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Mild Cognitive Impairment (MCI) is a modern concept introduced to bridge the gap between normal cognition and Dementia. It can also sometimes be referred to as Incipient Dementia. Kral (1962) was the first to describe the natural aging effects on cognitive skils. This concept was originally known as Benign Senescent Forgetfulness, and described the difficulties the aging population had in terms of their difficulty in recalling and remembering information. Recently Petersen (2001) coined the term MCI to define the concept of cognitive problems outside the normal rate of age-related decline. Mild cognitive impairment can affect many cognitive abilities and is often thought of as a precursor to Alzheimer's disease or Dementia. It has been classified in its own right to enable early detection of cognitive decline in the aging population.

=Mild Cognitive Impairment= Mild Cognitive Impairment (MCI) is a recent term to define the slow and gradual decline in cognition which is not due to the normal effects of aging. It identifies the transitional stage between normal age related decline in cognition and Dementia. Symptoms are synonymous with early onset Dementia. Like Dementia, MCI can affect many cognitive functions: memory, language, visuo-spatial skills, executive functioning and orientation to time and space. However unlike Dementia, impairments do not affect a person’s ability to carry out everyday activities.

Amnestic and Non-Amnestic Forms of MCI
MCI has two distinct forms; Amnestic MCI and Non-Amnestic MCI. Amnestic MCI is a form of mild cognitive impairment that primarily affects episodic memory. However impairment in other domains along side memory can be present. In contrast patients with Non-Amnestic MCI have impairments in cognitive domains such as language, attention and visuospatial skills. Patients with Non-Amnestic MCI do not have problems with their memory. .

Prevalence
The likelihood of an MCI diagnosis increases with age and tends to be most prevalent in people over the age of 60. Additionally, the Einstein study of aging shows that MCI is more commonly found in Women than Men.

The occurrence of MCI varies between countries. MCI is most prevalent in Finland where around 38% of people aged 60-78 have the deficit. Whereas, in the UK MCI is thought to affect around 15% of the population aged between 65-84.

=Diagnostic Criteria=

ICD-10
The ICD-10 characterises MCI as a disorder in which many elements of cognition can be affected. Primarily, a patient has to display symptoms of learning difficulties in regards to the use of novel or new things. In addition to this, reduced concentration and feelings of mental fatigue are also synonymous of MCI. For a diagnosis, a patient must not have any other underlying causes for their cognitive/ memory impairment that could be attributed to a behavioural or mental disorder.

The Mayo Clinic
Recently the Mayo Clinic have outlined the criteria for diagnosis of MCI. This is a guide to diagnosing MCI which has been developed by a panel of clinicians and experts. It includes the following:
 * The patient is experiencing problems with their memory or any other cognitive ability.
 * This could include a patient displaying difficulties with their ability to follow instructions, planning or decision making.


 * Decline of memory or cognitive functioning should occur gradually over time.
 * This is visible through a patient's medical history and identifies that their functioning was once at a higher level.


 * Activities of daily living and overall mental abilities are not affected''' by MCI.
 * A patient's general ability to complete daily activities should not be impaired, although impairments can lead to patient's struggling to complete high frequency tasks, like shopping and using the washing machine.


 * Cognitive tests should show slight impairment in cognitive functioning, compared to the normal rate of decline (adjusted to fit age and level of education).
 * Overall cognitive performance can be tested using the Mini-mental state examination (MMSE). Further testing measures can be used to asses the function of different cognitive abilities in isolation.


 * A patient can not be diagnosed with Dementia.
 * If the problems or difficulties the patient expresses are not severe enough for a diagnosis of Dementia, then a diagnosis of MCI should be given.

The Mayo Clinic suggests that a family member or close friend should corroborate the patient’s anecdotal information about their abilities.

=Risk Factors= Many factors can contribute to an individual's risk of developing MCI.

Environmental Risk Factors
Certain environmental factors have been linked to increasing the likelihood of Mild Cognitive Impairment. For instance a recent study found that people with Diabetes were at an increased risk of developing MCI. In addition to this, smoking, depression and high blood pressure. A number of observational studies have also identified that lack of excercise can also contribute to MCI.

Biological Risk Factors
There are also biological risk factors that have been linked to developing MCI. The gene connected to MCI is known as APOE-e4. This gene is found in approximately 14% of the population. The presence of this gene in the aging population, is linked to decline in executive functioning and deficits in episodic memory. However, it has been shown that just the presence of APOE-e4 does not predict MCI.

