Much of the time, our model of reality is viewed from the perspective of ourselves, right now. The notion of Theory of Mind (ToM) is that to a certain extent we can instead take the perspective of another person. We can metaphorically walk in their shoes. This ability seems to reside in the posterior temporo-parietal junction (pTPJ). This is also the location involved in prosocial behaviour. A recent paper (Soutschek, Ruff, Strombach, Kalenscher, Tobler; Boutrain stimulation reveals crucial role of overcoming self-centeredness in self-control; Science Advances, Oct 2016, Vol. 2, no. 10) finds this area is also involved in controlling impulses to take immediate rewards, rather than wait for greater rewards in future.
The researchers used disruptive transcranial magnetic stimulation (TMS) to shut down the junction and then tested for prosocial vs selfish behavior in a sharing money game, the ability to recognize what another person could see (extent of ToM), and the ability to show self-control to achieve a larger reward. These measures appeared to move together, implying that they might share the same mechanism, most likely that mechanism is a switch between the perspective of the current self and the perspective of another, either another person or the self at another time. This fits with previous findings by others that selfishness and impulsiveness appear to go together in many people.
The paper notes that the frontal lobe is also involved in self-control and discusses how the two areas might cooperate in controlling impulsiveness.
Here is their abstract:
Neurobiological models of self-control predominantly focus on the role of prefrontal brain mechanisms involved in emotion regulation and impulse control. We provide evidence for an entirely different neural mechanism that promotes self-control by overcoming bias for the present self, a mechanism previously thought to be mainly important for interpersonal decision-making. In two separate studies, we show that disruptive transcranial magnetic stimulation (TMS) of the temporo-parietal junction—a brain region involved in overcoming one’s self-centered perspective—increases the discounting of delayed and prosocial rewards. This effect of TMS on temporal and social discounting is accompanied by deficits in perspective-taking and does not reflect altered spatial reorienting and number recognition. Our findings substantiate a fundamental commonality between the domains of self-control and social decision-making and highlight a novel aspect of the neurocognitive processes involved in self-control.
So when the marshmallow test is quoted as showing that children with greater self-control end up being more successful adults, it could be down to more than self-control. They probably also are more prosocial, understand others better and are less selfish.