Our visual long-term memory has a massive storage capacity for object details

In the Sept 23 issue of PNAS Brady et al. make some striking observations on the capacity of our visual memory stores:

One of the major lessons of memory research has been that human memory is fallible, imprecise, and subject to interference. Thus, although observers can remember thousands of images, it is widely assumed that these memories lack detail. Contrary to this assumption, here we show that long-term memory is capable of storing a massive number of objects with details from the image. Participants viewed pictures of 2,500 objects over the course of 5.5 h. Afterward, they were shown pairs of images and indicated which of the two they had seen. The previously viewed item could be paired with either an object from a novel category, an object of the same basic-level category, or the same object in a different state or pose. Performance in each of these conditions was remarkably high (92%, 88%, and 87%, respectively), suggesting that participants successfully maintained detailed representations of thousands of images. These results have implications for cognitive models, in which capacity limitations impose a primary computational constraint (e.g., models of object recognition), and pose a challenge to neural models of memory storage and retrieval, which must be able to account for such a large and detailed storage capacity.


Figure: Example test pairs presented during the two-alternative forced-choice task for all three conditions (novel, exemplar, and state). The number of observers reporting the correct item is shown for each of the depicted pairs.

How do you like your coffee?

A cute piece by Katherine Sanderson from the Oct. 1 Nature:

The floating fractal (top, left) is formed 90 seconds after a drop of instant coffee falls into a cup of milk.

Coffee is heavier than milk and the battle between gravity and surface tension plays out at the boundary between the two liquids. The coffee falls vertically through the milk (bottom, left, with water replacing milk for ease of viewing), and the fractal pattern emerges.

The pattern constantly shifts as parts of it are sucked into the milk, producing a fractal structure with the same dimension as a Sierpi´nski carpet — formed when a square is cut into nine identical squares; the central square is removed; and the procedure is repeated with the remaining eight squares and so on infinitely.

Michiko Shimokawa and Shonosuke Ohta, fluid scientists at Kyushu University in Fukuoka City, Japan, say that it is the first time this kind of fractal has been shown experimentally (http://www.arxiv.org/abs/0809.2458), and they managed to recreate the process using a magnetic liquid instead of coffee (far right).

A Grieg Air for Monday morning

Yesterday was a rainy afternoon at my home on Twin Valley Road in Middleton Wisconsin, so I decided to a video recording of a relatively tranquil, lyrical piece by Edvard Grieg that I enjoy playing - the Air from his Holberg Suite.

Political Attitudes Vary with Physiological Traits

Not exactly surprising, but fascinating never the less, from Oxley et al.

Although political views have been thought to arise largely from individuals' experiences, recent research suggests that they may have a biological basis. We present evidence that variations in political attitudes correlate with physiological traits. In a group of 46 adult participants with strong political beliefs, individuals with measurably lower physical sensitivities to sudden noises and threatening visual images were more likely to support foreign aid, liberal immigration policies, pacifism, and gun control, whereas individuals displaying measurably higher physiological reactions to those same stimuli were more likely to favor defense spending, capital punishment, patriotism, and the Iraq War. Thus, the degree to which individuals are physiologically responsive to threat appears to indicate the degree to which they advocate policies that protect the existing social structure from both external (outgroup) and internal (norm-violator) threats.

Subliminal Neuroeconomics

It turns out that we can learn to assess risks on the basis of visual hints we are not aware of seeing. In other words, without conscious processing of contextual cues, our brains can learn their reward value and use them to provide a bias on decision making. Functional neuroimaging reveals a correlation of cue values and prediction errors with activity in ventral striatum during conditioning. From the summary in Nature:

Mathias Pessiglione et al. repeatedly showed 20 subjects abstract symbols as they played a gambling game. Each symbol presentation involved one of three choices and was followed by a 'masking image' in a series that flickered so fast that the subjects could not consciously perceive the symbol shapes. The subjects were told that the symbols were associated with winning or losing, and then allowed to gamble.

