Blogs / The Loom

Earlier this year I wrote in the New York Times about the remarkable minds of hyenas. The evolution of their brains appears to have followed the same pattern ours have: an increasingly social life drives the expansion of some parts of their brains. This research is the work of Kay Holekamp, a zoologist at Michigan State University who has spent many years observing hyenas in East Africa. And now, continuing a trend that should strike fear into the heart of any science writer, another of my subjects has started a blog of her own. Notes from Kenya chronicles the adventures of Holekamp and her colleagues in their new field season watching spotted hyenas. (The picture above is from a recent spat they had with a lion.) Check it out.

Writing about the brain is one of the Black-Diamond challenges of science writing. We all think we know what’s going in our heads, and yet the cells and neurotransmitters and signal patterns don’t fit comfortably into our everyday metaphors. Linguist Mark Liberman at Language Log regularly writes devastating posts about how lousy a job journalists sometimes do writing about neuroscience news–especially when the research touches on our pat assumptions and stereotypes. (”See, women really do think differently…” etc.)

I’ve written a lot about the brain in the past (including a book about the dawn of neurology), but now I’m setting out to write a column every month for Discover about our gray matter. The first one is now online: it’s about how we perceive time. The first thing I had to do was throw out the metaphor of the clock, because it just doesn’t do a good job of capturing our brains’ beautiful strategies for gauging the flow of now into yesterday.

As I write these pieces, I hope that readers will leave comments–neuroscientists if you’re out there, and everyone else. I hope to get things right; I expect to get things wrong; and I’m prepared to learn along the way.

[Image: Fabiola Medeiros, reprinted under a Creative Commons licence]

Back in the 1600s, when neurology was born, it wasn’t scientists who were looking at brains. The word scientist didn’t exist. Instead, those visionary folks would have called themselves natural philosophers. As I researched this chapter of scientific history for my book Soul Made Flesh, I was struck by the way philosophers–and philosophical questions–are now making their way back into the scientific study of the brain. Last year in Discover I wrote about the work of the philosopher/neuroscientist Joshua Greene, who studies how we make moral judgments. But it turns out that neuroscientists are tackling an even deeper philosophical question: what is the self? They may not have the whole answer, but they’ve found some very interesting pieces of it. I’ve written an article on the neurobiology of the self, which appears in the November issue of Scientific American.

If you live in the New Haven area, I hope you’ll consider joining me tomorrow at 5 pm for a talk at the Yale Medical School about my book Soul Made Flesh.

The talk will be at 5 pm, Thursday October 6, in the Beaumont Room at the Sterling Hall of Medicine, 333 Cedar Street. It is free and open to the public. If you need directions, here’s a map.

I can promise lots of cool images to accompany my talk, of stuff like excorcisms, miraculous resurrections of murderers, and alchemy. All the normal things you’d expect from a seventeenth-century powerpoint.

I’ve got an article in today’s New York Times about one of my perennial fascinations—musical hallucinations. One of the reasons that I find this condition so interesting is that it gives us a look under the neurological hood. Our brains do not simply take in objective impressions of the world. They are continually coming up with theories, and they test them against perceptions every moment of our waking lives. It would be impossible to test them against a complete picture of reality, because the world is simply too complex and ever-changing. Instead, the brain makes quick judgments on scraps of information, revising bad theories that don’t make good predictions or using good theories as the basis for actions. Some scientists argue that musical hallucinations are evidence that our brains even make theories about music. When we hear stray sounds, we match them to tunes in our memory, in a sort of internal game of Name That Tune. Unfortunately, some people can’t test their theories well enough, it seems, and so they wind up thinking a church choir is singing in the next room, when in fact there is only silence.

There’s one line of evidence that supports this explanation of musical hallucinations that I didn’t have room in the article to explore. It turns out that some people have an analogous problem with their vision. They suffer from a condition known as Charles Bonnet syndrome, in which they have visual hallucinations. In some cases, the hallucinations are nothing but textures or wallpaper-like patterns. In other cases, people may see a row of people floating in front of them. Reginald King, the elderly gentleman who described his musical hallucinations to me, also suffers from Charles Bonnet syndrome. He told me about how he would see patterns on the ceiling, or sometimes a cat or a dog running across his bed.

