Sensory gating and EEG oscillatory markers in the context of cognitive reserve in healthy ageing

Staley, Emma (2024). Sensory gating and EEG oscillatory markers in the context of cognitive reserve in healthy ageing. University of Birmingham. Ph.D.

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Abstract

The number of older adults (> 65 years) developing a neurological or neuropsychiatric disease will rise as the population aged over 80 years old grows. Ageing has diverse impacts on cognitive function, significantly affecting daily life in older adults. Cognitive Reserve (CR), the brain's ability to resist age-related changes, is thought to be built up over a person's lifetime through various intellectual, educational, and social activities. Measuring CR consistently proves challenging due to varied approaches and tools used throughout the literature.
Studies utilising electroencephalography (EEG) and magnetoencephalography (MEG) for non-invasive brain measurement demonstrate that high CR individuals exhibit increased connectivity and amplified event-related potentials (ERPs) or oscillatory amplitudes. However, establishing causal relationships between MEG or EEG measures and CR remains challenging due to methodological variations and participant heterogeneity.
We investigated inhibitory EEG measures using sensory gating (SG). A paired stimulus click paradigm was applied to measure the P50, N100 and P200. Our study found an age-related decline in neuropsychological function and CR but not in SG among healthy older adults (n = 27). Significant relationships were observed between P200 and verbal as well as visual long-term memory (both p < .05), and N100 with inhibitory memory (p < .001). No other neuropsychological measures correlated with SG.
Auditory Steady-State Responses (ASSR) are electrophysiological evoked oscillatory responses entrained to the frequency and phase of temporally modulated tones. These responses are often deficient in disorders of consciousness, such as schizophrenia. Three blocks of tones were presented: 2.5 Hz and 40 Hz, 2.5 Hz and 80 Hz, and 2.5 Hz and 40 Hz. Results revealed associations between verbal fluency and lower ASSR power responses (n = 14, p = .039), independent of age or other neuropsychological assessments.
Alpha frequency is thought to represent inhibiting irrelevant sensory pathways, and the peak frequency can be calculated over a short period of EEG recording time (~4 minutes). Older participants had significantly lower peak alpha results than the younger participants (p = .023), and age significantly predicted the peak alpha frequency (PAF) (p = .017). The PAF was also significantly predicted by IQ (p = .017) and a digit span task (p = .039), but this was not seen when age was controlled for, implying that this relationship isn’t robust. Similar predictors were found for SG measures as well as PAF.
Results from each chapter contribute to the overall understanding of the relationships between SG, neural measures, and CR in healthy older adults. Our chosen EEG responses all demonstrated associations with inhibition measures. These findings provide insights into the neural underpinnings of sensory processing and inhibitory functions, contributing to our understanding of their potential impact on overall cognitive functioning in the ageing population. Limitations of methodological chapters are discussed with recommendations for future research.
Emphasising clinical significance, the thesis suggests using an EEG setup with fewer electrodes and a passive listening task for faster, less burdensome assessments. This approach allows for a faster setup, reducing burden on patients. The findings suggest that measuring cognitive vulnerability, especially in older adults, is crucial in clinical settings, offering support before major healthcare events such as planned major surgery.

Type of Work:

Thesis (Doctorates > Ph.D.)

Award Type:

Doctorates > Ph.D.

Supervisor(s):