Switching between executive and default mode networks in posttraumatic stress disorder [excerpts and notes]

From: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2895156/?tool=pubmed

Daniels et al, 2010

We decided to use global scaling because we were not analyzing anticorrelations in this paradigm and because data presented by Fox and colleagues66 and Weissenbacher and coworkers65 indicate that global scaling enhances the detection of system-specific correlations and doubles connection specificity. Weissenbacher and colleagues65 compared different preprocessing approaches in human and simulated data sets and recommend applying global scaling to maximize the specificity of positive resting-state correlations. We used high-pass filtering with a cut-off at 128 seconds to minimize the impact of serial autocorrelations in the fMRI time series that can result from scanner drift.

Very useful methodological clipping!

The control condition was a simple fixation task, requiring attention either to the response instruction or to a line of 5 asterisks in the centre of the screen. We chose this control task to resemble the activation task as closely as possible; it therefore differed considerably from previous resting state analyses because it was relatively short in duration and thus necessitated fast switches between the control condition and the activation task. It also prompted the participants to keep their eyes open and fixated on the stimulus, which has been shown to result in stronger default mode network activations than the closed-eyes condition.60

Good to remember: closed-eyed resting states result in weaker default mode activity.

To ensure frequent switching between an idling state and task-induced activation, we used a block design, presenting the activation task (8 volumes) twice interspersed with the fixation task (4 volumes) within each of 16 imaging runs. Each task was preceded by an instruction block (4 volumes duration), amounting to a total acquisition of 512 volumes per participant. The order of the working memory tasks was counterbalanced between runs and across participants. Full details of this working memory paradigm are provided in the study by Moores and colleagues.6 There were 2 variations of this task in each run concerning the elicited button press response; however, because we were interested in the effects of cognitive effort on default network connectivity, rather than specific effects associated with a particular variation of the task, we combined the response variations to model a single “task” condition for this study. The control condition consisted of periods of viewing either 5 asterisks in the centre of the screen or a notice of which variation of the task would be performed next.

Psychophysiological interaction analyses are designed to measure context-sensitive changes in effective connectivity between one or more brain regions67 by comparing connectivity in one context (in the current study, a working memory updating task) with connectivity during another context (in this case, a fixation condition). We used seed regions in the mPFC and PCC because both these nodes of the default mode network act independently across different cognitive tasks, might subserve different subsystems within the default mode network and have both been associated with alterations in PTSD.8

This paradigm is very interesting. The authors have basically administered a battery of working memory tasks with interspersed rest periods, and carried out ROI inter-correlation, or seed analysis. Using this simple approach, a wide variety of experimenters could investigate task-rest interactions using their existing data sets.

Limitations

The limitations of our results predominantly relate to the PTSD sample studied. To investigate the long-lasting symptoms that accompany a significant reduction of the general level of functioning, we studied alterations in severe, chronic PTSD, which did not allow us to exclude patients taking medications. In addition, the small sample size might have limited the power of our analyses. To avoid multiple testing in a small sample, we only used 2 seed regions for our analyses. Future studies should add a resting state scan without any visual input to allow for comparison of default mode network connectivity during the short control condition and a longer resting state.

The different patterns of connectivity imply significant group differences with task-induced switches (i.e., engaging and disengaging the default mode network and the central-executive network).
2010
08/18
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My response to Carr and Pinker on Media Plasticity

Our ongoing discussion regarding the moral panic surrounding Nicolas Carr’s book The Shallows continues over at Carr’s blog today, with his recent response to Pinker’s slamming the book. I maintain that there are good and bad (frightening!!) things in both accounts. Namely, Pinker’s stolid refusal to acknowledge the research I’ve based my entire PhD on, and Carr’s endless fanning of the one-sided moral panic.

Excerpt from Carr’s Blog:

Steven Pinker and the Internet

And then there’s this: “It’s not as if habits of deep reflection, thorough research and rigorous reasoning ever came naturally to people.” Exactly. And that’s another cause for concern. Our most valuable mental habits – the habits of deep and focused thought – must be learned, and the way we learn them is by practicing them, regularly and attentively. And that’s what our continuously connected, constantly distracted lives are stealing from us: the encouragement and the opportunity to practice reflection, introspection, and other contemplative modes of thought. Even formal research is increasingly taking the form of “power browsing,” according to a 2008 University College London study, rather than attentive and thorough study. Patricia Greenfield, a professor of developmental psychology at UCLA, warned in a Science article last year that our growing use of screen-based media appears to be weakening our “higher-order cognitive processes,” including “abstract vocabulary, mindfulness, reflection, inductive problem solving, critical thinking, and imagination.”

