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.