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Language and executive functioning in the brain

A couple years ago, I had the opportunity to meet Dr. Angie Laird, a professor at UTHSCSA‘s Research Imaging Institute. Her work involves mapping pathways of neural activity using neuroimaging data and connecting these pathways to behavioral and cognitive processes. During our meeting, Dr. Laird shared with me some fascinating discoveries, which were recently published in the Journal of Cognitive Neuroscience (Laird et al., 2011).

Let me just say that I am not a neuroscientist. I’d need a whole stack of books (and maybe some classes) in order to fully understand this paper. Still, this paper—specifically Figure 4—has stuck with me. Every so often, I come back to it, still trying to wrap my head around what it means.

Dendrogram resulting from hierarchical cluster analysis of neuroimaging data (Figure 4, Laird et al., 2011). Categories on the x-axis represent types of experimental tasks, and the similarity of these tasks is illustrated by the height of the line connecting tasks. When the neurological pathways involved in two tasks are similar, the tasks are close together and connected by a short line. A dendrogram listing the individual tasks can be found here.

Most of this figure shows what you would expect. Music, speech, and hearing are closely related to each other. Some bodily perceptions (e.g., pain) are closely related to action. But one unexpected piece really caught my attention: executive function and language.

Executive functioning includes high-order processes like self-control, attention, working memory, problem-solving, goal pursuit, and decision-making. In studies on ego depletion, researchers have shown that executive functioning resources are limited. If all the resources are “used up” on one task (studying for a test), they will be temporarily unavailable for another task (resisting a delicious plate of cookies). It works in the other direction, too. Because these tasks can affect each other, we assume they use the same energy source and may follow similar neural pathways.

Here’s where Laird’s paper comes in. As I understand it, the cluster analysis shows that executive function tasks use relatively similar neural networks. But importantly, they are split, with language in between. Group A (working memory and reasoning) is more closely tied to language than Group B (inhibition and attention). The figure also shows that the neural pathways involved in language are more similar to both executive function groups than the groups are to each other.

This is interesting, but is it important? All of these tasks are still highly related, so the neurological distinctions are probably subtle. They are all highly complex tasks—what the prefrontal cortex lives for. But the differences, however subtle, tell us something about how humans think. Language is heavily involved in most working memory and reasoning tasks. This doesn’t seem to be the case for inhibition and attention tasks. Take, for example, the n-back and go/no-go tasks. The n-back task requires participants to keep a sequence of letters in working memory, then respond when the newest letter is a repetition from n places back (for a 3-back, you’d respond when the sequence is . . . U S X U . . .). To complete working memory tasks, many people rehearse what they’re trying to remember. That is, they repeat it either aloud or in their head. The go/no-go task, on the other hand, presents participants with two stimuli (e.g., a red square or a blue square). Participants respond when one stimulus is presented (GO response) but do not respond when the other is presented (NO-GO response). Comparing these two tasks, it is easy to see how the n-back task might be more closely tied to language pathways.

So, let’s say a person is on a diet but sees a chocolate cake in the break room at work. Attention processes will determine if the person notices the cake, and inhibition processes will determine if he/she eats it. To inhibit the cake-eating response, he/she may list all the reasons why eating the cake would be bad. But the cluster analysis suggests that these two processes don’t follow the same pathways. This could explain why we sometimes fail to exercise self-control, even when there’s a hundred good reasons to do so. It may also explain why it’s so effective to divert attention away from things that interfere with reaching our goals.

On another note, there’s one other finding that struck me in this paper. While language and executive function are highly related, emotion follows completely different pathways. I’m also interested in the pathways associated with social cognition tasks, which are more related to emotion than to executive functioning. Social cognition tasks include theory of the mind tasks, which require participants to understand how someone else experiences the world. This sparks several questions for me. Does this suggest that emotions are related to “social” pathways in our brain? What does this say about emotions and perspective-taking in non-human animals? What is the significance of the fact that emotion pathways are more separated from inhibition pathways?

I’ll be interested to follow how this research impacts our understanding of why we think, feel, and act the way we do.

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