Victor Aziz, one of the scientists I interviewed for this story, has noticed that some other people also experience both visual and musical hallucinations, and doesn’t think it’s a coincidence. It’s possible that regions of the brain that handle processing complex structures of both sound and sight can short-circuit in a similar way, producing similar hallucinations. And interestingly, brain scans of people with visual hallucinations are strikingly similar to those of people with musical hallucinations. In each case, the higher information-processing centers become active even when the regions that normally relay information from the senses are quiet. If we accept a theory of what we see, it’s as real as the theories of what we hear.

How long can an idea stay tantalizing?

Back in 2003, I blogged about an experiment that suggested, incredibly enough, that our long-term memories are encoded by prions— the misfolded proteins that are generally accepted to be the cause of mad cow disease. The evidence came from studies of a protein (known as CPEB) that plays a key role in laying down memories in neurons. Scientists found that it had a structure much like prions. When a normal protein misfolds and becomes a prion, it acquires the ability to lock onto other proteins and force them to misfold in the same way. The misfolding can spread until it has devastating results—as in the case of mad cow disease, in which prions from cow brains get into our own brains. But the discovery of prion-like memory proteins hinted that maybe they could play a beneficial role as well.

Not long after I blogged on this research, I ran into a neuroscientist I know (and who shall remain nameless). He sneered at the prion paper, pointing out that the authors of the paper didn’t show that the protein acts like a prion in neurons. Instead, they had only shown that it acts like a prion when it is inserted into yeast. They took this peculiar step because yeast have prions, and they had the tools to study prion behavior in yeast. It is far harder to experiment with prions in neurons. But this neuroscientist I spoke to thought they shouldn’t have gone public until they had taken this last, hard step.

I’ve been waiting ever since. And in the June issue of Nature Review Genetics I came across a paper entitled “Prions as adaptive conduits of memory and inheritance.” One of the co-authors is Susan Lindquist of MIT, one of the scientists who made the memory-prion connection back in 2003. Eager for an update, I read on. And what do I find? There’s a lot of new research on the role of prions in yeast, where they may play an important role in evolution. But as for prions and memory, there’s nothing beyond what Lindquist had to offer in 2003.

My patience has probably been irreparably damaged by today’s minute-by-minute news cycle, but I have to wonder why we’re still in prion-memory limbo. Is the next experiment too hard to do? Does it take years to finish? Or is the link between memories and prions just not there?

Just as I’m tempted to give up hope, out comes another paper. It may not seal the deal, but at least keeps me eager for more. Psychiatrists in Switzerland were inspired by the original prion-memory experiments to look for evidence in people’s genes. Some studies have suggested that the strength of people’s memories is at least partly the result of genetic variation. But no one knew which genes were involved. So the psychiatrists took a look at the prion protein gene (PRNP), which causes mad-cow disease when it misfolds. (No one is sure what it does for us in its normal shape.) People have different versions of PRNP, some of which are more prone to misfolding than others. The scientists genotyped 354 subjects to see which version they carried and then gave them a memory test.

In a paper in press at Human Molecular Genetics, they report that people with one or two copies of the misfolding version recalled 17% more information than those without a copy. It’s a puzzling result for many reasons, not the least of which is the fact that the link originally proposed between prions and memory did not involve PRNP but CBEP. But it’s enough to keep me wanting more.

Blogging will be light for a few days because my hard drive devoured itself last night. I just wanted to mention a couple brain-related items. First off, I’ve got a profile in today’s New York Times of Michael Gazzaniga, one of the most fascinating people involved in science today. His research on the split minds of people with split brains would be fascinating enough, but now he’s trying to use these insights to make sense of the confusing choices that bioethics now forces us to make. (Gazzaniga’s a feisty member of the President’s Council on Bioethics.)

