I will survive...

A bit of relief from heavy mind-blogging, from Igudesman and Joo:

The anti-aging pill...

Another approach to finding the elixir of the fountain of youth.... a screening finds a compound 10,000 times more potent than the anti-aging compound resveratrol, obtained from grape skins.

Many researchers are betting that ageing and disease are two sides of the same coin. Here is the abstract of relevant work from Milne et al. in the Nov. 29 Nature, followed by a clip from a Nov. 28 Nature News Feature from Hayden.

Calorie restriction extends lifespan and produces a metabolic profile desirable for treating diseases of ageing such as type 2 diabetes1, 2. SIRT1, an NAD+-dependent deacetylase, is a principal modulator of pathways downstream of calorie restriction that produce beneficial effects on glucose homeostasis and insulin sensitivity. Resveratrol, a polyphenolic SIRT1 activator, mimics the anti-ageing effects of calorie restriction in lower organisms and in mice fed a high-fat diet ameliorates insulin resistance, increases mitochondrial content, and prolongs survival. Here we describe the identification and characterization of small molecule activators of SIRT1 that are structurally unrelated to, and 1,000-fold more potent than, resveratrol. These compounds bind to the SIRT1 enzyme–peptide substrate complex at an allosteric site amino-terminal to the catalytic domain and lower the Michaelis constant for acetylated substrates. In diet-induced obese and genetically obese mice, these compounds improve insulin sensitivity, lower plasma glucose, and increase mitochondrial capacity. In Zucker fa/fa rats, hyperinsulinaemic-euglycaemic clamp studies demonstrate that SIRT1 activators improve whole-body glucose homeostasis and insulin sensitivity in adipose tissue, skeletal muscle and liver. Thus, SIRT1 activation is a promising new therapeutic approach for treating diseases of ageing such as type 2 diabetes.

And, from Hayden's article:

The idea that growing old and growing ill are two sides of the same coin remains controversial. Backers of the concept include David Sinclair of Harvard Medical School who made headlines with findings that a chemical in red wine called resveratrol extends lifespan and might prevent diabetes-like symptoms in mice3 (see also page 712). “I don't see ageing as a disease, but as a collection of quite predictable diseases caused by the deterioration of the body,” Sinclair says.

But others don't see it that way. The University of Michigan's Richard Miller says that Sinclair's characterization is “missing the point in a subtle but important way”. Ageing is a major cause of many diseases, but not the only one, Miller argues. And, he adds, ageing has some effects that aren't considered disease states. “It's important to make a distinction between ageing and disease,” Miller says.

Still, those who differ agree that interfering with the ageing process could help patients who are suffering from age-related disease. Sinclair is already running a clinical trial using resveratrol to prevent diabetes in humans.

Cockroach Art

A review in the Nov. 28 issue of Nature of an exhibition: "The Art of Arthropods". An excerpt:

A Californian entomologist uses insects as living paintbrushes to create abstract art. After loading water-based, non-toxic paints on to the tarsi and abdomens of insects, Steven Kutcher directs his bugs to create their 'masterpieces'.

Kutcher controls the direction and movement of his arthropods — such as hissing cockroaches (pictured), darkling beetles and grasshoppers — by their response to external lighting. The result is controlled and random movements, created in a co-authorship between the artist — with predetermined ideas about colour, form, shape and creative flexibility — and his living brushes.

Kutcher's art is more than just a novelty, because it reveals the hidden world of insect footprints. "When an insect walks on your hand, you may feel the legs move but nothing visible remains, only a sensation," he says. "These works of art render the insect tracks and routes visible, producing a visually pleasing piece."

For more see http://www.BugArtbySteven.com

Emotion as Motion

Richie Davidson and Jeffrey Maxwell do some cute experiments to integrate two different literatures on our approach and withdrawal behaviors. One concerns the localization of approach and avoidance behaviors in the left and right hemispheres, respectively. The lateralization of these processes is very ancient, observed in primitive invertebrates. The other is a description of the general association of flexor (towards the body) movements with approach and extensor (away from the body) movements with avoidance. They do the simple experiment of measuring the reaction time for a subject to point a finger in response to the direction of a flashed image of an arrow pointing away (extension) or towards (flexion).

