Science by machine....

Two rather amazing papers in Science on automating scientific discovery describe a computer program that can sift raw and imperfect data to uncover fundamental laws of nature and a robot that can not only devise a hypothesis but can also run and analyze experiments to test the hypothesis. One wonders how soon old-fashioned bench scientists like myself will become obsolete.

Schmidt and Lipson use genetic programming that starts with random guesses at a solution and then employs an evolution-inspired algorithm to shuffle and change pieces of the equations until it finds a solution that works. They demonstrate their approach:

...by automatically searching motion-tracking data captured from various physical systems, ranging from simple harmonic oscillators to chaotic double-pendula. Without any prior knowledge about physics, kinematics, or geometry, the algorithm discovered Hamiltonians, Lagrangians, and other laws of geometric and momentum conservation. The discovery rate accelerated as laws found for simpler systems were used to bootstrap explanations for more complex systems, gradually uncovering the "alphabet" used to describe those systems.

King et al. constructed a robot scientist named Adam that used artificial intelligence to come up with a hypothesis about genes in baker’s yeast and the enzymes produced by the genes. It then designed and ran experiments to test its hypothesis. Using the results, it revised its hypothesis and ran more experiments before arriving at its conclusions. From their abstract:

Adam has autonomously generated functional genomics hypotheses about the yeast Saccharomyces cerevisiae and experimentally tested these hypotheses by using laboratory automation. We have confirmed Adam's conclusions through manual experiments. To describe Adam's research, we have developed an ontology and logical language. The resulting formalization involves over 10,000 different research units in a nested treelike structure, 10 levels deep, that relates the 6.6 million biomass measurements to their logical description. This formalization describes how a machine contributed to scientific knowledge.

Pride

Benedict Carey summarizes work showing that that pride, in ways that are not obvious, is centrally important not just for surviving physical danger but for thriving in difficult social circumstances. A few edited clips:

As with the laid-off lawyer, who’s commuting in every day after getting dressed up — to his Starbucks, networks, and meets with colleagues...The fine art of keeping up appearances may seem shallow and deceitful, the very embodiment of denial... but to the extent that it sustains good habits and reflects personal pride, this kind of play-acting can be an extremely effective social strategy, especially in uncertain times.

...the expressions associated with pride in Western society — most commonly a slight smile and head tilt, with hands on the hips or raised high — are nearly identical across cultures. Children first experience pride about age 2 ½, studies suggest, and recognize it by age 4...It’s not a simple matter of imitation, analyses of spontaneous responses to winning or losing a judo match during the 2004 Olympic and Paralympic games found that expressions of pride after a victory were similar for athletes from 37 nations, including for 53 blind competitors, many of them blind from birth...people tend to associate an expression of pride with high status — even when they know that the person wearing it is low on the ladder. In one study, participants impulsively assigned higher status to a prideful water boy than to a team captain who looked ashamed.

A feeling of pride, when it’s convincing, acts something like an emotional magnet.(See my March 24 post). Participants in experiments who have had their sense of pride artificially and unconsciously manipulated are perceived by other participants as more dominant and likable.

...wearing a sad or happy face can have a top-down effect on how a person feels: Smile and you may feel fleetingly happier. The same most likely is true for an expression of pride...Pride, in short, begets perseverance. All of which may explain why, when the repo man is at the door, people so often remind themselves that they still have theirs, and that it’s worth something. Because they do, and because it is...However much pride may go before a fall, it may be far more useful after one.

Sleeping to reset overstimulated brain connections

Here are a few slightly edited clips from Greg Miller's review of two papers and fragments of the paper abstracts. In fruit flies, as surely will also be shown for us humans, sleep is needed for brain connections (synapses) to let go of all the garbage they have accumulated during the day:

Cirelli, Tononi, and postdoc Giorgio Gilestro report that depriving flies of sleep, either by periodically shaking the vials they call home or by forcing individual male flies to cohabitate with an unwelcome stranger (a male from another fly strain), resulted in higher levels of several synaptic proteins throughout the brain. Levels of these proteins, which included components of the transmitting and receiving sides of the synapse as well as proteins involved in neurotransmitter release, declined after flies had a chance to sleep. This pattern held up even when flies slept at odd hours, confirming that the proteins fluctuate with the sleep-wake cycle, not the time of day...The decrease of synaptic markers during sleep was progressive, and sleep was necessary for their decline. Thus, sleep may be involved in maintaining synaptic homeostasis altered by waking activities.