The subjects won more than they lost, indicating that their brains recognized the unperceived symbols and learned to associate them with reward or punishment. Functional neuroimaging showed that the mechanism involves the ventral striatum (see figure), a brain area associated with assessing reward value.

Is the bisphenol (BPA) in plastic products making us dumb?

Estrogens are known to increase the number of excitatory synapses in our hippocampus and enhance both cognitive performance and spatial memory. This is why there is such interest in the possible disruptive effects of estrogenic compounds in the environment, particularly bisphenol A (BPA) that is present in some plastics. Leranth et al. now demonstrate in monkeys that a daily dose of BPA considered within the safe range for humans (50 μg/kg) completely blocks the estradiol-induced increase in axospinous synapses in three distinct fields of the hippocampus. This would be expected to have profound effects on the highly plastic excitatory (glutamatergic) circuits in both our hippocampus and prefrontal cortex. Here is their chilling abstract:

Exposure measurements from several countries indicate that humans are routinely exposed to low levels of bisphenol A (BPA), a synthetic xenoestrogen widely used in the production of polycarbonate plastics. There is considerable debate about whether this exposure represents an environmental risk, based on reports that BPA interferes with the development of many organs and that it may alter cognitive functions and mood. Consistent with these reports, we have previously demonstrated that BPA antagonizes spine synapse formation induced by estrogens and testosterone in limbic brain areas of gonadectomized female and male rats. An important limitation of these studies, however, is that they were based on rodent animal models, which may not be representative of the effects of human BPA exposure. To address this issue, we examined the influence of continuous BPA administration, at a daily dose equal to the current U.S. Environmental Protection Agency's reference safe daily limit, on estradiol-induced spine synapse formation in the hippocampus and prefrontal cortex of a nonhuman primate model. Our data indicate that even at this relatively low exposure level, BPA completely abolishes the synaptogenic response to estradiol. Because remodeling of spine synapses may play a critical role in cognition and mood, the ability of BPA to interfere with spine synapse formation has profound implications. This study is the first to demonstrate an adverse effect of BPA on the brain in a nonhuman primate model and further amplifies concerns about the widespread use of BPA in medical equipment, and in food preparation and storage.

Take a bird-nap, not a cat nap.

A complete group of sleep characteristics (rapid-eye-movement sleep and slow-wave sleep as well as transition stages and quick spikes) has been found outside of mammals, in zebra finches, a surprising finding because birds lack a neocortex, the part of the mammalian brain thought necessary for such patterns. Low et al. suggest that ancestral characteristics of sleep evolved under selective pressures common to songbirds and mammals. This would fit with Tononi's suggestion that sleep is required for synaptic homeostasis and regenerations (a form of sleep is also observed in fruitflies). Here is their abstract:

A suite of complex electroencephalographic patterns of sleep occurs in mammals. In sleeping zebra finches, we observed slow wave sleep (SWS), rapid eye movement (REM) sleep, an intermediate sleep (IS) stage commonly occurring in, but not limited to, transitions between other stages, and high amplitude transients reminiscent of K-complexes. SWS density decreased whereas REM density increased throughout the night, with late-night characterized by substantially more REM than SWS, and relatively long bouts of REM. Birds share many features of sleep in common with mammals, but this collective suite of characteristics had not been known in any one species outside of mammals. We hypothesize that shared, ancestral characteristics of sleep in amniotes evolved under selective pressures common to songbirds and mammals, resulting in convergent characteristics of sleep.

For a kid to learn - positive strokes work way better than negative.

An interesting study by van Duijvenvoorde et al. compares the utility of positive versus negative strokes during learning in three age groups (8–9, 11–13, and 18–25 year of age). Cognitive control areas are engaged best by positive feedback in the youngest group, and by negative feedback in the oldest. Here is their abstract:

