Effect of white matter tract microstructural integrity on gamma entrainment using flickering light stimulation
Yeseung Park, Euisuk Yoon, Jieun Park, Jun Sung Kim, Ji Won Han, Ki Woong Kim- Psychiatry and Mental health
- Cellular and Molecular Neuroscience
- Geriatrics and Gerontology
- Neurology (clinical)
- Developmental Neuroscience
- Health Policy
- Epidemiology
Abstract
Background
Although gamma entrainment using flickering light stimulation (FLS), which was found to reduce Alzheimer’s disease pathologies in mice model, it failed to reduce cerebral amyloid burden in patients with AD or mild cognitive impairment. We investigated the optimal parameters of the FLS for entraining gamma waves in older adults in their brain may be influenced by white‐matter tract microstructural integrity (WMMSI) in humans.
Method
We enrolled 31 cognitively normal volunteers aged ≥ 65 years and measured resting‐state electroencephalography and the steady‐state visually evoked potential (SSVEP) of gamma rhythms induced by optimal FLS. We analyzed the spectral power change of the electroencephalogram induced by FLS using event‐related synchronization (ERS) and the propagation of gamma rhythms from the visual cortex to other brain regions using spectral Granger causality (sGC). Diffusion tensor images were acquired, and the microstructural integrity of white‐matter tracts of interest was measured. We investigated the relationship between white matter integrity and entrainment and propagation using fractional anisotropy (FA).
Result
After excluding five participants with SSVEP deficit, 26 participants were included in the final analysis. The lowest quartile group of the FA of the left posterior thalamic radiation exhibited a significantly lower ERS of gamma rhythms in the visual cortex than the second‐to‐highest quartile group (p = 0.045). In the multiple linear regression analyses, the effects of the FA of the middle longitudinal fasciculus and superior longitudinal fasciculus 3 on the sGC of the gamma rhythm connectivity from the occipital to the temporal, central, and frontal regions were statistically significant in both hemispheres (p < 0.05).
Conclusion
These findings suggest intact WMMSI may be required for proper gamma entrainment using FLS. Therefore, future clinical trials on gamma entrainment using FLS needs to consider WMMSI for participant selection.