Donlea et al. find that disrupting any one of three genes, including period, an integral component of the circadian clock, prevents flies from sleeping longer after a socially stimulating day. Restoring the genes in just 16 so-called ventral lateral neurons--out of some 200,000 neurons in the fly brain--is enough to restore increased sleep after social enrichment...The circadian clock tells animals when to sleep, but the duration of sleep depends on how long they've been awake and what they've done during that time...the same social experiences that increase the need for sleep also increase the number of synapses between lateral ventral neurons and their partners in the brainstem. After sleep, synapse numbers had declined

However,

...it's unlikely that downscaling happens only during sleep or that synaptic strengthening is limited to waking hours. Human and rodent studies have suggested that sleep may be important for consolidating newly formed memories, a process that's widely assumed to depend on strengthening synapses.

Cognitive gains in bilingual infants

Interesting work from Kovács and Mehler. Infants exposed to two languages demonstrate a domain-general enhancement of their cognitive control system well before the onset of speech:

Children exposed to bilingual input typically learn 2 languages without obvious difficulties. However, it is unclear how preverbal infants cope with the inconsistent input and how bilingualism affects early development. In 3 eye-tracking studies we show that 7-month-old infants, raised with 2 languages from birth, display improved cognitive control abilities compared with matched monolinguals. Whereas both monolinguals and bilinguals learned to respond to a speech or visual cue to anticipate a reward on one side of a screen, only bilinguals succeeded in redirecting their anticipatory looks when the cue began signaling the reward on the opposite side. Bilingual infants rapidly suppressed their looks to the first location and learned the new response. These findings show that processing representations from 2 languages leads to a domain-general enhancement of the cognitive control system well before the onset of speech.

Illusory control

Interesting observations from Fast et al. on why the powerful often seem to exhibit hubristic overconfidence:

Three experiments demonstrated that the experience of power leads to an illusion of personal control. Regardless of whether power was experientially primed (Experiments 1 and 3) or manipulated through roles (manager vs. subordinate; Experiment 2), it led to perceived control over outcomes that were beyond the reach of the power holder. Furthermore, this illusory control mediated the influence of power on several self-enhancement and approach-related outcomes reported in the power literature, including optimism (Experiment 2), self-esteem (Experiment 3), and action orientation (Experiment 3). These results demonstrate the theoretical importance of perceived control as a generative cause of and driving force behind many of power's far-reaching effects. A fourth experiment ruled out an alternative explanation: that positive mood, rather than illusory control, is at the root of power's effects.

Here is a bit more detail from the article (slightly edited) on the procedures that produced the predicted results:

Experiment 1 manipulated power by asking participants to recall an experience with high power, an experience with low power, or an event unrelated to power. Illusory control was measured using a classic die-rolling paradigm in which participants are offered a reward for predicting the outcome of a roll and are given a choice of rolling the die themselves or having another person roll the die for them. Choosing to roll the die reflects an illusory sense of control; it indicates that the actor believes he or she can personally influence the outcome of the random roll and, thus, increase the odds of obtaining the reward. We predicted that participants in the high-power condition would be more likely than those in the other two conditions to choose to roll the die.

Experiment 2 tested whether illusory control mediates the established relationship between power and optimism. We manipulated power by instructing participants that they would be matched with a partner and play the role of either a manager or a worker. Before completing any tasks associated with their roles, participants were asked to complete a separate study that was unrelated to their power role and assessed perceived control and optimism.

Experiment 3 tested whether illusory control mediates power's effects on self-esteem and action orientation. We used a context for action—voting in a national election—that is particularly important given that democracies are based on active citizen involvement and are largely shaped by voter mobilization and turnout. Power was manipulated with the same experiential prime used in Experiment 1. We compared the high-power condition with a baseline condition in order to demonstrate that the effects observed in Study 2 were driven by the experience of power and not by powerlessness. After the power manipulation, participants completed measures of sense of control, self-esteem, and action orientation. We predicted that those imbued with a sense of power would demonstrate illusory control, which would mediate power-induced increases in self-esteem and action orientation.

In summary...power led to perceived control over outcomes that were uncontrollable or unrelated to the power. Power predicted perceived control over a chance event (Experiment 1), over outcomes in domains that were unrelated to the source of power (Experiment 2), and over future outcomes that were virtually impossible for any one individual to control (e.g., performance of the national economy, national election results; Experiment 3). Furthermore, this inflated sense of control mediated power's positive effects on optimism (Experiment 2), self-esteem (Experiment 3), and action orientation (Experiment 3).

