#prefontal cortex

The activity of two specific neuron types correlates with foraging decisions in mice  You are sitting on your couch flipping through TV channels trying to decide whether to stay put or get up for a snack.  Such everyday decisions about whether to “stay” or to “go” are supported by a brain region called the anterior cingulate cortex (ACC), which is part of the prefrontal cortex. Neuroscientists from Cold Spring Harbor Laboratory (CSHL) have now identified key circuit elements that contribute to such decisions in the ACC. CSHL Associate Professor Adam Kepecs and his team today publish results that, for the first time, link specific brain cell types to a particular behavior pattern in mice – a “stay or go” pattern called foraging behavior. The paper, published online in Nature, shows that the firing of two distinct types of inhibitory neurons, known as somatostatin (SOM) and parvalbumin (PV) neurons, has a strong correlation with the start and end of a period of foraging behavior.   The activity of two types of inhibitory nerve brain cells, PV and SOM neurons, correlates with decisions made during "foraging" behavior in mice. On the left a mouse has decided to leave the water reward area and the PV neurons have increased activity, shown by the uptick in 'spikes' of nerve impulses (PV; red). On the right, a mouse has decided to enter the water reward zone, which correlates with a decrease in SOM (NS-SOM; blue) neuron activity. The activity of these neurons is linked "stay" or "go" decisions during foraging behavior. Adapted from figure 3 in the paper. (click to enlarge)

A new technology promises to supercharge your brain with electricity. Is it too good to be true?

Scientists have rediscovered a centuries-old procedure for supercharging your brain. Depending on how it’s used, it could improve anything from focus to motor control to mathematical or even moral reasoning. It’s simple. It’s relatively cheap. The known side effects are minimal. And it’s so easy that you can do it in your own home, anytime you want. All you need are a pair of electrodes and a power source.

 The procedure is called transcranial direct-current stimulation, or tDCS, and the idea has been around for 200 years, though it languished in disrepute until recently. The setup: You attach one electrode to your scalp above the part of the brain you’re trying to stimulate, and another electrode on the other side of your head, to complete the circuit. Then you turn on a milliampere or two of juice, and watch the mental sparks fly—figuratively, if you’re doing it right.

Almost every expert who talks about tDCS will tell you, “Don’t try this at home.” But a lot of people are starting to do just that. And it’s no wonder, given the parade of amazing results that researchers have reported achieving on subjects in the lab. It seems like you can make people better at just about anything if you just put the electrodes in the right place. To name just a few of the findings:

Applying the electrodes to the prefrontal cortex can improve learning and increase your working memory.

Applying them to the motor cortex can raise your threshold for pain and make you more adept with your nondominant hand.

Position them above the posterior portion of the left perisylvian area (in right-handed people) and they can facilitate language acquisition.

Stimulation of the parietal cortex can improve numerical reasoning.

The potential applications for tDCS (and a related technology called repetitive transcranial magnetic stimulation, which uses magnets to induce a current) range from healing to educating to killing. Doctors are experimenting with tDCS to treat severe depression and help stroke victims regain their speaking skills. Students in theory could use it to solve math problems or pick up Russian. Air Force researchers are using it to make people better at guiding killer drones, and DARPA has found it could improve snipers’ marksmanship.

A few studies claim results that are even more jaw-dropping. In Neuroscience Letters last year, Australian researchers reported applying tDCS to 33 people as they tried to solve the notoriously tricky “nine-dot” logic problem. Not one was able to crack it without stimulation, or with “sham” stimulation (in which electricity is applied only briefly to mimic the feeling of tDCS). With current coursing between their left and right anterior temporal lobes, 40 percent solved it.