Legend - Examples of target arrows linked to flexor/extensor movements. On each trial, a single target arrow appeared in either the left or the right target zone (box outline). These target arrows were always flanked by either two diamond distractors or two arrow distractors that fell outside the target zone. Down target arrows pointed both downward and toward the participant. Up target arrows pointed both upward and away from the participant. Down arrows were responded to via finger flexion (i.e., self-directed movements) and up arrows via finger extension (i.e., movements directed away from the self).

The hemispheres were differentially stimulated by presenting the stimuli to either the left (LVF) or right (RVF) visual field. Visual input from the LVF (i.e., the right side of the retinas) projects to visual cortex in the right hemisphere (RH), and visual input from the RVF (i.e., the left side of the retinas) projects to visual cortex in the left hemisphere (LH). Sure enough, facilitation of flexor (compared with approach) responses relative to extensor (compared with avoidant) responses was greater in the LH (i.e., RVF targets) than in the RH (i.e., LVF targets). This pattern of hemispheric specialization was observed to a greater degree the higher participants' self-reported level of daily positive affect and the lower their self-reported level of dispositional anxiety.

Theory of Mind Is Independent of Episodic Memory

This is the title of a brief article by Rosenbaum et al. in the 23 Nov. Science. The authors studied two patients who, as a result of severe traumatic brain injury, lost their ability to consciously recollect personal happenings from their own lives. They applied an array of tests widely used tests known to be sensitive to perspective-taking and Theory of Mind impairment (False belief, animations, sarcasm and empathy, visual perspective-taking/deception). The subjects with brain injury performed as well as controls. These results are at variance with the idea that the ability to simulate or reconstruct one's own past mental states is necessary to imagine the contents of other people's minds. (This doesn't say anything about whether this ability was necessary for the development of Theory of Mind capabilities before the brain injury occurred.)

Evolutionary origins of dance and art...

Natalie Angier does a fascinating piece on evolutionary perspectives on how human dance and art originated. Here are some (slightly edited) clips from her article in the Nov. 27 NY Times science section (whole text here), which emphasize the work of Ellen Dissanayake, an independent scholar affiliated with the University of Washington:

...the creative drive has all the earmarks of being an adaptation on its own. The making of art consumes enormous amounts of time and resources, an extravagance you wouldn’t expect of an evolutionary afterthought. Art also gives us pleasure, she said, and activities that feel good tend to be those that evolution deems too important to leave to chance.

What might that deep-seated purpose of art-making be? Geoffrey Miller and other theorists have proposed that art serves as a sexual display, a means of flaunting one’s talented palette of genes... Ms. Dissanayake has other ideas. To contemporary Westerners, she said, art may seem detached from the real world, an elite stage on which proud peacocks and designated visionaries may well compete for high stakes. But among traditional cultures and throughout most of human history, she said, art has also been a profoundly communal affair, of harvest dances, religious pageants, quilting bees, the passionate town rivalries that gave us the spires of Chartres, Reims and Amiens...engaging in what Ms. Dissanayake calls “artifying,” people can be quickly and ebulliently drawn together, and even strangers persuaded to treat one another as kin. Through the harmonic magic of art, the relative weakness of the individual can be traded up for the strength of the hive, cohered into a social unit ready to take on the world.

She suggests that many of the basic phonemes of art, the stylistic conventions and tonal patterns, the mental clay, staples and pauses with which even the loftiest creative works are constructed, can be traced back to the most primal of collusions — the intimate interplay between mother and child.

