Visuospatial oscillations in Alzheimer’s disease associated cognitive decline

Kanikah Mehndiratta, MSc, University of Glasgow

Alzheimer’s disease (AD) is a progressive neurodegenerative condition that causes brain atrophy or shrinking, ultimately leading to death of brain cells. It is considered to be the biggest cause of dementia globally. The death rate due to AD in U.S came out as 37 per 100,000 people in 2019. About 60% of the AD patients aged above 70, die within the next 10 years. This automatically puts a strain on healthcare to work towards effective diagnostic and treatment strategies for AD. Healthcare related investment towards AD is about $500 billion a year. A recent study published in the BMC journal discusses visuospatial neural oscillations to help classify patients under the AD spectrum.

The AD spectrum

Dementia is a syndrome marked by a gradual decline in cognitive domains, such as memory, personality and behaviour, language, visuospatial functioning. This in turn affects the day-to-day crucial activities of the patient. About 80% of dementia cases occur due to AD. At the pathophysiological level, the disease is characterized by extracellular deposition of β-amyloid peptides and neurofibrillary tangles of tau protein. A definitive diagnostic criterion for AD includes post-mortem analysis of the damaged brain tissue. Analysis of biomarkers of cerebrospinal fluid (CSF) and positron emission tomography (PET) are more recent approaches aiding in diagnosis. Cholinesterase inhibitors are recommended to AD patients at any stage of dementia. Memantine is usually prescribe to a moderate-to-severe AD patient.

Current treatment therapies work towards attenuation of a progressive cognitive decline. Use of rhythmic alpha and gamma-frequency radiation stimuli visually to attenuate the deposition load of β-amyloid is one such therapy. The therapy could potentially rescue cognitive function from declining via microglial recruitment. It could also enhance hemodynamic response, helping in improvement of patient’s condition. Not much is known regarding such role of neural oscillations, particularly visual in the cognitive impairment in AD patients. Functional MRI studies indicate aberrant hemodynamic responsiveness, especially during visuospatial activities. Many studies reported a decrease in such responses particularly in the occipital regions, thus making it the focus of this study.

Research strategy adopted

The research under discussion uses the rhythmic visual stimuli externally for entraining neural oscillations. The specific occipital cortices are targeted for such a therapy. Visuospatial processed helps in recruiting stereotyped multi-spectral responses in the neural posterior cortices’ region. The responses usually include an early frequency synchronization in the theta range i.e., 3-7 Hz. This is followed by an alpha band desynchronization in the parieto-occipital region. A gamma frequency synchronization at 50-80 Hz is then used to support the processing of stimulus associated features.

The current study uses the responses to such stimuli to differentiate between cognitively healthy, biomarker-negative aged people and AD patients. Magnetoencephalography and logistic regression modelling have been used for such an investigation. A general linear approach has been used to explore the relevance of such responses in cognitive decline. This was done by relating the Montreal Cognitive Assessment (MoCA) and Mini-mental State Examination (MMSE) scores of healthy negatives to AD patient scores.

Conclusive results

Visuospatial oscillations in different frequency ranges successfully classified patients on the AD spectrum. Oscillations particularly in the alpha and gamma range robustly predicted MMSE and MoCA scores in patients with cognitive decline. In comparison with biomarker-negative individuals, AD patients exhibited weaker responses in the alpha-frequency range. Such responses were specifically in the lateral occipital regions of the brain. While in the primary visual cortex region, a stronger gamma-frequency response was observed in comparison with the negative control. The data concludes to be quite substantial for further clinical interventions in diagnosis and treatment of AD.

References:

Wiesman, A. I., Murman, D. L., May, P. E., Schantell, M., Wolfson, S. L., Johnson, C. M., & Wilson, T. W. (2021). Visuospatial alpha and gamma oscillations scale with the severity of cognitive dysfunction in patients on the Alzheimer’s disease spectrum. Alzheimer’s Research & Therapy, 13(1), 139. https://doi.org/10.1186/s13195-021-00881-w

2. Weller, J., & Budson, A. (2018). Current understanding of Alzheimer’s disease diagnosis and treatment. F1000Research, 7, 1161. https://doi.org/10.12688/f1000research.14506.1

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Author info:

Kanikah Mehndiratta is an avid researcher in the field of Genetics with a background in Biotechnology. She is a postgraduate from the University of Glasgow in their Medical Genetics and Genomics program. Currently, based in Chandigarh as a scientific writer, she involves herself mainly in projects related to neurological disorders. Outside of academics, she likes to read novels, travel and is involved in volunteer work mostly.

LinkedIn profile- https://www.linkedin.com/in/kanikah-mehndiratta-301830171

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