Compassion and charity. Envy and spite. The most human of emotions are defined by how we feel about others. How we feel about others forms the core of modern society. People work together to build common resources and care for the sick, but their behavior is regulated by laws and institutions that prevent exploitation or harm. For most people, the concern for others that shapes social interaction emerges spontaneously and effortlessly, even extending to pets or inanimate objects. Nonetheless, not everyone finds it so easy to engage with others. Despite a desire to function within and contribute to society, individuals with autism spectrum disorders (ASD) struggle with the social interactions that healthy humans engage in so naturally. The biological reasons for this social dysfunction remain poorly understood. We propose that the brain processes that underlie basic social emotions, such as the ability to feel vicarious reward or punishment when things happen to other individuals, are abnormal in ASD. Understanding the neural building blocks that mediate the social emotions that shape interactions with others thus has clinical importance for the treatment of ASD.
Brain imaging studies in humans can provide valuable insight into what parts of the brain may be involved in how we feel about others. However, brain imaging studies cannot determine precisely how these brain areas work or how we can treat problems in these areas that may occur in ASD. For these reasons, we will develop an animal model that allows us to precisely determine how specific brain regions respond when watching another individual receive a reward, what happens when that brain region is shut off or turned on, and how particular naturally occurring chemicals may enhance this process.
To do this, we have designed a simple task that allows us to unmask how monkeys feel about watching other monkeys receive a reward. Our preliminary data confirm that monkeys care about sharing rewards with another monkey and will even work to give rewards to another individual. We will use this task to examine how nerve cells in the orbitofrontal cortex, a part of the brain that responds to both primary (e.g., food) and social (e.g., attractive face) rewards, respond when monkeys give rewards to another monkey. Our hypothesis is that the same neurons respond when the monkey receives a reward himself or gives a reward to another monkey. This vicarious reward may be the precursor to empathy that is so well-developed in ourselves. We will test this idea by temporarily inactivating these nerve cells to see whether this makes monkeys less likely to share with another monkey. We will also increase the activity of these cells to see if this makes monkeys more likely to share with another monkey. This would provide evidence that this brain area has a causal role in empathy and social reward.
Finally, we will examine the effects of the hormone oxytocin on monkeys' concern for others. Oxytocin enhances trust in people, influences nerve cell activity in orbitofrontal cortex, and its functioning may be abnormal in ASD. Together, these observations suggest that oxytocin may influence empathy and sharing by changing how orbitofrontal nerve cells respond. By comparing the behavioral effects of oxytocin on reward giving with the effects of stimulation and inactivation of orbitofrontal cortex, we can understand how oxytocin promotes social empathy, providing insight into potential new treatments for ASD.