Direct electrical stimulation of the mid-thalamus, near the mediodorsal nucleus, alters conscious experience and reveals asymmetric brain connectivity. In 30 patients with focal epilepsy, 50 Hz stimulation changed conscious experience in 11 of 12 patients, producing visceral, emotional, or somatosensory sensations, often unpleasant. Single-pulse 0.5 Hz stimulation showed strong electrophysiological connectivity between the mid-thalamus and the insula, anterior and midcingulate, prefrontal cortices, and medial temporal lobe. Inflow signals from some cortical sites to the mid-thalamus were significantly stronger than outflow, indicating a clear directional asymmetry in thalamocortical connectivity.
Direct electrical stimulation of the human insular cortex in 17 neurosurgical patients with 142 implanted electrodes induced reportable changes in conscious experience at 40% of stimulation sites, spanning visceral/autonomic, anxiety, taste/olfactory, pain/temperature, and somatosensory domains. These subjective responses mapped onto specific microstructural areas defined by cytoarchitectonic parcellation: pain and thermal responses localized to areas lg2/ld2, non-painful somatosensory responses to area ld3, and visceroceptive responses to area Id6. Stimulation of area Id7 in the dorsal anterior insula did not produce reportable subjective changes, despite intracranial EEG recordings showing significant time-locked high-frequency activity. The findings provide a multimodal functional map linking fine-grained microstructural subdivisions to distinct subjective experiences.
Intracranial electrical stimulation of the anterior cingulate cortex (ACC), orbitofrontal cortex (OFC), and insula (INS) in 18 neurosurgical patients produced distinct subjective experiences: ACC stimulation elicited somatic and visceral sensations, OFC stimulation predominantly olfactory and gustatory responses, and INS stimulation a mix of these. The magnitude of electric current correlated positively with the perceived intensity of subjective experience and evoked emotional state across all three regions. Most reported experiences were negatively valenced and unpleasant, especially those from ACC stimulation. These findings demonstrate a direct relationship between electrical stimulation magnitude and the qualia of subjective experience, highlighting the importance of charge magnitude for eliciting specific changes in human experience.