Author(s): Venugopal Kochiyil, DNB; MCSO
Originally published: October 2, 2015 Last updated: October 10, 2024
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Overview and Description

Distinguishing neurologic changes of healthy aging from those of age-related disease influences decisions about evaluation and treatment. The following facts on biological aging are important to consider before we summarize neurological changes in healthy aging.

  • Individuals age chronologically at the same rate, but biological aging is variable. Multiple factors influence the variability in biological aging.35
  • Biological aging is a process of progressive, intrinsic, and cumulative cellular and organ changes that result in decrease of the organism’s ability to withstand stressors and changes eventually result in the organism’s decreased ability to survive. Biological aging is also characterized by universality across populations, cultures, and physical environments.1 Those with accelerated biological aging are likely to develop chronic diseases and cognitive decline.35
  • The exact causes of aging remain unknown. Prominent themes in theories include accumulation of free radical damage, imbalance between cellular damage vs. repair, disorders of mitochondrial function, telomere attrition, epigenetic alterations, genomic instability and immune aging.2,36 Men and women tend to age differently, with women living longer than men.36
  • A characteristic of biological aging is increased variability in the normal presentation, whether it be in populations, organ systems, or tissues.3 Not all cells in a tissue age at the same rate, nor do all tissues and organs age at the same rate within an organism. Likewise, in populations of healthy older adults, there is a wide range of what can be considered to be normal functions.4,5 This variability can blur the distinction between healthy aging and disease of aging. Therefore, the clinician may benefit from observation of patients over a period.3

Relevance to Clinical Practice

In this section, the framework of a standard neurologic examination will be used to briefly summarize common neurologic changes of healthy aging.

Mental status, cognition5-10

The most consistently found change in cognition of healthy older adults is slowed processing speed, especially for new or complex information. It is difficult to test other aspects of cognition without involving a component of processing speed. Other common changes of cognitive aging include decreased mental flexibility, decreased maintenance of sustained and/or divided attention (focusing on multiple tasks), and decrements in working memory (ability to manipulate information held in short term memory/fluid intelligence) but there is significant variability in the rate of decline. Most executive functions decline with age. Not decreased, however, are semantic memory (vocabulary, recall of facts learned in past/crystallized intelligence), and ability to learn new skills. One must account for changes in other sensory systems, particularly vision, which can influence cognitive testing performance. Performance on tests which are complex and timed tend to decline with age.

The anatomic findings associated with these cognitive changes are not uniform throughout the brain. Findings from human MRI studies include decreased volume of gray matter in the prefrontal cortex (associated with executive functioning) and in the hippocampus (associated with memory). This decrease is not thought to be due to large amounts of neuron loss, but rather to decrease in neuron soma size, decrease in synapse number and decrease in complexity of dendrite branching. MRI studies of older brains have also reported a decrease in white matter volume related to increased myelin degeneration, decreased myelin repair, and shortening of myelinated nerve fibers. These changes in myelination are associated with slowed nerve conduction velocities. Due to the volume loss of cortex and white matter (about 5% per decade after the age of 40 years) there is enlargement of ventricles and other CSF spaces as well as wide and shallow sulci36. Occipital cortex seems to be least affected with aging. Accumulation of neurofibrillary tangles, lipofuscins and senile plaques also occurs in brains of healthy older persons.11,36

Depression is not considered a requisite neurological change of aging. However, with the potential multiple stresses that older adults may experience depression is important to recognize and treat. Theories regarding the etiology of depression include decrease in neurotransmitter function and alterations in cell signaling,13 factors that are also influenced by aging.7 Recent evidence points towards increase of aging related adverse outcomes in people with major depressive disorder as there is overlap between biological abnormalities in both situations.38

Cranial nerves

Vision4,5,14
Age-related stiffening of the lens results in decreased lens accommodation for near vision (presbyopia). Other vision changes of aging include slowed adjustment to low light, decreased color discrimination, decreased depth perception, and decreased ability to detect contrast. Visual acuity may also decrease (higher incidence of low vision), and upward gaze can be limited. Many of these changes are related to a drop-out of photoreceptors and retinal ganglion cells. Slowed adjustment to dark is also related to slowed pupillary reflexes, and color discrimination is affected by yellowing of the lens with aging.

