My brain and my ACL

My life, though generally fortunate, has been peppered by a small number of somewhat serious injuries: broken hand, broken collarbone, broken wrist, torn meniscus, ruptured anterior cruciate ligament (ACL). The hand and collarbone were consequences of my big sister tripping and crushing me, respectively, but the rest I managed to accrue on my own. (Even though I sustained these latter injuries on the soccer field, I was unaccompanied by the touch of another player).

My mom always insisted that my proclivity for injury was due to the intrinsic grace of my bones and joints—"elegant and delicate, like a bird!"—but a recent study in the June edition of the American Journal of Sports Medicine suggests something different is to blame: my brain.

From the University of Delaware News:

A torn anterior cruciate ligament (ACL) is among an athlete's most-dreaded injuries, often requiring surgery and months of rehab, as has been the case with Philadelphia Eagles quarterback Donovan McNabb. While being tackled in football or hurtling into an embankment on an icy ski course can tear this major knee ligament, most athletes actually “do themselves in”--they don't collide with a person or object, they end up injuring themselves when they land off-balance during a jump or run.

“We had some data from previous research which suggested that these noncontact knee injuries occur when a person gets distracted or is 'caught off guard,'“ Charles Buz Swanik, the UD assistant professor of health sciences who led the study, said. These awkward movements have the biomechanical appearance of a knee buckling, but can be reproduced safely in the lab to study how people mentally prepare and react to unanticipated events.

Based on my personal experiences, the connection between sport-induced injury and distraction is not surprising. Both my wrist and my ACL/meniscus injuries (the latter being a simultaneous double-whammy) occurred while I wasn't particularly focused on the games. In both situations, I was slightly anxious because these were the only two soccer games my dad had attended since I was 10 (one in high school (wrist), one in college (knee)). Further, I was not involved in the plays that immediately preceded my injuries; it was precisely when ball unexpectedly approached, summoning my mildly reluctant participation, that my "delicate" limbs met with disaster.

But Swanik believes these momentary lapses in attention are indicative of more extensive deficiencies.

“This made me wonder if we could measure whether these individuals had different mental characteristics that made them injury-prone,” Swanik said.

To identify subjects for their study, the researchers administered neurocognitive tests to nearly 1,500 athletes at 18 universities during the preseason. This testing also provided baseline data for athletes who might sustain a concussion after the season started, Swanik said.

Visual memory, verbal memory, processing speed, and reaction time all were assessed.

...

In analyzing the data, the scientists found that the athletes who ended up with noncontact ACL injuries demonstrated significantly slower reaction time and processing speed and performed worse on visual and verbal memory tests when compared to the control group.

As Swanik writes in his report, "physical activity requires situational awareness of a broad attentional field to continuously monitor the surrounding environment, filter irrelevant information, and simultaneously execute complex motor programs. Increased arousal or anxiety changes an athlete's concentration, narrows their attentional field, and alters muscle activity, which has been associated with poor coordination and inferior performance."

These conclusions remind me of one of David Foster Wallace's essays in Consider the Lobster, "How Tracy Austin Broke My Heart." Wallace devotes this essay to the devastating contrast between Tracy Austin's brilliance on the tennis court (both physical and mental) and her abominable ability to intellectualize her experiences in her memoir. He ultimately concludes that the vacuity and lack of insight of sports memoirs, such as hers, is inextricably linked to the qualities that lead to great athletes in the first place.

Their ability to maintain exceptional focus under the scrutiny of thousands of viewers (including their parents), makes them incapable of an appreciation of their athletic genius, and thus of significant insight into its nature. During games that are crucial to the careers to which they have been devoted since childhood, they manage to "invoke for themselves a cliché as trite as 'One ball at a time' or 'Gotta concentrate here,' and mean it and then do it." Meanwhile, if the rest of us were under such circumstances, we would founder and crumple and fail precisely because we think too much about matters that have nothing to do with the direction and velocity of the ball, or the appropriate bending of the knee during complicated, high-velocity movements.

