The Primate Lineage

Two items on primates:

John Noble Wilford does a nice review of the recent primatology meeting in Chicago in the NY Times science section 4/17/07. His emphasis is on recent work with Chimps, showing them to be social creatures that appear to be capable of empathy, altruism, self-awareness, cooperation in problem solving and learning through example and experience. PDF is here.

The April 13 issue of Science Magazine has a series of articles on the sequencing of the genome of the rhesus macaque monkey. This begins to put the previously sequenced chimp and human genomes into perspective. Macaques are Old World monkeys, which split perhaps 25 million years ago from the ape lineage that led to both chimpanzees and humans. I thought I would pass on this graphic from from Pennisi's article showing the primate evolutionary line.

Researchers plan to eventually sequence the genomes of all these primates and related species, with human, macaque, and chimp now published. The animals are arranged in an artist's rendition of their family tree, with estimated divergence dates in millions of years. CREDITS: (ILLUSTRATION) N. KEVITIYAGALA/SCIENCE; (ADAPTED FROM) E. EIZIRIK ET AL., IN ANTHROPOID ORIGINS: NEW VISIONS, C. F. ROSS AND R. F. KAY (KLUWER/PLENUM, 2004), PP. 45-64.

Amygdala damage impairs eye contact

Here is the abstract of an article from Adolph's group at Cal. Tech.:

The role of the human amygdala in real social interactions remains essentially unknown, although studies in nonhuman primates and studies using photographs and video in humans have shown it to be critical for emotional processing and suggest its importance for social cognition. We show here that complete amygdala lesions result in a severe reduction in direct eye contact during conversations with real people, together with an abnormal increase in gaze to the mouth. These novel findings from real social interactions are consistent with an hypothesized role for the amygdala in autism and the approach taken here opens up new directions for quantifying social behavior in humans.

And a clip from their discussion:

It is intriguing ...to consider similarities between our findings and those in autism. People with autism do not fixate photographs and videos of faces normally, and are anecdotally reported to gaze at the mouth in social interactions. It has been suggested that the amygdala dysfunction is in part to blame for these abnormalities in autism, and recent findings using neuroimaging with photographs of faces support this hypothesis.

Sexual Desire

Natalie Angier writes an engaging review of research into factors regulating sexual desire and sexual arousal (PDF here). The Science section of the April 10 New York Times contains a number of other interesting articles on sex and desire.


One brief edited clip from Angier:

According to the sequence put forward in the mid-20th century by the pioneering sex researchers William H. Masters, Virginia E. Johnson and Helen Singer Kaplan, a sexual encounter begins with desire, a craving for sex that arises of its own accord and prods a person to seek a partner. That encounter then leads to sexual arousal, followed by sexual excitement, a desperate fumbling with buttons and related clothing fasteners, a lot of funny noises, climax and resolution...A plethora of new findings, however, suggest that the experience of desire may be less a forerunner to sex than an afterthought, the cognitive overlay that the brain gives to the sensation of already having been aroused by some sort of physical or subliminal stimulus — a brush on the back of the neck, say, or the sight of a ripe apple, or wearing a hard hat on a construction site and being surrounded by other men in similar haberdashery.

In a series of studies at the University of Amsterdam, Ellen Laan, Stephanie Both and Mark Spiering demonstrated that the body’s entire motor system is activated almost instantly by exposure to sexual images, and that the more intensely sexual the visuals, the stronger the electric signals emitted by the participants’ so-called spinal tendious reflexes. By the looks of it, Dr. Laan said, the body is primed for sex before the mind has had a moment to leer.... arousal is not necessarily a conscious process. In other experiments... when college students were exposed to sexual images too fleetingly for the subjects to report having noticed them, the participants were nevertheless much quicker to identify subsequent sexual images than were the control students who had been flashed with neutral images.

By reordering the sexual timeline and placing desire after arousal, rather than vice versa, the new research fits into the pattern that neurobiologists have lately observed for other areas of life. Before we are conscious of wanting to do anything — wave at a friend, open a book — the brain regions needed to perform the activity are already ablaze. The notion that any of us is the Decider, the proactive plotter of our most lubricious desires, scientists say, may simply be a happy and perhaps necessary illusion.

This is precisely the message of my I-Illusion essay on this website.