As someone who has enjoyed and learned a lot from Steven Pinker’s books about language and cognition, I was disappointed to see the Harvard psychologist write, in Friday’s New York Times, a cursory op-ed column about people’s very real concerns over the Internet’s influence on their minds and their intellectual lives. Pinker seems to dismiss out of hand the evidence indicating that our intensifying use of the Net and related digital media may be reducing the depth and rigor of our thoughts. He goes so far as to assert that such media “are the only things that will keep us smart.” And yet the evidence he offers to support his sweeping claim consists largely of opinions and anecdotes, along with one very good Woody Allen joke.

Right here I would like to point out the kind of leap Carr is making. I’d really like a closer look at the supposed evidence demonstrating  “our intensifying use of the Net and related digital media may be reducing the depth and rigor of our thoughts.” This is a huge claim! How does one define the ‘depth’ and ‘rigor’ of our thoughts? I know of exactly one peer-reviewed high impact paper demonstrating a loss of specifically executive function in heavy-media multi-taskers. While there is evidence that generally speaking, multi-tasking can interfere with some forms of goal-directed activity, I am aware of no papers directly linking specific forms of internet behavior to a drop in executive function. Furthermore, the HMM paper included in it’s measure of multi-tasking ‘watching tv’, ‘viewing funny videos’, and ‘playing videogames’. I don’t know about you, but for me there is definitely a difference between ‘work’ multitasking, in which I focus and work through multiple streams, and ‘play’ multitasking, in which I might casually surf the net while watching TV. The second claim is worse- what exactly is ‘depth’? And how do we link it to executive functioning?

Is Carr claiming people with executive function deficits are incapable or impaired in thinking creatively? If it takes me 10 years to publish a magnum opus, have I thought less deeply than the author that cranks out a feature length popular novel every 2 years? Depth involves a normative judgment of what separates ‘good’ thinking from ‘bad’ thinking, and to imply there is some kind of peer-reviewed consensus here is patently false. In fact, here is a recent review paper on fmri creativity research (is this depth?) indicating that the existing research is so incredibly disparate and poorly defined as to be untenable. That’s the problem with Carr’s claims- he oversimplifies both the diversity of internet usage and the existing research on executive and creative function. To be fair to Carr, he does go on to do a fair job of dismantling Pinker’s frighteningly dogmatic rejection of generalizable brain plasticity research:

One thing that didn’t surprise me was Pinker’s attempt to downplay the importance of neuroplasticity. While he acknowledges that our brains adapt to shifts in the environment, including (one infers) our use of media and other tools, he implies that we need not concern ourselves with the effects of those adaptations. Because all sorts of things influence the brain, he oddly argues, we don’t have to care about how any one thing influences the brain. Pinker, it’s important to point out, has an axe to grind here. The growing body of research on the adult brain’s remarkable ability to adapt, even at the cellular level, to changing circumstances and new experiences poses a challenge to Pinker’s faith in evolutionary psychology and behavioral genetics. The more adaptable the brain is, the less we’re merely playing out ancient patterns of behavior imposed on us by our genetic heritage.

Here is my response, posted on Nick’s blog:

Hi Nick,

As you know from our discussion at my blog, I’m not really a fan of the extreme views given by either you or Pinker. However, I applaud the thorough rebuttal you’ve given here to Stephen’s poorly researched response. As someone doing my PhD in neuroplasticity and cognitive technology, it absolutely infuriated me to see Stephen completely handwave away a decade of solid research showing generalizable cognitive gains from various forms of media-practice. To simply ignore findings from, for example the Bavalier lab, that demonstrate reliable and highly generalizable cognitive and visual gains and plasticity is to border on the unethically dogmatic.

Pinker isn’t well known for being flexible within cognitive science however; he’s probably the only person even more dogmatic about nativist modularism than Fodor. Unfortunately, Stephen enjoys a large public following and his work has really been embraced by the anti-religion ‘brights’ movement. While on some levels I appreciate this movement’s desire to promote rationality, I cringe at how great scholars like Dennett and Pinker seem totally unwilling to engage with the expanding body of research that casts a great deal of doubt on the 1980′s era cogsci they built their careers on.

