Summary: A new study reports that a measure of brain complexity, calculated by recording EEG signals after a pulse of magnetic stimulation, is significantly reduced in people with Alzheimer’s disease. This method, previously used to detect consciousness in coma patients, could provide a new way to assess the integrity of conscious processing in dementia.
Source: Boston University School of Medicine
Key facts:
New metric: The study used the “state transitions-perturbation complexity index” (PCI-ST), a measure derived from transcranial magnetic stimulation (TMS) combined with EEG. Reduced complexity: Brain complexity in response to stimulation was lower in Alzheimer’s patients compared to healthy older adults. Conscious versus unconscious: The findings align with the clinical observation that Alzheimer’s disease disrupts conscious processes (such as episodic memory) while often preserving unconscious ones (such as muscles). memory).Study participants: The research compared 28 participants with Alzheimer’s disease with 27 healthy controls.
As individuals with Alzheimer’s disease (AD) progress from the stage of mild cognitive impairment to moderate and severe dementia, complex awareness deteriorates, although lower-level sensory awareness is relatively maintained. Most conscious processes also become more impaired as AD progresses, including attention, working memory, episodic memory, and executive function, while unconscious processes, such as procedural or muscle memory, operant conditioning (behavior controlled by consequences), and priming (where the experience of a stimulus affects the processing of a similar stimulus) are relatively spared. However, as damage spreads to different cortical regions in dementias such as AD, the corresponding aspects of consciousness diminish and are then lost.
A measure of brain complexity, state transitions-perturbation complexity index (PCI-ST), can be calculated by recording EEG signals after a pulse of transcranial magnetic stimulation. This measure has previously been used to determine when people are in a coma or in a minimally conscious state. A new study asks whether this same measure could be used to assess the integrity of conscious processing in people with AD.
According to researchers at Boston University Chobanian & Avedisian School of Medicine, the answer is yes. They found that brain complexity in response to magnetic stimulation was reduced in people with AD compared to people aging normally.
“Despite their impaired conscious memory, people with Alzheimer’s disease can use intact, implicit, and unconscious forms of memory, such as procedural memory (often called ‘muscle memory’) to continue their daily routines at home. However, when they travel, their home routines are not helpful, and their dysfunctional conscious memory can lead to disorientation and distress,” explains lead author Andrew Budson, MD, a professor of neurology at the school.
The researchers evaluated 28 participants with AD and 27 healthy controls, measuring their cognition and disease severity. They found lower PCI-ST in the AD group compared to controls at both motor cortex and parietal stimulation sites, suggesting that PCI-ST may reflect the impaired conscious cognitive processes and functional ability observed in AD.
“This research paves the way for future studies in people with cortical dementia to examine the relationship between conscious processes, global measures of consciousness, and their underlying neuroanatomical correlates, as well as improve our understanding of dementia and suggest potential therapeutic strategies,” adds Budson, who is also chief of Cognitive and Behavioral Neurology and director of the Center for Translational Cognitive Neuroscience at the Veterans Affairs (VA) Boston Health System.
Lead author Brenna Hagan, a PhD candidate in Behavioral Neuroscience at the school, notes that drug therapies, including donepezil (Aricept) and memantine (Namenda), alter neurotransmitters that can improve conscious abilities in people with Alzheimer’s disease. Additionally, nonpharmacological interventions can take advantage of relatively preserved procedural memory and other unconscious forms of memory to strengthen habits that can lead to improved quality of life.
Editorial notes
This article was edited by a Neuroscience News editor. Magazine article reviewed in its entirety. Additional context added by our staff.
About this news about Alzheimer’s research
Author: Gina DiGravio Source: Boston University School of Medicine Contact: Gina DiGravio – Boston University Image: Image is credited to Neuroscience News
Original research:
Brenna Hagan, Stephanie S Buss, Peter J Fried, Mouhsin M Shafi, Katherine W Turk, Kathy Y Xie, Brandon Frank, Brice Passera, Recep Ali Ozdemir, Andrew E Budson, Assessment of Alzheimer’s Disease with the TMS-EEG Disturbance Complexity Index, Neuroscience of Consciousness, Volume 2026, Number 1, 2026, niaf062, https://doi.org/10.1093/nc/niaf062
Funds:
This work was the result of data collected through the NIH (R01 AG060987) and the BrightFocus Foundation (A2021288S). BH is a PhD student and RAO and KX are research fellows. SB is funded in part by the NIA (NIH; 1K23AG068384), the Alzheimer’s Association (2019-AACSF-643094), and a BIDMC SPARK internal award. PJF is funded in part by BrightFocus (A2021288S). MMS is funded in part by the NIH (R01 AG060987, MH115949, EB032820; P01 AG031720). KWT is funded in part by the Veterans Health Administration (IK2 CX002065) and NIH/NIA (P30 AG072978). AEB is funded in part by the Veterans Health Administration (I01 CX002400) and NIH/NIA (P30 AG072978). BF is funded in part by the Veterans Health Administration (IK2 CX002625).
This work was the result of data collected through NIH (R01 AG060987) and the BrightFocus Foundation.
Abstract:
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. People with early-stage Alzheimer’s disease (AD) show dysfunction of conscious processes, such as attention, working memory, episodic memory, and executive function, with relatively preserved unconscious processes, such as procedural memory, operant conditioning, and priming. We sought to test the hypothesis that PCIST would be reduced in AD compared to healthy aging. We evaluated 28 participants with AD and 27 healthy controls (HC), measuring cognition with the Montreal Cognitive Assessment (MoCA) and disease severity with the Clinical Dementia Rating scale: Global (CDR-Global) and Sum of Boxes (CDR-SB). Results indicated lower PCIST in the AD group (M = 20.1) compared to controls (M = 28.2) at TMS stimulation sites of the motor cortex (M1) and inferior parietal lobe (IPL), suggesting that PCIST may reflect the impaired conscious cognitive processes and functional ability observed in AD. Therefore, we speculate that cortical dementias involve alterations in cortical complexity that may be related to the impairment of their conscious processes. This research paves the way for future studies in individuals with cortical dementia to examine the relationship between conscious processes, global measures of consciousness, and their underlying neuroanatomical correlates, as well as improve our understanding of dementia and suggest potential therapeutic strategies.
