[2][3] Wallis moved to the United States for her postdoctoral research fellowship in the laboratory of Earl K. Miller studying neuronal activity in the prefrontal cortex,[4] or the region of the brain that plays a key role in executive functions, which allow animals to coordinate appropriate responses to plan, reason, problem solve, and effectively reach goals.
[7][8] Wallis's research centers on understanding how the frontal cortex of the brain is functionally organized to help people set and attain goals at the level of single neurons.
Wallis's group has investigated how cost-benefit analysis is undertaken in the brain to make effective decisions by monitoring single neuronal activity.
They found that single prefrontal cortex neurons played a role in encoding the type of cost decision the monkeys faced.
She was first drawn to the field after her PhD supervisor introduced her to patients who sustained damage to their orbitofrontal cortex and had difficulty making decisions, despite having other cognitive processes intact.