Introduction: Consciousness has been linked to functional connectivity across broad cortical networks that enable rapid integration of information across distant areas. Thus, potential targets for neuromodulation should have broad projections throughout the cortex. Here, we used single-pulse stimulation of two potential targets, prefrontal cortex and anterior cingulate cortex, to probe the connectivity of relevant cortical networks.
Methods: We enrolled four comatose traumatic brain injury patients with GCS < 8 and with no major brain structural abnormalities. After informed consent by a legally authorized representative, we implanted a stereotactic 10-contact depth electrode spanning anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC), used clinically for seizure monitoring. To probe frontal connectivity, we administered repetitive single-pulse stimulation to ACC and DLPFC (200 µS, 1 Hz stimulation, 100 reps). We recorded evoked potentials on the depth electrode, as well as on scalp contacts. Evoked responses were compared to consciousness, as measured using the Coma Recovery Scale-Revised.
Results: Both ACC and DLPFC stimulation caused broad evoked potentials, but ACC stimulation lead to bihemispheric responses. The spatial extent and amplitude of the evoked response were correlated with level of consciousness. Different patterns of activation were observed with PFC and ACC stimulation, with ACC showing a broader response.
Conclusions: ACC stimulation lead to broad evoked potentials, which correlated with the level of consciousness, a finding which was less clearly seen with PFC stimulation. This suggests that ACC could be a potential neuromodulation target for disorders of consciousness.
Patient Care: New treatments for coma will represent a new direction in therapy for sever brain injury.
Learning Objectives: By the conclusion of this session, participants should be able to:
1) Describe how electrical stimulation can be used to map corticocortical effective connectivity
2) Identify the critical criteria in selecting a potential neuromodulation target