Selflessness can be sexy. Generosity has been shown to pique the fancy of people seeking long term partners. It seems understandable that generosity to others might promise generosity in a relationship, but beyond identifying love interests, helping others seems to strengthen all human relations. Without selflessness, the logic goes, we as a society would devolve into chaos. Those who do not share at the metaphorical sandbox are not invited back to play.

So where does selflessness come from? This question, sustaining centuries of philosophical debate, is whether selflessness is an effort or a default. Recent research hints at the neural answer, locating specific areas of the brain which seem to rein in our better nature. This suggests that selflessness is the default option. Your conscience aside, surrendering your seat on the train for someone else might be a little less effort for your brain.

People participating in the experiment received transcranial magnetic stimulation (TMS) to one of two wedges of the prefrontal cortex, the dorsomedial or dorsolateral, and decided how to split ten dollars with recipients pictured on a screen. A TMS coil forms alternating magnetic fields, like a wireless phone charger, to stir up electrical currents nearby. Rather than charging our brains, of course, researchers use TMS to alter brain activity. In this case, the TMS temporarily disrupted the prefrontal cortex. By throwing this wrench in the works, the researchers could test if people acted more or less generous without this area’s contribution.

The prefrontal cortex, famous for maturing last in the brain, is believed to help us resist temptations and make complex judgments, but this was a first direct test of its role in altruistic generosity. If disruption of the brain area led to less giving, then the undisturbed prefrontal cortex might restrain self-serving urges. If TMS disruption led to more giving, that would suggest that it restrains our natural generosity.

The second possibility proved true. Disruption of prefrontal cortex by TMS led to greater giving, on average, than disruption of unrelated motor areas. This region seemed to act like a control valve for generosity, aligning with its other roles in impulse control. But the impulse here looked to be selfless, not selfish.

Another puzzle emerged, though, when researchers noticed where people gave the additional money. During the experiment, the participants saw an annual income next to each recipient’s face. Disrupting the dorsomedial prefrontal cortex led participants to give more to poorer recipients, while disrupting the adjacent dorsolateral part produced greater giving to wealthy recipients. What kind of brain regulates generosity so specifically? The researchers proposed that one region might act as a “contextual” control, holding back generosity towards higher earning recipients, while the other region might act as a baseline control of generosity. In this interpretation, the brain has subcomittees on whether we should give and where the gifts should go. The contextual control area seems more analytic, active during tough logical decisions, while the baseline control area activates while sensing others’ states of mind, perhaps distinguishing ourselves versus others.

Some research on TMS has reported side effects like headaches or odd sensations. These symptoms could conceivably have confused the participants or made them perform in a haze during the experiment. Leonardo Christov-Moore, lead author of the study, states there were no obvious side effects in people participating. And, he said, “if the default is to be selfish, why would making you confused make you less selfish?”

Studies like these can have trouble pinning down exactly when people are acting thoughtful or selfish. Research from 2006 concluded that TMS disruption of prefrontal cortex caused participants to act more self-interested, which doesn’t square with a role holding back generosity. However, the 2006 experiment involved a complex task in which people could either accept or reject money after someone split ten dollars with them. (Rejecting an offer punished both people, because neither received money from the round.) People who received TMS to disrupt the prefrontal cortex accepted more stingy offers, but at least two interpretations are possible. They could have sacrificed their sense of fairness in order to grab any money they could. Or, Christov-Moore suggests, they could have been accepting a raw deal as an act of generosity. The underlying cognitive brain is no less complex. Numerous cognitive tasks rely on any given region, and the latest human studies point to the vigorous multitasking of brain space. We still have much to understand about how fairness or altruism arise, not to mention how to use what we do know.

Charity is often described as an effort one should make. We should donate. We should be humanitarians. We should volunteer. This study suggests that in some ways, selflessness is actually less demanding than selfishness. While we logically decide to look after ourselves, an undercurrent of empathy might push us to be generous. For Christov-Moore, what stays with him is that altruism is “not something that’s very abstract and rational. It’s actually a very emotional impulse.”