So I give you kudos there. I close as usual, by saying that you’re presenting a ‘sexy’ and somewhat sensationalistic account that while sure to sell books and generate controversy, is probably based more in moral panic than sound theory. I have no doubt that the evidence you’ve marshaled demonstrates the cognitive potency of new media. Further, I’m sure you are aware of the heavy-media multitasking paper demonstrating a drop in executive functioning in HMMs.

However, you neglect in the posts I’ve seen to emphasize what those authors clearly did: that these findings are not likely to represent a true loss of function but rather are indicators of a shift in cognitive style. Your unwillingness to declare the normative element in your thesis regarding ‘deep thought’ is almost as chilling as Pinker’s total refusal to acknowledge the growing body of plasticity research. Simply put, I think you are aware that you’ve conflated executive processing with ‘deep thinking’, and are not really making the case that we know to be true.

Media is a tool like any other. It’s outcome measures are completely dependent on how we use it and our individual differences. You could make this case quite well with your evidence, but you seem to embrace the moral panic surrounding your work. It’s obvious that certain patterns, including the ones probably driving your collected research, will play on our plasticity to create cognitive differences. Plasticity is limited however, and you really don’t play on the most common theme in mental training literature: balance and trade-off. Your failure to acknowledge the economical and often conservative nature of the brain forces me to lump your work in with the decade that preceded your book, in which it was proclaimed that violent video games and heavy metal music would rot our collective minds. These things didn’t happen, except in those who where already at high risk, and furthermore they produced unanticipated cognitive gains. I think if you want to be on the ‘not wrong’ side of history, you may want to introduce a little flexibility to your argument. I guess if it makes you feel better, for many in the next generation of cognition researchers, it’s already too late for a dogmatic thinker like Pinker.

Final thoughts?

//a note on the distribution of ideas on this blog

I’m somewhat at pains to point this out, but today is the second time I’ve read commentary from a popular author on this debate and felt my stomach crinkle. First Jonah Lehrer posted a blog entitled ‘Tradeoffs?‘ a few days after I (as far as I can tell) broached the angle of ‘cognitive trade-offs’, and now Nicholas points out that Stephen has a nativist axe to grind, a point also first brought up here on my blog. I could be wrong- but I know Nick saw my post and I’ve yet to see these points mentioned elsewhere. Obviously it’s common knowledge that Pinker’s a nativist- yet it seems a bit strange that I’ve yet to get any recognition outside of comments on my blog. Neither has given me any kind of public credit on their respective blogs and as much as I appreciate their research and contributions to the discussion, would it hurt to throw me a link or mention? Unlike these guys, I’m not actually making any money of this blog or publishing pop-sci books; I’m trying to do the kind of formal, professional research that is actually capable of answering these questions. While I’m not one of the big players running a lab (like the ones cited in Nicholas’ recent post), I don’t think it would do much harm to give a little credit to a hard working PhD student that may have contributed to their ideas. Of course, maybe I’m just dumbing them down, so in fact I owe THEM something! ;)

2010
06/30
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The Neural Basis of Multitasking (via dlPFC)

The Neural Basis of Multitasking In a headline-grabbing recent study, the NHTSA revealed that talking on a cell phone–even with a hands free headset–is effectively the same as driving with a .08 blood alcohol reading, or legal intoxication.  Texting is even worse, but a poll released yesterday showed that a majority (52%) of the world's drivers often have their thumbs occupied behind the wheel.  These are only particularly dangerous examples of a common and rather curious fact … Read More

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2010
06/11
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The Neural Case for Health Care Reform (via dlPFC)

The Neural Case for Health Care Reform The moral case for health reform was not the focus of President Obama's address to Congress Wednesday night. It did, however, form the core of the most eloquent and compelling section of the speech, which followed the invocation of the late Senator Ted Kennedy: That large-heartedness – that concern and regard for the plight of others – is not a partisan feeling.  It is not a Republican or a Democratic feeling.  It, too, is part of the American ch … Read More

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2010
06/11
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Snorkeling ’the shallows’: what’s the cognitive trade-off in internet behavior?

I am quite eager to comment on the recent explosion of e-commentary regarding Nicolas Carr’s new book. Bloggers have already done an excellent job summarizing the response to Carr’s argument. Further, Clay Shirky and Jonah Lehrer have both argued convincingly that there’s not much new about this sort of reasoning. I’ve also argued along these lines, using the example of language itself as a radical departure from pre-linguistic living. Did our predecessors worry about their brains as they learned to represent the world with odd noises and symbols?

