Your Brain Makes Its Decisions Before You Consciously Realise It

Pondering a decision for a few extra seconds could actually be a waste of time. A team of international researchers have discovered unconscious neural activity precedes subsequent free decisions by as much as four seconds. It can even influence the outcome of your responses.

Thinking picture from Shutterstock

It has long been known that the human brain can spur spontaneous movement several seconds before a person actively realises it — just place your hand on a hotplate if you don’t believe us. However, it has now been put forward that these same preparatory processes also occur for higher-level, more abstract types of decisions.

To study the effect of unconscious neural activity on free decision making, researchers monitored the brain activity of subjects as they were asked to either add or subtract numbers in simple arithmetic questions:

We investigated the neural precursors of abstract intentions by asking participants to perform an abstract decision task in which they spontaneously and freely chose to perform either of two mental arithmetic tasks: adding or subtracting. Participants were presented with a continuous stream of stimulus frames, each consisting of a letter and five single-digit numbers. They were asked to stay relaxed while monitoring the letter stream, which served essentially as a “clock” for reporting the timing of their decision. Immediately when they felt the spontaneous urge to perform either addition or subtraction, they first had to memorize the letter visible on the screen, which allowed us to reconstruct the timing of their free choice. Then they had to immediately perform the freely chosen task on the two numbers that were subsequently presented in the center of the two following frames.

 
The third frame from the time of decision served as a response mapping screen for the calculation task, with four possible response options in the four corners: the correct addition answer, the correct subtraction answer, and two incorrect response options. The positions of these answers were randomized from trial to trial, and participants had to press a button to indicate their choice, thereby also revealing which calculation task they had chosen. After this first response, a second response-mapping screen consisting of four letters was displayed and participants indicated which of the letters was visible on the screen when they consciously made their decision. Seventeen participants performed the task while undergoing functional magnetic resonance imaging (fMRI), with one functional scan acquired every 2,000 ms. To identify any neuralprecursors that may be shaping the upcoming abstract intentions, multivariate pattern classification was used in separate analyses to look for brain activity that could predict the content and timing of the abstract decision

Using the above method, the research team was able to successfully decode the outcome from neural activity in the medial prefrontal and parietal cortex four seconds before the participant reported they were consciously making their choice.

“Our results show that regions of medial frontopolar cortex and posterior cingulate/precuneus encode freely chosen abstract intentions before the decisions have been consciously made. Our results suggest that unconscious preparation of free choices is not restricted to motor preparation. Instead, decisions at multiple scales of abstraction evolve from the dynamics of preceding brain activity,” the report concludes.

Predicting free choices for abstract intentions [PNAS]