Psychometric Properties of the TMS/EEG/PCI Device
INSTITUTE: Massachusetts General Hospital/Department of Psychiatry
PROJECT LEADER: Darin Dougherty, MD
PROJECT DURATION: 2019-2022
LAB WEBSITE: Mass General Division of Neurotherapeutics
The purpose of this study is to validate an objective, quantitative index of consciousness that does not rely on an individual's capacity to access or respond to the surrounding environment. We are using Transcranial Magnetic Stimulation (TMS) to perturb the brain and measuring the brain’s response through electroencephalographic (EEG) activity. The complexity of this response is represented by the quantitative Perturbational Complexity Index (PCI).
For this project, we are investigating the usability, reliability, and validity of the TMS/EEG/PCI index in healthy individuals during conscious awake states. This study will also assess PCI values in patients undergoing a cingulotomy or anterior capsulotomy. These procedures create lesions in the brain and reduce the number of possible brain states, which could lower PCI. On the other hand, after receiving cingulotomies or capsulotomies, patients are more able to hold their goals in mind and act, which could introduce higher capacity for healthy behavior and higher complexity.
Figure 1. TMS-evoked potentials recorded while stimulating different cortical areas (Premotor, Parietal, and Occipital) averaged across awake healthy participants. PCI values for each subject are shown in the boxes. The red dashed line indicates the operational PCI threshold that discriminates between the unconscious and the conscious conditions. TMS-EEG potentials are specific for stimulation sites and the PCI values evaluated in awake healthy controls are above the cutoff irrespectively by the stimulation site.
Broader Impact:
The results from this study would contribute to ongoing efforts to develop an objective quantitative index of consciousness. This index could next be used to assess levels of consciousness in patients with disorders of consciousness and individuals with restricted ranges of consciousness.
Future work could explore the effect of different interventions (e.g., psychedelics, transcranial Focused Ultrasound) on expanding consciousness (i.e. increasing PCI levels).
Publications:
A.C. Paulk, et al. Local and distant cortical responses to single pulse intracranial stimulation in the human brain are differentially modulated by specific stimulation parameters. Brain Stimul., 15, 491-508 (2022).
C.K. Starkweather, S.K. Bick, J.M. McHugh, D.D. Dougherty, Z.M. Williams Lesion location and outcome following cingulotomy for obsessive compulsive disorder. J Neurosurg., 136, 221-230 (2021).
S.H. Siddiqi, et al., Brain stimulation and brain lesions converge on common causal circuits in neuropsychiatric disease. Nat Hum Behav., 5, 1707-1716 (2021).
B. Crocker, et al., Local and distant responses to single pulse electrical stimulation reflect different forms of connectivity. Neuroimage., 237, 118094 (2021).
Y. Tu, et al. Perturbing fMRI brain dynamics using transcranial direct current stimulation. Neuroimage. 237, 118100 (2021).
J.C. Yang, D.T. Ginat, D.D. Dougherty, N. Makris, E.N. Eskandar Lesion analysis for cingulotomy and limbic leucotomy: Comparison and correlation with clinical outcomes. J Neurosurg. 120, 152-163 (2014).
S.K. Bourne, et al., Beneficial effect of subsequent lesion procedures after nonresponse to initial cingulotomy for severe, treatment-refractory obsessive-compulsive disorder. Neurosurgery 72, 196-292 (2013).