Researchers have long been fascinated by the gulf that separates procrastinators and doers. But even though several social and psychological differences have been identified, until now, no one has compared the brains of these two groups.
A new study has investigated the neural basis for impulse control, and has found that the brains of procrastinators and doers really do differ at a fundamental level.
Using magnetic resonance imaging (MRI), the study examined the brains of 264 women and men. Afterwards, the participants filled out a survey measuring their ability to control actions and impulses - receiving a score for decision-related action orientation (AOD). Or in other words how much they were 'doers' or 'procrastinators'.
The findings reveal that those with poor action control - procrastinators - tended to have a larger amygdala, which is the brain's main control center for fear and emotions.
"Thus, people with higher amygdala volume appear to be more state oriented and therefore tend to hesitate to initiate an intention and tend to delay the beginning of tasks without any good reason," the authors explain in their paper published in Psychological Science.
So instead of just being lazy or unambitious as often assumed, procrastinators may simply be more risk-averse.
The amygdala controls how we respond to fear, but because of its connection to memory centers in the thalamus and cortex, our responses to fear can change over time due to past experience.
In other words, the amygdala lies at the core of action control. It guides and selects the most desirable behavior, while also inhibiting action that can lead to unfavourable outcomes. And much of this is based on our memory.
"Regarding action control, this could mean that individuals with a larger amygdala volume have learned from past mistakes and evaluate future actions and their possible consequences more extensively," the authors propose.
"This, in turn, might lead to greater concern and hesitation, as observed in individuals with low AOD scores".
When it comes to inter-connectivity in the brain, there were also observable differences between the two groups.
The researchers found that the connections between the amygdala and the dorsal anterior cingulate cortex (dorsal ACC), were less pronounced among those with poor action control.
This supports the authors suggestion that if the connection between the amygdala and the dorsal ACC is impaired, action control is impaired.
"Individuals with a higher amygdala volume may be more anxious about the negative consequences of an action – they tend to hesitate and put off things," speculates one of the authors Erhan Genç, a researcher in cognitive neuroscience from Ruhr-University Bochum in Germany.
"Due to a low functional connection between amygdala and dorsal ACC, this effect may be augmented, as interfering negative emotions and alternative actions might not be sufficiently regulated".
The study is the first of its kind to show that individual differences in action control are associated with the brain's anatomy and its connectivity.
But because this research is still in its infancy, the authors are calling for further studies to buttress their results.
"Even though the differences regarding our ability to control our actions affect our private and professional success as well as our mental and physical health to a considerable degree, their neural foundations haven't as yet been sufficiently studied," says co-author Caroline Schlüter, a PhD student researching biological psychology and personality neuroscience.
The study has been published in Psychological Science.