Gregariousness of early-adolescent mice influenced by genetic background

Panskepp et al have studied two inbred mouse strains whose infants on weaning show high versus low levels of gregarious social behavior, They controlled a host of behavioral variables during the course of adolescent development to demonstrate specific differences in social motivations among juveniles of the two mouse strains — behavioral variations that could only be explained by genetic differences. Young mice from the gregarious strain seek environments that predict the possibility of a social encounter and avoid places where they have experienced social isolation. The review by Devitt edited for this post quotes the senior author Lahvis: "There is an association between high-pitched calls in mice and positive experience. The quality and quantity of the call are tightly associated with the nature of the interaction itself."

As the mice neared sexual maturity, the genetic influence on social behavior ebbed and the animals became much more responsive to social cues such as gender...the initial genetic predisposition apparently gets masked by reproductive maturity.
Their work suggests that genetic influences on juvenile social behavior may be quite distinct from genetic factors that affect adult social behavior, a finding the potentially useful for understanding social evolution, as well as developing more realistic animal models of pervasive developmental disorders, such as autism.

Just a nap will do it.....

It doesn't take overnight, Nishida and Walker show that just taking a nap boosts memory consolidation.

Two groups of subjects trained on a motor-skill task using their left hand – a paradigm known to result in overnight plastic changes in the contralateral, right motor cortex. Both groups trained in the morning and were tested 8 hr later, with one group obtaining a 60–90 minute intervening midday nap, while the other group remained awake. At testing, subjects that did not nap showed no significant performance improvement, yet those that did nap expressed a highly significant consolidation enhancement. Within the nap group, the amount of offline improvement showed a significant correlation with the global measure of stage-2 NREM sleep. However, topographical sleep spindle analysis revealed more precise correlations. Specifically, when spindle activity at the central electrode of the non-learning hemisphere (left) was subtracted from that in the learning hemisphere (right), representing the homeostatic difference following learning, strong positive relationships with offline memory improvement emerged–correlations that were not evident for either hemisphere alone.

(Note: sleep spindles are a defining electrophysiological signature of NREM sleep involving short (~1 ) synchronous burst of activity (12–15 Hz) that may represent triggers of synaptic potentiation leading to neural plasticity.)

Legend (click to enlarge figure): Spindle density and offline (nap) memory enhancement. a, Correlations between offline motor memory enhancement and spindle density in the non-learning hemisphere (electrode site C3) and learning hemisphere (electrode site C4) individually. b, Correlations between offline motor memory improvement and the subtracted difference in spindle density between the learning hemisphere versus the non-learning hemisphere (C4–C3).

Pain Mechanisms

Nature Magazine offers a nice free summary poster on pain mechanisms.

Framing Science

I give you in its entirety an essay by Nisbet and Mooney in a recent issue of Science Magazine (Vol. 316. no. 5821, p. 56):

Issues at the intersection of science and politics, such as climate change, evolution, and embryonic stem cell research, receive considerable public attention, which is likely to grow, especially in the United States as the 2008 presidential election heats up. Without misrepresenting scientific information on highly contested issues, scientists must learn to actively "frame" information to make it relevant to different audiences. Some in the scientific community have been receptive to this message (1). However, many scientists retain the well-intentioned belief that, if laypeople better understood technical complexities from news coverage, their viewpoints would be more like scientists', and controversy would subside.

In reality, citizens do not use the news media as scientists assume. Research shows that people are rarely well enough informed or motivated to weigh competing ideas and arguments. Faced with a daily torrent of news, citizens use their value predispositions (such as political or religious beliefs) as perceptual screens, selecting news outlets and Web sites whose outlooks match their own (2). Such screening reduces the choices of what to pay attention to and accept as valid (3).

Frames organize central ideas, defining a controversy to resonate with core values and assumptions. Frames pare down complex issues by giving some aspects greater emphasis. They allow citizens to rapidly identify why an issue matters, who might be responsible, and what should be done (4, 5).

Consider global climate change. With its successive assessment reports summarizing the scientific literature, the United Nations' Intergovernmental Panel on Climate Change has steadily increased its confidence that human-induced greenhouse gas emissions are causing global warming. So if science alone drove public responses, we would expect increasing public confidence in the validity of the science, and decreasing political gridlock.