As Wallace writes, "those who receive and act out the gift of athletic genius must, perforce, be blind and dumb about it—and not because blindness and dumbness are the price of the gift, but because they are its essence." (Their vastly superior speed, strength, and visual acuity probably isn't trivial).

Another major risk factor for ACL injuries is gender. Girls are four to eight times more likely to tear or rupture their ACLs than men, with female soccer and basketball players at the highest risk. There are a few theories as to why this gender difference exists: 1) bone alignment of the pelvis/femur/tibia create excess stress on the ACL; 2) female hormones relax ligaments, muscles and joints, making joints more flexible and prone to injury; 3) as girls pass through adolescence, their muscular control of the knee may not keep up with their skeletal growth.

To incorporate Swanik's conclusion with the gender discrepancy, female hormones can also result in concentration deficits, which may result in a sub-optimal state of arousal in a given athletic situation. In any case, this study has interesting implications for injury prevention. Not only should female athletes stop running like girls, but perhaps cognitive exercises that train processing speed and reaction time may also benefit the accident prone.

Humans to the rescue

Images like the one above are familiar to any of us who have ever used webmail, Ticketmaster, or any other web service that wants to prevent automated spammers and scalpers from exploiting their systems. The distorted, fuzzy letters don't provide a challenge to humans, but are indecipherable to the most sophisticated computer algorithms. Our genius is facilitated by our "invariant" perceptual abilities; that is, we can recognize objects, faces, and letters independent of rotation, translation, and scale.

However, these CAPTCHAs (Completely Automated Public Turing Test to Tell Computers and Humans Apart) were designed with a wonderfully clever ulterior motive. In addition to preventing rogue bots from devastating our virtual lives, CAPTCHAs like the one above are actually exploiting you, the human, and the invariance of your human perception, to help digitize the world. The words presented in these CAPTCHAs are pulled from the book-scanning project of the Internet Archive, which aims to scan millions of public-domain books and put them online for free. One word of the CAPTCHA is known to the computer, and is used to verify your humanness, while the other was indecipherable to the Archive's scanners. When you type in that word, you're actually translating the image into text for the Archive.

There's a fantastic article in Wired Magazine about this type of "human computation," "the art of using massive groups of networked human minds to solve problems that computers cannot." The article profiles the work of Luis von Ahn, who designs clever ways to harness the powerful brains of bored web surfers to solve computing problems (e.g. judging random pictures as "pretty," tagging images and audioclips, etc.)

From Wired Magazine:

If people could so easily recognize pictures of letters and numbers, could [they] use this ability to identify and label the vast number of images on the Web?

...

The way to do it, he realized, was as a game. It would pull images off the Web, then randomly pair two players from around the world. They would be shown the same images, then each would type in as many words as they could to describe those images, hoping to hit upon the same ones as their anonymous partner. They'd get 50 points for each match, and two and a half minutes to earn as many points as possible. Von Ahn suspected that whenever the players agreed on a word — "meadow" to describe a tree-lined clearing, for example — they would be choosing a highly accurate label for the picture.

Von Ahn cobbled the game together in a week — "crappy, totally terrible code," he admits — and threw it online. He dubbed it The ESP Game and emailed the URL to a few friends. Within days it was Slashdotted, whereupon his server nearly crashed under the load of new players. Astonished, von Ahn watched for the next four months as 13,000 players produced 1.3 million labels for some 300,000 images — with a few hardcore fans clocking more than 50 hours of play. "It's like crack," as one player complained in an email to von Ahn. The labels his players generated were far more accurate than what other image-search technologies produced. Most search engines are limited to sniffing out words associated with a picture, such as the name given to the image, words in the page around it, or links pointing to it. That's inherently imprecise: When von Ahn recently searched for "dog" on Google, a third of the pictures showed no dogs at all. When he queried the ESP database, almost all the results contained canines. Better yet, players often generated labels that were subtle and nuanced. A search for "funny" found a picture of Ronald McDonald being hauled away by police and one of Queen Elizabeth picking her nose.