After studying hundreds of hours of interactions between infants and mothers from many different cultures, Ms. Dissanayake and her collaborators have identified universal operations that characterize the mother-infant bond. They are visual, gestural and vocal cues that arise spontaneously and unconsciously between mothers and infants, but that nevertheless abide by a formalized code: the calls and responses, the swooping bell tones of motherese, the widening of the eyes, the exaggerated smile, the repetitions and variations, the laughter of the baby met by the mother’s emphatic refrain. The rules of engagement have a pace and a set of expected responses, and should the rules be violated, the pitch prove too jarring, the delays between coos and head waggles too long or too short, mother or baby may grow fretful or bored.

To Ms. Dissanayake, the tightly choreographed rituals that bond mother and child look a lot like the techniques and constructs at the heart of much of our art. “These operations of ritualization, these affiliative signals between mother and infant, are aesthetic operations, too,” she said in an interview. “And aesthetic operations are what artists do. Knowingly or not, when you are choreographing a dance or composing a piece of music, you are formalizing, exaggerating, repeating, manipulating expectation and dynamically varying your theme.” You are using the tools that mothers everywhere have used for hundreds of thousands of generations.

In art, as in love, as in dancing the hora, if you don’t know the moves, you really can’t fake them.

Experiencing beauty in art - a biological basis?

One of the most debated issues in aesthetics is whether beauty may be defined by some objective parameters or whether it merely depends on subjective factors. The first perspective goes back to Plato's objectivist view of aesthetic perception, in which beauty is regarded as a property of an object that produces a pleasurable experience in any suitable viewer. This stance may be rephrased in biological terms by stating that human beings are endowed with species-specific mechanisms that resonate in response to certain parameters present in works of art. The alternative stance is that the viewers' evaluation of art is fully subjective. It is determined by experience and personal values

The above text begins a paper in PLoS ONE from Rizzolatti and colleagues, and addresses this issue. Here is their abstract and one figure from the paper.

Is there an objective, biological basis for the experience of beauty in art? Or is aesthetic experience entirely subjective? Using fMRI technique, we addressed this question by presenting viewers, naïve to art criticism, with images of masterpieces of Classical and Renaissance sculpture. Employing proportion as the independent variable, we produced two sets of stimuli: one composed of images of original sculptures; the other of a modified version of the same images. The stimuli were presented in three conditions: observation, aesthetic judgment, and proportion judgment. In the observation condition, the viewers were required to observe the images with the same mind-set as if they were in a museum. In the other two conditions they were required to give an aesthetic or proportion judgment on the same images. Two types of analyses were carried out: one which contrasted brain response to the canonical and the modified sculptures, and one which contrasted beautiful vs. ugly sculptures as judged by each volunteer. The most striking result was that the observation of original sculptures, relative to the modified ones, produced activation of the right insula as well as of some lateral and medial cortical areas (lateral occipital gyrus, precuneus and prefrontal areas). The activation of the insula was particularly strong during the observation condition. Most interestingly, when volunteers were required to give an overt aesthetic judgment, the images judged as beautiful selectively activated the right amygdala, relative to those judged as ugly. We conclude that, in observers naïve to art criticism, the sense of beauty is mediated by two non-mutually exclusive processes: one based on a joint activation of sets of cortical neurons, triggered by parameters intrinsic to the stimuli, and the insula (objective beauty); the other based on the activation of the amygdala, driven by one's own emotional experiences (subjective beauty).


Figure legend: The original image (Doryphoros by Polykleitos) is shown at the centre of the figure. This sculpture obeys to canonical proportion (golden ratio = 1∶1.618). Two modified versions of the same sculpture are presented on its left and right sides. The left image was modified by creating a short legs∶long trunk relation (ratio = 1∶0.74); the right image by creating the opposite relation pattern (ratio = 1∶0.36). All images were used in behavioral testing. The central image (judged-as-beautiful on 100%) and left one (judged-as-ugly on 64%) were employed in the fMRI study.

An antidepressant that extends lifespan.