Social motives for syntax.

Enfield offers a review of Tomasello's new book "Origins of Human Communication." Some clips:

One dominant philosophy, grounded in the work of linguist Noam Chomsky, sees language as primarily an instrument of thought, not action. On this view, the key event in the evolution of language was a mutation resulting in an organlike faculty in the human mind, with selective advantage in the realm of reasoning. This faculty happened also to be useful for generating complex communicative behavior, though perhaps in the same way that a foot happens to be good for playing soccer: it did not evolve under the selective pressure of that function.

Tomasello sees language as a means for doing things, not a device for processing or merely externalizing thoughts....to communicate is to act on others in the social realm. For language to have this function presumes not only a conspecific with a comprehending mind but also a willingness to cooperate...Requests form one of three classes of social action...The others are informing-helping (e.g., when one person points to keys that another just dropped) and sharing (e.g., when two people's attitudes toward a third person align in the course of a gossip session). He summarizes research showing that all three social motives are fully evident in the communicative behavior of prelinguistic infants and all but absent among our closest relatives, the great apes. Humans have a special combination of cooperative instincts, prosocial motives, high-level intention attribution, and moral propensities. Tomasello contends that without this unique psychological wherewithal in the domain of social cognition, language as we know it could never have evolved.

Tomasello's work represents a long-standing and now rapidly growing view that language is not restricted to abstract structures of grammatical patterning but includes gestures and other bodily movements of the kinds that typically accompany speech... Gestures, he argues, are necessary for the development of language in both phylogeny and ontogeny...9-month-olds use gestures for multiple, often sophisticated social functions, including the three basic social motives. These favorable conclusions on the social cognitive sophistication of human infants contrast with the findings on primates.

Gestures lack the highly structured complexity of grammar: How to get from one to the other? ...Tomasello's solution is an ingenious linking of requesting, informing, and sharing with three distinct levels of complexity in the grammatical possibilities that any language will furnish. He dubs these "simple syntax" (strongly dependent on immediate context), "serious syntax" (for making unambiguous reference across contexts), and "fancy syntax" (for organizing long and complex narratives). But this is essentially as far as his links to grammar go, promissory notes notwithstanding. Precisely because the author is a linguist, this omission is a missed opportunity to complete the argument, to connect the dots that lead from basic social actions ultimately to the radically varying, historically developed complex linguistic systems that are found around the world.

Social isolation enhances neuroinflammatory response to stroke.

Karelina et al. give more detail on how social isolation can alter the expression of the interleukin molecules that regulate inflammation:

Social isolation has dramatic long-term physiological and psychological consequences; however, the mechanisms by which social isolation influences disease outcome are largely unknown. The purpose of the present study was to investigate the effects of social isolation on neuronal damage, neuroinflammation, and functional outcome after focal cerebral ischemia. Male mice were socially isolated (housed individually) or pair housed with an ovariectomized female before induction of stroke, via transient intraluminal middle cerebral artery occlusion (MCAO), or SHAM surgery. In these experiments, peri-ischemic social isolation decreases poststroke survival rate and exacerbates infarct size and edema development. The social influence on ischemic damage is accompanied by an altered neuroinflammatory response; specifically, central interleukin-6 (IL-6) signaling is down-regulated, whereas peripheral IL-6 is up-regulated, in isolated relative to socially housed mice. In addition, intracerebroventricular injection of an IL-6 neutralizing antibody (10 ng) eliminates social housing differences in measures of ischemic outcome. Taken together, these data suggest that central IL-6 is an important mediator of social influences on stroke outcome.

Sinning Saints and Saintly Sinners

From Sachdeva et al (The first two experiments measured altruistic behavior as a donation amount pledged by participants. The third experiments used a cooperative decision-making task in an environmental context to assess whether people would show moral cleansing and licensing when they were asked to cooperate with others for the good of the environment.):

The question of why people are motivated to act altruistically has been an important one for centuries, and across various disciplines. Drawing on previous research on moral regulation, we propose a framework suggesting that moral (or immoral) behavior can result from an internal balancing of moral self-worth and the cost inherent in altruistic behavior. In a first experiment, participants were asked to write a self-relevant story containing words referring to either positive or negative traits. Participants who wrote a story referring to the positive traits donated one fifth as much as those who wrote a story referring to the negative traits. In the second experiment, we showed that this effect was due specifically to a change in the self-concept. Finally, in experiment 3, we replicated these findings and extended them to cooperative behavior in environmental decision making. We suggest that affirming a moral identity leads people to feel licensed to act immorally. However, when moral identity is threatened, moral behavior is a means to regain some lost self-worth.

