Use Viagra to recover from jet lag?

I always perk up when I see reports of new side effects of sildenafil (Viagra), because it is an inhibitor of one form of an enzyme, cyclic GMP phosphodiesterase, that my earlier research showed to be central to changing light into a nerve signal in the rod and cone cells of our retinas (check here if you are curious about this previous life..). One of the interesting side effects of viagra is on color vision. Here is another interesting bit from Agostino et al. in PNAS:

Mammalian circadian rhythms are generated by a master clock located in the suprachiasmatic nuclei and entrained by light-activated signaling pathways. In hamsters, the mechanism responsible for light-induced phase advances involves the activation of guanylyl cyclase, cGMP and its related kinase (PKG). It is not completely known whether interference with this pathway affects entrainment of the clock, including adaptation to changing light schedules. Here we report that cGMP-specific phosphodiesterase 5 is present in the hamster suprachiasmatic nuclei, and administration of the inhibitor sildenafil (3.5 mg/kg, i.p.) enhances circadian responses to light and decreases the amount of time necessary for reentrainment after phase advances of the light–dark cycle. These results suggest that sildenafil may be useful for treatment of circadian adaptation to environmental changes, including transmeridian eastbound flight schedules.

Possible RSS feed errors

If you are seeing old posts in your feed, go directly to the blog. During this next period when I am adding labels (keywords) to old posts, the RSS feed may be presenting the old posts as new posts. I'll try to get around this by usually reposting the last five or so most recent posts when I have finished a session of labeling. Also, the previous posts shown in the adjacent right column are in the right sequence.

Synesthesia - evidence for increased cortical connectivity

Synesthesia, in which letters or numbers elicit color perception, could be due to increased brain connectivity between relevant regions, or due to failure to inhibit feedback in cortical circuits. Diffusion tensor imaging now provides evidence for increased connectivity in word processing and binding regions of the brain. Hubbard comments (PDF here) on the article by Rouw and Scholte (PDE here):

If looking at this page of text causes you to see a cascade of colors, you have grapheme-color synesthesia, in which viewing letters and numbers in black and white elicits the experience of seeing colors... grapheme-color synesthesia occurs in as many as 2 out of every 100 people...

To study this:

...the authors used diffusion tensor imaging (DTI), a neuroimaging technique that measures the diffusion of water molecules in the living human brain. Water molecules diffuse more easily parallel than perpendicular to the direction of white-matter fibers, because of the myelin sheaths and axonal membranes. By measuring relative differences in how easily water diffuses along different axes (termed fractional anisotropy), it is possible to infer the size, orientation and degree of myelination of white matter tracts in vivo... this technique demonstrated increased structural connectivity in synesthetes compared with controls in three brain regions: the right fusiform gyrus, which is near regions involved in word and color processing, and the left intraparietal sulcus (IPS) and frontal cortex, both of which are part of a network of regions involved in binding and consciousness

Figure - The outer cortical surface with relevant brain regions indicated.
The color-selective hV4 is indicated in red, and the visual word form area is indicated in green. Cross-activation between these regions, mediated by increased anatomical connectivity, correlates with the generation of the additional experiences of grapheme-color synesthesia, and the degree of connectivity determines their strength. The posterior IPS, thought to be involved in binding, is in blue. Additional anatomical connectivity in this region may be critical for synesthetic binding, which must operate on the colors generated by the cross-activation between grapheme regions and hV4. These regions have been projected to the left hemisphere for simplicity.

EVOLUSHARK

Here is Evolushark (spelling evolution) - to intimidate the conservation Christian mascot Ichthys.

Memory depends on how well you can forget...