Despite recent media attention, however, many surveys show major partisan differences on the issue. A Pew survey conducted in January found that 23% of college-educated Republicans think global warming is attributable to human activity, compared with 75% of Democrats (6). Regardless of party affiliation, most Americans rank global warming as less important than over a dozen other issues (6). Much of this reflects the efforts of political operatives and some Republican leaders who have emphasized the frames of either "scientific uncertainty" or "unfair economic burden" (7). In a counter-strategy, environmentalists and some Democratic leaders have framed global warming as a "Pandora's box" of catastrophe; this and news images of polar bears on shrinking ice floes and hurricane devastation have evoked charges of "alarmism" and further battles.

Recently, a coalition of Evangelical leaders have adopted a different strategy, framing the problem of climate change as a matter of religious morality. The business pages tout the economic opportunities from developing innovative technologies for climate change. Complaints about the Bush Administration's interference with communication of climate science have led to a "public accountability" frame that has helped move the issue away from uncertainty to political wrongdoing.

As another example, the scientific theory of evolution has been accepted within the research community for decades. Yet as a debate over "intelligent design" was launched, antievolutionists promoted "scientific uncertainty" and "teach-the-controversy" frames, which scientists countered with science-intensive responses. However, much of the public likely tunes out these technical messages. Instead, frames of "public accountability" that focus on the misuse of tax dollars, "economic development" that highlight the negative repercussions for communities embroiled in evolution battles, and "social progress" that define evolution as a building block for medical advances, are likely to engage broader support.

The evolution issue also highlights another point: Messages must be positive and respect diversity. As the film Flock of Dodos painfully demonstrates, many scientists not only fail to think strategically about how to communicate on evolution, but belittle and insult others' religious beliefs (8).

On the embryonic stem cell issue, by comparison, patient advocates have delivered a focused message to the public, using "social progress" and "economic competitiveness" frames to argue that the research offers hope for millions of Americans. These messages have helped to drive up public support for funding between 2001 and 2005 (9, 10). However, opponents of increased government funding continue to frame the debate around the moral implications of research, arguing that scientists are "playing God" and destroying human life. Ideology and religion can screen out even dominant positive narratives about science, and reaching some segments of the public will remain a challenge (11).

Some readers may consider our proposals too Orwellian, preferring to safely stick to the facts. Yet scientists must realize that facts will be repeatedly misapplied and twisted in direct proportion to their relevance to the political debate and decision-making. In short, as unnatural as it might feel, in many cases, scientists should strategically avoid emphasizing the technical details of science when trying to defend it.

References

1. T. M. Beardsley, Bioscience 56, 7 (2006). www.aibs.org/bioscience-editorials/editorial_2006_07.html.
2. S. L. Popkin, The Reasoning Voter (Univ. of Chicago Press, Chicago, IL, 1991).
3. J. Zaller, Nature and Origins of Mass Opinion (Cambridge Univ. Press, New York, 1992).
4. W. A. Gamson, A. Modigliani, Am. J. Sociol. 95, 1 (1989).
5. V. Price, et al., Public Opin. Q. 69, 179 (2005).
6. Pew Center for the People and the Press (2007); http://pewresearch.org/pubs/282/global-warming-a-divide-on-causes-and-solutions.
7. A. M. McCright, R. E. Dunlap, Soc. Probl. 50, 3 (2003).
8. Film promotion, www.flockofdodos.com/
9. Virginia Commonwealth University Life Sciences Survey (2006); www.vcu.edu/lifesci/images2/ls_survey_2006_report.pdf
10. Pew Center for the People and the Press (2006); http://peoplepress.org/reports/display.php3?ReportID=283.
11. M. C. Nisbet, Int. J. Public Opin. Res. 17 (1), 90 (2005).

Relationships in an e-society: small versus large groups

From the editor's summary of an article in Nature by Palla et al. (PDF here):

The dynamics of social groups as they interact electronically is central to how modern society operates. A study of patterns of information exchange between two groups of individuals — collaborating scientists and cell phone users — has been used to devise an algorithm that relates information exchange to group stability. The data show that small groups have a few strong relationships at their core. And as long as these persist, the clique remains. But for large communities, continuous change is the key to stability. These findings offer a new view on the fundamental differences between the dynamics of small groups and large institutions.