You might suspect the procedure would be painful or unpleasant. Many subjects report a tickling or burning sensation from the electrodes, and some say they feel different when the current is flowing, with time seeming to pass quickly. But far from finding it painful, an editor at New Scientist who tried it out during a marksmanship test described tDCS as “the most powerful drug I’ve ever used in my life” and “a near-spiritual experience.” The editor, Sally Adee, wrote:

“When a nice neuroscientist named Michael Weisend put the electrodes on me, what defined the experience was not feeling smarter or learning faster: The thing that made the earth drop out from under my feet was that for the first time in my life, everything in my head finally shut up. …  I felt clear-headed and like myself, just sharper. Calmer. Without fear and without doubt. From there on, I just spent the time waiting for a problem to appear so that I could solve it.”

Oh, and she nailed the target.

Exactly how all of this works is not yet fully clear. But the process appears to make neurons in the stimulated area more malleable, so that new connections form more readily while under the influence of the current. It remains to be seen whether those changes are short-lived or enduring, but at least one study has found positive effects persisting for up to six months. The beauty of it, in theory, is that the electric current doesn’t rewire the brain on its own—it just makes it easier for the brain to rewire itself.

At this point it seems obvious that this is far too good to be true. So what’s the catch?

The catch is that we don't know what the catch is. And to Peter Reiner, a neuroscientist at University of British Columbia, that's a biggie. If tDCS can so quickly change the brain in ways that we can easily measure, he says, there’s a good chance it could also change the brain in ways we can’t easily measure—or that researchers so far haven’t tried to measure. Scientists often assume they can target the effects of tDCS by stimulating only the part of the brain relevant to the task that the subject is concentrating on. But most would admit there’s some guesswork involved, since brain topography can vary from one person to the next. And Reiner warns that there’s no guarantee the subject’s mind won’t wander, say, to “something horrific that occurred earlier today.” What if tDCS ends up forging traumatic connections along with useful ones?

Less dramatically, it seems plausible that researchers are overlooking subtle drawbacks of tDCS. One of the first papers to identify downsides to the procedure was published last month in the Journal of Neuroscience, titled “The Mental Cost of Cognitive Enhancement.” Subjects who had their parietal lobes stimulated during a numerical-processing task performed better than those who received fake stimulation. But a week later, they struggled to apply the newly learned techniques to a different task. “They had trouble accessing what they’d learned,” study co-author Roi Cohen Kadosh of Oxford told Wired. Subjects who had a different region of their brain stimulated during the task showed the opposite effect, performing slowly at first but better at week’s end.

As for the amateur applications, you don't need to be an Oxford professor to deduce that building your own tDCS kit and sticking electrodes onto your head willy-nilly might have some adverse consequences. All you need are some YouTube videos, like the one in which a teen describes his first forays into electrical brain stimulation. “I’ve been experimenting on where, which places on my head would improve memory—more specifically, visual memory,” the young DIY-er says in the video. “So I’ve been thinking, OK, does the left dorsal, uh, prefrontal cortex—which I thought would be around, about, left side, right here (points to head)—and that would be where the cathode goes, and the anode would go right up here. Well I put it on, and after about five minutes, I felt really angry and depressed. So … I guess that wasn’t a good idea.”

An observant YouTube commenter pointed out that the young man had reversed the anode and the cathode, a mistake akin to putting the wrong jumper cables on your car battery. “Flip it around and try again,” the commenter suggested.

The fact that tDCS may pose unknown risks, that its benefits and drawbacks are not yet fully understood, that it can be dangerous in the wrong hands—none of these arguments should keep scientists from carefully exploring its potential. Having spent the better part of two months immersed in the vertiginous world of human enhancement, I’ve become convinced that societal and academic taboos against the use of technology to give healthy people extraordinary powers are, on the whole, counterproductive. College students are already popping Adderall in droves. Body hackers are implanting microchips in their bodies. Entrepreneurs are hawking tDCS kits for $99 online. Some athlete, somewhere, is probably experimenting with gene doping. The riskiness of some of these behaviors makes it tempting to simply outlaw them all and expect everyone to comply. But that’s as unrealistic as it is blinkered.