Even the DHS wants to employ your brainpower as you procrastinate on the web:

This spring, von Ahn got a call from the Department of Homeland Security. He went to Washington to meet with DHS officials, and together they devised a game in which people are challenged to find dangerous objects in images of x-rayed baggage. The pictures would be fed from airport scanners, and players would act as a second set of eyes for overtaxed security employees. If enough players noticed something amiss, an alert would be triggered.

Von Ahn's other games that capitalize on human superiority (supposedly available at Games with a Purpose "in July," but as of now the site isn't running yet) include:

1) Matchin' Players are shown the same pair of images, then each tries to pick the one they'll both agree is more attractive. Creates a database of images searchable by aesthetic value, a task no algorithm can perform.

2) Babble Two English-speaking players are shown a sentence in a foreign language that neither of them speak. A list of possible English meanings appears below each word. Players try to agree upon a set of English words that forms the most coherent sentence. Translates foreign text into English without requiring anyone fluent in both languages.

3) InTune Players listen to the same audioclip and then try to come up with the same phrase to characterize it. Tags sounds with searchable descriptive text.

4) Squigl Two players are shown the same picture and a word describing an element within the image (e.g., a picture of a dog and the word "leash"). They each draw a border around the element. Produces a set of pictures with their internal components tagged — terrific for very specific image searches.

5) Verbosity One player is given a word, and the other tries to guess that word by completing phrases such as "It is near a ____" or "It is a type of ____." The first player answers "true" or "false" but can't use the word itself. Creates a database of commonsense knowledge describing the objects.

Link to the full Wired article.

New and improved robot CPGs

In my first post ever, I discussed how specialized circuits in the spinal cord (called "central pattern generators," or CPGs) coordinate the intricate motions and muscle patterns involved in running and walking, without significant input from the brain. The autonomy of these circuits allows animals to run and walk while their mental efforts are otherwise engaged; for example, we can talk on the phone while walking to dinner, and decapitated chickens can still run away.

One of the most important features of CPGs is their adaptability. Whether running through a forest, walking on an oily surface, or dribbling a soccer ball, we need to continuously modify our movements. Thus, as opposed to generating rigid action patterns, CPGs provide a flexible template for coordinating our muscles and various joints. This template interacts with sensory information, allowing us to elegantly adapt to our unpredictable world. Flexibility, however, poses a challenging computational problem; not only must we decipher how circuits of neurons coordinate hundreds of muscles, but also how their output can be refined by incoming sensory information.

Without understanding these fundamental issues, it is difficult to produce machines that can move as intelligently as we. Honda's ASIMO, "The World's Most Advanced Humanoid Robot," is capable of executing an astounding range of human-like movements (running, walking smoothly, reaching for objects), but has previously stumbled and fallen down stairs. A recent article in PLoS Computational Biology describes a new and improved droid named RunBot, which is capable of adapting to unfamiliar terrain in an animal-like way.

Although not nearly as cute as ASIMO, RunBot's motor circuitry is more "intelligent" (i.e. more human). As I mentioned in my earlier post, the motor system is arranged in a hierarchy: the "higher" control centers give the signal to initiate a movement, recruiting the "lower" CPGs to take care of the details. These lower circuits respond to the environment reflexively, incorporating localized feedback to generate intricate adjustments in muscle tone. This responsiveness allows us to immediately compensate for small perturbations, such as unnoticed rocks on a trail. When we need to significantly modify our gait, however, such as stepping over a baby, we must enlist the higher centers, which will generate more dramatic modifications to the CPGs.

ASIMO lacks this hierarchy, requiring it to continuously calculate the position and motion of every joint. RunBot, however, has been engineered with several levels of control, allowing it to adapt to changes in terrain in a more computationally efficient manner. RunBot interprets the environment with an infrared sensor, which communicates with the lower circuits to regulate their activity. Thus, when RunBot encounters an alteration to its terrain and becomes unbalanced, this sensor modifies the pattern of the lower circuits, allowing the bot to change its gait.