Surely they did not. And yet we can also be sure that the brain underwent a massive revolution following the acquisition of language. Chomsky’s linguistics would of course obscure this fact, preferring us to believe that our linguistic abilities are the amalgation of things we already possessed: vision, problem solving, auditory and acoustic control. I’m not going to spend too much time arguing against the modularist view of cognition however; chances are if you are here reading this, you are already pretty convinced that the brain changes in response to cultural adaptations.

It is worth sketching out a stock Chomskyian response however. Strict nativists, like Chomsky, hold that our language abilities are the product of an innate grammar module. Although typically agnostic about the exact source of this module (it could have been a genetic mutation for example), nativists argue that plasticity of the brain has no potential other than slightly enhancing or decreasing our existing abilities. You get a language module, a cognition module, and so on, and you don’t have much choice as to how you use that schema or what it does. The development of anguage on this view wasn’t something radically new that changed the brain of its users but rather a novel adaptation of things we already and still have.

To drive home the point, it’s not suprising that notable nativist Stephen Pinker is quoted as simply not buying the ‘changing our brains’ hypothesis:

“As someone who believes both in human nature and in timeless standards of logic and evidence, I’m skeptical of the common claim that the Internet is changing the way we think. Electronic media aren’t going to revamp the brain’s mechanisms of information processing, nor will they supersede modus ponens or Bayes’ theorem. Claims that the Internet is changing human thought are propelled by a number of forces: the pressure on pundits to announce that this or that “changes everything”; a superficial conception of what “thinking” is that conflates content with process; the neophobic mindset that “if young people do something that I don’t do, the culture is declining.” But I don’t think the claims stand up to scrutiny.”

Pinker makes some good points- I agree that a lot of hype is driven by the kinds of thinking he mentions. Yet, I do not at all agree that electronic media cannot and will not revamp our mechanisms for information processing. In contrast to the nativist account, I think we’ve better reason than ever to suspect that the relation between brain and cognition is not 1:1 but rather dynamic, evolving with us as we develop new tools that stimulate our brains in unique and interesting ways.

The development of language massively altered the functioning of our brain. Given the ability to represent the world externally, we no longer needed to rely on perceptual mechanisms in the same way. Our ability to discriminate amongst various types of plant, or sounds, is clearly sub-par to that of our non-linguistic brethren. And so we come full circle. The things we do change our brains. And it is the case that our brains are incredibly economical. We know for example that only hours after limb amputation, our somatosensory neurons invade the dormant cells, reassigning them rather than letting them die off. The brain is quite massively plastic- Nicolas Carr certainly gets that much right.

Perhaps the best way to approach this question is with an excerpt from social media. I recently asked of my fellow tweeps,

To which an astute follower replied:

Now, I do realize that this is really the central question in the ‘shallows’ debate. Moving from the basic fact that our brains are quite plastic, we all readily accept that we’re becoming the subject of some very intense stimulation. Most social media, or general internet users, shift rapidly from task to task, tweet to tweet. In my own work flow, I may open dozens and dozens of tabs, searching for that one paper or quote that can propel me to a new insight. Sometimes I get confused and forget what I was doing. Yet none of this interferes at all with my ‘deep thinking’. Eventually I go home and read a fantastic sci-fi book like Snowcrash. My imagination of the book is just as good as ever; and I can’t wait to get online and start discussing it. So where is the trade-off?

So there must be a trade-off, right? Tape a kitten’s eyes shut and its visual cortex is re-assigned to other sensory modalities. The brain is a nasty economist, and if we’re stimulating one new thing we must be losing something old. Yet what did we lose with language? Perhaps we lost some vestigial abilities to sense and smell. Yet we gained the power of the sonnet, the persuasion of rhetoric, the imagination of narrative, the ability to travel to the moon and murder the earth.

In the end, I’m just not sure it’s the right kind of stimulation. We’re not going to lose our ability to read in fact, I think I can make an extremely tight argument against the specific hypothesis that the internet robs us of our ability to deep-think. Deep thinking is itself a controversial topic. What exactly do we mean by it? Am I deep thinking if I spend all day shifting between 9 million tasks? Nicolas Carr says no, but how can he be sure those 9 million tasks are not converging around a central creative point?