In worms, that is. Petrascheck et al. show that mianserin, a serotonin receptor antagonist used as an antidepressant in humans, extends the lifespan of the nematode, Caenorhabditis elegans, by one third. Its action shows similarities to lifespan extension by dietary restriction. One possibility is that mianserin induces a state of perceived — rather than real — starvation. Intriguingly, appetite stimulation is a side effect of mianserin in humans, raising the possibility of linkage between appetite and lifespan.

Morality starts young...

The title of this post is the title of an editor's summary in the Nov. 22 issue of Nature:

The key to successful social interactions is the ability to assess others' intentions — be they friend or foe. A new study in 6- and 10-month-old infants shows that humans engage in social evaluations even earlier than was thought, before they can use language. The infants could evaluate actors on the basis of their social acts — they were drawn towards an individual who helps an unrelated third party to achieve his or her goal, and they avoided an individual who hinders a third party's efforts to achieve a goal. The findings support the claim that precursors to adult-like social evaluation are present even in babies. This skill could be a biological adaptation that may also serve as the foundation for moral thought and action later in life.

Here is a figure from the paper by Hamlin et al. showing the actors being evaluated by the children:

Figure legend: a, Helping and hindering habituation events of experiments 1 and 3. On each trial, the climber (red circle) attempts to climb the hill twice, each time falling back to the bottom of the hill. On the third attempt, the climber is either bumped up the hill by the helper (left panel) or bumped down the hill by the hinderer (right panel). Infants in experiment 1 saw these two events in alternating sequence; infants in experiment 3 saw either a helping or hindering event in alternation with the corresponding neutral event depicted in d. b, Looking time test events of experiments 1 and 3. The climber moves from the top of the hill to sit with the character on the right (left panel) or the left (right panel). c, Pushing-up and pushing-down habituation events of experiment 2. An inanimate object (red circle) rests (left panel) at the bottom of the hill and is pushed up, or rests (right panel) at the top of the hill and is pushed down. Infants saw these two events in alternation. d, Neutral habituation events from helper/neutral (left panel) and hinderer/neutral (right panel) conditions of experiment 3. The neutral character, without interacting with the climber, traces a path identical to that of the helper (left panel) or hinderer (right panel). Each infant saw either the helping or hindering event depicted in a, in alternation with the corresponding neutral event.

Brain changes associated with congenital amusia

About four percent of the population has congenital amusia, a lifelong disability that prevents otherwise normal functioning individuals from developing basic musical skills. The condition has also been variously termed note deafness, tone deafness, or tune deafness. Here is an interesting abstract from Hyde et al. on the amusic brain, along with one figure from the paper:

Congenital amusia (or tone deafness) is a lifelong disorder characterized by impairments in the perception and production of music. A previous voxel-based morphometry (VBM) study revealed that amusic individuals had reduced white matter in the right inferior frontal gyrus (IFG) relative to musically intact controls. However, this VBM study also revealed associated increases in gray matter in the same right IFG region of amusics. The objective of the present study was to better understand this morphological brain anomaly by way of cortical thickness measures that provide a more specific measure of cortical morphology relative to VBM. We found that amusic subjects (n = 21) have thicker cortex in the right IFG and the right auditory cortex relative to musically intact controls (n = 26). These cortical thickness differences suggest the presence of cortical malformations in the amusic brain, such as abnormal neuronal migration, that may have compromised the normal development of a right frontotemporal pathway.

Figure - Group cortical thickness differences. Results from the statistical analysis of data from 21 amusics versus 26 controls are displayed at each vertex of the surface of a standardized brain in terms of a t statistical color map. A, Areas of significant thickness increases in the amusic brain relative to controls. B, areas of significant thickness decreases in the amusic brain relative to controls. Predicted group cortical thickness differences are in pink, and nonpredicted differences in green as follows: right superior precentral gyrus (a), right lateral occipital gyrus (b), right inferior precentral gyrus (c), right middle frontal gyrus (d), left inferior temporal gyrus (e), right anterior cingulate (f), right medial orbital frontal gyrus (g), right inferior temporal gyrus (h), left medial orbital frontal gyrus (i).