Hearing5,15,16
High frequency hearing loss (presbycusis or age related hearing loss) becomes more common with increasing age. This is often related to atrophy of the capillary bed in the stria vascularis, atrophy of spiral ganglion cells or damage to cochlear hair cells. Hearing loss can be significantly influenced by environmental noise exposure. High frequency hearing loss can affect ability to discern specific speech sounds, such as consonants. This leads to impairment in understanding speech, especially in noisy environments. This problem is thought to be due not only to hearing loss, but also to altered auditory processing. The increased cognitive effort of listening may cause reduced cognitive functioning, especially reduced memory for spoken information in older adults with hearing loss.

Motor system (strength, tone, posture and gait)5,17,18,19

Sarcopenia is the age-associated loss of muscle mass and function, resulting in decreased muscle strength associated with physical disability and poor quality of life. Factors related to sarcopenia include decreased physical activity, altered hormone status, decreased total caloric and protein intake, increased inflammatory mediators, altered protein synthesis, and motor unit remodelling.17, 39 Sarcopenia is associated with increased motor unit size. Animal studies have also identified age-related alterations in neuromuscular junction structure, including increased branching of the pre-synaptic nerves, and receptor redistribution in the post-synaptic membrane. Diagnosis requires low muscle mass and lower muscle strength (assessed by hand grip strength) and or low physical performance (assessed by gait speed). Assessing muscle mass using imaging (described below) is increasingly used in the diagnosis of sarcopenia. There are several aging-related changes in posture and movement. Posture may become mildly forward flexed, gait speed may be slowed, and arm swing decreased. Step length shortens and duration of double support phase increases. These changes may be influenced also by the presence of age related diseases such as osteoarthritis. Taken together, such changes can predispose the older adult to the serious problem of falls.

Reflexes4,5

Deep tendon reflexes at the ankles may be decreased in up to ~30% of older adults by the age of 80 years. Other deep tendon reflexes are usually preserved. So-called pathological reflexes (palmomental, glabellar, snout, and grasp.) may be present in the healthy older adult without a specific pathology. Presence of multiple pathological reflexes at the same time increases likelihood of having a disease. Observation of the patient over time can help to determine whether there may indicate sub-clinical neurologic disease.

Sensation4,5,10

The most common sensory change in older adults is a decrease in lower extremity vibratory sensation especially in big toe (in about 30% of persons over age 60 yrs.). Upper extremities tend not to show this decrement (less than 10% showing impairment). Sensation for joint position sense, light touch and pain are generally preserved. Peripheral neuropathy can affect 5-10% of geriatric population, increasing risks of falls.

Coordination5,20

Due to the enlargement of motor units with aging, there can be a decline in accuracy of fine motor task performance. Healthy aging is not associated with ataxia. Age related changes in vision, hearing, muscle mass and strength can also affect coordination.

Other

Sleep21
Older adults experience reduced sleep time, sleep efficacy (percentage of time spend asleep while in bed), reduced slow wave sleep and rapid eye movement (REM) sleep, shorter sleep cycles and more frequent night-time waking. Aging also causes a phase advance, resulting in earlier onset of sleepiness in the evening and earlier morning waking. Reduction in REM sleep can have an independent effect on learning and memory.

EMG/NCV22,23,24

Aging motor and sensory peripheral nerves show loss of both myelinated and unmyelinated neurons. These changes result in increased latencies, slowed nerve conduction velocities, and decreased action potential amplitudes (SNAPs and CMAPs) and longer F wave latency. Nerve conduction velocities decrease by 0.5-4.0 m/s per decade in persons over age 60 years old; action potential amplitude may decrease by as much as 50% by age 70 years old.24 Due to anterior horn cell loss, with reinnervation, aging motor unit action potentials (MUAPs) have longer durations, more phases, and lower amplitudes than in younger adults.

