Archive for May, 2014

Why we yawn

Wednesday, May 28th, 2014

Ever wonder why you yawn? A recent study published in the journal Physiology and Behavior supports a theory that the reason why we yawn is to cool our brains down. Turns out that yawns are preceded by warmer-than-normal brain temperature, and are followed immediately by a cooler brain. Check this out:

I had a look at the study. It was a fun experiment. The experimenters approached people in public places in the city of Vienna and asked them to participate in a survey about contagious yawning (the phenomenon wherein we yawn when we see, hear about, or think about someone else yawning), look at a series of pictures of people yawning, and then fill out a brief survey reporting how often they had yawned, or felt the urge to yawn, during the process. The experiment was conducted once during the winter, and again during the summer, and the researchers were collecting temperature and humidity data during each person’s participation. Sure enough, the warmer it was when someone took the survey, the more likely it was that they yawned. Interestingly, that was only true up to a point, though. A previous study conducted in Tuscon, AZ when the temperature was over 37°C (i.e., body temperature), found that yawning decreased at that temperature. This also aligns with the theory, because filling the lungs with body-temperature air wouldn’t have any cooling effect.

As for the phenomenon of contagious yawning, researchers think it’s a way of promoting the wide distribution of peak levels of vigilance within a social group, because when the brains of all group members are working optimally, they’ll be more likely to spot predators, potential food sources, etc.

Because, of course, cooler heads always prevail.

Another reason your dad was right that you should stay in school

Sunday, May 25th, 2014

This study is interesting. Published last December in the Archives of Physical Medicine and Rehabilitation, it looked at cognitive performance of people who had suffered a traumatic brain injury (TBI). A TBI is basically any injury to the brain that results from externally applied physical forces, as would happen, for example, in a car accident. The study, authored by James Sumowski, Nancy Chiaravalotti, Denise Krch, Jessica Paxton and John DeLuca, examined a variable that might partially account for why impacts of TBIs on cognitive ability can be so variable from one case to another. It’s well known in TBI circles that it’s difficult to predict, simply on the basis of the type or extent of a brain injury, just how much the injury will affect subsequent cognitive functioning.

The variable the authors examined was the number of years of schooling the individual had undergone prior to the injury. The number of years of schooling is what is known as a “proxy variable”, that is, a variable that’s assumed to reflect another variable indirectly. In the case of educational attainment, what researchers think they’re measuring is the amount of intellectual stimulation a person has received in his or her lifetime—and that’s a reasonable assumption, provided she didn’t study fine arts. Okay, okay, don’t be so touchy; I was just kidding! Anyway, what the authors were interested in was a phenomenon that’s already known in research on other conditions, namely, the fact that people with more years of education seem to have brains that are more resistant to the performance-degrading impacts of various diseases or illnesses. The most striking of these is Alzheimer’s Disease, for which it’s been well documented that people with more education tend to be spared partially or totally from dementia, despite their brains on autopsy being riddled with the same Alzheimer’s pathology that is assumed to cause the cognitive decline in other people. The term for this seemingly greater resilience characterizing better-educated brains is cognitive reserve. The researcher whose excellent work is most associated with the construct of cognitive reserve is Yaakov Stern, of Columbia University in New York.

So, most of the work on cognitive reserve has shown that people with more years of education are more resistant to the onset of dementia in old age. The researchers in the current study looked at whether the same would be the case for people who had suffered a TBI. To examine this question, they compared the cognitive performances of a group of 44 TBI sufferers, on average about a year after their injury, to a group of normal, healthy control subjects. All of the participants completed a group of cognitive tests measuring processing speed, working memory (the ability to hold information in a highly active state while using it), and episodic memory (the ability to remember events that have happened to you). These were chosen because they’re among the most consistently impaired functions following a TBI. The three tests were summarized into a single performance score, and then the joint impact of TBI status and educational attainment (expressed as number of years of schooling) on this score was tested.

The results clearly showed that, although the TBI patients performed significantly worse on the cognitive tests than the controls (not a surprising finding), those who had more years of schooling were not impaired as badly as those who had fewer years of schooling. The following figure taken from the study illustrates this difference. The red dots represent members of the TBI group, and the blue dots, members of the control group:

In fact, it’s clear from the graph that if a person had had, say, 25 years of schooling, he would perform better after a TBI than before! Okay, not really. That was a joke. But it is a pretty interesting indication of how the extensive and varied intellectual experiences that accompany higher education can actually be not only personally enriching, but also neurologically protective.

I find the concept of cognitive reserve to be fascinating, because it’s one case in which there’s a clear crossing-over between what we normally think of as mind/psychology on the one hand, and brain/neurology on the other. What the study suggests is that educational experiences not only change your psychology, but also change the physical stuff of your brain, in a way that is strikingly evident as (relatively) spared functioning following a physical injury. Cool, huh? See, I knew it was worth it to stay in school for that long!

Ouch. Turns out football isn’t very good for your brain.

