The Neurology of Decision-Making

Talha, in this response to the introductory post, discusses some fascinating aspects of decision-making. I thought I’d pull that discussion up to the level of a new posting. He writes:

a decision is based on the cummulative data we gather from surroundings until we have enough data to reach a certain threshold where the decision is executed. But the rate of approach to threshold is not always the same despite the same data being presented on several different occurences; the rate (gradient) varies in a normal (Gaussian distribution). Where does this element of ‘randomness’ come from? Who introduces it? Why does it vary from one decision to the other? Science and empirical observation has not so far answered that question and I think, never will. :)

A clinical example might be the decision whether to proceed with an MRI in a stroke case. We might first think about whether we can localize the lesion and ascertain the stroke mechanism clinically, without MRI. We might then decide that we’d like the study in order to help pin down the stroke mechanism and determine the need for specific therapy such as endarterectomy or anticoagulation. We might then consider that the patient is elderly and frail and wouldn’t be a good candidate for those therapies even if the test were “positive”.  But then the daughter shows up and isn’t comfortable with the plan to accept this uncertainty about the stroke mechanism and rule out these treatments so soon, so the patient and family change their minds and request that we proceed. Then it turns out that our patient has chronic renal disease, and our radiology colleagues are reluctant to give gadolinium for fear of provoking nephrogenic systemic fibrosis. Meanwhile, the patient, family, and nurses might be frustrated by how the plan keeps changing. Why can’t the doctors just make up their minds? And the next case might be simpler. Or harder.

A neuroscientific analogy that comes quickly to mind is that of the action potential. Excitatory and inhibitory post-synaptic potentials (EPSPs and IPSPs) are constantly coming and going and when they sum in the right way, an action potential is fired. Just as the speed with which a clinical decision threshold is reached varies from decision to decision, so too the ease of action potential firing depends on factors such as the timing of the EPSPs, their location relative to the axon hillock, and other factors both known and unknown. The impulses in favor and against obtaining an MRI have a superficial resemblance to EPSPs and IPSPs crashing on the beach for a while until the action potential fires (or doesn’t).

Having said that, I should emphasize that the foregoing is only an interesting resemblance and should not be taken to mean that human behavior can be reduced to psychological laws firmly rooted in the laws of neurophysiology. In their fantastic book Philosophical Foundations of Neuroscience, M.R. Bennett and P.M.S. Hacker debunk that proposition and many others. If anyone’s interested, see chapter 13, “Reductionism”.

I very much agree that we’re never going to scientifically understand all of the myriad variables at play in decision-making, medical or otherwise. The intellectual joy of science lies in trying to figure this stuff out. The spiritual joy lies in accepting that we never fully will . . .

About Justin A. Sattin

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