Seeing is remembering

A fascinating article from Harrison and Tong on how we hold fine details in our working memory by a top down mechanism in which frontal working memory areas apparently instruct early visual areas (V1-V4) at the rear of our cortex to retain information about visual features held in working memory :

Visual working memory provides an essential link between perception and higher cognitive functions, allowing for the active maintenance of information about stimuli no longer in view. Research suggests that sustained activity in higher-order prefrontal, parietal, inferotemporal and lateral occipital areas supports visual maintenance, and may account for the limited capacity of working memory to hold up to 3–4 items. Because higher-order areas lack the visual selectivity of early sensory areas, it has remained unclear how observers can remember specific visual features, such as the precise orientation of a grating, with minimal decay in performance over delays of many seconds. One proposal is that sensory areas serve to maintain fine-tuned feature information, but early visual areas show little to no sustained activity over prolonged delays. Here we show that orientations held in working memory can be decoded from activity patterns in the human visual cortex, even when overall levels of activity are low. Using functional magnetic resonance imaging and pattern classification methods, we found that activity patterns in visual areas V1–V4 could predict which of two oriented gratings was held in memory with mean accuracy levels upwards of 80%, even in participants whose activity fell to baseline levels after a prolonged delay. These orientation-selective activity patterns were sustained throughout the delay period, evident in individual visual areas, and similar to the responses evoked by unattended, task-irrelevant gratings. Our results demonstrate that early visual areas can retain specific information about visual features held in working memory, over periods of many seconds when no physical stimulus is present.

The 100 year old neuroscientist

Nature does a brief review of the life of Rita Levi-Montalcini, the first Nobel Laureate to reach their 100th birthday. It makes a fascinating read. I was just getting into neuroscience in the late 1950's when she, along with others, discovered NGF (nerve growth factor). Things were very competitive, a number of priority disputes arose, there were accusations of dishonest behavior. (My own bit of gossip from the sidelines: a colleague of mine at the time sent a letter to her describing in detail some of his recent experimental results, then told me that three verbatim paragraphs from his letter appeared in Levi-Montalcini's next paper, which claimed priority for the discoveries.) Here is a striking clip about her more recent, and laudable, efforts.

...on the morning of 18 November 2006, she had the attention of the entire Italian government. A senator for life, Levi-Montalcini held the deciding vote on a budget backed by the government of Romano Prodi, which held a parliamentary majority of just one.

A few days earlier, Levi-Montalcini had said she would withdraw her support for the budget unless the government reversed a last-minute decision to sacrifice science funds. It was Levi-Montalcini versus Prodi — and Levi-Montalcini won. On the morning of the vote, immaculately turned out as always, she walked regally on the arm of an usher to her seat in the Italian senate and cast her vote. At one stroke, she secured the budget, won a battle for Italian science and snubbed Francesco Storace, leader of the Right party and part of the opposition coalition. A few weeks earlier, Storace had caused a national scandal by announcing his intention to send crutches to Levi-Montalcini's home — symbolic of her both being a crutch to an ailing government, he said, and her age, which he considered too old to be allowed to vote.

Levi-Montalcini didn't consider herself too old then, when she was 97 years old, and she certainly doesn't now when, on 22 April, she will become the first Nobel laureate to reach the age of 100. Italy — and quite possibly the world — has never seen a scientist quite like her.

Family Tree

Check out this site. The artist has photographed father/son, mother/daughter, and even father/daughter and mother/son individually, sized and printed the photos at the same proportions, then torn and glued them together to make one portrait. (click to enlarge).

Sites for abstract versus concrete actions in frontal lobes.

By observing behavioral deficits of lesion patients Badre et al. find that there is a hierarchical organization of cognitive control, with rostral (towards top of head) areas of the frontal lobes being required for decisions about more abstract actions and lower caudal areas (towards spinal column or tail) being required for decisions about more concrete actions.