Roach Robots

Here is a moment of visual relief:

Genetic variation in the enhancement of intelligence by breastfeeding.

It's the environment AND the genes...Caspi et al. provide a fascinating example of how genetic differences can moderate the effects of environmental influences on an individuals' health and behavior. The authors chose breastfeeding as the environmental exposure because the biological processes underlying its benefits for the developing brain are increasingly well understood. Here are some edited clips from the paper:

The predominant long-chain polyunsaturated fatty acids (LC-PUFAs) present in human milk, but not in cow's milk or most infant formulas, are docosahexaenoic acid (DHA; 22:6n-3) and arachidonic acid (AA or ARA; 20:4n-6). Substantial amounts of DHA and AA accumulate in the human brain during the first postnatal months, and infants who are breastfed have higher concentrations of DHA and AA than infants fed unsupplemented formulas. Evidence, in general, is consistent with the hypothesis that LC-PUFAs in breast milk may enhance cognitive development. In humans, children who are breastfed have higher IQs than children not fed breast milk, and this advantage persists into adulthood.

The authors chose to study people with two allelic variants of FADS2, which they termed C and G. FADS2 is an attractive candidate gene because of its role in the modification of dietary fatty acids. FADS2, located on chromosome 11q12.2, encodes the delta-6 desaturase that is the rate-limiting step on the metabolic pathway leading to AA and DHA production.

Examination of different cohorts of several thousand children from ongoing longitudinal studies in New Zealand, England and Wales revealed that breastfed children carrying the C allele showed a 6.4-IQ-point advantage relative to children not fed breast milk. GG homozygotes neither gained an advantage from breastfeeding nor suffered a disadvantage from not being fed breast milk. The authors ruled out alternative explanations of the finding involving gene–exposure correlation, intrauterine growth, social class, and maternal cognitive ability, as well as maternal genotype effects on breastfeeding and breast milk.

...the finding has implications for the public understanding of genetics. The pendulum of opinion surrounding nature versus nurture has swung back and forth, yielding global estimates of heritability versus "environmentality" that have overlooked the contribution of interactions between specific genes and specific experiences. To date, research on gene–environment interactions has been dominated by the search for genetic variants that increase disease susceptibility to environmental pathogens; for example, carriers of "short" 5-HTT alleles who encounter stressful life events are at risk of becoming depressed; carriers of "rapid" NAT2 alleles who eat red meat are at risk of developing colorectal cancer. However, genes are not only implicated in disease; here we have shown that a genetic variant (in FADS2) may also enhance a favorable response (increased IQ) to a salubrious exposure present throughout human ancestry (breastfeeding).

Pay me for my content!

This is the title of a brief Op-Ed piece by Jaron Lanier, a well known guru of the information age, in the Nov. 20 N.Y. Times. It is worth reproducing in full:

INTERNET idealists like me have long had an easy answer for creative types — like the striking screenwriters in Hollywood — who feel threatened by the unremunerative nature of our new Eden: stop whining and figure out how to join the party!..That’s the line I spouted when I was part of the birthing celebrations for the Web. I even wrote a manifesto titled “Piracy Is Your Friend.” But I was wrong. We were all wrong.

Like so many in Silicon Valley in the 1990s, I thought the Web would increase business opportunities for writers and artists. Instead they have decreased. Most of the big names in the industry — Google, Facebook, MySpace and increasingly even Apple and Microsoft — are now in the business of assembling content from unpaid Internet users to sell advertising to other Internet users. (Disclosure: I’m the scholar at large for Microsoft Live Labs, and I once was part of a company that Google bought.)

There’s an almost religious belief in the Valley that charging for content is bad. The only business plan in sight is ever more advertising. One might ask what will be left to advertise once everyone is aggregated...How long must creative people wait for the Web’s new wealth to find a path to their doors? A decade is a long enough time that idealism and hope are no longer enough. If there’s one practice technologists ought to embrace, it is the evaluation of empirical results...To help writers and artists earn a living online, software engineers and Internet evangelists need to exercise the power they hold as designers. Information is free on the Internet because we created the system to be that way.