However, like humans, RunBot must learn how to modify its movements with respect to sensory input. When we learn how to walk, our brains "train" our CPGs until they can execute the movement relatively independently. These same mechanisms come into play when a runner learns to hurdle or a soccer player learns a new move; these behaviors initially require significant concentration, but with practice can be executed with little mental effort. To replicate this learning process, RunBot's circuitry includes, according to the authors, "online learning mechanisms based on simulated synaptic plasticity." Thus, when RunBot first attempts to climb a slope, it falls over like poor ASIMO. With trial and error, however, its circuitry learns to properly compensate for the relevant sensory input, shortening and slowing its steps just like a human.

Why are blondes more attractive than brunettes?

As a young brown-eyed, brown-haired girl growing up in Orange County, CA, I found this "stereotype" repeatedly, bewilderingly, validated. Although I defended myself with Van Morrison and a sizeable artillery of blonde-jokes, behind my façade of self-assurance I continued to wonder: why are blonde hair and blue eyes "prettier"? Now, as a slightly more mature brunette with a more comprehensive understanding of natural selection, I still find the question intriguing. Why did Europeans evolve to prefer blonde hair and blue eyes? What do these features indicate about health and fertility?

Psychology Today has an excerpt from the book Why Beautiful People Have More Daughters, by Alan S. Miller and Satoshi Kanazawa, which explores "Ten Politically Incorrect Truths About Human Nature," including the mystery of the "blonde bombshell":

Long before TV—in 15th- and 16th- century Italy, and possibly two millennia ago—women were dying their hair blond. Women's desire to look like Barbie—young with small waist, large breasts, long blond hair, and blue eyes—is a direct, realistic, and sensible response to the desire of men to mate with women who look like her. There is evolutionary logic behind each of these features.

Blond hair is unique in that it changes dramatically with age. Typically, young girls with light blond hair become women with brown hair. Thus, men who prefer to mate with blond women are unconsciously attempting to mate with younger (and hence, on average, healthier and more fecund) women. It is no coincidence that blond hair evolved in Scandinavia and northern Europe, probably as an alternative means for women to advertise their youth, as their bodies were concealed under heavy clothing.

Women with blue eyes should not be any different from those with green or brown eyes. Yet preference for blue eyes seems both universal and undeniable—in males as well as females. One explanation is that the human pupil dilates when an individual is exposed to something that she likes. For instance, the pupils of women and infants (but not men) spontaneously dilate when they see babies. Pupil dilation is an honest indicator of interest and attraction. And the size of the pupil is easiest to determine in blue eyes. Blue-eyed people are considered attractive as potential mates because it is easiest to determine whether they are interested in us or not.

The irony is that none of the above is true any longer. Through face-lifts, wigs, liposuction, surgical breast augmentation, hair dye, and color contact lenses, any woman, regardless of age, can have many of the key features that define ideal female beauty. And men fall for them. Men can cognitively understand that many blond women with firm, large breasts are not actually 15 years old, but they still find them attractive because their evolved psychological mechanisms are fooled by modern inventions that did not exist in the ancestral environment.

The article also explains why men prefer women with small waists and large breasts (both are correlated with levels of estrogen and progesterone, indicating greater fecundity), why beautiful people have more daughters (physical attractiveness is more important for girls than boys, and parents can bias the sex ratio depending on the traits they can offer), why men sexually harass women (it's about respect), and why most suicide bombers are Muslim (the 72 virgins waiting patiently in heaven aren't trivial). Some of the hypotheses are a little dubious to me, but it's an interesting read nonetheless.

Link to the article.

