Stimulating a certain brain region makes people take less time to consider their decisions, a new study reports.
One particular area of the frontal lobe – the medial prefrontal cortex (mPFC) – is involved in helping us take conscious control over our decision-making process. While the mPFC is stuck on a problem, an ancient brain structure called the subthalamic nucleus (STN) slams the brakes on other brain activity, allowing us to think without acting impulsively.
By applying electrical stimulation to the STNs of volunteers, researchers found they could shorten the time it took for them to come to a decision – and lessen the amount of evidence it took to make them lean one way or the other.
As the journal Neuron reports, a team led by Brown University’s Michael Frank set out to better understand how the process of impulse control works on a neurophysiological level. Though the mPFC’s role in decision-making has been fairly well studied, Frank suspected that other brain areas might jump in to help control impulses when the mPFC was especially busy.
Frank had previously worked with patients suffering from Parkinson’s - a disease known for the impulsive movements it causes – and had noticed that a treatment called deep brain stimulation (DBS) helped suppress those movements by stimulating the STN. So he set out to explore this connection further:
To test that theory for how areas of the brain interact to prevent you from making impulsive decisions … you have to do experiments where you record brain activity in both parts of the network that we think are involved. Then you also have to manipulate the system to see how the relationship between recorded activity in one area and decision making changes as a function of stimulating the other area.
To do this, the team selected 65 healthy volunteers and 14 subjects with Parkinson’s. The volunteers lay in an fMRI scanner as the researchers showed them pairs of simple images, and asked to choose one image from each pair – some images resulted in rewards, while others didn’t.
The researchers noticed that mPFC activity was especially high when the volunteers were choosing between two images carrying equal rewards. But when the researchers used DBS to stimulate the STN in Parkinson’s patients, they reached their decisions much more quickly – even though their mPFC activation was as high as ever:
Trial-to-trial increases in mPFC activity … were related to an increased threshold for evidence accumulation (decision threshold) as a function of conflict. Deep brain stimulation of the STN in individuals with Parkinson’s disease reversed this relationship, resulting in impulsive choice. In addition, intracranial recordings of the STN area revealed increased activity … during these same high-conflict decisions.
In other words, the researchers could directly influence the decision-making time of volunteers by turning DBS on and off.
Aside from the obvious implications for supervillain technology (perhaps in a mind-control plot that also involves using magnets to make people lie), scientists hope this breakthrough may help DBS designers create systems that take mPFC activity into account, to replicate a healthy relationship between the mPFC and the STN more accurately.
And for the rest of us, I’m pretty sure this means, “My STN made me do it” is now a perfectly valid legal defense.