We could design information systems so that people can pay for content — so that anyone has the chance of becoming a widely read author and yet can also be paid. Information could be universally accessible but on an affordable instead of an absolutely free basis...People happily pay for content in certain Internet ecosystems, provided the ecosystems are delightful. People love paying for virtual art, clothing and other items in virtual worlds like Second Life, for instance. Something similar is going on for music within the ecosystem of the iPod. (I am an adviser to Linden Lab, the creator of Second Life.)

Affordable turns out to be much harder than free when it comes to information technology, but we are smart enough to figure it out. We owe it to ourselves and to our creative friends to acknowledge the negative results of our old idealism. We need to grow up.

How our brains process inequity in rewards.

This work suggests that the calculation of social standing - as indexed by payment - may be an unconscious and automatic process in the brain. The previous post on monkeys judging inequity in rewards suggests an evolutionary origin in earlier primate behavior. Here we have a very similar experiment done on humans, with fMRI data that we can't get from the monkeys. The results provide neurophysiological evidence for the importance of social comparison on reward processing in the human brain. Several studies show that most of us place as much value on relative remuneration, comparing ourselves with others, as on its absolute level. In the current work, when subjects were given different compensation for solving the same puzzle, this was reflected by different activation levels in the ventral striatum, a brain region known to be involved in the comparison of predicted and actually received rewards (i.e., reward prediction error). Here is the abstract from Fliessbach et al., followed by a figure from the paper:

Whether social comparison affects individual well-being is of central importance for understanding behavior in any social environment. Traditional economic theories focus on the role of absolute rewards, whereas behavioral evidence suggests that social comparisons influence well-being and decisions. We investigated the impact of social comparisons on reward-related brain activity using functional magnetic resonance imaging (fMRI). While being scanned in two adjacent MRI scanners, pairs of subjects had to simultaneously perform a simple estimation task that entailed monetary rewards for correct answers. We show that a variation in the comparison subject's payment affects blood oxygenation level–dependent responses in the ventral striatum. Our results provide neurophysiological evidence for the importance of social comparison on reward processing in the human brain.

Figure - Glassbrain projection of brain regions showing stronger BOLD responses in conditions in which a subject received a reward while the other did not compared with conditions in which a subject did not receive a reward at all.

Monkeys judge inequity like humans

DeWaal and collaborators expand on previous observations to show that capuchin monkeys get really pissed off if they worked harder for a reward than another monkey, and then see that monkey get a greater reward! This suggests that our human resentment of inequity in rewards my have a very ancient origin in primate behavior. Here is their abstract:

Without joint benefits, joint actions could never have evolved. Cooperative animals need to monitor closely how large a share they receive relative to their investment toward collective goals. This work documents the sensitivity to reward division in brown, or tufted, capuchin monkeys (Cebus apella). In addition to confirming previous results with a larger subject pool, this work rules out several alternative explanations and adds data on effort sensitivity. Thirteen adult monkeys exchanged tokens for rewards, showing negative reactions to receiving a less-favored reward than their partner. Because their negative reaction could not be attributed to the mere visibility of better rewards (greed hypothesis) nor to having received such rewards in the immediate past (frustration hypothesis), it must have been caused by seeing their partner obtain the better reward. Effort had a major effect in that by far the lowest level of performance in the entire study occurred in subjects required to expend a large effort while at the same time seeing their partner receive a better reward. It is unclear whether this effort–effect was based on comparisons with the partner, but it added significantly to the intensity of the inequity response. These effects are as expected if the inequity response evolved in the context of cooperative survival strategies.

Varieties of denial...