Williams Syndrome and human sociality

There's a great article by David Dobbs in the New York Times Magazine about Williams Syndrome (WMS), a condition with a diverse and remarkable array of cognitive symptoms. I have vivid memories of my first exposure to WMS--watching a documentary hosted by Oliver Sacks for my "Psychology of Music" class. In one of the first scenes, Dr. Sacks introduces himself to a 6-year old girl with WMS, who eagerly and cheerfully insists "Don't be shy, Mr. Sacks." In another scene he takes her to a sandwich shop, where she enthusiastically engages the employees and fellow customers in conversation, offering hugs to all within reach. This behavior exemplifies one of the most remarkable endowments of children with WMS--endearing, socially fearless personalities, marked by extreme gregariousness and emotional empathy.

This charm is facilitated by a peculiarly rich vocabulary and proficiency with language; for example, when asked to name some animals, a WMS child responded "Brontosaurus, tyranadon, brontasaurus rex, dinosaurs, elephant, dog, cat, lion, baby hippopotamus, ibex, whale, bull, yak, zebra, puppy, kitten, tiger, koala, dragon..." quickly and fluidly naming exotic (though occasionally non-existent) animals as if reading them off a list. When striking conversations with strangers, they are extremely loquacious, to the point where they appear to burden the listener with verbosity.

Adding to the list of aptitudes of WMS people is a great affinity for music (hence learning about the condition in my "Psychology of Music" class). People with WMS can have savantlike musical skills, and those without notable musical gifts nevertheless feel "drawn" to music, an inclination likely aided by an acute sensitivity to sound. One scene of the documentary featured WMS children walking through the woods, commenting on how loud the bees and rustling leaves were (sounds which were more or less unnoticed by Sacks).

These remarkable virtuosities with language, social interaction, and music are accompanied, however, by profound cognitive impairments. The average IQ of a person with WMS is in the 60's, and the vast majority cannot live independently. Despite their seeming fluency with verbal communication, people with WMS have poor language comprenension, incapable of understanding the underlying meaning of most conversations. Their communication, though voluminous, lacks depth and subtlety, and rarely goes beyond "small talk."

This intriguing disconnect pervades social interactions beyond spoken language; in spite of their gregariousness, people with WMS often fail to grasp social cues, including facial expression and body language. Moreover, the extreme geniality of WMS people is indicative of an underlying problem: a complete lack of social fear. According to the article, "functional brain scans have shown that the brain’s main fear processor, the amygdala, which in most of us shows heightened activity when we see angry or worried faces, shows no reaction when a person with Williams views such faces. It’s as if they see all faces as friendly."

Children with WMS also have significant deficiencies in spatial processing and dealing with numbers. In another memorable scene from the documentary, Sacks presents the child with a plate of muffins, asking her how many she thought were on the plate. "3," she immediately and eagerly replied. There were clearly over 10. When then asked to make a + shape out of four rectangular pieces, she arranged them haphazardly, seemingly at random, at which point she cheerfully announced "Done!"

WMS thus provides a captivating mélange of cognitive strengths and weaknesses. Unlike most forms of mental retardation, in which most or all cognitive abilities are concurrently impaired, the distinct peaks and valleys of aptitudes in WMS allows a dissociation between specific abilities and "general intelligence." Further, the genetic basis of WMS is known: it arises from a deletion of ~28 known genes from chromosome 7. Thus, WMS offers a tantalizing opportunity to understand the genetic influences on complex brain functions, which I plan to explore in a future post.

This post, however, was inspired by a separate, equally captivating story woven by the WMS condition: the implications for human social behavior. Why, despite their affability and charm, do WMS people find it hopelessly difficult to make friends? According to Dobbs, this paradox "makes clear that while we are innately driven to connect with others, this affiliative drive alone will not win this connection. To bond with others we must show not just charm but sophisticated cognitive skills."

So why is it that all our relationships, even casual friendships, demand intelligence? Why was it so difficult to believe that Jenny would marry Forrest Gump? The article broaches two related and overlapping evolutionary theories, the "social brain" theory and the "Machiavellian-intelligence" theory. These theories propose, respectively, that humans evolved large brains to generate complex social relationships, and that deception and manipulation (and the ability to identify these two behaviors) are necessary to successfully compete amongst other members of society. Thus, as Steven Pinker suggests in The Language Instinct, "human evolution was propelled more by a cognitive arms race among social competitors than by mastery of technology and the physical environment."