Benedict Carey reviews (PDF here) new work on memory (PDF here) by a Stanford group that is the first to record visual images of people’s brains as they suppress distracting memories:

Blocking out a distracting memory is something like ignoring an old (and perhaps distracting) acquaintance... it that much harder to reconnect the next time around...recent studies suggest that the brain plays favorites with memories in exactly this way, snubbing some to better capture others. A lightning memory... is not so much a matter of capacity as it is of ruthless pruning

The experiments:

...had 20 young men and women, mostly Stanford students, view in quick succession a list of 240 word pairs. These included 40 capitalized words, each paired with six related, lower-case words: For example, “ATTIC-dust,” “ATTIC-junk,” and so on....After studying the pairs, the participants were instructed to memorize three selected pairs from each of 20 capitalized words. In effect, this forced them to flag individual pairs, like ATTIC-dust, while trying to tune out very similar, distracting ones, like ATTIC-junk, for half of the total list of pairs they saw...They were told not to memorize any pairs from the other half of the list.....while participants were having their brains scanned by an M.R.I. machine, each person’s memory was tested several times, and scores ranged from about 30 percent accuracy to 80 percent. ...how well each person suppressed the distracting word pairs was also measured by comparing recall of those pairs with recall of the half of the list that was studied at first but later ignored.

from Kulh et al.'s abstract:

Functional magnetic resonance imaging during selective retrieval showed that repeated retrieval of target memories was accompanied by dynamic reductions in the engagement of functionally coupled cognitive control mechanisms that detect (anterior cingulate cortex) and resolve (dorsolateral and ventrolateral prefrontal cortex) mnemonic competition. Strikingly, regression analyses revealed that this prefrontal disengagement tracked the extent to which competing memories were forgotten; greater forgetting of competing memories was associated with a greater decline in demands on prefrontal cortex during target remembering. These findings indicate that, although forgetting can be frustrating, memory might be adaptive because forgetting confers neural processing benefits.

Figure Legend: A whole-brain regression analysis showed that memory suppression at test was predicted by repetition-related activation decreases in (a) left dorsal ACC (anterior cingulate) (b) right anterior VLPFC (ventrolateral prefrontal cortex) In the ACC and right VLPFC, high suppressors showed reliable decreases in activation from first to third retrieval practice trials, whereas low suppressors did not. High suppressors showed greater initial ACC activation than low suppressors, but comparable initial right VLPFC activation. (c) A whole-brain regression analysis showed that the repetition-related activation decline in the right DLPFC covaried with that in the ACC, showing a functional coupling between ACC and right DLPFC that specifically relates to changes in demands on cognitive control across retrieval repetitions.

Learning after movement error, a memory trace.

Huang and Shadmehr report an interesting study in J. Neurophysiol. "Evolution of Motor Memory During the Seconds After Observation of Motor Error." Here is their abstract:

When a movement results in error, the nervous system amends the motor commands that generate the subsequent movement. Here we show that this adaptation depends not just on error, but also on passage of time between the two movements. We observed that subjects learned a reaching task faster, i.e., with fewer trials, when the intertrial time intervals (ITIs) were lengthened. We hypothesized two computational mechanisms that could have accounted for this. First, learning could have been driven by a Bayesian process where the learner assumed that errors are the result of perturbations that have multiple timescales. In theory, longer ITIs can produce faster learning because passage of time might increase uncertainty, which in turn increases sensitivity to error. Second, error in a trial may result in a trace that decays with time. If the learner continued to sample from the trace during the ITI, then adaptation would increase with increased ITIs. The two models made separate predictions: The Bayesian model predicted that when movements are separated by random ITIs, the learner would learn most from a trial that followed a long time interval. In contrast, the trace model predicted that the learner would learn most from a trial that preceded a long time interval. We performed two experiments to test for these predictions and in both experiments found evidence for the trace model. We suggest that motor error produces an error memory trace that decays with a time constant of about 4 s, continuously promoting adaptation until the next movement.

How the body shapes intelligence

Kitano reviews a new book in Nature (PDE of review here): How the Body Shapes the Way We Think: A New View of Intelligence. by Rolf Pfeifer & Josh Bongard, Bradford Books: 2006. A few clips:

...a chess computer, unlike a human, does not have a body to enable it to interact with its environment, for example. This distinction differentiates two views on intelligence. One view is that intelligence is independent of the body and is unaffected by its existence, shape and function. The other view is that intelligence is contained within a physical body and that the body shapes the mind, an idea often referred to as physical embodiment or the presence of a behaviour-based agent.

