Top-Down Control?

In a recent paper, distinguished neuroscientist Chris D. Frith calls attention to a simple but arresting point: “there are no brain areas that have only outputs and no inputs”. Instead, every area that provides its output to other areas also receives inputs from other areas (as well as feedback from areas to which it sends output).

For example, if we act, the motor neurons that drive our muscles fire. Areas in which these motor neurons lie receive input from areas that lie a little farther forward in the brain. These more forward areas receive input from an area still farther forward (the prefrontal cortex), which receives input from many other areas, and so on. We never come to an outputter whose activity is not conditioned by inputs from elsewhere.

The context for this point will be clear from the article’s title: “Free Will and Top-Down Control in the Brain”. Frith contrasts top-down control with bottom-up control. The “bottom” is sensory inputs and in bottom-up control, action is driven by sensory inputs. Reflexes would be the clearest sort of case: if your knee is tapped in the right way, your lower leg will move as a direct result of the tap.

In contrast, Frith takes top-down control to occur when goals or plans are involved in actions. A key point is that goals or plans do not depend directly on what we are immediately sensing. Which food you purchase for dinner may well depend on the quality of what you see in the grocery store, but your goal to get some food did not depend on what you were seeing or hearing when you went to the store.

Your goal to get food did, however, depend on conditions somewhere in your brain, and if there is no area that is solely an outputter, the goals you have are the result of contributions from many brain areas. In Frith’s thinking, a true “top level” would be a brain area that affects other brain areas, but is not affected by other areas. The significance of the fact that all brain areas receive inputs from other areas is that there is no “top level” in this sense. There is no unaffected effector from which our goals emanate.

Frith sees this fact as a problem for locating free will in an individual. His view seems to be that free will requires a top level that is only a top level, i.e., is not affected by anything else. “Nothing must control the controller.” Since there is no top level of this kind in the brain, we cannot find a physiological area in an individual person that provides free will.

One might draw the conclusion that there is no such thing as “free will” if this term is understood to require a top level that has no inputs. That would, of course, leave open the possibility of offering some other conception of “free will” that would not imply a requirement that we know is not satisfied.

Interestingly, that is not the conclusion that Frith draws. Instead, he considers experiments on free actions. Typical tasks in these experiments include moving one’s finger whenever one wishes to do so; or moving the right or left index finger, whichever one wishes, in response to a signal; or generating a series of “random” digits. Frith notes that results in such experiments depend on a social interaction between participants and experimenters – the latter give instructions, and the participants cooperate in agreeing to try to follow them.  So, he says, “The top-down constraints that permit acts of will come from outside the individual brain. . . . If we are to understand the neural basis of free will, we must take into the account the brain mechanisms that allow minds to interact”.

This does not seem to be a happy solution to the problem as Frith sets it up. That’s because social interactions plainly do not provide a “top level” in the sense of something that gives outputs but receives no inputs. Participants and experimenters are themselves subject to many social influences; there are no people who give outputs to others but receive no inputs from others.

It seems that a better conclusion to draw from Frith’s reflections is that there is no “free will” in the sense of an outputter that has no inputs. If there is such a thing as “free will” at all, there must be some other way of conceiving what it amounts to.

[The paper from which I’ve quoted is Chris D. Frith, “Free Will and Top-Down Control in the Brain”, in Murphy, N., Ellis, G. F. R., and O’Connor, T., Downward Causation and the Neurobiology of Free Will (Berlin: Springer-Verlag, 2009), pp. 199-209. Frith attributes the simple point with which this post begins to another distinguished neuroscientist, Semir Zeki.]

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