Social life presents a convoluted tension, involving (as stated by Ralph Adolphs and quoted by Dobbs), a “complex and dynamic interplay between two opposing factors: on the one hand, groups can provide better security from predators, better mate choice and more reliable food; on the other hand, mates and food are available also to competitors from within the group.” Thus, our survival is contingent on a delicate balance between getting along with others and outperforming them. Requisite for maintaining this balance is a comprehensive understanding of subtle and complicated social dynamics, enabling both manipulation and the detection of manipulation by others. Dobbs writes that:

"People with Williams, however, don’t do this so well. Generating and detecting deception and veiled meaning requires not just the recognition that people can be bad but a certain level of cognitive power that people with Williams typically lack. In particular it requires what psychologists call “theory of mind,” which is a clear concept of what another person is thinking and the recognition that the other person a) may see the world differently than you do and b) may actually be thinking something different from what he’s saying.

...it’s clear that Williamses do not generally sniff out the sorts of hidden meanings and intentions that lie behind so much human behavior."

The article concludes with a fascinating question about being human: is our social behavior driven more by the urge to connect or the urge to manipulate the connection? Are we trying to make friends, or do we only care about being genetically more successful than our peers?

"We dominate the planet because we can think abstractly, accumulate and relay knowledge and manipulate the environment and one another. By this light our social behavior rises more from big brains than from big hearts.

...

The disassociation of so many elements in Williams — the cognitive from the connective, social fear from nonsocial fear, the tension between the drive to affiliate and the drive to manipulate — highlights how vital these elements are and, in most of us, how delicately, critically entwined. Yet these splits in Williams also clarify which, of caring and comprehension, offers the more vital contribution. For if Williams confers disadvantage by granting more care than comprehension, reversing this imbalance creates a far more problematic phenotype.

As Robert Sapolsky of the Stanford School of Medicine puts it: “Williams have great interest but little competence. But what about a person who has competence but no warmth, desire or empathy? That’s a sociopath. Sociopaths have great theory of mind. But they couldn’t care less.”"

Link to the NYTM article.

Babies: cheating bastards

From The Globe and Mail:

Babies aren't as innocent as they look, according to new research out of the United Kingdom.

Sweet little infants actually learn to deceive before they can talk, says University of Portsmouth psychology department head Vasudevi Reddy in a study that challenges traditional notions of innocence while confirming many parents' suspicions about their sneaky babies.

Most psychologists have believed that children cannot really lie until about four years of age. But after dozens of interviews with parents, and years spent observing children, Dr. Reddy has determined that infants as young as seven months are quite skilled at pulling the wool over their parents' eyes.

Fake crying and laughing are the earliest and most common forms of deception, but as babies continue to develop their skills of subterfuge, they become far more calculating.

There was the 11-month-old who, caught in the act of reaching for the forbidden soil of a house plant, quickly turned his outstretched hand into a wave, his mother reported to Dr. Reddy, "as though he was saying, 'Oh, I wasn't really going to touch the soil, Mom, I was waving at you.' "

Babies also seem to think they are masters of the Jedi mind trick, using steady eye contact as a distraction technique. Another 11-month-old, upon being presented with toast she didn't want to eat, would hold eye contact with her mother while discreetly chucking the toast onto the floor.

"She's very sneaky," the mother told Dr. Reddy, "she thinks you can't see it."

Via OmniBrain.

Sexy neurogenesis

Animal communication is wonderfully diverse, ranging from the dance of a bee, to written language, to a dog urinating on a tree. For many (all?) animal species, the majority of animal communication is strategically targeted with one goal in mind: sex. Most species lack our oratory competence, yet seem to be procreating rather successfully, able to wordlessly identify and attract mates with desirable genetic backgrounds.