The Pfeifer and Bongard book offers perspective on how artificial-intelligence and robotics researchers are dealing with the increasing recognition in the artificial-intelligence and robotics communities that the nature of the body significantly affects the mind, although it does not totally control it. The book focuses on artificial agents, but with a lot of inspiration from nature.

One salient difference between the intelligent agents discussed in this book and traditional artificial-intelligence systems, as represented by chess computers, is the contextual thickness of system behaviours. Many of the robotics systems discussed in the book can cope, at least to some extent, with changes in the expected environment, tasks and other assumed conditions, whereas chess computers and other traditional artificial-intelligence systems are usually extremely fragile when faced with even a small change in such conditions. Behaviour-based robots should be able to perform almost flawlessly if the size of road or unevenness of terrain deviates from the initial assumption. However, the results will be catastrophic if a chess computer is given a chess board with nine rows and columns, rather than eight, as they are tuned specifically for the existing rules of chess. Imagine a thought experiment on a chess game between a behaviour-based system and an existing chess computer. The chess computer would be unbeatable with the defined rules, but if the rules were modified the behaviour-based system may do better.

Dumb Blondes and Athletes, smart brains...

Robert Frank has a nice piece in the New York Times (PDF here) describing some recent sociology/economics articles. Why are there so many jokes about dumb blondes and athletes despite persuasive evidence that blondes and athletes are no less intelligent than others? First the dumb blonde joke:

A married couple were awakened by a call at 2 a.m. The wife, a blonde, picked up the phone, listened a moment and said, “How should I know, that’s 200 miles from here!” and hung up. Her husband asked, “Who was that?” She replied, “I don’t know; some woman wanting to know if the coast is clear.”

Now the dumb athlete joke:

Two offensive linemen in a rented boat catch an unusually large number of trout in a secluded cove. As they start back to the marina, one reaches over with his felt-tip pen and marks an X on the starboard bow. “I want to make sure we can find this spot again tomorrow,” he explained. “Idiot,” his friend replied, “what makes you think we’ll get the same boat?”

Actually the hypothesis that beauty (blondness is viewed as a positive characteristic in women) and brains to together is more likely:

(1) men generally place relatively greater emphasis on looks; (2) women generally place relatively greater emphasis on income and status. (3) more-intelligent men tend to achieve higher income and status; (4) both intelligence and physical attractiveness are traits with significant inheritable components...if both beauty and intelligence are inheritable, then the offspring of such unions will tend to display above-average values of both traits.

So why the dumb blonde and athlete jokes?

If blondes are perceived as more attractive, then being blond may create valuable opportunities that do not require onerous investments in education and training. The dumb blonde stereotype may thus stem from the fact that blondes rationally choose to invest less than others in education and other forms of human capital.

and,

...because gifted athletes enjoy many attractive social and employment opportunities that others do not, they may rationally choose to invest less, on average, in human capital.

The bottom line is that popular perceptions about the intelligence of blondes and athletes may stem more from the academic choices made by members of these groups and from choices that others make about them than from any innate differences in mental ability.

Cosmic Ignorance

Although I don't usually mention physics and cosmology in this blog, I would recommend a rather fascinating piece by Dennis Overbye in the science section of the New York Times (PDF here) "The Universe, Expanding Beyond All Understanding." We know space is sprinkled from now to forever with galaxies rushing away from one another under the impetus of the Big Bang. Overbye discusses several pieces of work showing that:

If things keep going the way they are... in 100 billion years the only galaxies left visible in the sky will be the half-dozen or so bound together gravitationally into what is known as the Local Group, which is not expanding and in fact will probably merge into one starry ball...Unable to see any galaxies flying away, those astronomers will not know the universe is expanding and will think instead that they are back in the static island universe of Einstein...observers in our ‘island universe’ will be fundamentally incapable of determining the true nature of the universe...future cosmologists...will puzzle about why the visible universe seems to consist of six galaxies.

Quote from cosmologist James Peebles at Princeton:

"I have the uneasy feeling that the U.S.A. is headed into asymptotic futility well before that."

