Archive for March, 2014

Into every life a little rain must fall…

Monday, March 17th, 2014

…but can you please just refrain from posting about it on Facebook? Because it bums me out. And it’s sunny here.

This recent study, published in the journal PLOS One, put together weather data and Facebook posts in American cities. The authors wanted to test a few hypotheses having to do with the impact of a variable like weather not only on people’s state of mind, but on the state of mind of members of their social network. First, they determined that people’s Facebook posts on rainy days tend to be less positive in tone than on non-rainy days. Specifically, on rainy days there were 1.19 percent fewer positively toned Facebook posts, and 1.16 percent more negatively toned posts, than on non-rainy days. That in itself isn’t terribly surprising, except maybe that the effect is pretty small. Indomitable folks, those Americans. Besides, they’re not gonna stop the rain by complainin’, am I right?

Anyway, that wasn’t the interesting part. This was the interesting part: on those same days, people’s positive and negative posts were impacted by the weather in their friends’ cities. Based on the models they constructed from the data, the authors estimated that a rainy day in New York City directly results in an extra 1500 negative posts by New Yorkers, and also results in about an extra 700 negative posts by their Facebook friends in other cities, irrespective of the weather there. Here’s a figure from their study that shows, for each city, the effect of rain in that city, as well as the (indirect) effect of rain when it happens elsewhere.

This is all direct evidence of an emotional contagion effect that occurs across social networks, and the authors argue that social media may serve to amplify natural social contagion effects by giving people more and quicker access than they would otherwise have to the emotional states of other people, even people who are miles away. This, they speculate, may result in “greater spikes in global emotion that could generate increased volatility in everything from political systems to financial markets”. Boy, that’s not at all scary, is it?

Diffusion-weighted MRI image of the human brain

Wednesday, March 12th, 2014

This picture shows up as a finalist in the Wellcome Image Awards for 2014 (check out the rest, they’re cool!). It shows an image of the connecting fibres in the human brain (I mentioned those in my last post), captured using MRI diffusion-weighted imaging. This type of imaging captures the position and direction of fibres in the brain by capitalizing on the fact that water molecules move more easily along fibres than across them. In the image the front of the head is to the right, and the left side of the head is at the top. The fibres are colour-coded to show you their direction in three dimensions: green ones run front to back along the main axis of the brain, red ones run left to right between the ears, and blue ones run top to bottom, between crown and neck. I don’t know about you, but I find images like this breathtakingly beautiful:

Diffusion weighted imaging has been an important tool recently, as neuroscience has enlarged its emphasis from the functions of particular brain structures to the way these structures are joined together, structurally and functionally, into networks. Scientists identify these networks structurally using imaging such as is shown here. They also have some cool ways of identifying them functionally, by noting which parts of the brain tend to wax and wane together across time in their oxygen uptake while a person is lying in an MRI scanner and doing some sort of task. The premise is that areas that consistently “light up” (become active) together are working together.

There’s been a lot of really neat work in this area, with several networks now reliably identified and characterized in terms of their participating brain areas and their probable functions. For example, there’s the pioneering observation of a network called the Default Mode Network, which was first characterized when neurologist Marcus Raichle and colleagues noticed that the brain always seems to be shutting off the same areas when people are in the scanner doing an experimental task. Raichle got curious about these areas, and found that they’re active when a person is not asked to engage in any task in particular, but simply lying still in the scanner. More recent work has shown that the DMN isn’t just an idling state, though: it also activates in some states of focused but inwardly-directed attention, such as thinking thoughts about oneself or recalling autobiographical events. The other thing about the DMN that’s really interesting from the perspective of psychopathology and neurology is that a lot of clinical conditions are associated with a failure to deactivate the DMN when it’s supposed to quiet down and let other, more externally directed networks do their thing. It just keeps chugging along, interfering with the external allocation of attention, which researchers think may be why so many different conditions have impaired atttention as one of their features.

Thinning of cortex correlates with changes in IQ

Wednesday, March 5th, 2014

This article describes a recent multi-site study that measured changes in children’s brains as they aged, and correlated those changes with increases or decreases in their general intelligence, as measured by their IQ. The study was published in January in the journal NeuroImage by Miguel Burgaleta, Wendy Johnson, Debra Waber, Roberto Colom and Sherif Karama. The authors compared the thickness of the brain’s cortex in children and adolescents at a two-year interval, to provide a snapshot of their development at those two time points. Cortex is Latin for “bark”, as in tree bark. It refers to the outermost layer of brain tissue, which is grey in colour and distinct from the white matter that lies underneath it. The cortex is basically where most of the computational action happens in the brain. Much of the remaining brain tissue enclosed by this “bark” consists of fibres connecting cortex to cortex, cortex to deep brain structures, and cortex to the rest of the body.

As adolescents develop, the thickness of their cortex generally decreases, a process of refinement that supports their ongoing development. What this study showed was that some people have more thinning than others in particular brain areas. Those who had moderate thinning in those areas (mostly on the left side of the brain, in front of the sensorimotor strip) maintained a similar IQ score across the two-year gap, while those who had extreme thinning showed a drop in IQ scores across the two-year interval. Interestingly, some had no thinning at all, or even a little bit of thickening, and these individuals showed increases in their IQ across the two-year period. Here’s a figure from the study showing which part of the brain showed correlations between cortex thinning and IQ changes, and what those changes were for the various IQ change groups (those who showed a decrease in IQ, stable IQ, or an increase in IQ).

The implications? Well, there are a few. One is that IQ isn’t always stable across time—although we psychologists generally assume that it will be, and that any changes we do see are the result of random measurement error. It appears that people sometimes actually get smarter, or less smart, and that these changes have real, solid neurological reasons behind them. Another is that the left frontal cortex seems particularly associated with intelligence, more so than other brain areas, although there is obviously a lot of contribution from a lot of intracranial neighbourhoods.

Best of all, I will now have a ready answer the next time my wife refers to me as being “a little bit thick in the head”.