This isn’t a call to legalize everything and let God or Darwin sort ’em out. It’s a plea to lawmakers, the media, academics, and those who fund academic research to take seriously the growing availability of and demand for human-enhancement technologies. Only by acknowledging and researching their potential benefits as well as their risks can we hope to craft mature policies that promote public safety and welfare. If that means continuing to classify Adderall as a Schedule II controlled substance until we’re even more convinced that it doesn’t pose long-term health risks, so be it. But here’s where we’re going astray: One university professor who studies ADHD drugs told me he has learned that every public-health research paper “has to have a certain (cautionary) tone to it” in order to be accepted for publication. “I know what I have to write, and it has to be, basically, ‘Drugs are bad.’ ”

Maybe he’s wrong. But I’ve talked with enough academics over the past two months who flat-out refused to even discuss the potential use of various medical technologies for human enhancement—or to even have their name attached to an article that discusses them—to suspect that there’s some legitimacy to his paranoia. Too many people seem to think that humans are fine the way we are, and that the only proper use of these technologies is to restore “normal” human functions to people with disabilities.

Why is that short-sighted? As Duke philosophy professor and bioethicist Allen Buchanan told Ross Andersen in the Atlantic:

“The list of design flaws in human beings is pretty long, as it is in other organisms, and so to think that somehow we're at the summit of perfection and that we're stable is to have the wrong idea of human nature. The misleading assumption is that if we don't interfere, we're going to continue the way we are, and of course that goes completely contrary to everything we know about evolution. In fact it might turn out that the only way to prevent us from going extinct, or to prevent some great worsening of our condition, is to enhance some of our capacities.”

I’m skeptical of a lot of the advertised merits of tDCS as a wonder tool for cognitive enhancement. After all, the modern field is still young, and it’s always easier to get research published and publicized if a result is dramatic. Already one study has cast doubt on the use of “sham” stimulation as an effective control for tDCS experiments. Perhaps it will take a backlash like the one against ADHD drugs to spur studies that debunk some of the more outlandish positive results.

When the brain's primary "learning center" is damaged, complex new neural circuits arise to compensate for the lost function, say life scientists from UCLA and Australia who have pinpointed the regions of the brain involved in creating those alternate pathways — often far from the damaged site.

  The research, conducted by UCLA's Michael Fanselow and Moriel Zelikowsky in collaboration with Bryce Vissel, a group leader of the neuroscience research program at Sydney's Garvan Institute of Medical Research, appears this week in the early online edition of the journal Proceedings of the National Academy of Sciences.

  The researchers found that parts of the prefrontal cortex take over when the hippocampus, the brain's key center of learning and memory formation, is disabled. Their breakthrough discovery, the first demonstration of such neural-circuit plasticity, could potentially help scientists develop new treatments for Alzheimer's disease, stroke and other conditions involving damage to the brain.

  For the study, Fanselow and Zelikowsky conducted laboratory experiments with rats showing that the rodents were able to learn new tasks even after damage to the hippocampus. While the rats needed more training than they would have normally, they nonetheless learned from their experiences — a surprising finding.

  "I expect that the brain probably has to be trained through experience," said Fanselow, a professor of psychology and member of the UCLA Brain Research Institute, who was the study's senior author. "In this case, we gave animals a problem to solve."

  After discovering the rats could, in fact, learn to solve problems, Zelikowsky, a graduate student in Fanselow's laboratory, traveled to Australia, where she worked with Vissel to analyze the anatomy of the changes that had taken place in the rats' brains. Their analysis identified significant functional changes in two specific regions of the prefrontal cortex.

  "Interestingly, previous studies had shown that these prefrontal cortex regions also light up in the brains of Alzheimer's patients, suggesting that similar compensatory circuits develop in people," Vissel said. "While it's probable that the brains of Alzheimer's sufferers are already compensating for damage, this discovery has significant potential for extending that compensation and improving the lives of many."

  The hippocampus, a seahorse-shaped structure where memories are formed in the brain, plays critical roles in processing, storing and recalling information. The hippocampus is highly susceptible to damage through stroke or lack of oxygen and is critically inolved in Alzheimer's disease, Fanselow said.