Cognitive control permits us to make decisions about abstract actions, such as whether to e-mail versus call a friend, and to select the concrete motor programs required to produce those actions, based on our goals and knowledge. The frontal lobes are necessary for cognitive control at all levels of abstraction. Recent neuroimaging data have motivated the hypothesis that the frontal lobes are organized hierarchically, such that control is supported in progressively caudal regions as decisions are made at more concrete levels of action. We found that frontal damage impaired action decisions at a level of abstraction that was dependent on lesion location (rostral lesions affected more abstract tasks, whereas caudal lesions affected more concrete tasks), in addition to impairing tasks requiring more, but not less, abstract action control. Moreover, two adjacent regions were distinguished on the basis of the level of control, consistent with previous functional magnetic resonance imaging results. These results provide direct evidence for a rostro-caudal hierarchical organization of the frontal lobes.

Neural mechanism of first impressions.

From Schiller et al:

Evaluating social others requires processing complex information. Nevertheless, we can rapidly form an opinion of an individual during an initial encounter. Moreover, people can vary in these opinions, even though the same information is provided. We investigated the brain mechanisms that give rise to the impressions that are formed on meeting a new person. Neuroimaging revealed that responses in the amygdala and the posterior cingulate cortex (PCC) were stronger while encoding social information that was consistent, relative to inconsistent, with subsequent evaluations. In addition, these responses scaled parametrically with the strength of evaluations. These findings provide evidence for encoding differences on the basis of subsequent evaluations, suggesting that the amygdala and PCC are important for forming first impressions.

Figure. (Click to enlarge) a - Functional regions of interest (ROIs) were identified by contrasting faces with person-descriptive sentences versus face-alone presentations. The dmPFC and left amygdala are denoted by yellow circle on the statistical activation map. b - To examine whether these ROIs show differential neural response to information that is relevant versus irrelevant to later evaluations, we extracted the BOLD response from each of these regions and compared the mean percentage BOLD signal change during the presentation of evaluation-relevant versus evaluation-irrelevant person-descriptive sentences. The differential score was calculated by subtracting evaluation-irrelevant from evaluation-relevant responses, so positive scores correspond to stronger responses to the evaluation-relevant information. A significant differential responding was shown by the PCC and the amygdala, but not by the dmPFC.

Thinking like a trader reduces your loss aversion.

Sokol-Hessnera et al (open access). note that a cognitive regulation strategy can reduce loss aversion:

Research on emotion regulation has focused upon observers' ability to regulate their emotional reaction to stimuli such as affective pictures, but many other aspects of our affective experience are also potentially amenable to intentional cognitive regulation. In the domain of decision-making, recent work has demonstrated a role for emotions in choice, although such work has generally remained agnostic about the specific role of emotion. Combining psychologically-derived cognitive strategies, physiological measurements of arousal, and an economic model of behavior, this study examined changes in choices (specifically, loss aversion) and physiological correlates of behavior as the result of an intentional cognitive regulation strategy. Participants were on average more aroused per dollar to losses relative to gains, as measured with skin conductance response, and the difference in arousal to losses versus gains correlated with behavioral loss aversion across subjects. These results suggest a specific role for arousal responses in loss aversion. Most importantly, the intentional cognitive regulation strategy, which emphasized “perspective-taking,” uniquely reduced both behavioral loss aversion and arousal to losses relative to gains, largely by influencing arousal to losses. Our results confirm previous research demonstrating loss aversion while providing new evidence characterizing individual differences and arousal correlates and illustrating the effectiveness of intentional regulation strategies in reducing loss aversion both behaviorally and physiologically.

Fetal ethanol exposure increases ethanol intake of offspring

More sobering information on how maternal patterns of drug use, can be passed on to offspring, presumably by means of epigenetic chemosensory mechanisms.