How children learn from positive and negative performance feedback lies at the foundation of successful learning and is therefore of great importance for educational practice. In this study, we used functional magnetic resonance imaging (fMRI) to examine the neural developmental changes related to feedback-based learning when performing a rule search and application task. Behavioral results from three age groups (8–9, 11–13, and 18–25 years of age) demonstrated that, compared with adults, 8- to 9-year-old children performed disproportionally more inaccurately after receiving negative feedback relative to positive feedback. Additionally, imaging data pointed toward a qualitative difference in how children and adults use performance feedback. That is, dorsolateral prefrontal cortex and superior parietal cortex were more active after negative feedback for adults, but after positive feedback for children (8–9 years of age). For 11- to 13-year-olds, these regions did not show differential feedback sensitivity, suggesting that the transition occurs around this age. Pre-supplementary motor area/anterior cingulate cortex, in contrast, was more active after negative feedback in both 11- to 13-year-olds and adults, but not 8- to 9-year-olds. Together, the current data show that cognitive control areas are differentially engaged during feedback-based learning across development. Adults engage these regions after signals of response adjustment (i.e., negative feedback). Young children engage these regions after signals of response continuation (i.e., positive feedback). The neural activation patterns found in 11- to 13-year-olds indicate a transition around this age toward an increased influence of negative feedback on performance adjustment. This is the first developmental fMRI study to compare qualitative changes in brain activation during feedback learning across distinct stages of development.

Brain correlates of the muting of our emotions as we age.

My boyfriend in the early 19980’s was a pharmacy graduate student whose t-shirt read “Drugs are my life.” If I were to wear such a t-shirt now it would read “Hormones and neurotransmitters are my life.” I increasingly feel that all this verbal stuff we do - chattering in person or in the electronic ether, writing blogs, etc. - is a superficial veneer, noise on top of what is really running the show, which is the waxing and waning of hormones and neurotransmitters directed by an “it”, a martian inside us utterly running its own show. These compounds regulate our assertiveness versus passivity , our trust versus mistrust, our anxiety versus calm, our pleasure during antipication and reward. (They function, respectively, in neural systems that use testosterone, oxytocin, adrenaline, and dopamine.). The swings in these systems become less dramatic as we 'mellow' with aging.

Dreher et al. have published an interesting bit of work that deals specifically with the muting of the intensity of the pleasures we feel during anticipation and reward, in their article on “Age-related changes in midbrain dopaminergic regulation of the human reward system.” Their data show what is going on as we experience less excitement at opening a present when we are 60 than when we are 10 years old. There are changes in the brain's production of dopamine, which plays a central role in our reward system, as well as in which parts of the brain respond to it, and by how much they respond. (a recent brief article on dopamine and the reward system of the brain is here.) Here is their abstract, followed by a figure from the paper.

The dopamine system, which plays a crucial role in reward processing, is particularly vulnerable to aging. Significant losses over a normal lifespan have been reported for dopamine receptors and transporters, but very little is known about the neurofunctional consequences of this age-related dopaminergic decline. In animals, a substantial body of data indicates that dopamine activity in the midbrain is tightly associated with reward processing. In humans, although indirect evidence from pharmacological and clinical studies also supports such an association, there has been no direct demonstration of a link between midbrain dopamine and reward-related neural response. Moreover, there are no in vivo data for alterations in this relationship in older humans. Here, by using 6-[18F]FluoroDOPA (FDOPA) positron emission tomography (PET) and event-related 3T functional magnetic resonance imaging (fMRI) in the same subjects, we directly demonstrate a link between midbrain dopamine synthesis and reward-related prefrontal activity in humans, show that healthy aging induces functional alterations in the reward system, and identify an age-related change in the direction of the relationship (from a positive to a negative correlation) between midbrain dopamine synthesis and prefrontal activity. These results indicate an age-dependent dopaminergic tuning mechanism for cortical reward processing and provide system-level information about alteration of a key neural circuit in healthy aging. Taken together, our findings provide an important characterization of the interactions between midbrain dopamine function and the reward system in healthy young humans and older subjects, and identify the changes in this regulatory circuit that accompany aging.