Benedict Carey writes a nice piece in the Nov. 20 New York Times about the utility of - and evolutionary rationale for - mild forms of denial, which can take the form of inattention, passive acknowledgment, reframing or willful blindness. Ignoring the "elephant in the living room" is sometimes the best strategy for getting along! A few clips from the article, which you can read in whole here:

...recent studies from fields as diverse as psychology and anthropology suggest that the ability to look the other way, while potentially destructive, is also critically important to forming and nourishing close relationships. The psychological tricks that people use to ignore a festering problem in their own households are the same ones that they need to live with everyday human dishonesty and betrayal, their own and others’. And it is these highly evolved abilities, research suggests, that provide the foundation for that most disarming of all human invitations, forgiveness...“The closer you look, the more clearly you see that denial is part of the uneasy bargain we strike to be social creatures,” said Michael McCullough, a psychologist at the University of Miami and the author of the coming book “Beyond Revenge: The Evolution of the Forgiveness Instinct.” “We really do want to be moral people, but the fact is that we cut corners to get individual advantage, and we rely on the room that denial gives us to get by, to wiggle out of speeding tickets, and to forgive others for doing the same.”...The capacity for denial appears to have evolved in part to offset early humans’ hypersensitivity to violations of trust. In small kin groups, identifying liars and two-faced cheats was a matter of survival. A few bad rumors could mean a loss of status or even expulsion from the group, a death sentence.

Do you really want to know your own genome?

Nicholas Wade offer a brief essay in the Nov. 16 New York Times which notes several companies, such as DeCode Genetics, 23andMe, and Navigenics that are now offering to give you an analysis of your own individual genome for $1000 or less. While knowing that you have a gene that predisposes you to a given disease might reinforce life style choices that make that disease less likely (in the case of potential heart disease, for example, converting from red meat and potatoes to complex carbohydrates) such information could also cause needless alarm, for many factors other than genotype contribute to actual outcomes in each of us.

A gradient of representational hierarchy in the prefrontal cortex.

Badre and D'Esposito have designed a set of tasks requiring increasingly abstract representations, each level requiring the classing of representations at the next subordinate level. They find a systematic posterior to anterior gradient of activity with the prefrontal cortex depending on the manipulated level of representation. Here is their abstract and a figure from the paper:

The prefrontal cortex (PFC) is central to flexible and organized action. Recent theoretical and empirical results suggest that the rostro-caudal (head to tail) axis of the frontal lobes may reflect a hierarchical organization of control. Here, we test whether the rostro-caudal axis of the PFC is organized hierarchically, based on the level of abstraction at which multiple representations compete to guide selection of action. Four functional magnetic resonance imaging (fMRI) experiments parametrically manipulated the set of task-relevant (a) competing responses, (b) competing features, (c) competing dimensions, and (d) overlapping cue-to-dimension mappings. A systematic posterior to anterior gradient was evident within the PFC depending on the manipulated level of representation. Furthermore, across four fMRI experiments, activation in PFC subregions was consistent with the sub- and superordinate relationships that define an abstract representational hierarchy. In addition to providing further support for a representational hierarchy account of the rostro-caudal gradient in the PFC, these data provide important empirical constraints on current theorizing about control hierarchies and the PFC.

Figure (click to enlarge) - Whole-brain analysis of parametric effect across the four experiments. A rostro-caudal gradient was evident as the level of abstraction increased. Specifically, response competition activated the PMd (A), feature competition activated the pre-PMd (B), dimension competition activated the IFS (C), and context competition activated the FPC (D). Graphs from ROI analyses for the PMd, pre-PMd, and IFS depict the integrated peak signal, whereas analysis of the frontal pole depicts the mean percent signal change over the entire block. Graphs from ROI analyses for PMd, pre-PMd, and IFS depict the integrated peak signal for each parametric level in each experiment (C = Context, D = Dimension, F = Feature, and R = Response). Bars for FPC depict the mean percent signal change over the entire block.

