Assessing motor cortex excitability and its relationship with brain atrophy in Ahlzeimer’s disease
Renee P Lawson, Reza Zomorrodi, Michael Joseph, Hiba Alhabbal, Gifty Asare, Daniel M. Blumberger, Zafiris J. Daskalakis, Corinne E. Fischer, Benoit H. Mulsant, Bruce G. Pollock, Tarek K. Rajji, Aristotle N. Voineskos, Sanjeev Kumar- Psychiatry and Mental health
- Cellular and Molecular Neuroscience
- Geriatrics and Gerontology
- Neurology (clinical)
- Developmental Neuroscience
- Health Policy
- Epidemiology
Abstract
Background
Cortical excitability detected using resting electroencephalography (EEG) or transcranial magnetic stimulation (TMS) combined with EEG has been proposed as a new neurophysiological marker of Alzheimer’s dementia (AD). However, the link between cortical excitability and structural changes in AD is not well understood. The objective of this study was to assess the relationship between cortical excitability and brain structure (cortical thickness) in the motor cortex of patients with AD and healthy older individuals.
Methods
63 participants (38 females) with AD (Mage = 74.5, SD = 8.0) and 48 healthy individuals (27 females) (Mage = 71.1, SD = 7.8) were included. hot spot’ over the left motor cortex was defined as the location that generated maximal motor‐evoked potentials in the abductor pollicis brevis muscle. Each participant’s resting motor threshold (rMT) was determined using the ‘hotspot’ by finding the lowest stimulus strength to evoke a motor‐evoked potential with a peak‐to‐peak amplitude of ≥50 µV in at least five of ten consecutive single pulse TMS trials. T1w MRI scans were pre‐processed using the anatomical pipeline in fMRIPrep v20.2.6. This pipeline includes recon‐all from Freesurfer v6.0.1, which estimates cortical thickness based on ROIs defined in the Desikan‐Killiany atlas.
Results
Participants with AD had lower motor cortex thickness than healthy individuals (t(93) = ‐4.398, p = <0.001). Participants with AD had lower rMT (indicative of higher excitability) than healthy individuals (t(109) = ‐2.265, p = 0.026). Within the total sample, rMT was correlated with motor cortex thickness (r = 0.216, df = 95, p = 0.036).
Conclusions
Consistent with previous literature, our study supports that AD is associated with decreased cortical thickness and higher motor cortex excitability. We also found that changes in cortical thickness positively correlated with rMT, suggesting that cortical hyperexcitability is influenced by cortical neurodegeneration. Future studies may wish to examine the association between cortical excitability and functional imaging measures to understand specific mechanisms.