Health and Medicine
PUBLISHED
Our days are filled with innumerable decisions, ranging from the mundane to the consequential. For instance, you may start the day by choosing which sugary treat to buy from the café en route to work, but soon you’re having to decide whether to have a difficult conversation with a colleague. It may look like these choices were freely made – but can we say they are truly our choices or is there more going on behind the scenes?
The rest of this article is behind a paywall. Please sign in or subscribe to access the full content.Each of the choices described above are referred to as voluntary choices – they involve us recognizing that there are different courses of action for each one.
But let’s go with a different scenario. Rather than being able to choose the pastry you want to buy at the café, you reach the front of the line and there’s only a croissant left, which you didn’t actually want today. The absence of other choices means it’s croissant or nothing, and you like croissants enough to know that “nothing” is not an option here. Alternatively, rather than deciding whether or not to tackle your difficult colleague at work, your boss puts you in a position where you cannot avoid it.
On the face of it, these two sets of scenarios may seem different – one involves making free choices while the other comes down to responding to limited options. But new research from the University of Melbourne suggests that our brains use similar processes to make these decisions.
When we make a voluntary decision, our choice is guided by internal goals, values, and preferences. For instance, “I prefer a pain aux raisins to croissants”, or, “I prefer not talking to this jerk in the office”. These decisions are less impacted by situational context or external cues. Once our brains have collected sufficient evidence, we make a decision and commit to the choice.
In contrast, a forced decision is the result of there being only one or a much more limited number of choices. They feel like they have less to do with our sense of self than free choices. This has led neuroscientists to assume these types of decisions come from different processes in our brains.
Previous research using MRI has consistently shown that voluntary actions activate the medial frontal region of the brain, including the pre-supplementary motor areas, the supplementary motor area, the anterior cingulate cortex, as well as the parietal areas.
Work with electroencephalography (EEG) has added to this, showing millisecond-level resolution of motor preparation in the medial frontal cortex leading up to a voluntary action. This comes down to what’s referred to as the readiness potential (RP), which is essentially a slow buildup of electrical activity that starts around a second before a decision to move is made. The RP has been found to be more pronounced in spontaneous decisions, rather than when you are following instructions.
But while this research may show where the free decisions are made in the brain, it says little about how they are made. Nor does it indicate whether there is a difference between these decisions and forced ones.
When it comes to examining how we make decisions, neuroscientists have traditionally used the Diffusion Decision Model (DDM). This can be understood as a process whereby the brain gradually accumulates evidence for each option before you make a decision. Like a judge evaluating a case, once there is enough evidence for a verdict, the brain can make a decision. In some circumstances, this type of decision can be made very quickly – in hundreds of milliseconds – which can make it feel like the choice just occurred naturally.
Scientists have discovered a neural signal that reflects the accumulation of evidence during decision making. They did so using simple decision tests, such as deciding whether a traffic light is red or green. The signal has been detected for forced decisions with very clear correct answers, but what about open-ended voluntary decisions?
To find out, the team in Australia used EEG to measure the brain activity of 49 participants as they completed a color decision task. This involved choosing between different colored balloons – the participants were either given the option to freely choose between two different colors or were shown just one color that they were forced to pick.
They were instructed to press a button the moment they made a decision, allowing the team to monitor brain activity in the run up to that decision.
“For both free and forced decisions, the brain activity unfolded in a very similar way. Like a loading bar, it climbed steadily to the same peak level just before a choice was made. When people decided quickly, the signal increased faster. When they took longer, it rose more slowly,” first author Lauren Claire Fong and senior author Daniel Feuerriegel explained in a Conversation article.
“That’s exactly what you would expect if the brain were tracking and weighing up evidence over time, rather than simply reacting to a decision at the last moment.”
The results suggest that decision making in the brain is possibly more automatic than it may feel. In both tasks, regardless of how fast they made their decision, the signal reached the same height before the participant pressed the button. So regardless of whether they were choosing a balloon they preferred or whether they were forced into a decision, it had the same outcome.
The study adds to an overall demystification of free will. While freely made decisions take into account preferences, values, and goals, this study shows they are informed by a sophisticated internal weighing system. So rather than reacting to the world, we are treating our goals, values, and preferences as evidence to be accumulated and acted upon. Decisions are therefore not spontaneous things, but calculations.
The study is published in Imaging Neuroscience.
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