The neuroscience of aging is the study of the changes in the nervous system that occur with

ageing Ageing ( BE) or aging ( AE) is the process of becoming older. The term refers mainly to humans, many other animals, and fungi, whereas for example, bacteria, perennial plants and some simple animals are potentially biologically immortal. In ...

. Aging is associated with many changes in the central nervous system, such as mild atrophy of the cortex that is considered non-pathological. Aging is also associated with many neurological and neurodegenerative disease such as

amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

dementia Dementia is a disorder which manifests as a set of related symptoms, which usually surfaces when the brain is damaged by injury or disease. The symptoms involve progressive impairments in memory, thinking, and behavior, which negatively affe ...

mild cognitive impairment Mild cognitive impairment (MCI) is a neurocognitive disorder which involves cognitive impairments beyond those expected based on an individual's age and education but which are not significant enough to interfere with instrumental activities of ...

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms becom ...

, and

Creutzfeldt–Jakob disease Creutzfeldt–Jakob disease (CJD), also known as subacute spongiform encephalopathy or neurocognitive disorder due to prion disease, is an invariably fatal degenerative brain disorder. Early symptoms include memory problems, behavioral changes, ...

Normal structural and neural changes

Neurogenesis occurs very little in adults, only occurring in the hypothalamus and striatum to a small extent in a process called

adult neurogenesis Adult neurogenesis is the process in which neurons are generated from neural stem cells in the adult. This process differs from prenatal neurogenesis. In most mammals, new neurons are born throughout adulthood in two regions of the brain: * Th ...

. The volume of the brain actually decrease roughly 5% per decade after forty. It is currently unclear why brain volume decreases with age, however, a few causes may include: cell death, decreased cell volume, and changes in synaptic structure. The changes in brain volume is heterogenous across regions with prefrontal cortex receiving the most significant reduction in volume followed in order by the striatum, the temporal lobe, cerebellar vermis, cerebellar hemispheres, and the hippocampus. However, one review found that the amygdala and ventromedial prefrontal cortex remained relatively free of atrophy, which is consistent with the finding of emotional stability occurring with non-pathological aging. Enlargement of the ventricles, sulci and fissures are also common in non-pathological aging. Changes may also be associated with neuroplasticity, synaptic functionality and

voltage gated calcium channels Voltage-gated calcium channels (VGCCs), also known as voltage-dependent calcium channels (VDCCs), are a group of voltage-gated ion channels found in the membrane of excitable cells (''e.g.'', muscle, glial cells, neurons, etc.) with a permeabi ...

. Increased magnitude of hyperpolarization, possibly a result of dysfunctional calcium regulation, leads to decreased firing rate of neurons and decreased plasticity. This effect is particularly pronounced in the hippocampus of aged animals, and may be an important contributor to age-associated memory deficits. The hyperpolarization of a neuron can be divided into three stages: the fast, medium and slow hyperpolarization. In aged neurons, the medium and slow hyperpolarization phases involve the prolonged opening of calcium-dependent potassium channels. The prolonging of this phase has been hypothesized to be a result of deregulated calcium and hypoactivity of cholinergic, dopaminergic, serotonergic and glutaminergic pathways.

Normal functional changes

Episodic memory starts to decline gradually from middle age, while semantic memory increases all the way into early old age and declines thereafter. Older adults tend to engage their prefrontal cortex more often during working memory tasks, possibly to compensate with executive functions. Further impairments of cognitive function associated with aging include decrease in processing speed and inability to focus. A model proposed to account for altered activation posits that decreased neural efficiency driven by amyloid plaques and decreased dopamine functionality lead to compensatory activation. Decreased processing of negative stimuli as opposed to positive stimuli appear in aging, become significant enough to detect even with autonomic nervous responses to emotionally charged stimuli. Aging is also associated with decreased

plantar reflex The plantar reflex is a reflex elicited when the sole of the foot is stimulated with a blunt instrument. The reflex can take one of two forms. In healthy adults, the plantar reflex causes a downward response of the hallux (flexion). An upward r ...

and

achilles reflex The ankle jerk reflex, also known as the Achilles reflex, occurs when the Achilles tendon is tapped while the foot is dorsiflexed. It is a type of stretch reflex that tests the function of the gastrocnemius muscle and the nerve that supplies it. ...

response. Nerve conductance also decreases during normal aging.

DNA damage

Certain genes of the human

frontal cortex The frontal lobe is the largest of the four major lobes of the brain in mammals, and is located at the front of each cerebral hemisphere (in front of the parietal lobe and the temporal lobe). It is parted from the parietal lobe by a groove betwe ...

display reduced

transcription Transcription refers to the process of converting sounds (voice, music etc.) into letters or musical notes, or producing a copy of something in another medium, including: Genetics * Transcription (biology), the copying of DNA into RNA, the fir ...

al expression after age 40, and especially after age 70. In particular, genes that have central roles in

synaptic plasticity In neuroscience, synaptic plasticity is the ability of synapses to strengthen or weaken over time, in response to increases or decreases in their activity. Since memories are postulated to be represented by vastly interconnected neural circuit ...

display reduced expression with

age Age or AGE may refer to: Time and its effects * Age, the amount of time someone or something has been alive or has existed ** East Asian age reckoning, an Asian system of marking age starting at 1 * Ageing or aging, the process of becoming older ...

. The promoters of genes with reduced expression in the cortex of older individuals have a marked increase in

DNA damage DNA repair is a collection of processes by which a cell identifies and corrects damage to the DNA molecules that encode its genome. In human cells, both normal metabolic activities and environmental factors such as radiation can cause DNA da ...

, likely oxidative DNA damage.

