Oxytocin in the Amygdala Sustains Prosocial Choices

Why do we feel generous on some days, but act selfishly on others? Understanding the neural mechanisms behind social decision-making is essential for decoding primate behavior. In a 2025 study published in The Journal of Neuroscience, Olivia C. Meisner and colleagues explored how oxytocin in the brain’s amygdala influences prosocial choices, demonstrating that our baseline social motivation dictates how effective “social brain chemicals” truly are.

Tracking Choices via Gaze

To examine how social decisions unfold in real time, the researchers trained rhesus macaques to perform a social reward allocation task:

1. Gaze-Driven Choice Task: An “actor” monkey sat facing a screen across from a recipient monkey. During each trial, visual targets appeared to the actor monkey on a monitor. The visual targets represented different juice reward outcomes—such as delivering juice to the recipient (“other”), sharing it (“both”), or withholding it (“bottle” / “self”).
2. High-Precision Eye Tracking: The actor monkey indicated their decision simply by holding their gaze on the selected target for 150 milliseconds. To monitor these brief visual fixations accurately, researchers used an EyeLink 1000 eye tracker. This enabled seamless gaze-contingent task control and exact tracking of choice reaction times.
3. Focal Drug Delivery & Neural Recordings: Researchers infused either oxytocin or a saline control directly into the basolateral amygdala (BLA) while simultaneously recording spiking neural activity across both the BLA and the anterior cingulate cortex (ACCg).

Oxytocin’s Behavioral Impact is State-Dependent

The team discovered that oxytocin’s behavioral impact is strictly state-dependent. On “high prosocial” days—when monkeys were naturally inclined to share—oxytocin in the BLA sustained generous choices and overall task engagement, counteracting the natural decline seen in control sessions over time. Neural data showed that oxytocin boosted decision-related activity and stabilized communication between the BLA and ACCg. However, on “low prosocial” days, oxytocin had minimal behavioral effect.

Oxytocin is not a simple “prosocial switch” that creates kindness out of nowhere. Instead, oxytocin in the amygdala acts as a state-dependent amplifier, sustaining prosocial behavior only when baseline social motivation is already high. By combining precise EyeLink gaze tracking with direct brain infusions, the study proves that our internal motivational state determines whether social neuromodulators can keep our generous impulses alive.

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