Cognitive Ageing: Biological Theories

• People over 60 are the fastest-growing age group, estimated to reach 2 billion by 2050.
• Over half of adults over 65 are concerned about their memory.
• Ageing effects on cognitive function have been studied for many years.
• Older adults often face difficulties with episodic and working memory.

Biological Theories of Cognitive Ageing

• Current theories suggest that basic cellular processes change with age, reducing cellular functioning efficiency.
• The causes of physical ageing are linked to basic cellular processes.

Hayflick Limit

• Species exhibit varying lifespans.
• Some biologists believe a universal genetic process triggers age-related declines and limits lifespan.
• Tortoises, for example, have longer lifespans than humans.
• Cells taken from embryos of different species double a fixed number of times in nutrient solution before degenerating.
• Each chromosome has a telomere, repetitive DNA at its tip, which serves as a timekeeping mechanism.
• Every cell division reduces the number of telomeres slightly.

Wear and Tear Theory

• Ageing occurs when stressors are no longer adequately countered by the body's protection.
• The body wears down due to cumulative exposure to inadequate nutrition, disease, pollution, and other stressors.
• This includes damage from free radicals and the accumulation of injurious proteins.
• These processes can decrease the integrity of neuronal membranes and lead to cell death.
• Neurodegeneration is the loss of structure or function of neurons, including cell death.
• Mitochondria, the part of the cell generating energy, may affect ageing through increased free radical production.
• The immune system contributes to neurodegeneration; inflammatory chemicals may worsen neurodegenerative diseases.
• Dementia is a clinical disorder caused by neurodegeneration that impairs cognitive function; Alzheimer's is the most common type.
• There are approximately 64,000 people in Ireland living with dementia.

Alzheimer's Disease

• Frontal and temporal lobes shrink due to synapse degeneration and death of neurons.
• Examination after death reveals plaques and tangles, especially in the prefrontal and temporal regions of Alzheimers patients.
• Plaques are deposits of amyloid β protein around neurons.
• Tangles are aggregates of tau protein inside neurons.
• Neuropsychological tests help diagnose dementia and track deterioration, deficits may be detected years before diagnosis.
• The initial symptom is often poor storage and retrieval of episodic memories.
• Patients perform poorly on delayed recall tasks.
• Early deficits may involve language, facial recognition, and visuospatial skills, assessed via tests like the WAIS Block Design and the Benton visual retention test.

Brain Research Using MRI

• A study collected 123,984 MRI scans to track brain changes across the lifespan from around the world.
• This research shows that brains expand rapidly in early life and shrink slowly with age.
• Researchers used Brain Charts to quantify structural brain changes using MRI to calculate growth curves.
• The data included structural MRI data from 67 individuals with psychosis and 249 controls from Trinity College Dublin and the University of Galway.
• Functional MRI (fMRI) studies show older adults exhibit increased neural response compared to younger adults during cognitive tasks.
• Greater activity is seen in particular brain regions such as the prefrontal cortex.
• Over-recruitment is sometimes associated with improved performance, compared to older adults who don't over-recruit.
• Neural activity increased across prefrontal and parietal regions when older adults performed a Go-No Go task.
• This over-engagement correlated with a lower error rate.
• Some fMRI studies suggest over-recruitment is associated with poorer performance, suggesting inefficient processing.
• Older adults also show increased activity in the auditory cortex during memory tasks, possibly reflecting distraction in the MRI environment.
• Increased neural activity in older adults can be associated with either better or worse performance, pointing to both functional compensation and less efficient use of neural resources.

Ageing and Memory Summary

• Older adults report difficulties with episodic and working memory
• Biological theories of ageing relate to the effect of basic cellular processes on the reduction of efficiency of cellular functioning.
• Neurodegeneration is a Loss of structure or function of neurons and can cause dementia, like Alzheimer's disease.
• Reduced cortical volume; reduced white matter integrity; changed cortical activity and altered function of the default mode network represent ways the brain changes with age.
• Cognitive reserve may buffer effects of neuropathology and depend on physical health, life style, education and social environment, slowing age-related decline.