A new study in which researchers observed people making moral decisions while taking prescription drugs sheds light on how the neurotransmitters serotonin and dopamine are deeply connected to a variety of human behaviors.
When healthy people were given citalopram, a serotonin-boosting antidepressant, they became significantly harm aversive. In fact, they were willing to pay twice as much to prevent harm to themselves or others compared to people given placebo drugs.
In contrast, when healthy people were given levodopa, a dopamine-boosting Parkinson’s drug, they became more selfish, virtually eliminating altruistic behaviors.
The findings provide insight into the neural basis of clinical disorders characterized by a lack of concern for others, such as psychopathy.
“Our findings have implications for potential lines of treatment for antisocial behavior, as they help us to understand how serotonin and dopamine affect people’s willingness to harm others for personal gain,” said lead author Dr. Molly Crockett, who conducted the study at University College London (UCL) and is now at Oxford University.
“We have shown that commonly prescribed psychiatric drugs influence moral decisions in healthy people, raising important ethical questions about the use of such drugs.”
“It is important to stress, however, that these drugs may have different effects in psychiatric patients compared to healthy people. More research is needed to determine whether these drugs affect moral decisions in people who take them for medical reasons.”
The study compared how much pain people were willing to anonymously inflict on themselves or strangers in exchange for money. Of the 175 healthy adults who participated, 89 were randomized to receive citalopram or placebo and 86 were randomized to receive levodopa or placebo.
Next, subjects were randomly assigned to the roles of decision-maker or receiver and anonymously paired up so that each decision-maker did not know who the receiver was and vice-versa. All participants were given mildly painful electric shocks matched to their pain threshold so that the intensity was not intolerable. Decision-makers were informed that shocks to receivers would be at the receiver’s own pain threshold.
In a previous experiment conducted by the same team, researchers found that people disliked harming others more than harming themselves, a behavior known as “hyper-altruism.” This behavior was seen again in this study, with most people more willing to harm themselves than others for profit.
On average, people given a placebo were prepared to pay approximately $53 (£35) per shock to prevent harm to themselves and $67 (£44) per shock to prevent harm to others. Those on citalopram were significantly more harm-averse, willing to pay an average $92 (£60) per shock to prevent harm to themselves and $112 (£73) per shock to prevent others from being harmed.
Over the course of the study, this meant that people on citalopram delivered an average 30 fewer shocks to themselves and 35 fewer shocks to others than those on placebo.
People taking levodopa, however, did not want to pay a greater amount of money to prevent shocks to others compared to themselves.
On average, they were prepared to pay about $53 (£35) per shock to prevent harm to themselves or others. In fact, they delivered on average 10 more shocks to others during the study than the placebo group. They were also less hesitant to deliver shocks to others, making the decision faster than those on placebo.
The findings are published in the journal Current Biology.
Source: University College London