Abstract
The subjective and behavioral effects of intracranial electrical stimulation (iES) have been studied for decades, but there is a knowledge gap regarding the relationship between the magnitude of electric current and the type, intensity and valence of evoked subjective experiences. We report on rare iES data from 18 neurosurgical patients with implanted intracranial electrodes in the orbitofrontal cortex (OFC), the insula (INS) and the anterior portion of cingulate cortex (ACC). ACC stimulation elicited somatic and visceral sensations, whereas OFC stimulation predominantly elicited olfactory and gustatory responses, and INS stimulation elicited a mix of effects involving somatic and visceral sensations, olfaction and gustation. Further, we found striking evidence that the magnitude of electric current delivered intracranially correlated positively with the perceived intensity of subjective experience and the evoked emotional state, a relationship observed across all three regions. Finally, we observed that the majority of reported experiences were negatively valenced and unpleasant, especially those elicited by ACC stimulation. The present study provides novel case studies from the human brain confirming that these structures contribute causally to the creation of affective states and demonstrates a direct relationship between the magnitude of electrical stimulation of these structures and the qualia of elicited subjective experience. Summary: This study provides critical knowledge about the effect of electrical charge magnitude on the intensity of human subjective experiences and emotional states. We shed light on the fundamental relationship between the electrical (physical) state of cortical tissue and the modality and intensity of human (subjective) experience. As electroceutical interventions are increasingly employed to treat neurological and psychiatric disorders, these findings highlight the importance of electrical stimulation magnitude for eliciting specific changes in human subjective experience.