  "Until now, we've been trying to figure out how to stimulate repair within the hippocampus," he said. "Now we can see other structures stepping in and whole new brain circuits coming into being."

   Zelikowsky said she found it interesting that sub-regions in the prefrontal cortex compensated in different ways, with one sub-region — the infralimbic cortex — silencing its activity and another sub-region — the prelimbic cortex — increasing its activity.

  "If we're going to harness this kind of plasticity to help stroke victims or people with Alzheimer's," she said, "we first have to understand exactly how to differentially enhance and silence function, either behaviorally or pharmacologically. It's clearly important not to enhance all areas. The brain works by silencing and activating different populations of neurons. To form memories, you have to filter out what's important and what's not."

  Complex behavior always involves multiple parts of the brain communicating with one another, with one region's message affecting how another region will respond, Fanselow noted. These molecular changes produce our memories, feelings and actions.

  "The brain is heavily interconnected — you can get from any neuron in the brain to any other neuron via about six synaptic connections," he said. "So there are many alternate pathways the brain can use, but it normally doesn't use them unless it's forced to. Once we understand how the brain makes these decisions, then we're in a position to encourage pathways to take over when they need to, especially in the case of brain damage.

  "Behavior creates molecular changes in the brain; if we know the molecular changes we want to bring about, then we can try to facilitate those changes to occur through behavior and drug therapy," he added. I think that's the best alternative we have. Future treatments are not going to be all behavioral or all pharmacological, but a combination of both."

   Fanselow and Vissel have worked closely over the last several years. For more information on Fanselow's research, visit the Fanselow Lab website. For more on the Garvan Institute of Medical Research, visit their website.

It's a wonder that good decisions are ever made by the species known as Homo sapiens. The reality is that the cards are stacked against us whenever we are faced with choices, especially when the decisions are of consequence. Think about all the horrendously bad decisions that have been made in recent history and how obviously bad they look in our rearview mirrors: the Iraq war, securitizing mortgages, Congress not voting for background checks on gun purchases, another season of The Bachelor, and the list goes on. And bad decisions don't just occur at the highest levels of government or business; rather, everyday folks can make appalling decisions as well, whether getting married to that particular person, wearing those low-cut jeans, buying a Hummer or going into debt to remodel the kitchen.

The fact is that humans are behind the 8 ball from the get-go when it comes to making decisions. Children are wholly ill-equipped for decision making. They lack knowledge, experience and perspective. Children are myopic, impulsive and easily persuaded. It doesn't get much better during adolescence, when teenagers are driven by raging hormones, underdeveloped self-identities and peer and cultural pressure.

Perhaps the biggest obstacle is neurological, where the prefrontal cortex, the part of the brain associated with executive functioning, doesn't fully develop until the early 20s. Executive functioning directly influence decision making because it regulates, controls and manages our thoughts, emotions and behavior. It influences our reactions to new, ambiguous and difficult situations. It helps us weigh risks and rewards and short- and long-term consequences. Executive functioning assists us in planning, organizing and executing decisions, and, importantly, it can prevent us from making rash and potentially harmful decisions.

It doesn't get any easier as adults to make good decisions either. A wide range of research has demonstrated that we are often at the mercy of psychological, emotional, social and situational influences when we make decisions. Daniel Kahneman, a Nobel Prize winner in economics, has demonstrated the powerful effect that cognitive biases have on our decision making. Cognitive biases involve the tendency to draw conclusions and make decisions based on limited information or self-interest. An extensive body of research has demonstrated that these biases can lead to irrational decisions at every level of society.

Our decision making is also influenced by our emotional states and social world in ways both overt and subtle, making us appear quite fickle in what we decide. For example, feeling stressed or rushed alters our decisions. The decisions we make are affected by our mood. We make different decisions based on whether we are feeling happy, contemplative or disgusted. As considerable research on peer pressure and groupthink has demonstrated, our decisions are also significantly influenced by social forces, whether friends and family, cultural messages or societal norms.

