The weight of the brain reaches its peak of approximately 1.4 kg in the early twenties and then undergoes a slow decline. By the age of 80, the loss reaches 7% or about 100 gm. During the aging process, the ratio of grey to white matter changes, indicating that there is some loss of cells and fibres. The blood supply of brain in a young adult is about 50-60 ml/min/100g, which reduces to 40ml/min/100g in old age.
Neurological disorders are important cause of disability and hospitalization, especially in old age. Not only does old age play an important role in increasing the frequency and severity of neurological diseases, but it can also modify the progression of an existing disease. Even normal aging may be associated with loss of some neurological signs.
Frequency of cognitive disorders increases dramatically with advancing age. In general, knowledge and experience increases throughout life. New memories are constantly formed, or al least exposure to new memories never stops throughout the lifetime of an individual. Learning ability too, does not decline much with age.
Normal cognitive changes seen in old age are:
- Reduced processing speed
- Reduced flexibility
- Reduced attention span
- Decreased visual perception
- Working memory lapses
- Trouble in recollection of remotely acquired information
Practical problem solving, knowledge gained from experience, and vocabulary tends to be cumulative and does not seem to decline with age.
But the ability to solve abstract problems, acquiring a new skill set, and speedy performance have shown to decline with age.
Cranial Nerve Function
Smell and Taste: Normal ageing is associated with decreased perception of smell, both at threshold levels and higher levels. Elderly people also have a decreased ability to differentiate between closely related odours. It must be noted that the reduced perception of smell may not only be due to the aging process, but also as a result of medications, viral infections of the upper respiratory tract and head trauma, all of which are common in old age.
Taste which is closely related to smell also gets reduced in old age. The sensitivity to a broad range of tastes is grossly impaired in elderly compared to young adults. The number of taste buds does not seem to get altered much during the life of an individual, their response decreases significantly.
Vision: There is a reduction in all visual parameters in old age: visual sharpness, visual fields, contrast perception, depth perception, judgement of movement (of objects with respect to oneself and of oneself with respect to the surroundings), all get impaired.
In fact the decline in the light receptors in the retina have been shown to start reducing from late 20s and by the age of 60s and 70s the decline is too much to enable the person to see as compared to the days of youth. Another common visual disability in old age, is loss of accommodation, that is, decline in near vision and acquirement of reading glasses.
Other conditions significantly affecting the vision of an elderly are as under:
- Development of cataracts (opacification of the lens),
- Macular degenerations
- Pupillary sluggishness
- Disorders of muscles of eye
- Other co-existing neurological conditions
Hearing and Balance
Condition leading to decreased hearing ability in the elderly are:
- Gradual loss of cochlear hair cells (hearing cells in the ear)
- Degeneration of the blood supply (stria vascularis) in the hearing organ (organ of Corti)
- Thickening of the cochlear basilar membrane
The diminution is predominantly in the higher frequencies and the speech discrimination also gets reduced.
Vestibular function, which is related to balance of an individual also gets reduced with age. There is reduction in the vestibulo-spinal reflexes and ability to detect head position and motion in space.
There is marked reduction in the muscle bulk, a condition called Sarcopenia. Most obvious loss of muscle bulk is from the small muscles of hand and feet. Some studies have shown that the reduction in the strength of voluntary contraction of muscles reduces by as much as 50% in old age compared to youth. Sometimes, fasciculation (repeated twitching of muscles) appear, which are not a part of normal healthy aging and need to be investigated.
Not only muscle bulk but coordination and speed of muscle function also decline over age. Hesitation, slowness in movement, especially initiation of movement, and mild tremors appear. These may interfere with the normal day to day activities of life, like dressing, grooming, eating, getting out of a chair, and may cause significant dependence on care-providers.
Tremors are extremely common movement disorder in the elderly, prevalent in as much as 98% of the elderly after the age of 70. Postural tremor is attributed to secondary causes like alcohol and thyroid disease.
Way of walking (Gait)
The term idiopathic (without any medical disorder) senile gait is used to describe a stooped posture, backwardly rotated immobile pelvis, excessive bending at the hips, reduced lifting of feet off the ground while walking, slightly broad based walk and reduced arm swing.
There is a tendency to adopt a bent over posture in old age. There is also a tendency to sway. This may be due to increased muscle tone, decreased neuro-muscular power, degenerative joint disease, or visual disorders. Even healthy elderly have trouble maintaining balance while standing on one foot with their eyes closed.
Reflexes tend to get diminished in old age. Moreover they are asymmetric in both the sides in about 3% of the elderly. The ankle jerk is the first one to disappear in old age among all the deep tendon jerks.
Superficial reflexes may become sluggish or may also disappear with advanced age.
Primitive reflexes (like grasp, suckling, palmo-mental and glabellar tap) tend to reappear.
The most common and evident abnormality is the loss of joint position sense and loss of vibration. Joint sense is lost in 2-44% of elderly whereas vibration loss is far more common in 12-68% between the ages of 65-85 years. Some research also reports the loss of light touch in old age. Pain threshold increases. i.e., the person does not feel pain easily and this may lead to multiple unnoticed injuries, especially on the feet.
A slowing of alpha rhythm is typical of healthy older person. Sleep studies of young and elderly persons have revealed the following findings.
- Elderly take longer to fall asleep than the young
- Total time spent asleep is not different between groups
- Elderly wake up more frequently during the night and spend a longer time awake on each occasion, thus spend longer total time in bed
- The transition between sleep and wakefulness is abrupt in elderly and hence they are considered as “light sleepers”
The neurological findings in old age include reduced sensory perception and motor activity, reduced cognition, memory and speed, change in sleeping pattern and some behavioural changes. The risk of developing neuro-psychiatric illnesses like Alzheimer’s disease, stroke, dyskinesias, etc. is also higher in old age.
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