For another take on the brain and our sense of who we are, let me also direct your attention to the paperback edition of Soul Made Flesh, which is due in bookstores in June and is already available on Amazon. It looks at the birth of neurology in the 1600s. If you think these are strange times, neurologically speaking, imagine an era when people thought the brain was no more capable of thought than a bowl of curds.

Evolutionary psychologists argue that we can understand the workings of the human mind by investigating how it evolved. Much of their research focuses on the past two million years of hominid evolution, during which our ancestors lived in small bands, eating meat they either scavenged or hunted as well as tubers and other plants they gathered. Living for so long in this arrangement, certain ways of thinking may have been favored by natural selection. Evolutionary psychologists believe that a lot of puzzling features of the human mind make sense if we keep our heritage in mind.

The classic example of these puzzles is known as the Wason Selection Task. People tend to do well on this task if it is presented in one way, and terribly if it is presented another way. You can try it out for yourself.

Version 1:

You are given four cards. Each card has a number on one side and a letter on the other. Indicate only the card or cards you need to turn over to see whether any of these cards violate the following rule: if a card has a D on one side, it has a 3 on the other side.

Version 2:

Now you’re a bouncer at a bar. You must enforce the rule that if a person is drinking beer, then he must be over 21 years old. The four cards below each represent one customer in your bar. One side shows what the person is drinking, and the other side shows the drinker’s age. Pick only the cards you definitely need to turn over to see if any of these people are breaking the law and need to be thrown out.

The answer to version one is D and 5. The answer to version two is beer and 17.

If you took these tests, chances are you bombed on version one and got version two right. Studies consistently show that in tests of the first sort, about 25% of people choose the right answer. But 65% of people get test number two right.

This is actually a very weird result. Both tests involve precisely the same logic: If P, then Q. Yet putting this statement in terms of social rules makes it far easier for people to solve than if it is purely descriptive.

Leda Cosmides and John Tooby of the University of California at Santa Barbara have argued that the difference reveals some of our evolutionary history. Small bands of hominids could only hold together if their members obeyed social rules. If people started cheating on one another–taking other people’s gifts of food, for example, without giving gifts of their own–the band might well fall apart. Under these conditions, natural selection produced a cheating detection system in the brain. On the other hand, our hominid ancestors did not live or die based on their performance on abstract logic tests. Rather than being a general-purpose problem-solver, the human brain became adapted to solving the problems that our ancestors regularly faced in life.

The Wason Selection Task has become the center of the debate over evolutionary psychology. Some critics, such as the French psychologist Dan Sperber, claim that Cosmides and Tooby can’t make such strong statements about human reasoning from the Wason Selection Task. Others claim that the brain can’t be sliced up into modules so nicely.

The controversy has taken a very interesting turn now, thanks to brain imaging. A team of Italian psychologists had people lie in an MRI scanner and work their way through a set of puzzles that followed the same line of logic as the ones I presented above. They then compared how the brain responded to the challenges to see if indeed the brain works differently when it is solving problems in terms of social exchange than when the problem is more abstract.

The psychologists didn’t use a conventional Wason Selection Task like the ones above, because they wanted to make the problems as similar as possible, except that one dealt with social exchanges. Brain imaging requires this sort of strict experimental design, because it’s very easy to see differences in brain activity that aren’t actually relevant to the question a scientist wants to answer. For example, if one puzzle just so happens to involve picturing an object, some of the brain’s visual processing may become active. So the researchers told their subjects that the puzzles would involve a hypothetical tribe. A purely descriptive puzzle might require subjects to consider the rule, "If a person cracks walnut shells, then he drinks pond water." The subjects might then see a set of cards that read, "He didn’t drink pond water," "He didn’t crack walnut shells," He cracked walnut shells," and "He drank pond water." The researchers also had their subjects solve puzzles that involved social exchanges. The rule in these cases might be, "If you give me sunflower-seeds, then I give you poppy petals."