Another thing I learned recently is that emotionally laden information (i.e., information that is threatening in some way) goes directly to the emotional center of the brain, including the amygdala and related structures. This connection isn't surprising given the role that our emotions play in our survival; we need to receive and act on threatening information right away or we may die.

Unfortunately, the rapid decision making associated with triggering the fight-or-flight reaction that served humans well during primitive times is generally ineffective at helping us make good decisions about complex issues in modern times. And emotionally relevant decisions are the ones that are usually the most important and most necessary to get right. What is even more unsettling is that there are no direct neurological pathways to the prefrontal cortex; all emotional information goes through the primitive emotional brain. So the prefrontal cortex is at a severe disadvantage in contributing to decision making, because the information it receives is "old news," secondhand and tainted by emotions.

We can only conclude that we humans are behind the 8 ball when it comes to making decisions, and we have a long history documenting just that. Yet somehow we do find ways to make good decisions, whether buying a Prius, not investing with Lehman Brothers or not invading Iran.

With such a strong current pulling us in the direction of bad decisions, what can we do to increase our chances of making good decisions? Here are a few strategies:

Don't make knee-jerk decisions. Give yourself time to reflect on your decisions before you commit to them.

Don't let your emotions make your decisions. The more distance you can create between your emotions and your decisions, the easier it will be for your prefrontal cortex to "get in the game."

Look at your decisions from many perspectives. The more information you have, the more you will engage your prefrontal cortex, and the more reasoned your decisions will be.

Talk to other people about your decisions. People who know you well can identify your biases, offer helpful viewpoints and reality test your decisions.

  By stimulating one part of the brain with laser light, researchers at the National Institutes of Health (NIH) and the Ernest Gallo Clinic and Research Center at UC San Francisco (UCSF) have shown that they can wipe away addictive behavior in rats – or conversely turn non-addicted rats into compulsive cocaine seekers.

    “When we turn on a laser light in the prelimbic region of the prefrontal cortex, the compulsive cocaine seeking is gone,” said Antonello Bonci, MD, scientific director of the intramural research program at the NIH’s National Institute on Drug Abuse (NIDA), where the work was done. Bonci is also an adjunct professor of neurology at UCSF and an adjunct professor at Johns Hopkins University.

  Described this week in the journal Nature, the new study demonstrates the central role the prefrontal cortex plays in compulsive cocaine addiction. It also suggests a new therapy that could be tested immediately in humans, said Billy Chen of NIDA, the lead author of the study.

Any new human therapy would not be based on using lasers, but would most likely rely on electromagnetic stimulation outside the scalp, in particular a technique called transcranial magnetic stimulation (TMS). Clinical trials are now being designed to test whether this approach works, Chen added.

The High Cost of Cocaine Abuse

Cocaine abuse is a major public health problem in the United States today, and it places a heavy toll on society in terms of lost job productivity, lost earnings, cocaine-related crime, incarcerations, investigations, and treatment and prevention programs.

The human toll is even greater, with an estimated 1.4 million Americans addicted to the drug. It is frequently the cause of emergency room visits – 482,188 in 2008 alone – and it is a top cause of heart attacks and strokes for people under 35.

One of the hallmarks of cocaine addiction is compulsive drug taking – the loss of ability to refrain from taking the drug even if it’s destroying one’s life.

What makes the new work so promising, said Bonci, is that Chen and his colleagues were working with an animal model that mimics this sort of compulsive cocaine addiction. The animals, like human addicts, are more likely to make bad decisions and take cocaine even when they are conditioned to expect self-harm associated with it.

Electrophysiological studies involving these rats have shown that they have extremely low activity in the prefrontal cortex – a brain region fundamental for impulse control, decision making and behavioral flexibility. Similar studies that imaged the brains of humans have shown the same pattern of low activity in this region in people who are compulsively addicted to cocaine.

Altering Brain Activity with a Laser

To test whether altering the activity in this brain region could impact addiction, Chen and his colleagues employed a technique called optogenetics to shut the activity on and off using a laser.