Legend (click on figure to enlarge). Statistical t maps of the within-groups effects in the different phases of the reward paradigm. (A) (Left) Main effect of anticipating reward in young subjects during the delay period, showing activation in the left intraparietal cortex, ventral striatum, caudate nucleus, and anterior cingulate cortex. (Right) Main effect of anticipating reward in older subjects during the delay period, showing activation in the left intraparietal cortex only. The glass brain and the coronal slice indicate that no ventral striatum activity was observed in older subjects. (B) (Left) Main effect of reward receipt in young subjects at the time of the rewarded outcome showing activation in a large bilateral prefronto-parietal network. (Right) Main effect of reward receipt in older subjects at the time of the rewarded outcome showing bilateral prefronto-parietal activation.

Is Art the future of Science?

I want to point out a lovely essay by Johan Lehrer that explores how esthetic and artistic explorations have influenced paradigm shifting insights in physics, psychology and neuroscience - metaphorical leaps that have broken the iron grip of models that have reached their dead end.

Can you see me?

Check out this interesting piece from John Tierney on modern camouflage that is based on knowledge of how a deer's eye perceives the world.

Male promiscuity versus monogamy in humans nudged by same genes as in Prarie Voles

A series of elegant experiments done on meadow voles versus prairie voles (promiscuous versus monogamous males) show that the different behaviors correlate with genetic variation in the gene for a vasopressin receptor (V1aR). Nonmonogamous meadow voles become more monogamous when V1aR density is increased in relevant brain areas by using viral vector gene transfer. As you might suspect, a similar genetic variation has now been shown by Walum et al.(open access) to correlate with pair-bonding behavior in human males. (I would be most curious to know whether I have the repeat polymorphism that would correlate with my wandering ways!) Here is their abstract:

Pair-bonding has been suggested to be a critical factor in the evolutionary development of the social brain. The brain neuropeptide arginine vasopressin (AVP) exerts an important influence on pair-bonding behavior in voles. There is a strong association between a polymorphic repeat sequence in the 5′ flanking region of the gene (avpr1a) encoding one of the AVP receptor subtypes (V1aR), and proneness for monogamous behavior in males of this species. It is not yet known whether similar mechanisms are important also for human pair-bonding. Here, we report an association between one of the human AVPR1A repeat polymorphisms (RS3) and traits reflecting pair-bonding behavior in men, including partner bonding, perceived marital problems, and marital status, and show that the RS3 genotype of the males also affects marital quality as perceived by their spouses. These results suggest an association between a single gene and pair-bonding behavior in humans, and indicate that the well characterized influence of AVP on pair-bonding in voles may be of relevance also for humans.

The sucker to saint effect.

Here is an interesting tidbit in Psychological Science from Jordan and Monin. They suggest we protect our own self image by feeling morally superior when we otherwise might feel foolish.

When people's rationality and agency are implicitly called into question by the more expedient behavior of others, they sometimes respond by feeling morally superior; this is referred to as the sucker-to-saint effect. In Experiment 1, participants who completed a tedious task and then saw a confederate quit the same task elevated their own morality over that of the confederate, whereas participants who simply completed the task or simply saw the confederate quit did not. In Experiment 2, this effect was eliminated by having participants contemplate a valued personal quality before encountering the rebellious confederate, a result suggesting a role for self-threat in producing moralization. These studies demonstrate that moral judgments can be more deeply embedded in judges' immediate social contexts—and driven more by motivations to maintain self-image—than is typically appreciated in contemporary moral-psychology research. Rather than uphold abstract principles of justice, moral judgment may sometimes just help people feel a little less foolish.

Brain processing of action language influenced by sports experience.

There is abundant evidence that if we train and enhance our skill at a particular kind of action (piano playing, serving a tennis ball, etc.) areas of the premotor and motor cortex involved in the skill increase their relative area. Beilock et al. now provide evidence, in an open access article, that specialized (sports) motor experience enhances action-related language understanding by recruitment of left dorsal lateral premotor cortex, a region normally devoted to higher-level action selection and implementation—even when there is no intention to perform a real action. Thus, the language system is sufficiently plastic and dynamic to encompass expertise-related neural recruitment outside core language networks.

A memory activates the same brain cells as the original experience.