The psychologists report the results of the test in a paper in press at the journal Human Brain Mapping (click the html link to get the whole paper for free). The results are fascinating–although the researchers don’t claim to have settled the debate over the cheater module. Both the social exchange and descriptive version of the puzzle activated the same network of regions on the left side of the brain. One region (the angular gyrus) is considered important for semantic tasks. A second region is located near the left temple (the dorsolateral prefrontal cortex). It’s essential for considering many different pieces of information at once. The third region, the medial prefrontal cortex, becomes active when people need to bear in mind a larger goal while they solve the many small problems it poses. Previous studies have shown that the left side of the brain plays a much more important role than the right in reasoning and coming up with explanations for how the world works in general.

Now here’s the kicker: the social exchange version of the problem doesn’t just activate this left-brain network. It also activates the same regions in the right side of the brain. Many studies in which people have thought about social situations have tended to turn on the right side of the brain more than the left, and so in one sense this result isn’t too surprising. But it is surprising when you consider that the descriptive version of the puzzle that only switch on parts of the left side of the brain involved thinking about other people and their actions. You might think that that would be social enough to engage any parts of the brain specializing in social thinking. Apparently not. Only when the puzzle involved rules for social exchanges did the right-brain network come on line.

Is this the cheater module? It’s conceivable that the Italian psychologists tapped into some social brain circuit that isn’t specifically adapted for enforcing social rules, but for some somewhat broader group of social problems. It would be interesting if a test other than the Wason Selection Task could trigger the same left versus left-right patterns. The precise evolutionary forces that shaped this feature of the mind may not be clear yet. But this experiment is an important step towards working out the biology between the strange results of the Wason test. Clearly, our brains throw a lot more neurons at logic problems when they concern our social lives instead of abstractions. Analytic philosophers are made, you could say, but political philosophers are born.

Update: 7:15 pm– I decided to change the first version of the test to avoid ambiguity.

Update: Tuesday, 8:15 am– Some commenters have argued that people do better with the bar version of the puzzle because people have more experience with it than with abstract logic. Actually, many variations of the puzzle have been tested out, and the same results emerge. Notice, for example, that the Italian scientists who did the most recent study put the puzzles in terms of a hypothetical tribe, with which the subjects had no experience at all. Despite this different format, almost precisely the same fraction of the subjects got the different versions write as in more familiar versions of the test, such as the bartending example.

Thanks also to the sharp readers who pointed out that the puzzles need to be If-Then propositions.

I’ve got an article in tomorrow’s New York Times about a startling new way to control the nervous system of animals. Scientists at Yale have genetically engineered flies with neurons that grow light-sensitive triggers. Shine a UV laser at the flies, and the neurons switch on. In one experiment, the scientists were able to make decapitated flies leap into the air by triggering escape-response neurons. In another, they put the trigger in dopamine-producing neurons, and the flash sent healthy flies walking madly around their dish. (You can read the paper for free at Cell’s web site.)

In working on this story, I was reminded of the research being done now with implanted electrodes, which I wrote about last year in Popular Science. Much of this research focuses on listening in on neurons to control robots or computers. But the electrodes have also been used to send electricity into the brain to control an animal. In one case, scientists steered a rat by sending jolts into its brain.

But those who feel anxious about the genetic engineering I write about tomorrow should bear a couple things in mind. First off all, this method only lets scientists turn on an entire type of neurons. All the escape-response neurons became active in the first experiment. All the dopamine-producing neurons became active in the second. That’s a far cry from a complex set of signals that might make an animal carry out a complex behavior. But that’s not what the scientists who designed this new method had in mind, anyway. They want to develop new ways to do experiments on the nervous system.

Still, science fiction writers should pay heed. It’s conceivable, for example, that a completely unethical scientist could engineer similar triggers into a human brain (although it could also fail completely). And another thing that inspires the sci-fi imagination is the experiment on dopamine-producing neurons. Dopamine is a neurotransmitter that give the brain a sense of expectation and anticipation, priming it to learn how to gain rewards. It’s also what cocaine exploits to produce its addictive pleasure. In other words, when the scientists switched on their laser, the flies got the biggest high of their lives.