Novel invasive neurostimulation stimulation strategies through neurosurgical interventions are emerging as a promising therapeutical strategy for major depressive disorder. These have been applied mostly to the anterior cingulate cortex, but other limbic brain regions have shown promise as anatomical targets for new neurostimulation strategies. The researchers seek to study neural activity in limbic brain areas implicated in decision behavior and mood regulation to identify novel targets for treatment through electrical stimulation. To do this, the study team will record local field potentials (LFPs) from the orbitofrontal cortex, hippocampus and amygdala of epilepsy participants undergoing invasive monitoring (intracranial encephalography, iEEG) during choice behavior. Leveraging the high co-morbidity of depression and intractable epilepsy (33-50%), neural responses will be compared to reward across depression status to identify abnormal responses in depression. Finally, the researchers will use these as biomarkers to guide development of neurostimulation strategies for the treatment of depression.