Apr 15 2008

Decision Making in the Brain

Neuroscientists are wrangling with the question of decision-making and free will – by which I mean they are looking at what the brain is doing during the process of decision-making. The deeper questions of free will – what is it really and what are the implications of neuroscience for free will – are far more squirrelly. I am not convinced that free will questions are strictly scientific, at times they sound very philosophical, meaning that there are components of perspective and even meaning. But scientists and science reporters love to speculate about the deeper philosophical implications of fairly reductionist research.

The current issue of Nature Neuroscience contains a brief report about an fMRI study looking at brain function during a particular decision-making task. Subjects were asked to hit a button with either their right or left hand. The fMRI revealed that areas of their prefrontal and parietal cortex showed activity about 7 seconds before subjects hit the button. Prior research has shown that before we make a movement, about 300 miliseconds (3/10 of a second), the pre-motor cortex lights up. This makes sense, the premotor cortex is responsible for initiating movement. This new study shows that we plan our movement before we send a signal to the premotor cortex to initiate it – and then on to the motor cortex to actual perform the movement.

But here is where things get interesting. The subjects were not necessarily consciously aware of their decision until they were about to move, but the cortex showing they were planning to move became activated a full 7 seconds prior to the movement. This supports prior research that suggests there is an unconscious phase of decision-making. In fact many decisions may be made subconsciously and then presented to the conscious bits of our brains. To us it seems as if we made the decision, but the decision was really made for us subconsciously.

Then again – what does that really mean? Is not the subconscious parts of our brain still our brain – still us? This is where interpretation really gets tricky. The brain is a complex set of feedback loops interacting with itself – both conscious and subconscious. It is also not clear exactly what makes us conscious of certain parts of our brain function (those working when we are consciously thinking) and not other parts. This is not an intractable problem – we are beginning to explore which parts of the brain are responsible for attention and consciousness. It’s just really complex. And even though fMRI is a powerful tool for looking at brain function, it is still crude compared to the subtlety of the brain. It’s like trying to resolve an intricate picture that is low-resolution and therefore highly pixleated.

Another interesting aspect of the study is that the researchers claim they were able to predict which hand would press the button based upon the fMRI activity during the pre-conscious planning phase – therefore before the person was aware of their own decision. However, they could only predict with 60% accuracy – random guessing being 50%. Given the trickiness of interpreting fMRI data and performing these kinds of studies, I am not at all impressed by the 60% figure.  If it holds up to replication, and can be refined to be more accurate, then I would take it seriously. At this point I think any interpretation would be premature.

Also, it is premature to make any conclusions about how we can extrapolate from this one study. Perhaps the 7 second lag from brain activity to action is typical of this kind of task – one in which the subjects arbitrarily decide at some point to take action – and not to other tasks that involve different types of activity.

What we can say at this point is that brain function is complex (duh), and that taking action involves multiple steps – including planning, preparation/organization, and finally action. We can also conclude that subconscious brain processing contributes significantly to decision-making.

Given my recent posts concerning materialism vs dualism (does the brain cause mind), I also want to point out that this research falls squarely in the materialism camp. Causes precede their effects – brain activity precedes conscious awareness and action – the brain causes mind. That much seems pretty clear.

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