Infants distinguish languages by just looking at a talking face

In another example of how children have time windows of developmental plasticity and learning, Weikum et al. (PDF here) show that 4 to 6 month-old infants can discriminate languages (English from French) just from viewing silently presented articulations. By the age of 8 months, only bilingual (French-English) infants succeed at this task. This indicates that infants are prepared very early for visual language discrimination, but loose this ability once they begin to learn a single language. Through experience adults can regain this sensitivity, for they can use visual cues to discriminate between two languages if they know one of the languages.

Threatening the rubber hand illusion..cortical anxiety

Ehrsson et al. report an interesting extension of work on illusory feelings of body ownership:

The feeling of body ownership is a fundamental aspect of self-consciousness. The underlying neural mechanisms can be studied by using the illusion where a person is made to feel that a rubber hand is his or her own hand by brushing the person's hidden real hand and synchronously brushing the artificial hand that is in full view. Here we show that threat to the rubber hand can induce a similar level of activity in the brain areas associated with anxiety and interoceptive awareness (insula and anterior cingulate cortex) as when the person's real hand is threatened. We further show that the stronger the feeling of ownership of the artificial hand, the stronger the threat-evoked neuronal responses in the areas reflecting anxiety. Furthermore, across subjects, activity in multisensory areas reflecting ownership predicted the activity in the interoceptive system when the hand was under threat. Finally, we show that there is activity in medial wall motor areas, reflecting an urge to withdraw the artificial hand when it is under threat. These findings suggest that artificial limbs can evoke the same feelings as real limbs and provide objective neurophysiological evidence that the rubber hand is fully incorporated into the body. These findings are of fundamental importance because they suggest that the feeling of body ownership is associated with changes in the interoceptive systems.

Figure legend - Linear relationship between ownership and the anxiety responses in the bilateral anterior insula and bilateral ACC (circled). A regression analysis identified a significant relationship between the vividness ratings of the rubber-hand illusion obtained during the scans and the parameter estimates for the contrast between threat during ownership and threat during no ownership in left insula

Dog Brain

Brain activity that predicts choice of rewards...

McClure et al. offer an interesting study in J. Neurosci. (PDF here). Here is their abstract and one figure from the paper.

Previous research, involving monetary rewards, found that limbic reward-related areas show greater activity when an intertemporal choice includes an immediate reward than when the options include only delayed rewards. In contrast, the lateral prefrontal and parietal cortex (areas commonly associated with deliberative cognitive processes, including future planning) respond to intertemporal choices in general but do not exhibit sensitivity to immediacy (McClure et al., 2004). The current experiments extend these findings to primary rewards (fruit juice or water) and time delays of minutes instead of weeks. Thirsty subjects choose between small volumes of drinks delivered at precise times during the experiment (e.g., 2 ml now vs 3 ml in 5 min). Consistent with previous findings, limbic activation was greater for choices between an immediate reward and a delayed reward than for choices between two delayed rewards, whereas the lateral prefrontal cortex and posterior parietal cortex responded similarly whether choices were between an immediate and a delayed reward or between two delayed rewards. Moreover, relative activation of the two sets of brain regions predicts actual choice behavior. A second experiment finds that when the delivery of all rewards is offset by 10 min (so that the earliest available juice reward in any choice is 10 min), no differential activity is observed in limbic reward-related areas for choices involving the earliest versus only more delayed rewards. We discuss implications of this finding for differences between primary and secondary rewards.
Beta and delta brain areas. fMRI data were fit with two regressors. A, The beta regressor identified those brain areas that are preferentially activated by choices involving a reward available at a 0 min delay. Brain areas that correlated with this regressor included a set of brain areas all closely linked with the mesolimbic dopamine system. These include the NAc, PCC, mOFC, and ACC.

A bird brain with street smarts

Here is another example of a really smart bird, this time an urban crow. (I gave a another example, One Clever Raven, in a previous post.

Calorie restriction and life span extension

We are getting closer to knowing the specific chemical pathways that underlie age extension, at least in nematodes. Similar pathways are found in yeast and higher animals..from the editor's summary in Nature:

Severe calorie restriction extends life-span in mice and other species, but how near-starvation can prolong life remained a mystery. Now at last, specific links between calorie restriction and longevity have been found in that workhorse of ageing research, the nematode C. elegans. Nicholas Bishop and Leonard Guarente find that dietary restriction activates transcription factor SKN-1 in ASI neurons in the head, which signal peripheral tissues to increase metabolic activity, a mechanism suggestive of the involvement of an endocrine system. Panowski et al. report that increased activity of PHA-4, a transcription factor found in the intestine and in a few cells in head and tail, is also essential for diet-restricted longevity. PHA-4 resembles mammalian Foxa transcription factors, which affect development and regulate fasting glucagon and glucose levels. Knowledge of such links raises the prospect of drugs to mimic the benefits of calorie restriction.

