Scan shows how the brain brakes for decisions

It will take a long time, but there’s no material barrier to stop us from eventually observing all of the physical processes through which our brains function and from which we receive our perceptions of those functions, what we call our minds.

The way we make decisions offers one of the simpler but more appealing examples of the notion that our minds, rather than being representations of our brains, are somehow separate entities that control or oversee those brains.

We often act impulsively, but we also experience many situations in which we appear to control our impulses deliberately, to apply a kind of rational brake to our careering urges. What could be better evidence that our minds control our brains? Recent research, reported by Medical XPress last week, demonstrates the brain processes by which this type of cognitive control operates, and there’s nothing extra-physical or particularly “rational” about them.

It may strike some as strange that someone who calls himself a rationalist is comfortable with more evidence that our rational minds are composed of mostly automatic, mostly unconscious physical processes. However, to deny or explain away the mounting evidence that there is no “mind” beyond “brain,” that mind is a personal representation of universal brain functions, is itself not rational.

I am not at all uncomfortable accepting rationally that my rationality is fundamentally a percept, the way that certain brain functions are expressed to my consciousness. I don’t see how one can reject such a view without embracing some kind of dualism — a dualism which is itself irrational.

In the current research, Brown professor Michael Frank used fMRI readings to study the effects of deep brain stimulation (DBS) on Parkinson’s patients. He discovered that a brain whose subthalamic nucleus (STN) was receiving electrical impulses was a brain that made more impulsive decisions. Frank wondered if this was a general effect, rather than a characteristic of Parkinson’s patients alone.

Frank and his colleagues devised a task in which subjects had to choose between two images, one of which was more strongly associated with a reward. When the difference between the images was less obvious, requiring a more discerning choice, activity in the medial prefrontal cortex (mPFC) increased, and so did response time.

Parkinson’s patients whose DBS impulses were not activated performed the same as did subjects who did not have Parkinson’s. But those Parkinson’s patients who were receiving DBS impulses decided more quickly and less accurately.

Frank hypothesized that the DBS impulses interrupted signals coming to the mPFC from elsewhere in the brain. In effect, the DBS impulses were breaking an STN circuit that the mPFC uses to dampen impulse urges, thus giving it more time to consider its choice.

The focus of the Brown researchers is to develop a DBS system that will not interfere with decision-making, but the larger implication interests me much more.

When we make decisions, we like to think of ourselves as rational actors — at least, I do. There are people, including any number of self-help authors and advocates of some spiritual disciplines, who advise us to “go with the flow,” to be spontaneous and impulsive. Certainly there are circumstances in which this approach is appropriate, indeed quite enjoyable, but it’s not a general strategy with which I am comfortable. I like to think that I’m an essentially deliberative person, weighing options and considering consequences before acting. That’s my “personality,” the kind of person I am.

The research outlined above goes some way toward explaining what my brain is doing when I act deliberatively. Apparently, I’m getting impulses to do X or Y. These impulses are being delayed or muted temporarily by the activity of my STN, while my mPFC sorts out the choice.

Am I a more than usually deliberative person because my particular STN has more dampening power than usual? Is this the physical source of my typical behaviour? How much of this “extra” dampening comes from individual differences in universal brain structures? How much of it comes from learning and experience, from culture and environment?

If the STN’s impulse-blocking relationship with the mPFC is the source of my tendencies — and here’s the key philosophical question —  does this fact, or knowing this fact, have any real implications for things like consciousness, free will, and identity? In the simplest terms, does describing the physical processes of the brain undermine the personal experiences of the mind?

I don’t think so, for the fundamental reason that I’ve been emphasizing in the last few posts: the mind is a product of the brain, and the simple (but not simple to perform) act of mapping the brain’s processes doesn’t — can’t — change the nature of the mind.

A table is a table whether or not we know the type of wood of which it’s composed or the methods used in its construction. Its “tableness” is not dependent on those descriptions, but on its purpose and utilization. Similarly with the mind, I think. It was a mind before we knew anything about how it works; it will be a mind after we’ve mapped out all of its parts.

If you think that this is an obvious and simple observation, not worthy of providing the foundation for a theory of consciousness or will or self — if you insist on looking for something more complicated, more subtle, more profound on which to base our concept of mind — maybe you’re looking for something that isn’t there, or looking for it in a way that isn’t appropriate in our post-metaphysical world?

You decide — and may your mPFC get the help it needs from your STN while you’re thinking about it.


One thought on “Scan shows how the brain brakes for decisions

  1. Missing in this is a discussion of how the brain learns from experience, stores that learning, and how in turn that appears as rational intervention in impulsive action considered from the dualist position. Does education count? If learning and experience alter the physical brain and that plays a major role in the physical processes discussed then the concern about losing the separate mind
    could be lessened.

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