I believe, contrary to Carr, that internet and social media surfing is a unique form of self stimulation and expression. By interacting together in the millions through networks like twitter and facebook, we’re building a cognitive apparatus that, like language, does not function entirely within the brain. By increasing access to information and the customizability of that access, we’re ensuring that millions of users have access to all kinds of thought-provoking information. In his book, Carr says things like ‘on the internet, there’s no time for deep thought. it’s go go go’. But that is only one particular usage pattern, and it ignores ample research suggesting that posts online may in fact be more reflective and honest than in-person utterances (I promise, I am going to do a lit review post soon!)

Today’s internet user doesn’t have to conform to whatever Carr thinks is the right kind of deep-thought. Rather, we can ‘skim the shallows’ of twitter and facebook for impressions, interactions, and opinions. When I read a researcher, I no longer have to spend years attending conferences to get a personal feel for them. I can instead look at their wikipedia, read the discussion page, see what’s being said on twitter. In short, skimming the shallows makes me better able to choose the topics I want to investigate deeply, and lets me learn about them in whatever temporal pattern I like. Youtube with a side of wikipedia and blog posts? Yes please. It’s a multi-modal whole brain experience that isn’t likely to conform to ‘on/off’ dichotomies. Sure, something may be sacrificed, but it may not be. It might be that digital technology has enough of the old (language, vision, motivation) plus enough of the new that it just might constitute or bring about radically new forms of cognition. These will undoubtably change or cognitive style, perhaps obsoleting Pinker’s Bayesian mechanisms in favor of new digitally referential ones.

So I don’t have an answer for you yet ToddStark. I do know however, that we’re going to have to take a long hard look at the research review by Carr. Further, it seems quite clear that there can be no one-sided view of digital media. It’s not anymore intrinsically good or bad than language. Language can be used to destroy nations just as it can tell a little girl a thoughtful bed time story. If we’re to quick to make up our minds about what internet-cognition is doing to our plastic little brains, we might miss the forest for the trees. The digital media revolution gives us the chance to learn just what happens in the brain when its’ got a shiny new tool. We don’t know the exact nature of the stimulation, and finding out is going to require a look at all the evidence, for and against. Further, it’s a gross oversimplification to talk about internet behavior as ‘shallow’ or ‘deep’. Research on usage and usability tells us this; there are many ways to use the internet, and some of them probably get us thinking much deeper than others.

2010
06/08
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A defense of vegetarian fMRI (1/2)

Recently there’s been much ado about a newly published fMRI study of empathetic responding in vegetarians, vegans, and omnivores. The study isn’t perfect, which the authors admit, but I find it interesting and relatively informative for an fMRI paper. The Neurocritic doesn’t, rather he raises some seemingly serious issues with the study. I promised on twitter I’d defend my claim that the study is good (and that neurocritic could do better). But first, a motivated ramble to distract and confuse you.

As many of you might realize, neuroscience could be said to be going through something like puberty. While the public remains infatuated with every poorly worded research report, researchers within the neurosciences have to view brain mapping through an increasingly skeptical lens. This is a good thing: science progresses through the introduction and use of new technologies and the eventual skeptical refinement of their products.

And certainly there is plenty of examples shoddy neuroscience out there, whether it’s reports of voodoo correlations or inconsistencies between standard fMRI analyses packages. Properly executed, attention to these issues and a healthy skepticism of the methods will ultimately result in a refined science. Yet we must also be careful to apply the balm of skepticism in a refined manner: neuroscientists are people to, and we work in an increasingly competitive field where there are few well-defined standards and even less clarity.

Take an example from my lab that happened just today.  We’re currently analyzing some results from a social cognition experiment my colleague Kristian Tylen and I conducted last year. Like many fMRI results, our hypotheses (which were admitable a bit vague when we made them) were not exactly supported by our findings. Rather we ended up with a scattered series of blobs that appeared to mostly center on early visual areas. This is obviously boring and unpublishable, and after some time we decided to do a small volume correction on some areas we’d discussed in a published paper. This finally revealed some interesting findings somewhere around the TPJ, which brings me to the point of this story.

My research has thus far mostly focused on motor and prefrontal regions. We in neuroimaging can often fall victim to what I call ‘blob blind sight’ where we focus so greatly on a single area or handful of areas that we forget there’s’ a wide world of cortex out there. Imagine my surprise when I tried to get clear about whether our finding was situated in exactly the pSTS, TPJ, or nearby inferior parietal lobule (IPL) only to discover that these three areas are nearly indistinguishable from one another anatomically.

