Abstract
Dyadic interactions often involve a dynamic process of mutual reciprocity; to steer a series of exchanges
towards a desired outcome, both interactants must adapt their own behaviour according to that of their
interaction partner. Understanding the brain processes behind such bidirectional reciprocity is therefore
central to social neuroscience, but this requires measurement of both individuals’ brains during realworld
exchanges. We achieved this by performing functional magnetic resonance imaging (fMRI) on
pairs of male individuals simultaneously while they interacted in a modifed iterated Ultimatum Game
(iUG). In this modifcation, both players could express their intent and maximise their own monetary
gain by reciprocating their partner’s behaviour – they could promote generosity through cooperation
and/or discourage unfair play with retaliation. By developing a novel model of reciprocity adapted
from behavioural economics, we then show that each player’s choices can be predicted accurately
by estimating expected utility (EU) not only in terms of immediate payof, but also as a reaction to
their opponent’s prior behaviour. Finally, for the frst time we reveal that brain signals implicated in
social decision making are modulated by these estimates of EU, and become correlated more strongly
between interacting players who reciprocate one another.
towards a desired outcome, both interactants must adapt their own behaviour according to that of their
interaction partner. Understanding the brain processes behind such bidirectional reciprocity is therefore
central to social neuroscience, but this requires measurement of both individuals’ brains during realworld
exchanges. We achieved this by performing functional magnetic resonance imaging (fMRI) on
pairs of male individuals simultaneously while they interacted in a modifed iterated Ultimatum Game
(iUG). In this modifcation, both players could express their intent and maximise their own monetary
gain by reciprocating their partner’s behaviour – they could promote generosity through cooperation
and/or discourage unfair play with retaliation. By developing a novel model of reciprocity adapted
from behavioural economics, we then show that each player’s choices can be predicted accurately
by estimating expected utility (EU) not only in terms of immediate payof, but also as a reaction to
their opponent’s prior behaviour. Finally, for the frst time we reveal that brain signals implicated in
social decision making are modulated by these estimates of EU, and become correlated more strongly
between interacting players who reciprocate one another.
| Original language | English |
|---|---|
| Article number | 10896 |
| Journal | Scientific Reports |
| Volume | 8 |
| Issue number | 1 |
| DOIs | |
| Publication status | Published - 18 Jul 2018 |
Bibliographical note
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© The Author(s) 2018
Funding: This work was supported fnancially by project GA16-18261S.