Human epidemiologic studies reveal that fetal ethanol exposure is highly predictive of adolescent ethanol avidity and abuse. Little is known about how fetal exposure produces these effects. It is hypothesized that fetal ethanol exposure results in stimulus-induced chemosensory plasticity. Here, we asked whether gestational ethanol exposure increases postnatal ethanol avidity in rats by altering its taste and odor. Experimental rats were exposed to ethanol in utero via the dam's diet, whereas control rats were either pair-fed an iso-caloric diet or given food ad libitum. We found that fetal ethanol exposure increased the taste-mediated acceptability of both ethanol and quinine hydrochloride (bitter), but not sucrose (sweet). Importantly, a significant proportion of the increased ethanol acceptability could be attributed directly to the attenuated aversion to ethanol's quinine-like taste quality. Fetal ethanol exposure also enhanced ethanol intake and the behavioral response to ethanol odor. Notably, the elevated intake of ethanol was also causally linked to the enhanced odor response. Our results demonstrate that fetal exposure specifically increases ethanol avidity by, in part, making it taste and smell better. More generally, they establish an epigenetic chemosensory mechanism by which maternal patterns of drug use can be transferred to offspring. Given that many licit (e.g., tobacco products) and illicit (e.g., marijuana) drugs have noteworthy chemosensory components, our findings have broad implications for the relationship between maternal patterns of drug use, child development, and postnatal vulnerability.

Visual neglect overcome by pleasant music

Soto et al. make the fascinating observation that positive emotions can overcome the neglect of part of the visual field that can result from brain lesions:

During the past 20 years there has been much research into the factors that modulate awareness of contralesional information in neurological patients with visual neglect or extinction. However, the potential role of the individual's emotional state in modulating awareness has been largely overlooked. In the current study, we induced a pleasant and positive affective response in patients with chronic visual neglect by allowing them to listen to their pleasant preferred music. We report that the patients showed enhanced visual awareness when tasks were performed under preferred music conditions relative to when tasks were performed either with unpreferred music or in silence. These results were also replicated when positive affect was induced before neglect was tested. Functional MRI data showed enhanced activity in the orbitofrontal cortex and the cingulate gyrus associated with emotional responses when tasks were performed with preferred music relative to unpreferred music. Improved awareness of contralesional (left) targets with preferred music was also associated with a strong functional coupling between emotional areas and attentional brain regions in spared areas of the parietal cortex and early visual areas of the right hemisphere. These findings suggest that positive affect, generated by preferred music, can decrease visual neglect by increasing attentional resources. We discuss the possible roles of arousal and mood in generating these effects.

The end of moral philosophy

Again I am amazed at how well David Brooks keeps up with contemporary psychology and brain science, picking up on the recent upsurge in research on the good stuff in human nature like our evolved affiliative emotions. Check out this Op-Ed piece.

Another Twitter parody...

I couldn't resist passing this on:

Medial prefrontal cortex exhibits money illusion

My Feb. 23 post noted work showing, yet again, that we can be lured into making decisions by numbers that seem bigger than they really are. We apparently go with numerical values rather than real economic values. Weber et al. look at brain activity at accompanies the money illusion:

Behavioral economists have proposed that money illusion, which is a deviation from rationality in which individuals engage in nominal evaluation, can explain a wide range of important economic and social phenomena. This proposition stands in sharp contrast to the standard economic assumption of rationality that requires individuals to judge the value of money only on the basis of the bundle of goods that it can buy—its real value—and not on the basis of the actual amount of currency—its nominal value. We used fMRI to investigate whether the brain's reward circuitry exhibits money illusion. Subjects received prizes in 2 different experimental conditions that were identical in real economic terms, but differed in nominal terms. Thus, in the absence of money illusion there should be no differences in activation in reward-related brain areas. In contrast, we found that areas of the ventromedial prefrontal cortex (vmPFC), which have been previously associated with the processing of anticipatory and experienced rewards, and the valuation of goods, exhibited money illusion. We also found that the amount of money illusion exhibited by the vmPFC was correlated with the amount of money illusion exhibited in the evaluation of economic transactions.

Delayed brain development in humans compared with other primates

A prevailing view is that the appearance of many human-specific features during development has been made possible by a slowing down of the process, particularly in the brain (developmental retardation, or neoteny). Somel et al. prove the point by looking at gene expression in humans and other primates during development:

In development, timing is of the utmost importance, and the timing of developmental processes often changes as organisms evolve. In human evolution, developmental retardation, or neoteny, has been proposed as a possible mechanism that contributed to the rise of many human-specific features, including an increase in brain size and the emergence of human-specific cognitive traits. We analyzed mRNA expression in the prefrontal cortex of humans, chimpanzees, and rhesus macaques to determine whether human-specific neotenic changes are present at the gene expression level. We show that the brain transcriptome is dramatically remodeled during postnatal development and that developmental changes in the human brain are indeed delayed relative to other primates. This delay is not uniform across the human transcriptome but affects a specific subset of genes that play a potential role in neural development.