Ageing and the Central Nervous System: Brain and Spinal cord

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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.[1]

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 [2]. 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 [3] 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 [2], 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 [4]. Due to the changes in the mass of the neurons alongside others, the brain appears visibly different. Deposition of Brown (Lipofuscin) [5] or black (Neuromelanin)[6] 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 [7]. 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 [7]

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 [8]. 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[9].

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 [10].

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 [11]. 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. [12] Neuronal loss and the reduction in impulse velocity lead to a slowing of reaction times, and this can lead to problems with righting reactions, leading to falls etc.


Reduced intellectual reserves predispose to acute confusional states. Sustained mental, behavioural and motor changes of dementia may include depression[13] (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.

Sleep pattern shortens, is lighter and more broken[14], 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.

References

  1. https://www.britannica.com/EBchecked/topic/1354293/human-aging
  2. 2.0 2.1 Burke SN, Barnes CA. Neural plasticity in the ageing brain. Nature reviews neuroscience. 2006 Jan;7(1):30-40.
  3. Svennerholm L, Boström K, Jungbjer B. Changes in weight and compositions of major membrane components of human brain during the span of adult human life of Swedes. Acta neuropathologica. 1997 Sep 1;94(4):345-52.
  4. Murphy DG, DeCarli C, Mclntosh AR, Daly E, Mentis MJ, Pietrini P, Szczepanik J, Schapiro MB, Grady CL, Horwitz B, Rapoport SI. Sex differences in human brain morphometry and metabolism: an in vivo quantitative magnetic resonance imaging and positron emission tomography study on the effect of aging. Archives of general psychiatry. 1996 Jul 1;53(7):585-94.
  5. Ottis P, Koppe K, Onisko B, Dynin I, Arzberger T, Kretzschmar H, Requena JR, Silva CJ, Huston JP, Korth C. Human and rat brain lipofuscin proteome. Proteomics. 2012 Aug;12(15-16):2445-54.
  6. Clewett DV, Lee TH, Greening S, Ponzio A, Margalit E, Mather M. Neuromelanin marks the spot: identifying a locus coeruleus biomarker of cognitive reserve in healthy aging. Neurobiology of aging. 2016 Jan 1;37:117-26.
  7. 7.0 7.1 Knight J, Nigam Y. Anatomy and physiology of ageing 5: the nervous system. Nursing times. 2017 Jun 1;113(6):55-8.
  8. Chen JJ, Rosas HD, Salat DH. Age-associated reductions in cerebral blood flow are independent from regional atrophy. Neuroimage. 2011 Mar 15;55(2):468-78.
  9. Montagne A, Barnes SR, Sweeney MD, Halliday MR, Sagare AP, Zhao Z, Toga AW, Jacobs RE, Liu CY, Amezcua L, Harrington MG. Blood-brain barrier breakdown in the aging human hippocampus. Neuron. 2015 Jan 21;85(2):296-302.
  10. Mather M. The affective neuroscience of aging. Annual review of psychology. 2016 Jan 4;67.
  11. Fjell AM, McEvoy L, Holland D, Dale AM, Walhovd KB, Alzheimer's Disease Neuroimaging Initiative. What is normal in normal aging? Effects of aging, amyloid and Alzheimer's disease on the cerebral cortex and the hippocampus. Progress in neurobiology. 2014 Jun 1;117:20-40.
  12. Harada CN, Love MC, Triebel KL. Normal cognitive aging. Clinics in geriatric medicine. 2013 Nov 1;29(4):737-52.
  13. Fidalgo S, Ivanov DK, Wood SH. Serotonin: from top to bottom. Biogerontology. 2013 Feb 1;14(1):21-45.
  14. Mander BA, Winer JR, Walker MP. Sleep and human aging. Neuron. 2017 Apr 5;94(1):19-36.