Although sight and sound dominate human communication, many animals use smell to exchange information, able to convey age, social status, sexual receptivity, gender, and health with the chemicals released by their bodies. In fact, many species can recognize individuals by their olfactory "signature" alone, allowing, for example, a mother to recognize her young, and preventing siblings from mating with each other.

This type of communication is mediated, in part, by poorly understood chemicals called pheromones. Mammalian pheromones can elicit immediate behavioral responses, such as aggression (when a male mouse detects the urine of another male mouse) or sexual behavior (when a female mouse detects the same). Of course, the behavioral effects of pheromones are context-dependent; in fact, the fiercest, most aggressive mouse fights I’ve ever witnessed arise when lactating females catch a whiff of a novel male mouse, upon which she unleashes a bloody, ferocious attack on his genitals.

Mammalian pheromones can also elicit long-lasting effects that alter the physiological state of the animal. For example, the detection of male pheromones by a juvenile female mouse may result in an advance in the onset of puberty. If, however, a pregnant female mouse detects the pheromones of a novel male mouse (e.g. one who has dueled and defeated her current suitor and the “father” of her embryos), she will terminate her pregnancy. The latter is an act of mercy--if she did not abort her pups, the male mouse would have killed them upon birth, ensuring that his chosen mate devotes her time and efforts solely to his genetic material.

Crucial to these pheromone-elicited behaviors is the ability to recognize and discriminate between pheromones. Such social recognition thus requires olfactory memories; just as the evanescent taste of a madeleine cookie evokes the Belle Époque world of Proust’s childhood, a female mouse can associate the scent and taste of a “special” male mouse’s urine with the protection he offers her and her pups. Such olfactory memories may require not only the olfactory bulb (the neural structure involved in perceiving odors), but also the hippocampus (a structure crucial for certain types of memory formation).

These structures happen to be the two primary locations where new neurons continue to be born into adulthood (a process called adult neurogenesis). Since I began research on adult neurogenesis, I have been captivated by the myriad of factors (e.g. running, stress, pregnancy, cognitive stimulation, a multitude of drugs…) that affect the birth, survival, and functionality of new neurons. Given that such modulation must be functionally advantageous, this plasticity has fascinating implications for the evolution of adult neurogenesis, as well as the impact these neurons may have on neural circuits and behaviors.

One matter that has always intrigued me is that the modulators of neurogenesis affect either hippocampal or olfactory bulb neurogenesis, but not both. Thus, I was excited to see an advance online publication in Nature Neuroscience that sought to link neurogenesis in both structures to mating behavior. The research, performed by Sam Weiss at the University of Calgary, focused on female mice, and the olfactory memories endowing them with the ability to identify and select prospective mates.

The researchers found that week-long exposure to male mouse urine simultaneously increased the birth of new neurons in the hippocampus and a region called the subventricular zone (SVZ, the birthplace of neurons destined for the olfactory bulb). Congruent with female preference for powerful men, this response was specific for the urine of dominant males; exposure to urine of subordinate did not result in enhanced neurogenesis.

Two weeks after exposure to either dominant or subordinate male urine, the females were placed in a test cage, in which they could smell and see, but not contact, both the dominant and subordinate male. Females primed with the dominant male pheromones had a preference for the dominant male (determined by quantification of “sniffing time”), whereas females exposed to the subordinate male did not show a preference. When neurogenesis was inhibited by a chemical treatment, however, the females did not show a preference regardless of the male with which she was "primed," implicating that male pheromone-induced neurogenesis was necessary for olfactory recognition and/or discrimination.

The results imply that the exposure to a dominant male may provide the impetus for a female to form a new olfactory memory, mediated by the birth of new neurons. Her olfactory system, constantly barraged with olfactory signals, lies in wait for a whiff of something enchanting and unique, which calls it to attention and prompts it to take action. These specialized olfactory memories allow her to distinguish the males with the greatest genetic gifts from the undesirables.