Neuroscience elucidates how decisions form in the brain
Unravelling the mechanisms behind our decision-making has become possible thanks to advances in what is called ‘behavioural economics’ which combines elements of economy and psychology to understand what motivates people. Computational modelling of mental processes is also flourishing, as are novel neuroscience methods that allow imaging and causal manipulation of neural function. It’s a good time to be wondering what makes humans tick. Successful social interactions require the ability to guide our actions in line with the goals and expectations of the people around us. The European Research Council supported BRAINCODES project delved into the causes of disordered social decision-making, associated with criminal activity or psychiatric illnesses. “Brain regions can exchange information pretty much in the way humans communicate to work together. So, one brain region that may represent our perception of equity, or level of fairness, works with another that may underlie action selection,” says Christian Ruff, a professor of neuroeconomics and decision neuroscience at the University of Zurich. But the brain mechanisms that enable us to control our social behaviour are far from being understood. Ruff set out to elucidate the role of functional interactions in the brain networks responsible for steering strategic, prosocial and norm-compliant behaviour.
Multi-method approach to a causal understanding of decision-making
To gain a causal understanding of these processes, Ruff used a combination of methods. Game theory was one tool. He used an experiment involving the pairing of strangers who are then required to share out some money. The person not responsible for the split then decides what to spend the cash on. The other then has to decide whether to accept the proposal, in which case the money is shared out as decided, or not, in which no one gets anything. “By doing this repeatedly, with different amounts of money and different people in a group lab where the subjects are connected by computers, you can develop a ‘choice model’: A pattern of decision-making,” explains Ruff. These models formulate, mathematically, how different motives underlie choices. Each of these motives is assigned a weight that determines how strongly it affects the choices made. “Then the fun part starts as you try to find the weight combination that best explains each person’s choices,” he adds. Once that is known, you can then predict how strongly the motive should be expressed, which is where multimodal imaging comes in. Ruff explains: “Using fMRI, we can find out where in the brain neural activity correlates with the strength of this motive, from trial to trial.” Having established where in the brain the activity was taking place, the team then used an EEG to identify when in the choice process it occurs. Transcranial magnetic stimulation (TMS and alternating current stimulation (tACS)) then allowed Ruff to see what happens if we stimulate this brain area to manipulate the strength of feeling regarding the motive. “Does the motive get weaker or stronger? If this is the case, then we know that this particular motive, or belief representation, in the brain is causally steering our behaviour, so that patients who have trouble with this may have disruptions of this process,” he explains. The team also conducted patient studies with people diagnosed with borderline personality disorder or with Asperger’s syndrome, to test whether the models are correct. As a control, Ruff also tested age- and education-matched subjects from the general population.
Unique traits in the brain characterise differences in strategic social choices
The insights gained by the project potentially have clinical applications. “Due to our work, we are a good step closer to understanding how and why people care about fairness and honesty, and how people take strategic social choices when competing with others. We are gaining insights into what specific brain mechanisms are involved, how people differ in this respect, and why some people have problems with this,” Ruff notes. His findings are shared in various papers, such as ‘Dissecting functional contributions of the social brain to strategic behavior’, co-authored by Ruff. Work by BRAINCODES, and others in this developing field, has established that there is a clear brain basis for these behaviours which developed during the evolution of our species. This varies between people; much how many other aspects of our bodies vary. “It is pretty amazing to realise that a lot of our behaviour in social situations, which feels very personal, is in fact quite predictable and universally shared with others around us. “At the same time, we all have our unique traits that can be traced back to variations of these brain processes. I am glad that my work can underline both these aspects with hard data about causal brain behaviour relationships,” says Ruff.
Keywords
BRAINCODES, European Research Council, strategic social choices, fairness, game theory, multimodal imaging, functional interactions, Asperger’s syndrome
