sites and integrate them with visual images, at

http://www.ted.com/talks/neil_burgess...

Hi Ginger,
Great episode! I especially like the way you tied together Gazzaniga's work with related previous BSP episodes. Masterful!

John wrote: "Ginger,
Thanks. I had forgotten about the scrub jays and will think about it.

John"

I'm familiar with the NIH paper concerning bidirectional signal transmission in neurons. However, my exception detector went off when I saw it because I'm familiar with a phenomenon called "switch bounce" and realize that the instrumentation used these days are so sensitive, any perturbation in the signal transmission can muddy the interpretaive water. Most of the synaptic junctions are chemical and the triggering of a discharge necessarily involves the transient breakdown in the dielectric at the axon hillock. The surge of emf slams into a high impedance barrier at the presynapic junction, and that would produce a ringing behavior. If you take into consideration the recovery period required for the neuron to reset itself, the back propagation of energy probably does little more than re-establish homeostasis. I would be more inclined to accept Edelman's re-entry or feedback loops establishing resonate states for events attended too and focused on. While on the topic of signaling, I'd like to also comment on the nature of spiking signal transmission. There's been a lot of theory bouncing around that some sort of intelligent messaging is embodied in the spiking nature of signal propagation. Once again, I don't think so. Ultimately, data transmission depends on whether or not the neuron fires. Do one has demonstrated any sort of decoder for complex signaling in the target neurons.

That's my two cents.

New article on reverse signaling in neurons. Link to summary in ScienceDaily: http://www.sciencedaily.com/releases/...

Dalton,
Thanks. Sorry I did not reply. I am not sure that I understand the ion pumps down the axon that supposedly reinforce a decaying electric signal (if I remember correctly). In fact depletion layers in silicon and the use of Schrodinger's wave equation were a bit too mathematical for me at the time. Thanks to Kcuhcttenneb for the reference above. Although it does not say so in that article, it sounds like these ion pumps down the axon could spontaneously produce signals without the cell body sending a signal down to them. The article talks about filter cells that prevent these signals going back up to the cell body. That does sound a bit like ringing, which could initially reflect from the synapse.
Just at the moment my mind is on my slightly raised blood pressure, and I have been using isometric hand-grip exercises, to "retune the baroreflex", in the words of the single paper that attempts to explain why such exercise on the tiny forearm muscles should drop BP much more quickly than say walking or cycling. After 84 days of experiment, it has certainly worked very well. It strikes me that there must be an adaptive control system with a look-up table of safe pre-capillary sphincter settings at a given heart-volume output, that can be expected not to cause carotid BP to crash.
I hypothesize that the hand-grip exercises re-train this table, which is then reflected in resting dilation settings of the sphincters. But it must be a complex mechanism, since chimpanzees seem to use all their muscles for prolonged periods when shinning up and down trees in fights and when hunting monkeys, so the sphincter dilation must be shared out amongst all the muscles, in that sort of multi-muscle activity.
This sort of retraining is a bit closer to the sea-slug neuronal models that have been intensively studied, than say Pinker's models of learning past participles of verbs.
Reflection of pressure pulse waves at the bottom of the descending aorta might by delay reduce the effect of dilating sphincters in the legs on the baroreceptor output in the carotid, since the 80ms. reflection delays their effect until the baroreceptor has partially gone into saturation, well after the steep peak in ventricle pressure. Hence the legs don't retrain the baroreflex as quickly as the arms do.
A similar mechanism to reflection of axonal electrical signal, but this time in hydraulics?
So much still to learn about!