Palla et al.'s abstract:

The rich set of interactions between individuals in society results in complex community structure, capturing highly connected circles of friends, families or professional cliques in a social network. Thanks to frequent changes in the activity and communication patterns of individuals, the associated social and communication network is subject to constant evolution. Our knowledge of the mechanisms governing the underlying community dynamics is limited, but is essential for a deeper understanding of the development and self-optimization of society as a whole. We have developed an algorithm based on clique percolation that allows us to investigate the time dependence of overlapping communities on a large scale, and thus uncover basic relationships characterizing community evolution. Our focus is on networks capturing the collaboration between scientists and the calls between mobile phone users. We find that large groups persist for longer if they are capable of dynamically altering their membership, suggesting that an ability to change the group composition results in better adaptability. The behaviour of small groups displays the opposite tendency—the condition for stability is that their composition remains unchanged. We also show that knowledge of the time commitment of members to a given community can be used for estimating the community's lifetime. These findings offer insight into the fundamental differences between the dynamics of small groups and large institutions.

How pretty faces sell boring products - conditioning our brain's reward system

Bray and O'Doherty's report in the Journal of Neurophysiology illustrates the biology behind the selling power of beautiful models in advertisements for mundane products, and should be of interest to neuro-marketers everywhere. PDF here. Their abstract:

Attractive faces can be considered to be a form of visual reward. Previous imaging studies have reported activity in reward structures including orbitofrontal cortex and nucleus accumbens during presentation of attractive faces. Given that these stimuli appear to act as rewards, we set out to explore whether it was possible to establish conditioning in human subjects by pairing presentation of arbitrary affectively neutral stimuli with subsequent presentation of attractive and unattractive faces. Furthermore, we scanned human subjects with functional magnetic resonance imaging (fMRI) while they underwent this conditioning procedure to determine whether a reward-prediction error signal is engaged during learning with attractive faces as is known to be the case for learning with other types of reward such as juice and money. Subjects showed changes in behavioral ratings to the conditioned stimuli (CS) when comparing post- to preconditioning evaluations, notably for those CSs paired with attractive female faces. We used a simple Rescorla-Wagner learning model to generate a reward-prediction error signal and entered this into a regression analysis with the fMRI data. We found significant prediction error-related activity in the ventral striatum during conditioning with attractive compared with unattractive faces. These findings suggest that an arbitrary stimulus can acquire conditioned value by being paired with pleasant visual stimuli just as with other types of reward such as money or juice. This learning process elicits a reward-prediction error signal in a main target structure of dopamine neurons: the ventral striatum. The findings we describe here may provide insights into the neural mechanisms tapped into by advertisers seeking to influence behavioral preferences by repeatedly exposing consumers to simple associations between products and rewarding visual stimuli such as pretty faces.

Legend - Prediction error related activity in the nucleus accumbens. A: voxels in the nucleus accumbens were significantly activated in a contrast of prediction error signals for attractive faces vs. unattractive faces, voxels in yellow are significant at P <>

MindBlog back in Madison, Wisconsin

Turns out I got back just in time for what is hopefully the last snowstorm of the winter. This reminds me why I was in Ft. Lauderdale for the past five months.....

"Nest" cells in the mouse brain. Category knowledge shown.

An interesting article in PNAS from Lin et al. (PDF here). Their abstract:

As important as memory is to our daily functions, the ability to extract fundamental features and commonalities from various episodic experiences and to then generalize them into abstract concepts is even more crucial for both humans and animals to adapt to novel and complex situations. Here, we report the neural correlates of the abstract concept of nests or beds in mice. Specifically, we find hippocampal neurons that selectively fire or cease to fire when the mouse perceives nests or beds, regardless of their locations and environments. Parametric analyses show that responses of nest cells remain invariant over changes in the nests' physical shape, style, color, odor, or construction materials; rather, their responses are driven by conscious awareness and physical determination of the categorical features that would functionally define nests. Such functionality-based abstraction and generalization of conceptual knowledge, emerging from episodic experiences, suggests that the hippocampus is an intrinsic part of the hierarchical structure for generating concepts and knowledge in the brain.

Here is one figure and one movie from the paper:

Legend - Invariant responses over the geometric shapes, physical appearances, colors, construction materials, etc. (A) Invariant responses of Cell #1 to the geometric shapes of nests. As shown by both the perievent spike rasters and perievent spike histograms, Cell #1 exhibited a significant firing increase in response to a new circular nest made out of the top part of a cardboard coffee cup with a wall height of 2.5 cm and a diameter of 7.5 cm (Left), a square cardboard nest (Center), and a triangular cardboard nest (Right). (B) Invariant responses of Cell #1 to nests made from different materials. A metal nest (Left), plastic nest (Center), and porcelain nest (Right) were tested. (C) The cell also increased its firing when the mouse encountered natural cotton nests (Left and Center) but not to five cotton balls that were simply lumped together (Right). The bin width in the perievent spike histogram is 250 ms.