A fascinating observation from Gelbard-Sagiv et al., who studied patients with pharmacologically intractable epilepsy with implanted depth electrodes to localize the focus of seizure onset. Benedict Carey discusses the work. Here is the original abstract:

The emergence of memory, a trace of things past, into human consciousness is one of the greatest mysteries of the human mind. Whereas the neuronal basis of recognition memory can be probed experimentally in human and nonhuman primates, the study of free recall requires that the mind declare the occurrence of a recalled memory (an event intrinsic to the organism and invisible to an observer). Here, we report the activity of single neurons in the human hippocampus and surrounding areas when subjects first view television episodes consisting of audiovisual sequences and again later when they freely recall these episodes. A subset of these neurons exhibited selective firing, which often persisted throughout and following specific episodes for as long as 12 seconds. Verbal reports of memories of these specific episodes at the time of free recall were preceded by selective reactivation of the same hippocampal and entorhinal cortex neurons. We suggest that this reactivation is an internally generated neuronal correlate of the subjective experience of spontaneous emergence of human recollection.

The teenage brain.

Harvard Magazine has an interesting brief article describing work on the teenage brain being done at Harvard Medical School.

Online brain and cognitive science courses

Every week or so I get an email from a reader asking "how do I find out more about......" or "what is a good book on...." Apart from specific information that I can pass on, I should mention here what I suggest to them (in addition to a google search using proper search terms): The MIT open course ware, for example in Brain and Cognitive science, is amazing. There are a total of 1800 offerings in all college areas.

A taste test for depression?

From a report by Cahoon on the July Physiological Society Meetings in Cambridge, UK.

Melichar and Donaldson gave healthy volunteers a tiny dab of faint flavor on the tongue and asked if they could taste it. The sample was so diluted that they couldn't. The researchers then gave the volunteers pills that boosted brain levels of one of two neurotransmitters, serotonin or noradrenaline. To boost serotonin, for example, patients took a Prozac-like drug known as a selective serotonin-reuptake inhibitor. When volunteers got a serotonin jump, they were suddenly able to taste the feeble flavor if it was bitter or sweet. With noradrenaline boosted, the volunteers were able to taste the dab if it was bitter or sour. Donaldson and Melichar suspected that depressed people had blunted taste buds--the illness is often tied to a lack of either neurotransmitter--and that the right antidepressant would allow depressed people to experience the true vibrancy of flavors.

Experiments are being planned to determine the validity of a taste test for depression:

If those results validate the flavor test, it could become the equivalent of the cholesterol test that persuades someone to take action against heart disease. "The patient has no objective marker" that tells them they're depressed, says Melichar. As a result, he notes, a lot of people end up not taking their medication.

Moreover, given that the researchers have found that serotonin is linked to sweet and noradrenaline is linked to sour, the taste test could be a useful way to determine which drug to use, a big plus because antidepressants can take several weeks or more to have an effect. And with this disease, time is of the essence--if treated within 3 months of becoming depressed, a person has a very good chance of getting better.

Training young brains to behave

Benedict Carey offers an informative article on brain development in children, and the growth of self control as the prefrontal cortex matures. The article has an excellent interactive graphic that permits you to move a slider and see brain changes during development.

Social exclusion causes unconscious mimicry

Lakin et al. make some interesting observations on our reactions to being socially excluded by others, we are likely to unconsciously start mimicking their behaviors:

Research across various disciplines has demonstrated that social exclusion has devastating psychological, emotional, and behavioral consequences. Excluded individuals are therefore motivated to affiliate with others, even though they may not have the resources, cognitive or otherwise, to do so. The current research explored whether nonconscious mimicry of other individuals—a low-cost, low-risk, automatic behavior—might help excluded individuals address threatened belongingness needs. Our first experiment demonstrated that excluded people mimic a subsequent interaction partner more than included people do. A second experiment showed that individuals excluded by an in-group selectively (and nonconsciously) mimic a confederate who is an in-group member more than a confederate who is an out-group member. The relationship between exclusion and mimicry suggests that there are automatic behaviors people can use to recover from the experience of being excluded. In addition, this research demonstrates that nonconscious mimicry is selective and sensitive to context.