From the review by Antebi:

In response to dietary restriction, the activities of SKN-1 and PHA-4 gene-transcription factors increase (black arrows). Neuronal, but not intestinal, SKN-1 mediates longevity in response to reduced dietary intake, where it triggers the release of unidentified hormones (stars) from the pair of ASI neurons to increase mitochondrial activity throughout the body. The PHA-4 transcription factor may also induce hormonal production in the tissues where it is expressed — neurons, intestine and gonad.

Evolution of human and animal personalities

Here is another editor's summary, and a PDF of the review by Bell of the work by Wolf et al. is here.

Although 'personalities' such as boldness, aggressive behaviour and risk avoidance have been shown to exist in more than sixty animal species, from primates to ants, explaining their existence in terms of evolution has been a puzzle. Surely, evolution should not favour the maintenance of different personalities, but rather the convergence towards a single one. In a numerical life-history model, Wolf et al. show that the evolution of animal personalities, defined as consistent sets of behaviours shown in a variety of contexts, is related to an adaptive response to life-history trade-offs. In this model, decisions on trade-offs between current and future reproduction condition the response of individuals to risky situations, and this may be the basis for animal personalities and their maintenance in populations.

In Wolf et al.'s model (from their abstract)

...some individuals put more emphasis on future fitness returns than others. Life-history theory predicts that such differences in fitness expectations should result in systematic differences in risk-taking behaviour. Individuals with high future expectations (who have much to lose) should be more risk-averse than individuals with low expectations. This applies to all kinds of risky situations, so individuals should consistently differ in their behaviour. By means of an evolutionary model we demonstrate that this basic principle results in the evolution of animal personalities. It simultaneously explains the coexistence of behavioural types, the consistency of behaviour through time and the structure of behavioural correlations across contexts. Moreover, it explains the common finding that explorative behaviour and risk-related traits like boldness and aggressiveness are common characteristics of animal personalities.

Apologies to rss, atom feeds for seeing old posts...other details

I may figure out how to stop this from happening (if anyone out there knows how, please let me know), but as I add labels (keywords) to old posts, RSS and atom readers think they are new postings. This will be happening over the next period of time.

The new google search box works like gangbusters, bringing up all posts with the word(s) you enter. The old Technorati search box was useless. The labels on the right will give you an idea of the areas I find interesting and take you to relevant posts. This may be more non-techies want to know, but this blog now completely replaces my existing file systems. A PDF file or link to any article I might want to use is now obtained through the blog, no more storage of paper copies (three file drawers full, used for my book) or copies on my local hard drive apart from backups of the yahoo server that hosts dericbownds.net. My dericbownds.net website stays as it was, with professional and personal stuff, but MindBlog (mindblog.dericbownds.net) has now moved to the blogger servers.

PLEASE NOTE! MindBlog/RSS web URL change

Because I am upgrading my blogger setup to use labels (keywords) I'm having to assign a new URL to MindBlog.

The new URL is http://mindblog.dericbownds.net

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Children have symbolic arithmetic before formal instruction

The editor's summary of an interesting paper in Nature by Gilmore et al.:

It is commonly assumed that young children need to master the logic of number systems before learning symbolic arithmetic. Now a trial using 5-year-old children suggests that in fact they have symbolic arithmetic knowledge before they have received any arithmetic instruction. The children are capable of solving symbolic addition and subtraction problems with large numbers, provided that only approximate sums and differences must be computed. These findings shed light on the numerical competences that come naturally to children, and suggest ways to enrich children's learning of mathematics.

Some Edward Grieg..

Edward Grieg's "Wedding in Troldhaugen" ....(having just returned from my son's wedding in Mexico.)