Pertinence to patient care25

Care of older adults may be enhanced by implementing the following suggestions:

  • Cognition and communication: allow adequate time for information processing and learning, use less complex sentence structure, present one task at a time; encourage participation in measures to maintain good health in physical, cognitive and social domains.8
  • Depression: consider exercise an important part of the prevention and treatment of depression. Aerobic and strength training have both been shown to improve mood.13
  • Vision: provide adequate lighting without glare, identify potential environmental hazards (i.e. stairs) with high-contrast visual cues.14 Reduce clutter.
  • Hearing: provide quiet environments for conversation, present spoken information slowly and clearly, position listeners so they can see the speaker’s face and lips and encourage hearing aid use as appropriate. However, hearing aids will not assist with central auditory processing related to aging changes in the central nervous system.
  • Sarcopenia: include resistance training in exercise recommendations to address decreased physical activity and weakness; consider adding power training commensurate with patient ability.19Screening for malnutrition can be considered. Protein supplementations have an important role in addressing decreased dietary protein intake and altered protein synthesis. Adequate protein intake is vital to building and maintaining muscle mass.26
  • Falls risk, posture, joint contractures, and gait changes: include exercise in the prevention or treatment plan. Options include specific balance exercises, aerobic and resistance training. tai chi and/or function-based exercises.27 Stretching of the hip and knee flexor muscles should be considered if needed.
  • Sleep: recognize the influence that inadequate sleep can have on cognitive function. Encourage sleep hygiene techniques. Avoid benzodiazepines.  

To evaluate and follow an older adult’s motor function and balance, a number of standardized assessment tools exist. Such tools include the 6 Minute Walk Test, the Timed Up and Go test, and the Berg Balance Assessment (Rehabmeasures.org).

Cutting Edge/Unique Concepts/Emerging Issues

The extreme complexity of the nervous system leaves much that is yet to be studied. Imaging technologies like functional MRI, positron emission tomography show re-organization of some brain networks with aging, which may be related to maintenance of cognitive functions.28 Such techniques may not only provide additional knowledge about normal neurologic function but could also potentially provide data to allow for earlier diagnosis of neurologic disease, thereby assisting in the provision of early therapies. PET brain scan is already used for diagnosis of dementing illness especially FDG PET studies looking at glucose metabolism. Radiotracer amyloid PET studies binding beta amyloid can be used for earlier diagnosis of Alzheimer’s disease.42

Computed tomography (CT) is increasingly used in assessing skeletal muscle cross-sectional area as an index for sarcopenia. Sarcopenia has been associated with poor perioperative outcomes, especially in geriatric patients.29 MRI scans by virtue of not needing ionizing radiation is increasingly considered for assessing sarcopenia. Newer MRI techniques like T2 mapping, MR spectroscopy and diffuser tensor imaging are increasingly considered for assessing muscle mass.40 Use of ultrasound is evolving in assessment of muscle quality and quantity for detection and follow-up of sarcopenia but normative data and protocol standardization needs further research and standardization.41

Gaps in Knowledge/Evidence Base

The relationship between exercise, physical fitness, and cognition is a new and growing area of study. Quantitative MRI techniques have documented increased gray matter volumes in pre-frontal cortex and hippocampus in individuals who are at least moderately physically active.30 Early evidence suggest positive effect on executive functions especially with mild to moderate exercise programs. Exact mechanisms are unclear and much more research is necessary before firm conclusions can be reached.

Fatigue in older adults is a common complaint that merits further study.31 Often an etiology is not easily determined. Greater understanding of fatigue in aging may assist in treatment and decreasing morbidity.

Frailty in elderly is getting significant attention now a days. Multiple medical comorbidities increase the risk of Frailty. Further research is required in diagnosis of Pre-frailty and appropriate interventions to reduce adverse outcomes.

Covid 19 related neurological presentations especially cognitive decline and dysautonomia can cause significant disease burden in older adults. Further data and research on treatment options are warranted.

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Original Version of the Topic

LeAnn Snow, MD. Neurological consequences of aging. 10/2/2015

Previous Revision(s) of the Topic

LeAnn Snow, MD. Neurological Consequences of Aging. 12/29/2020

Author Disclosure

Venugopal Kochiyil, DNB; MCSO
Nothing to Disclose