Eric M. Van (ericmvan) wrote,
Eric M. Van

A Model for Attention-Switching, Part VIII: Norepinephrine in Humans

We’ve seen that there is not only a potent evolutionary rationale for the evolution of norepinephrine (NE) as the neuromodulator regulating attention, but that our hypothesis about its role gives us remarkable insight into the behavior of our earliest vertebrate ancestors.  But you probably don’t have any friends with file drawers full of unfinished projects who are also ray-finned fishes, let alone sharks.  So let’s see what sense our hypothesis makes of human behavior.

And let’s forget our NE hypothesis for a moment and just start with DA. We’ve proposed that it turns on phenomenal consciousness, especially the experience of emotion. This means that high-DA people are passionate and low-DA people are dispassionate. (This explains, incidentally, why highly opinionated people tend to talk loudly and gesture with their hands: remember that DA also controls motor activity through a second pathway.) In terms of cognition, high-DA people tend to be highly emotionally invested in the things they’re thinking about, while low-DA people tend to be less invested—more, well, dispassionate.

Is there a cognitive trait that would make sense to correlate with these two different emotional relationships to the contents of our thoughts? Well, sure: the more emotionally invested you are in what you’re thinking about, the longer you’d want to stay thinking about it. The more dispassionate you were, the more likely you’d be to move on and start thinking about something else. So it makes perfect good sense to correlate passion with length of attention span—and that means DA with NE.

And which of the four combinations of the two traits might be a particularly bad idea? Someone with high DA and low NE will be passionate about the contents of their thoughts, but flighty and prone to attentional shifts. Since attentional shifts can lead to creativity, that doesn’t sound like a bad combination. But low DA and high NE would give you someone dispassionate about the contents of their thoughts, but prone to linger on them. That doesn’t sound good: that sound like a recipe for boredom.

Note that we’re not saying that there aren’t dispassionate people with healthy attention spans; we are talking here about excluding the combination of the extremes of the traits. What you won’t see—what, in fact, we don’t see, except perhaps in rare variants of AD(H)D—is a dispassionate person who has trouble tearing themselves away from what they’re thinking about, as passionate people sometimes do.

You would think that that would be built into the brain: the dispassionate person would never have trouble tearing themselves away, because at some point they’d just get bored. But that’s begging the question or thinking circularly. What does it mean to be bored, cognitively? What controls boredom, chemically?

What we’ve found here is that the level of passion is controlled by one thing and the ability to tear oneself away is controlled by another completely independent thing. If in fact we observe that dispassionate people almost never have the problem of being unable to tear themselves away, we need to explain why that combination almost never exists. And our hypothesis about the roles of DA and NE explains that perfectly. Dispassionate people are that way because they have relatively inactive DA-producing enzymes, and that guarantees that they will never have levels of NE so high that they are prone to hyperfocusing. (It’s conceivable that someone dispassionate might have problem with hyperofocusing because of other defects in the attentional hardware, which is why I don’t rule out this being a rare form of ADD.)

So this correlation works really well for humans, and in fact has some explanatory power in terms of explaining why the vast majority of people who are prone to hyperfocus are passionate about thinking.

In the last installment of the model proper (there’ll be a second set of posts on implications), we’ll look at the history of the understanding of the role of NE in attention.

Tags: neuroscience
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