Click to download Movie 1. Description of movie: "Transient-on" type of nest cell responses and its functionality-based encoding of conceptual knowledge of nests. The first movie segment shows that Cell #1 of mouse-A exhibited "transient-on"-type responses to the home nest but not to another similarly shaped, smaller circular object (water cup). The second movie segment shows that Cell #1 did not respond to the plastic nest that was placed in an inverted manner (so that it would function as a small stage). However, once the plastic nest reverted back to its normal nest position, the cell exhibited robust firing up to 40 Hz. Because it is the same object and placed at the same location, this inversion experiment demonstrates that the nest cell encodes the functionality of the nest rather than merely physical appearances, materials, or spatial location, etc.

Why the rich behave badly... "disinhibition"

Richard Conniff writes an OpEd piece in the 4/4/07 NY Times (PDF here) pointing out the work of UC Berkely psychologist Dacher Keltner and others who study the effect of power on social perception and behavior. Their work suggests that elevated power leads to behavioral disinhibition and reduced vigilance. They find that ideological partisans with power construe their dispute in more stereotypical, polarized fashion, that elevated social status leads to disinhibited social behavior, and that power, whether derived from group status or experimental manipulation, relates to the experience of increased positive emotion and reduced negative emotion.

In what Conniff calls the "Cookie Monster Experiment" (a much milder version of the Stanford Prison Experiment) Keltner:

...took groups of three ordinary volunteers and randomly put one of them in charge. Each trio had a half-hour to work through a boring social survey. Then a researcher came in and left a plateful of precisely five cookies. Care to guess which volunteer typically grabbed an extra cookie? The volunteer who had randomly been assigned the power role was also more likely to eat it with his mouth open, spew crumbs on partners and get cookie detritus on his face and on the table.

It reminded the researchers of powerful people they had known in real life. One of them, for instance, had attended meetings with a magazine mogul who ate raw onions and slugged vodka from the bottle, but failed to share these amuse-bouches with his guests. Another had been through an oral exam for his doctorate at which one faculty member not only picked his ear wax, but held it up to dandle lovingly in the light.

Keltner theorizes:

...that getting power causes people to focus so keenly on the potential rewards, like money, sex, public acclaim or an extra chocolate-chip cookie — not necessarily in that order, or frankly, any order at all, but preferably all at once — that they become oblivious to the people around them.

Indeed, the people around them may abet this process, since they are often subordinates intent on keeping the boss happy. So for the boss, it starts to look like a world in which the traffic lights are always green (and damn the pedestrians). Professor Keltner and his fellow researchers describe it as an instance of “approach/inhibition theory” in action: As power increases, it fires up the behavioral approach system and shuts down behavioral inhibition.

Rapid memory consolidation shown...

Memory encoding occurs rapidly, and requires the hippocampus, but the consolidation of memory in the neocortex has long been held to be a more gradual process. Tse et al now show in experiments with rats learning the position of new treats placed in a maze:

...that systems consolidation can occur extremely quickly if an associative "schema" into which new information is incorporated has previously been created. In experiments using a hippocampal-dependent paired-associate task for rats, the memory of flavor-place associations became persistent over time as a putative neocortical schema gradually developed. New traces, trained for only one trial, then became assimilated and rapidly hippocampal-independent. Schemas also played a causal role in the creation of lasting associative memory representations during one-trial learning. The concept of neocortical schemas may unite psychological accounts of knowledge structures with neurobiological theories of systems memory consolidation. (PDF here)

And, from Larry Squire's perspective article on this paper (PDF here):

Legend. (click on figure to enlarge) When a rat learns associations between flavors and spatial locations, as studied by Tse et al. (1), the associations are initially learned as individual facts (left). With extended training, the animal develops an organized structure or schema for flavors and places (middle). This organized knowledge structure (bold lines) can then support rapid learning of new associations in a single trial and the rapid consolidation of information into the neocortex (right).

Do animals experience past and future?

Carl Zimmer writes a nice piece in the 4/3 NYTimes on "Time in the Animal Mind" (PDF HERE).