=Cognitive and Brain Measures=

Assessment Measures
Various testing methods can be used to measure levels of cognitive impairment across the different domains. Some tests like the MMSE can be used to identify a patient's global level of cognitive functioning and the individual cognitive domains. There are a number of tests that are used by clinicians and researchers to test cognitive functioning. All tests are adjusted to account for the effects age and education can have on cognitive skills. This also ensures that when the tests are used they are normalised to suit the individual. This is because, the type of education a person has, can affect the way their cognitive abilities decline.

Pathology
The biological hallmarks of MCI are similar to that found post-mortem in people with Dementia. These includes; senile plaque and neurofibrillary tangles within the brain. Little is known about what causes these hallmarks that cause a person's cognitive abilities to decline. However identifying the hallmarks of MCI is difficult, as there are not many longitudinal studies that provide confirmation of the structural pathology. A recent study has shown that changes in the volume of the Fornix, or white bundle of C-shaped fibers, may be an early indicator of cognitive decline.
 * Senile plaques are extracellular deposits on the cortex of the brain.
 * Neurofibrillary tangles are groups of a phosphorylated protein known as tau.

=Psychological Research= There are many researchers examining the differences between normal age related decline in cognition and MCI both from a cognitive and physiological perspective.

Bennett and colleagues(2002) identified the natural history of MCI. This is one of the first longitudinal studies to compare MCI against people without cognitive deficits. Participants consisted of around 800 members of the Catholic clergy, who were assessed using various cognitive and neuropsycological assessments. The test scores from participants with MCI were on average lower across all cognitive domains. After an average of 4.5 years of follow-up investigations, 30% of people with MCI died. This suggests that people with MCI are 1.7 times as likely to die at an earlier rate. Furthermore, Bennett and colleagues have highlighted that episodic memory, perceptual speed and semantic memory decline at a quicker rate. As a result, this study has shown the different effects MCI has on aspects of cognitive ability and lifespan.

Work on understanding the structural abnormalities that arise from MCI are also being researched. For instance, Dickerson and colleagues (2004) identified that changes in the metabolic rate in the Medial Temporal Lobe reflects the impending decline into Alzheimer's Disease. By using Functional Magnetic Resonance Imaging (fMRI) Dickerson was able to compare the activation of the Medial Temporal Lobe which is associated with memory. This study identified that activation in the Medial Temporal Lobe, and particularly the Parahippocampal gyrus is higher in people with MCI. Due to this increased activation, the researchers hypothesised that it was a compensatory effect caused by senile plaque and other marked pathologies associated with Alzheimer's disease.

MCI & Dementia Overlap
Current research highlights that MCI increases the likelihood of progressing to various forms of Dementia. Many studies suggest that MCI is the prodromal stage to Alzheimer's Disease and show that the pathologies associated with Amnestic MCI are homogenous with various types of Dementias.
 * Amnestic MCI is shown to increase likelihood of developing Alzheimer's Disease.
 * Postmortem studies show that there are similarities in the pathology of people with Amnestic MCI and people with Alzheimer's disease.


 * MCI with impairments across several cognitive domains is likely to progress to Alzheimer's disease.
 * Some studies suggest that Non-Amnestic MCI may be a result of cardiovascular disease and therefore likely to lead to Vascular Dementia or Parkinson's disease.


 * Non-Amnestic MCI increases likelihood of many degenerative diseases.
 * This includes; Frontotemporal Dementia, Lewy Bodies Dementia, Vascular Dementia , Primary Progressive Aphasia , Parkinson's Disease and Alzheimer's Disease.

=Implications and Application= Studying the prevalence of MCI can highlight the conversion rates to other disorders or forms of brain damage. This includes diseases like Alzheimer's disease or other subtypes of Dementias. Using patients with MCI as a clinical group in research, can increase the evidence-based validity of therapies that are available, for people with mild-moderate Dementia. This could include therapeutic treatments such as Cognitive Stimulation Therapy which work to increase cognitive skills across various domains through simple activities. As a result behavioural interventions can be issued earlier to prolong the onset of Dementia.

Additionally, diagnosis of MCI (Amnestic or Non-Amnestic) can shed light on the mechanisms involved in memory and executive functioning. This can be seen by examining the structural and functional abnormalities within the brain of a patient. By doing this, we gain a deeper understanding of the way the brain is organised; on both a cortical and a subcortical level. This can lead to further understanding of how the various brain mechanisms communicate in a typical individual.

=References=

=See Also= Alzheimer's Disease

Dementia

Cognition

=External Links= Alzheimer's Society - MCI

The Mayo Clinic