Memories play back on fast forward during sleep

It is know that correlations of nerve activity that are observed during learning sequence tasks replay during sleep, presumably to enhance learning and retention of the sequence. (I always find that I can play a difficult piano passage better when I wake up in the morning than when I was practicing it the day before). McNaughton and his collaborators now show that the replay during sleep occurs much faster than during actual awake behaviors. Here is their abstract:

As previously shown in the hippocampus and other brain areas, patterns of firing-rate correlations between neurons in the rat medial prefrontal cortex during a repetitive sequence task were preserved during subsequent sleep, suggesting that waking patterns are reactivated. We found that, during sleep, reactivation of spatiotemporal patterns was coherent across the network and compressed in time by a factor of 6 to 7. Thus, when behavioral constraints are removed, the brain's intrinsic processing speed may be much faster than it is in real time. Given recent evidence implicating the medial prefrontal cortex in retrieval of long-term memories, the observed replay may play a role in the process of memory consolidation.

Kewl Bio-inspired Robotics...

The Nov. 16 issue of Science has a special section on Robotics. I thought this graphic from the article by Pfeifer et al. - "Self-Organization, Embodiment, and Biologically Inspired Robotics" - was fascinating. It describes several biologically inspired robots.


Figure: Self-organization, dynamics, and materials in bio-inspired robotics. (A) Smooth transition between swimming and walking. This amphibious salamanderlike robot (~80 cm long) embeds a spinal cord model that explains the ability of salamanders to switch between swimming and walking. The locomotion model is built by extending a primitive neural circuit for swimming by phylogenetically more recent limb oscillatory centers. (B) Rich sensory stimulation through proper sensor morphology. This robot (~7 cm in diameter) owes its sophisticated sensory capacities to the specific arrangement, shape, and material characteristics of its whiskers. Natural whiskers from rodents (such as the ones used on this robot) are far superior to whiskers built from other materials in terms of richness of the signals relayed to the neural system. (C) Self-stabilizing rapid hexapod locomotion. This robot (~15 cm long) moves with a bouncing gait, achieving rapid (over 4 body lengths per second) locomotion. Its legs are built with compliant pneumatic actuators, which yield self-stabilization through mechanical feedback. (D) Passive dynamics–based walking. Designed to work on a slope as a dynamic walker, this robot (~45 cm tall) exploits dynamics and morphology (in particular, the shape and length of the body and feet) to achieve stable walking. The robot's natural dynamics serves as the target dynamics for a reinforcement learning mechanism, enabling the robot to quickly learn to walk on flat ground. (E) Self-stabilizing vertical takeoff through materials and morphology. Inspired by flies, this ultralight (60 mg, 3-cm wingspan) ornithopter (a device that flies by flapping its wings) generates sufficient lift to take off vertically (power is supplied externally). A large part of the control is delegated to the morphological and material properties of the robot. Compliant structures are driven into resonance to produce a large wing stroke, and flexible material is used in the wing hinges to allow for passive rotations of the wings. (F) Agile wall-climbing through materials. The bio-inspiration for this palm-sized robot is provided by the gecko and its uncanny climbing talents. The robot's tri-foot (three-footed wheel) is equipped with a polymer dry adhesive material, which to some extent has contact properties comparable to those of its biological analog. The robot can flexibly navigate on smooth vertical and even inverted surfaces. (G) Morphing through localized self-reconfiguration. This self-reconfigurable robot is composed of active (actuated, black) and passive (nonactuated, white) cubic modules (~400 g, ~60 to 65 mm side length). The modules connect to each other through hooks, which enables the robot to change its morphology in a large number of ways. The picture shows the metamorphosis from a four-legged (quadruped) structure to a linear (snakelike) structure. (H) Global movement through local interaction dynamics. The individual wheel-like modules (~10 cm in diameter) constituting this robot are equipped with spokelike parts driven by linear actuators. The wheels lie horizontally on the ground and attach to neighboring modules by Velcro. Although no module can move on its own, by using neural oscillators as drivers for the actuators and through the physical coupling between the units, a coordinated global wave of activation can be induced in clusters of more than 30 modules, which leads to forward movement, even though there is no global control.