All of these regions are involved in different aspects of social cognition, and across the literature there are no clear anatomical differentiation between them. In many cases, researchers will just lump them together as pSTS/TPJ, regardless of the fact that a great deal of research has gone on explicitly differentiating them. Now what does one do with a blob that lands somewhere in the middle, overlapping all three? More specifically, imagine the case where your activation foci lands smack dab in the middle, or a few voxels to the left. Is it TPJ? Or IPL? Or is it really the conjunction of all three, and if so, how does one make sense of that given the wide array of functions and connectivity patterns for these areas. IPL is a part of the default mode, whereas TPJ and pSTS are not. It’s really quite a mess, and the answer you choose will likely depend upon the interpretation you give, given the vast variety of functions allocated to these three regions.

The point of all this, which begins to lead to my critique of TNC critique, is that it is not a simple matter of putting ones foot down and claiming that the lack of an expected activation or the presence of an unexpected one is damning or indicative of bad science. It’s an inherent problem in a field where hundreds of papers are published monthly with massive tables of activation foci. To say that a study has gone awry because they don’t report your favorite area misses the point. What’s more important is to evaluate the methods and explain the totality of the findings reported.

So that’s one huge issue confronting most researchers. Although there are some open source ‘foci databases’ out there, they are underused and hard to rely on. One can of course try to pinpoint the exact area, but in reality the chance that you’ll have such a focused blob is pretty unlikely. Rather, researchers have to rely on extra-scanner measures and common sense to make any kind of interesting theoretical inferences from fMRI. This post was meant to be a response to The Neurocritic, who took issue with my taking issue of his taking issue with a certain vegetarian fmri study… but I’m already an hour late coming home from work and I’m afraid I’ve failed to deliver. I did take the time this afternoon to go thoroughly through both the paper and TNC’s response however, and I think I’ve got a pretty compelling argument. Next time: why the neurocritic is plain wrong ;)

2010
06/02
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Site update

As of today, neuroconscience.com is now redirecting to my wordpress.com blog. I did this to increase security- it appears my old blog may have been hacked- as well as usability. As I am still ironing out the kinks of the move, you may see little bits of construction dust here and there. This is also probably only a temporary solution- ideally I plan to move back to neuroconscience.com once I can get everything working correctly.

As for future posts, I’ve been on a serious hiatus due to work related issues. I’m currently trying to translate the ideas you see here to some summer experiments, a process that has proven extremely difficult. Hopefully things will really start to pick up in the next few weeks. In the meantime, updates will be sporadic at best.

2010
05/14
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Slides for my Zombies or Cyborgs Talk



2010
03/11
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My MA Thesis: The Body in Action: Intention, Action-Consciousness, & Compulsion

Presenting, my masters thesis. Hope someone out there enjoys it.

2010
02/12
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Synaptic Adaptation to Environmental Alteration

From Quartz & Sejnowski: Neural Basis of Cognitive Development (1997)

Quartz and Sejnowski. The neural basis of cognitive development: a constructivist manifesto. Behav Brain Sci (1997) vol. 20 (4) pp. 537-56; discussion 556-96

Above you see an excellent summary table found in a seminal work by Quartz and Sejnowski. I’m reading this paper now, and aside from the die-hard representationalist instincts of the authors, it is an excellent overview of the development of neuroplasticity research and the relation of various forms of plasticity to learning and cognition. I find the above table fascinating simply because it demonstrates in one tidy arena the scope and temporal shape of brain development. You see for example, infamous studies in which the eyes of rats are sutured shut at birth alongside equally high-impact studies in which alterations in environmental complexity alter synaptic densities.

Overall, this is a list of studies in which the alteration of sensory motor input alters synaptic density and complexity in a dynamical fashion. I find it particularity interesting that the overall direction appears to be on in which increased complexity equals increased density. One stand out result is Valverde (1971) where an 20 day period of darkness is synaptically overcome when the mice are returned to a normal environment. Overall this table is a historically stunning account of the resilience of neural systems.

One big question though- why has it taken so long for plasticity to make its way into neurological acceptance?? Clearly the data was there… guess we needed fancy magnets to believe in it!

2010
02/10
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