First they took light-sensitive proteins called rhodopsins and used genetic engineering to insert them into neurons in the rat’s prefrontal cortex. Activating this region with a laser tuned to the rhodopsins turned the nerve cells on and off.

Turning on these cells wiped out the compulsive behavior, while switching them off turned the non-addicted ones into addicted, researchers found.

What’s exciting, said Bonci, is that there is a way to induce a similar activation of the prelimbic cortex in people through a technique called transcranial magnetic stimulation (TMS), which applies an external electromagnetic field to the brain and has been used as a treatment for symptoms of depression.

Bonci and his colleagues plan to begin clinical trials at NIH in which they will use this technique a few sessions a week to stimulate the prefrontal cortex in people who are addicted to cocaine and see if they can restore activity to that part of the brain and help them avoid taking the drug.

The article, “Rescuing cocaine-induced prefrontal cortex hypoactivity prevents compulsive cocaine seeking” is authored by Billy T. Chen, Hau-Jie Yau, Christina Hatch, Ikue Kusumoto-Yoshida, Saemi L. Cho, F. Woodward Hopf and Antonello Bonci. It was published online by the journal Nature on April 3, 2013.

In addition to UCSF, the authors of this study are affiliated with the National Institute on Drug Abuse, the Ernest Gallo Clinic and Research Center and the Solomon H. Snyder Neuroscience Institute, Johns Hopkins School of Medicine.

Photo: D. Sharon Pruitt/Flickr

Science is painting a dramatic picture of how childhood neglect damages developing brains, so stunting them that neglect might be likened to physically violent abuse.

The latest addition to this research narrative comes from a study of mice placed in isolation early in their lives, an experiment that, on its surface, might seem redundant: After all, we already know that neglect is bad for humans, much less mice.

But they key to the study is in the details. The researchers found striking abnormalities in tissues that transmit electrical messages across the brain, suggesting a specific mechanism for some of the dysfunctions seen in neglected human children.

“This is very strong evidence that changes in myelin cause some of the behavioral problems caused by isolation,” said neurologist Gabriel Corfas of Harvard Medical School, a co-author of the new study, released Sept. 13 in Science.

Corfas and his team, led by fellow Harvard Med neuroscientist Manabu Makinodan, put 21-day-old mice in isolation for two weeks, then returned them to their colonies. When the mice reached adolescence, the researchers compared their brains and behavior to mice who hadn’t been isolated.

The isolated mice were antisocial, with striking deficits in memory. Their myelin, a cell layer that forms around neuronal networks like insulation around wires, was unusually thin, especially in the prefrontal cortex, a brain region central to cognition and personality.

'The first years of life are crucially important for brain architecture.'

Similar patterns of behavior have been seen, again and again, in children raised in orphanages or neglected by parents, as have changes to a variety of brain regions, including the prefrontal cortex. The myelin deficiencies identified by Corfas and Makinodan may underlie these defects.

“This is incredibly important data, because it gives us the neural mechanisms associated with the deleterious changes in the brain” that arise from neglect, said Nathan Fox, a cognitive neuroscientist at the University of Maryland.

Fox was not involved in the new study, but is part of a research group working on a long-term study of childhood neglect that is scientifically striking and poignantly tragic. Led by Harvard Medical School pediatricians Charles Nelson and Margaret Sheridan, the project has tracked for the last 12 years children who started their lives in an orphanage in Bucharest, Romania, a country infamous for the spartan, impersonal conditions of its orphanages.

Among children who spent their first two years in the orphanage, the researchers observed high levels developmental problems, cognitive deficits, mental illness, and significant reductions in brain size. When the researchers measured the sheer amount of electrical activity generated by the brains of children who’d been isolated as toddlers, “it was like you’d had a rheostat, a dimmer, and dimmed down the amount of energy in these institutionalized children,” said Fox.

