Altruism Hardwired in the Brain
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Medscape Medical News > Psychiatry
Altruism appears to be "hardwired" in the brain and is modulated by higher cortical processing that brings a context-dependent interpretation of how generous we should be, results of two studies indicate.
Analyses of individuals performing a task examining socially motivated decision-making revealed that activity in the somatosensory cortex drives a prosocial "resonance" or mirroring impulse.
In contrast, activity in the prefrontal cortex was linked to reduced generosity and an inhibition of prosocial inclinations, with specific areas linked to different aspects of social judgement of need.
"This suggests that our primary drive in nonstrategic social transactions may in fact be to behave prosocially, perhaps due to reflexive forms of empathy that blur the boundaries between individuals," said Leonardo Christov-Moore, PhD, postdoctoral scholar, Suthana Research Group, Laboratory of Neuroimaging and Neuromodulation, University of California, Los Angeles, who was lead author of both studies, and colleagues.
In the first study, published online February 1 in Human Brain Mapping, investigators asked 20 ethnically diverse adults with no neurologic or developmental disorders or history of drug or alcohol abuse to complete the Interpersonal Reactivity Index (IRI) and the Personal Altruism Level Scale. They were also asked to complete three tasks.
The first task was the Dictator Game. In this task, participants were given a sum of money, in this case, $10 per round for 24 rounds. They were then asked to either share the money with a stranger profile shown on a computer screen or keep the money.
For the second task, individuals were asked to imitate or observe pictures of 12 individuals in which four emotions were exhibited. The third task was a needle test, in which participants were shown a video of a hand being injected with a syringe. These tasks were performed while the individuals underwent fMRI.
On the needle task, there was a positive correlation with activity in brain areas associated with the experience of pain and emotion; these areas included the amygdala, the somatosensory cortex, and the anterior insula. A negative correlation was found regarding activity in the prefrontal cortex, which regulates behaviors and impulses.
These findings were supported by the imitation/observation task ? imitation of facial emotions elicited activity in the same brain regions that responded to the needle task.
When relating the fMRI findings to the results of the Dictator Game, the team found that individuals who gave out the least money to strangers, an average $1 to $3 vs the overall mean of $6.18, demonstrated the highest level of activity in the prefrontal cortex.
In contrast, individuals who demonstrated the highest level of activity in the somatosensory cortex and amygdala were the most generous, giving away around 75% of what they gained during the task.
The results also showed that payouts to people of the lowest socioeconomic status (SES) were correlated with scores on the empathic concern subscale of the IRI, whereas payouts to people of the highest SES were associated with personal distress subscale scores.
In the second study, published online March 21 in Social Neuroscience, investigators administered continuous theta burst transcranial magnetic stimulation (TMS) to the dorsolateral prefrontal cortex (DLPFC) and the dorsomedial prefrontal cortex (DMPFC), as well as a control area of the brain associated with vision.
The study included 58 participants (mean age, 21.31 years). As in the previous study, the participants had no history of neurologic or developmental disorders or drug or alcohol abuse. As before, individuals performed the Dictator Game and completed the IRI.
The results indicated that offers to strangers in the Dictator Game were significantly higher when activity in the DLPFC and DMPFC was dampened by TMS, indicating that the prefrontal cortex has an inhibitory effect on prosocial inclinations.
Interestingly, dampening of prefrontal cortex activity had a different effect on generosity, depending on which region was affected. Specifically, reducing activity in the DLPFC led to a significant increase in offers to strangers with a high SES (P = .003), whereas reducing DMPFC activity significantly increased offers to strangers with a low SES (P = .036).
"Transient disruption of the DLPFC seems to have reduced the inhibitory effect of contextual cues (offers to high-SES players), while transient disruption of DMPFC seemed to reduce context- independent control (offers to low-SES players)," the investigators write.
"These data suggest that DLPFC may implement a form of context-sensitive inhibition, consistent with its proposed role in integrating cognition and emotional responses during decision-making," they add.
Dr Christov-Moore told Medscape Medical News that it would be "too simple" to say that the prefrontal cortex acts as a "control valve" on the mirroring that occurs in the somatosensory cortex to inhibit prosocial inclinations, although that is one aspect of its function.
Rather, he said, "these areas of resonance or mirroring interact constantly and dynamically with systems in the prefrontal cortex, and that is what gives us not human altruism and morality but rather the very refined and complex and nuanced form that we see in humans, where we're able to modulate mirroring in response to these very-high-level aspects of the person or the people we're dealing with, such as their political affiliation or perceived worthiness.
"What the system like the prefrontal cortex or higher evolutionary status allows us to do is a more nuanced and more modulated, and more context-dependent, version of this mirroring process," he added.
Clinical Implications?
Dr Christov-Moore believes that the study findings have two principle applications. The first is to give insight into how empathy translates into decision-making, which points to further research opportunities.
"Our work highlights, in a very robust and simple, tractable way, a brain relationship between prefrontal cortex and areas of somatosensory motor cortex and the limbic system that can be more closely examined or even targeted with neuromodulation to affect behavior and understanding," he said.
The findings could also have clinical applications. Dr Christov-Moore said that there are circumstances in which the "control valve" of the prefrontal cortex could become "stuck in the 'on' position in such a way that it can impede these individuals' ability to empathize or to form warm, trusting human relationships, which is one of the main barriers to social reintegration.
"This is something we cite primarily for very violent offenders, but I think it also applies to veterans, or even to, in a very timely fashion, refugees from war zones," he added.
For individuals who have "had to put up an empathic barrier," it may be that the current results suggest that there is "now an actual physical, functional target in the brain for perhaps loosening up that control, perhaps in combination with behavioral and cognitive therapies."
The authors report no relevant financial relationships.
Hum Brain Mapp. Published online February 1, 2016. Abstract
Soc Neurosci. Published online March 21, 2016. Abstract
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