Tuesday, May 20th, 2014

Dang it. I’ve felt guilty about liking boxing for a while, and it looks like I’m going to have to feel guilty about liking football now, too. Last week a study was published in the Journal of the American Medical Association that makes a pretty interesting case for steering your boys toward other sports, like curling or synchronized swimming or something. The study’s authors, researchers at the Laureate Institute for Brain Research in Tulsa, Oklahoma, compared MRI scans of brains of NCAA football players, 25 of which had a documented history of concussions, and 25 of which had no reported history of concussions. They also added a control group, consisting of 25 young men matched for age and education.

So, this study was like the marijuana one, in that it compared the volume (size, in three dimensions) of particular brain structures between an identified group and a comparison group. Turns out it was similar in another way, too: the good ol’ hippocampus drew the short straw again and had to be the structure that got shrunk. Specifically, the football players had smaller hippocampi (that’s plural for hippocampus—because “hippocampuses” is just way too silly to say at academic meetings) than the matched controls. In fact, those with no concussion history had hippocampi that were, on average, about 15 percent smaller than the controls’ hippocampi. And as for those who had a concussion history, theirs were a whopping 25 percent smaller than the controls’. The differences among all three groups were significant from one another, for both the left and the right hippocampus. And that’s not all: there was a significant negative correlation between left hippocampus volume (but, oddly, not right) and the number of years of tackle football that had been played. That is, for every year of football played, the left hippocampus was that much smaller.

So it seems that all the physical roughness of the game results in cumulative injury to the brain. This is most vividly the case when people actually suffer from a series of concussions, but, importantly, this study suggests that the absence of concussions doesn’t mean the brain has not been damaged by the repeated forces associated with playing tackle football. The damaging effects of repeated concussions has been very much in the public eye for the last few years, resulting in some serious soul-searching in the world of competitive sports. This study adds to the literature in support of greater caution around head injury in sports, and raises the sobering idea that subtle damage may come about even when there is no history of overt symptoms.

Friends, I’m told, don’t let friends do drugs. Maybe they shouldn’t let friends play rough sports, either. Golly, how are we gonna have any fun?

Casual marijuana use among young adults leads to structural brain abnormalities

Wednesday, May 14th, 2014

Came across this study published last month in the Journal of Neuroscience. The study’s authors, led by Jodi Gilman of Harvard Medical School, looked at whether marijuana, used in typical quantities, is associated with any structural brain changes among users between the ages of 18 and 25. Previous research had shown that administration of THC (the psychoactive component of marijuana) to rats results in brain changes, and that extremely heavy use among humans can also lead to brain abnormalities. However, to date no studies had shown whether more typical usage patterns among young human adults were associated with any brain changes.

The authors compared MRI scans between 20 casual marijuana users and 20 other young people, matched to the marijuana group on the usual demographic variables. They found—perhaps remarkably considering the small sample—pronounced differences between the marijuana group and the matched controls. In fact, every single member of the marijuana group, even those who smoked pot only once a week, showed the same pattern of structural brain differences from the control subjects. Furthermore, these brain differences were correlated with usage patterns, such that they were more pronounced among those who used the drug more frequently.

The specific differences were that the users exhibited greater grey matter density (more cells packed into a given volume) in the left nucleus accumbens and the surrounding cortex, including the hypothalamus and the left amygdala. They also showed abnormalities in the morphometry (shape) of the left nucleus accumbens and right amygdala. Now, these are not structures that one wants to mess around with. They’re critical for the processing of information related to emotion and motivation, and the nucleus accumbens in particular is associated with the generation of reward motivation – that is, the ability of a reward stimulus to influence future behavior aimed at achieving further reward. The amygdala, of course, is important for the shaping of emotional experience, as well as the influence of emotional experiences on behavior.

We seem to be on a steady track toward the full mainstreaming of marijuana in our society. The drug is being used extremely widely now, especially among teens, and in popular culture it’s consistently portrayed as a harmless form of recreation. Legislatures are under pressure to legalize its use, the outcome of which now seems to be pretty much a foregone conclusion. But this study shows that marijuana is a more powerful and potentially damaging substance than is generally thought. The study suggests that even light use brings about quite profound changes in brain structure (and, consequently, in brain function). Moreover, the anatomical structures affected by the drug line up, in kind of a scary way, with the most frequently made behavioral observations about pot users: that they seem blunted in their motivation, unambitious, listless. I’ve seen these qualities in many of my own clients who use marijuana.

Listen, it’s easy to think of those qualities as charming and entertaining. So many movies have a lovable-pothead character who is portrayed as almost a personification of the drug itself: fun, mostly harmless, kind of goofy.

But what if the brain changes that are brought about by even casual pot use result in serious motivational deficits, deficits that make it harder for the person to persist with his studies, to enjoy life when not high, to think, remember, and make decisions? How will that affect individual lives? How will it affect relationships, the workforce, the economy? Zoinks!