Schedule of Events | Symposia

Graduate Student Award Winner

Assessing Consciousness and its Cognitive Correlates in Alzheimer's Disease with the TMS-EEG Perturbation Complexity Index

Poster Session F - Tuesday, April 1, 2025, 8:00 – 10:00 am EDT, Back Bay Ballroom/Republic Ballroom

Brenna Hagan^1,2 (haganb@bu.edu), Stephanie S. Buss³, Peter J. Fried³, Mouhsin M. Shafi³, Katherine W. Turk^1,2, Kathy Xie^1,2, Recep A. Ozdemir³, Andrew E. Budson^1,2; ¹Center for Translational Cognitive Neuroscience, VA Boston Healthcare System, ²Alzheimer's Disease Research Center, Boston University School of Medicine, ³Berenson-Allen Center for Noninvasive Brain Stimulation, Beth Israel Deaconess Medical Center

Introduction: The Memory Theory of Consciousness suggest that consciousness developed as part of the episodic memory system, with all areas of the cerebral cortex contributing to conscious awareness (Budson et al., 2022). Alzheimer’s disease (AD) has been postulated as a disorder of consciousness. The Perturbation Complexity Index - State Transitions (PCIST) measures the complexity of the brain’s response to transcranial magnetic stimulation (TMS) using electroencephalography (EEG) and is sensitive to consciousness, such as minimally conscious states. We sought to test the hypothesis that PCIST would be reduced in AD compared to healthy aging. Methods: We assessed 28 participants with AD and 28 healthy controls (HC), measuring cognition with the Montreal Cognitive Assessment (MoCA) and disease severity with the Clinical Dementia Rating scale – Sum of Boxes (CDR-SB). Results: Results indicated lower PCIST in the AD group (M = 20.1) compared to controls (M = 28.9). Moreover, PCIST correlated positively with MoCA scores and negatively with CDR-SB scores across the motor cortex (M1) and inferior parietal lobule (IPL) TMS stimulation sites, suggesting that PCIST may reflect conscious cognitive and functional capacity. Conclusion: These findings support the hypothesis that cortical dementias are disorders of consciousness. This research opens the avenue for future studies on the fundamental nature of consciousness and its neuroanatomical correlates, in addition to enhancing our understanding of dementia and possible therapeutic strategies.

Topic Area: METHODS: Electrophysiology