Legend: Scrub jays, left, seem able to plan for the future in experiments, hiding today’s pine nuts for tomorrow’s breakfast. Squirrel monkeys also seem to think about future consequences, while hummingbirds seem to recall time and location of visits to flowers, and rats to remember where they encountered food in a maze. (Credits: from left, Adam Jones/Photo Researchers; Luke MacGregor/Reuters; Esteban Felix/Associated Press; Will & Deni McIntyre/Photo Researchers)

The animals shown in the figure have been shown to have impressive powers of memory, but this doesn't have to imply having a sense of memory or self, i.e. 'thinking about' past or future.

Some argue that mental time travel is distinctive to hominids. Humans can remember events long past and envision the future, and recent experiments by Schacter's lab at Harvard have shown that brain areas involved in episodic memory become active also when people think of themselves in the future.

What about animal's sense of the future? Can they plan ahead? Nicola, Univ. of Cambridge, has done interesting experiments showing sophisticated memory in scrub jays, and she

"recently tested her scrub jays for foresight. She and her colleagues put the birds in three adjoining compartments for six days. Each morning the birds were shut for two hours in one of two rooms. In one room they got nothing to eat. In the other room, they got powdered pine nuts (the scrub jays can eat the powder, but they cannot cache it). For the rest of the day, each bird could move around all three rooms and enjoy more powdered nuts.

On the seventh day, the scientists switched the powdered pine nuts with real ones. If the birds were so inclined, they could cache the pine nuts in ice cube trays the scientists put in the two morning rooms. “If I’m a bird, what I could do is take some of the provisions and hide it in there so that if I do wake up there in the morning, I can get my own breakfast,” Dr. Clayton said.

Dr. Clayton found that the birds put over three times more pine nuts in the no-breakfast room than in the breakfast room. She argues that the results mean that birds can take action for their future needs, knowing what they’ll need and where they’ll need it."

This and similar experiments in other animals may over the next few years provide more compelling evidence that animals do plan ahead, and thus take away yet another feature that many have thought distinctive to humans.

Body Ritual among the Nacirema

This is a hoot!

Savant Autism - part 1

I thought this two part sequence on autism was worth passing on....

Savant Autism - part 2

MindBlog leaves 'paradise'

Postings may become erratic or non-existent for several days as I leave my snowbird site, Fort Lauderdale, and drive back to Madison Wisconsin on Monday, April 9.

This is what I leave behind: The beach and the condo:

Motor cortex for the hand and numerical counting

The April 2007 issue of the Journal of Cognitive Neuroscience has interesting articles on this topic by Andres et al. and Sato et al. Their abstracts:

Andres et al.

The finding that number processing activates a cortical network partly overlapping that recruited for hand movements has renewed interest in the relationship between number and finger representations. Further evidence about a possible link between fingers and numbers comes from developmental studies showing that finger movements play a crucial role in learning counting. However, increased activity in hand motor circuits during counting may unveil unspecific processes, such as shifting attention, reciting number names, or matching items with a number name. To address this issue, we used transcranial magnetic stimulation to measure changes in corticospinal (CS) excitability during a counting task performed silently and using either numbers or letters of the alphabet to enumerate items. We found an increased CS excitability of hand muscles during the counting task, irrespective of the use of numbers or letters, whereas it was unchanged in arm and foot muscles. Control tasks allowed us to rule out a possible influence of attention allocation or covert speech on CS excitability increase of hand muscles during counting. The present results support a specific involvement of hand motor circuits in counting because no CS changes were found in arm and foot muscles during the same task. However, the contribution of hand motor areas is not exclusively related to number processing because an increase in CS excitability was also found when letters were used to enumerate items. This finding suggests that hand motor circuits are involved whenever items have to be put in correspondence with the elements of any ordered series.

Sato et al.

Developmental and cross-cultural studies show that finger counting represents one of the basic number learning strategies. However, despite the ubiquity of such an embodied strategy, the issue of whether there is a neural link between numbers and fingers in adult, literate individuals remains debated. Here, we used transcranial magnetic stimulation to study changes of excitability of hand muscles of individuals performing a visual parity judgment task, a task not requiring counting, on Arabic numerals from 1 to 9. Although no modulation was observed for the left hand muscles, an increase in amplitude of motor-evoked potentials was found for the right hand muscles. This increase was specific for smaller numbers (1 to 4) as compared to larger numbers (6 to 9). These findings indicate a close relationship between hand/finger and numerical representations.

Creation Science