These problems persisted even when toddlers were later adopted, suggesting a crucial importance for those early years in setting a life’s neurological trajectory. “There’s a sensitive period for which, if a child is taken out of an institution, the effects appear to be remediated, and after which remediation is very, very difficult,” Fox said. The same pattern was observed in Corfas and Makinodan’s mice.

One phenomenon not studied in the mice, but regularly found in people neglected as children, are problems with stress: mood disorders, anxiety, and general dysfunction in a body’s stress responses.

Controlled for gender and age, average white matter volumes in the brains of children who grew up in a Romanian orphanage (left), started in an orphange but were placed in foster care (center), or never lived in an orphanage at all (right). Image: Sheridan et al./PNAS

Those mechanisms have been studied in another animal, the rhesus monkey. While deprivation studies on non-human primates — and in particular chimpanzees — are controversial, the results from the monkey studies have been instructive.

Early-life isolation sets off a flood of hormones that permanently warp their responses to stress, leaving them anxious and prone to violent swings in mood.

Isolation is so damaging because humans, especially as infants, literally depend on social stimulation to shape their minds, said psychologist John Cacioppo of the University of Chicago.

“Human social processes were once thought to have been incidental to learning and cognition,” Cacioppo wrote in an e-mail. “However, we now think that the complexities and demands of social species have contributed to the evolution of the brain and nervous system and to various aspects of cognition.”

Corfas and Makinodan’s team linked specific genetic changes to the abnormalities in their mice, and hope they might someday inform the development of drugs that can help reverse isolation’s effects.

A more immediate implication of the research is social. As evidence of neglect’s severe, long-term consequences accumulates, it could shape the way people think not just of orphanages, but policy matters like maternity and paternity leave, or the work requirements of single parents on welfare.

Brain organization, not overall size, may be the key evolutionary difference between primate brains, and the key to what gives humans their smarts, new research suggests.

In the study, researchers looked at 17 species that span 40 million years of evolutionary time, finding changes in the relative size of specific brain regions, rather than changes in brain size, accounted for three-quarters of brain evolution over that time. The study, published today (March 26) in the Proceedings of the Royal Society B, also revealed that massive increases in the brain's prefrontal cortex played a critical role in great ape evolution.

"For the first time, we can really identify what is so special about great ape brain organization," said study co-author Jeroen Smaers, an evolutionary biologist at the University College London.

Is bigger better?

Traditionally, scientists have thought humans' superior intelligence derived mostly from the fact that our brains are three times bigger than our nearest living relatives, chimpanzees.

But bigger isn't always better. Bigger brains take much more energy to power, so scientists have hypothesized that brain reorganization could be a smarter strategy to evolve mental abilities. [10 Odd Facts About the Brain]

To see how brain organization evolved throughout primates, Smaers and his colleague Christophe Soligo analyzed post-mortem slices of brains from 17 different primates, then mapped changes in brain size onto an evolutionary tree.

Over evolutionary time, several key brain regions increased in size relative to other regions. Great apes (especially humans) saw a rise in white matter in the prefrontal cortex, which contributes to social cognition, moral judgments, introspection and goal-directed planning. The white matter carries axons, the wires connecting different brain cells, suggesting that that the great apes' brains were evolving for greater neural connections.

"The prefrontal cortex is a little bit like the CEO of the brain," Smaers told LiveScience. "It takes information from other brain areas and it synthesizes them."

When great apes diverged from old-world monkeys about 20 million years ago, brain regions tied to motor planning also increased in relative size. That could have helped them orchestrate the complex movements needed to manipulate tools — possibly to get at different food sources, Smaers said.

Gibbons and howler monkeys showed a different pattern. Even though their bodies and their brains got smaller over time, the hippocampus, which plays a role in spatial tasks, tended to increase in size in relation to the rest of the brain. That may have allowed these monkeys to be spatially adept and inhabit a more diverse range of environments.

Prefrontal cortex

The study shows that specific parts of the brain can selectively scale up to meet the demands of new environments, said Chet Sherwood, an anthropologist at George Washington University, who was not involved in the study.

The finding also drives home the importance of the prefrontal cortex, he said.