Ageing and Memory: Biological Theories

Ageing and Memory

• People over 60 are the fastest-growing age group on Earth.
• It includes more than 700 million people worldwide.
• The global population of people over 60 is projected to rise to 2 billion by 2050.
• Over half of adults over 65 have concerns about their memory.
• Ageing effects on cognitive function have been studied for many years.
• Older adults report difficulties with episodic and working memory.

Biological Theories About Cognitive Ageing

• Current theories suggest the most likely explanation for physical aging lies in basic cellular processes.
• These cellular processes change with age, reducing the efficiency of cellular functioning.

The Hayflick Limit

• Species vary in lifespan.
• Biologists suggest a universal genetic process may trigger age-related declines and limit lifespan.
• Tortoises have longer lifespans than humans, for example.

The Hayflick Limit Evidence

• Cells from embryos of different species double a fixed number of times in nutrient solution before degenerating.
• Each chromosome has repetitive DNA, a telomere, at its tip.
• Telomeres appear to serve as a timekeeping mechanism for the organism.
• Every time a cell divides, the number of telomeres is slightly reduced.

Wear and Tear Theory

• Ageing is a process where stressors are no longer adequately countered by the body’s protection.
• The body wears down from accumulated exposure to inadequate nutrition, disease, pollution, and other stressors.
• Damage from free radicals and accumulation of injurious proteins are other factors.
• These processes can lead to decreased integrity of neuronal membranes and cell death.
• Loss of structure or function of neurons, including cell death, is called neurodegeneration.

Mitochondria and Ageing

• Mitochondria are parts of cells that produce energy.
• They may affect ageing through increased production of free radicals.
• The immune system plays a role in neurodegeneration.
• Inflammatory chemicals can exacerbate damage patterns caused by a neurodegenerative disease.

Dementia

• It is a clinical disorder caused by neurodegeneration.
• Dementia is characterized by progressive impairment in cognitive function, quality of life, and independent living.
• Alzheimer’s disease is the most common type of dementia.
• There are an estimated 64,000 people in Ireland currently living with dementia.

Alzheimer's Disease

• Frontal and temporal lobes are reduced in size.
• This is due to degeneration of synapses and death of neurons
• Post-mortem examinations reveal plaques and tangles, mainly in prefrontal and temporal regions.
• Plaques are deposits of amyloid-beta protein around neurons.
• Tangles are aggregates of tau protein inside neurons.

Alzheimer's Treatment

• Several drugs that aim to treat Alzheimer's disease are in clinical trials.
• Recent reports suggest some of these drugs may slow cognitive decline compared to a placebo.

Neuropsychological Testing

• These tests contribute to the diagnosis of dementia.
• They track deterioration over time.
• Cognitive deficits can be detected years before a clinical diagnosis.
• A first symptom is often poor storage and retrieval of episodic memories over time.
• Poor performance on a delayed recall task is an example.
• Early deficits may be observed in language, facial recognition, and visuospatial skills.
• Examples of tests are the Wechsler Adult Intelligence Scale (WAIS) Block Design and the Benton visual retention test.

Brain Charts for the Human Lifespan

• A study collected 123,984 MRI scans across the lifespan, using data from 100 MRI studies worldwide.
• It quantified brain structural changes using MRI to calculate growth curves.
• Brains expand rapidly in early life and slowly shrink with age.
• Structural MRI data from 67 individuals with psychosis and 249 controls were contributed.
• Data was collected by Trinity College Dublin and the University of Galway.

Functional Compensation in the Ageing Brain

• fMRI studies show older adults have increased neural response or over-recruitment of brain regions like the prefrontal cortex.
• This occurs relative to younger adults during cognitive tasks.
• Over-recruitment is associated with improved performance.
• In one study, older adults showed increased neural activity across prefrontal and parietal regions when task demands were high
• This occurred relative to younger adults while performing a Go-No Go task.
• The over-engagement of prefrontal and parietal regions in older adults was associated with a lower error rate.
• Some fMRI studies show that over-recruitment is associated with poorer performance.
• It may suggest inefficient processing.
• Other studies show that older adults have increased activity in the auditory cortex.
• It occurs during a memory task, and may reflect distraction in the noisy MRI environment.
• Increased neural activity in older adults relative to younger adults can lead to better performance on some tasks and worse performance on others.
• Sometimes increased activity may reflect functional compensation, and other times less efficient use of neural resources.