Pathological changes

Roughly 20% of persons greater than 60 years of age have a neurological disorder, with episodic disorders being the most common followed by extrapyramidal movement disorders, and nerve disorders. Diseases commonly associated with old age include *

Multiple system atrophy Multiple system atrophy (MSA) is a rare neurodegenerative disorder characterized by autonomic dysfunction, tremors, slow movement, muscle rigidity, and postural instability (collectively known as parkinsonism) and ataxia. This is caused by progr ...

Alzheimer's disease Alzheimer's disease (AD) is a neurodegeneration, neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in short-term me ...

Stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

. *

Amyotrophic lateral sclerosis Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

Frontotemporal Dementia Frontotemporal dementia (FTD), or frontotemporal degeneration disease, or frontotemporal neurocognitive disorder, encompasses several types of dementia involving the progressive degeneration of frontal and temporal lobes. FTDs broadly present as ...

Dementia with Lewy bodies Dementia with Lewy bodies (DLB) is a type of dementia characterized by changes in sleep, behavior, cognition, movement, and regulation of automatic bodily functions. Memory loss is not always an early symptom. The disease worsens over time ...

Corticobasal Degeneration Corticobasal degeneration (CBD) is a rare neurodegenerative disease involving the cerebral cortex and the basal ganglia. CBD symptoms typically begin in people from 50 to 70 years of age, and the average disease duration is six years. It is chara ...

Transient ischemic attack A transient ischemic attack (TIA), commonly known as a mini-stroke, is a minor stroke whose noticeable symptoms usually end in less than an hour. TIA causes the same Symptoms of stroke, symptoms associated with strokes, such as weakness or numbn ...

Vascular dementia Vascular dementia (VaD) is dementia caused by problems in the supply of blood to the brain, typically a series of minor strokes, leading to worsening cognitive abilities, the decline occurring piecemeal. The term refers to a syndrome consisting ...

The misfolding of proteins is a common component of the proposed pathophysiology of many diseases associated with aging, however there is insufficient evidence to prove this. For example, the tau hypothesis to Alzheimer's proposes that tau protein accumulation results in the breakdown neuron cytoskeletons leading to Alzheimer's. Another proposed mechanism for Alzheimer's is related to the accumulation of

amyloid beta Amyloid beta (Aβ or Abeta) denotes peptides of 36–43 amino acids that are the main component of the amyloid plaques found in the brains of people with Alzheimer's disease. The peptides derive from the amyloid precursor protein (APP), which is ...

,. in a similar mechanism to the prion propagation of Creutzfeldt-Jakob disease. Similarly the protein

alpha-synuclein Alpha-synuclein is a protein that, in humans, is encoded by the ''SNCA'' gene. Alpha-synuclein is a neuronal protein that regulates synaptic vesicle trafficking and subsequent neurotransmitter release. It is abundant in the brain, while smaller a ...

is hypothesized to accumulate in Parkinson's and related diseases.

Chemo brain

Treatments with anticancer

chemotherapeutic agents Chemotherapy (often abbreviated to chemo and sometimes CTX or CTx) is a type of cancer treatment that uses one or more anti-cancer drugs ( chemotherapeutic agents or alkylating agents) as part of a standardized chemotherapy regimen. Chemothera ...

often are toxic to the cells of the brain, leading to

memory Memory is the faculty of the mind by which data or information is encoded, stored, and retrieved when needed. It is the retention of information over time for the purpose of influencing future action. If past events could not be remembered, ...

loss and

cognitive dysfunction Cognitive disorders (CDs), also known as neurocognitive disorders (NCDs), are a category of mental health disorders that primarily affect cognitive abilities including learning, memory, perception, and problem solving. Neurocognitive disorders in ...

that can persist long after the period of exposure. This condition, termed chemo brain, appears to be due to DNA damages that cause epigenetic changes in the brain that accelerate the brain aging process.

Management

Treatment of an age related neurological disease varies from disease to disease. Modifiable risk factors for dementia include

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ap ...

hypertension Hypertension (HTN or HT), also known as high blood pressure (HBP), is a long-term medical condition in which the blood pressure in the arteries is persistently elevated. High blood pressure usually does not cause symptoms. Long-term high bl ...

smoking Smoking is a practice in which a substance is burned and the resulting smoke is typically breathed in to be tasted and absorbed into the bloodstream. Most commonly, the substance used is the dried leaves of the tobacco plant, which have bee ...

hyperhomocysteinemia Hyperhomocysteinemia is a medical condition characterized by an abnormally high level of homocysteine in the blood, conventionally described as above 15 μmol/L. As a consequence of the biochemical reactions in which homocysteine is involved ...

hypercholesterolemia Hypercholesterolemia, also called high cholesterol, is the presence of high levels of cholesterol in the blood. It is a form of hyperlipidemia (high levels of lipids in the blood), hyperlipoproteinemia (high levels of lipoproteins in the blood), ...

, and

obesity Obesity is a medical condition, sometimes considered a disease, in which excess body fat has accumulated to such an extent that it may negatively affect health. People are classified as obese when their body mass index (BMI)—a person's we ...

(which is usually associated with many other risk factors for dementia). Paradoxically, smoking confers protection against

. Also conferring protective benefits to age related neurological disease in consumption of coffee or caffeine. Consumption of fruits, fish and vegetables confer protection against dementia, as does a

Mediterranean diet The Mediterranean diet is a diet inspired by the eating habits of people who live near the Mediterranean Sea. When initially formulated in the 1960s, it drew on the cuisines of Greece, Italy, France and Spain. In decades since, it has also incor ...

. Physical exercise significantly lowers the risk of cognitive decline in old age, and is an effective treatment for those with dementia and

References

{{reflist Neuroscience Geriatrics Gerontology