Ageing and the Brain

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Introduction

Ageing refers to the changes that occur in the human body from the attainment of adulthood and ending in death. These changes often involve a decline of biological function and are accompanied by psychological, behavioural, and other changes. Some of these changes are quite obvious, while others are subtle.

Morphological changes to the brain with ageing

There are many specific effects of ageing on the brain, although it has been found that these changes are not uniform . It is considered that the volume of the brain is one of the more prominent changes due to neuronal loss, with an approximate reduction of 5% of brain weight, per decade, after the age of 40 Although the changes in diminished intellectual responsiveness, perception, mental agility and efficiency, impaired memory and learning ability are well-known, it is likely that the overall loss of cognition is not a result of widespread neuronal loss, but more small, specific areas affected , Additionally, the changes in brain volume have been purported to be a result of changes in white matter and degradation of the myelin as opposed to a reduction of the number of neurones present . Due to the changes in the mass of the neurons alongside others, the brain appears visibly different. Deposition of Brown (Lipofuscin) or black (Neuromelanin) pigments in the brain results in small discoloured areas due to normal ageing, although these are noted more in age-related brain pathologies such as Alzheimer's . In addition to these changes, the neuronal loss makes structures more pronounced such as the sulci of the cortex becoming deeper and the ventricles also becoming more pronounced

Physiological Changes to the brain with ageing

There are several physiological changes within the brain which are a result of normal ageing. These are often associated with direct changes in function. Cerebral blood flow has been shown to decrease by 27% decline over 70 years of age through direct changes in the cardiovascular system and may be exacerbated through blood vessel pathology . The effectiveness of the blood-brain barrier is found to be reduced with age and this leads to the increased opportunity for the pathogens and toxic materials crossing into the brain and the neural structures. Recent work has shown that this is often weakened in the hippocampus first which leads to damage to the area, and can result in a cognitive decline to the function of the brain region.

Ageing is also associated with declining production of some neurotransmitters, including noradrenaline, glutamate, dopamine and serotonin. Dopamine modulates motor-function and the acquisition of new skills and also one of the brain’s reward chemicals . The number of dopamine-producing neurons decreases as part of the normal ageing process, and this can adversely affect the ability to learn from past experiences .

How does age affect brain function?

Intellectual ability is not lost through age, but manifests as a gradual loss of neurones, alongside the depletion of neurotransmitters and slowing of nerve conduction may act together to slow down the processing of information. As a result, older people may take longer to complete certain tasks and experience other cognitive changes. Such as short-term, and episodic memory changes. These are often the earliest indicators of age-related changes in the brain, which does not tend to affect daily function and life skills but does start to present difficulties for the person . Although verbal skills often remain strong, there is a higher report of difficulties with recalling words in the older person, particularly after the age of 70.

Reaction time

The progressive loss of neurons, reduction in impulse velocity and minor changes in the spinal cord lead to a slowing down of reaction times (Spirduso, 1995). This can create problems, particularly when a fast reaction is essential (for example, to step out of the way of oncoming traffic).

Depression

In England, around 22% of men and 28% of women over the age of 65 are affected by depression; in care homes, the figures are even greater, with around 40% of residents affected (Age UK, 2017).

It is almost impossible to determine whether depression in older people occurs as a normal consequence of ageing or as a result of chemical imbalances seen in types of depression that also affect younger people. Concentrations of neurotransmitters involved in lifting mood (particularly serotonin) diminish with age and this can contribute to symptoms of depression (Fidalgo et al, 2013). The Royal College of Psychiatrists estimates that >85% of depressed older people receive no help from the NHS (Age UK, 2017). Depression can often produce symptoms that mimic dementia (pseudo-dementia) and this often causes great anxiety.

Emotional reactions

On the whole, older people are less prone to emotional outbursts than younger people. This may be related to the relative structural stability of some of the brain regions linked to emotions. Most studies of the amygdalae – which are heavily involved in impulsive behaviours and emotional reactions – reveal little evidence of atrophy or shrinkage at a much slower rate than in other brain regions. Additionally, the amygdalae also appear to retain most of their functional activity in older age (Mather, 2016).

Reduced intellectual reserves predispose to acute confusional states. Sustained mental, behavioural and motor changes of dementia may include depression (in 10–15% over 65s), persecutory symptoms of paraphrenia plus defective appreciation or localisation of pain. If the individual has an element of low mood, depression or dementia, motivation and participation may be a problem. The person or/and carer may need added emotional support plus teach the carer manual handling or specific exercise regimes. Counselling may form a large part of your role. Conditions such as acute confusion may be a result of dehydration, infection or a stroke, especially if the individual is nil by mouth, so encourage fluid as appropriate. As the therapist, you will need to be aware of mood swings, and if the patient has a tendency to verbal or physical aggression, this will affect your manual handling and their understanding. Remember to assess the risk to yourself first in these cases, especially if working alone.

Macroscopic changes include meningeal thickening, cerebral atrophy (brain weight down 10% between ages 30 and 70, and 20% by 90). Histological changes include: Deposits of lipofuscin in all cells, loss of RNA, mitochondria, enzymes in cytoplasm, decline in function and death of cell in neurones. Neurofibrillary tangles and senile plaques occur. Decrease in neurotransmitters can cause imbalance Vascular changes include fibrosis and degeneration, atheroma that increases in extent with age, but pathogenesis is multifactorial. Transient ischaemic cerebral episodes may progress to a complete stroke. Although different degenerative changes occur with increasing frequency in people over 60, they have not been shown to be directly related with each other.

Sleep pattern shortens, is lighter and more broken, with greater difficulty getting back to sleep again. Worst patterns are found in dementia where confusion increases in the evening or night (sundowning). Impaired sleeping patterns will affect the overall ability to concentrate and participate. Fatigue will also be an issue, so try and find the optimal treatment time.

Sensorimotor performance is slower to achieve accuracy plus impaired sensory awareness to pain, touch, heat, cold and joint position sense. Impaired mechanism controlling posture, antigravity support, balance and moving equipoise (with nerve conduction velocity reduced 10% by the age of 75). Can be a major predisposition to falls and injury.

Resources

Ageing and the Central Nervous System: Brain and Spinal cord