According to the International Working Group on MCI, the core features of MCI include: evidence of deterioration in cognition either objectively measured over time and/or through self-report or by an informant reporting cognitive deficits beyond that expected for age and education level; the person not presenting with dementia and activities of daily living being preserved, although there may be some mild impairment in complex activities.7 8
People with MCI are more likely to fall than those of the same age without cognitive impairment.9 This is often due to a decrease in motor function and balance, which may be associated with age-related change in white matter.10 MCI can also affect specific gait parameters, and falls risk is increased particularly when a person with MCI is cognitively challenged or during dual-tasking.11 12
The average age of the population is also increasing; therefore, MCI and falls are likely to affect thousands more people, including Australians as they age. This will not only negatively affect individuals and their families but will have a significant impact on health budgets over the coming decades unless successful interventions are developed and implemented widely (ie, Australian fall-related costs estimated at AUS$648 million in 2007–2008,13 and falls are the leading cause of injury-related hospitalisations in Australia,14 with age standardised rates increasing at >2% per annum).15
reference link : https://bmjopen.bmj.com/content/12/4/e054725
Original Research: Open access.
“New balance capability index as a screening tool for mild cognitive impairment” by Yasuhiro Suzuki et al. BMC Geriatrics
In the present study, we suggested that our new balance indicator VPS is useful to screen individuals with MCI with high sensitivity.
The new indicator VPS (visual dependency index of postural stability) was created from the combination of IPS (index of postural stability) quantification method [17, 18] and foam posturography technique [13], both established previously. Among three sensory inputs critical for balance, namely vestibular, visual, and somatosensory inputs [16], the usage of foam rubber dampens the somatosensory input, and eye closure additionally eliminates visual input.
Therefore, it is assumed that vestibular function can easily be assessed on foam rubber with eye-closed condition [13], and standing test with eyes closed on foam rubber has been well established as tests for clinical diagnosis of vestibular loss [34]. In fact, although we have not checked the point by ourselves, Fujimoto et al. examined the relationship between foam posturography data and direct vestibular function tests using cervical vestibular evoked myogenic potentials (cVEMPs), a well-established clinical test to examine vestibular function, and concluded that foam posturography on an eye-closed condition was useful for assessing vestibular impairment with abnormal cVEMPs [32].
Further taking the ratio between eye-closed and -opened conditions, we managed to raise the accuracy of measurement and named the value VPS. Since VPS is measured under the condition of getting almost no somatosensory and visual inputs as described above, its value is basically considered to reflect vestibular function.
In addition, it has previously been shown that vestibular loss causes hippocampal atrophy and impaired spatial memory in humans [36]. A further study in BLSA found that poorer vestibular function was associated with significantly reduced hippocampal volume [37]. Thus, hippocampal atrophy may underlie the link between vestibular loss and cognitive decline.
As mentioned above, our method is based on the link between vestibular loss and cognitive decline. We think that this is the point of differentiation that creates extra value of our test in comparison to existing cognitive tests, because direct assessments of cognitive function can often present a psychological hurdle for subjects, which they would prefer to avoid if possible. In contrast, our method is not a direct assessment of cognitive function but just a balance ability test, so the psychological hurdle for subjects is much lower than direct methods.
Related to the link between vestibular and cognitive functions, hearing impairment is also reported to be linked with cognitive decline; in a small US prospective cohort study of 194 adults without baseline cognitive impairment and at least two brain MRIs with a mean of 19 years follow-up, it was reported that midlife hearing impairment measured by audiometry is associated with steeper temporal lobe volume loss, including in the hippocampus and entorhinal cortex [38]. The positive association between the loss of inner ear function and cognitive impairment is noteworthy.
Considering further in this regard, inner ear dysfunction and hippocampal atrophy might have some underlying pathological processes shared in common. The hippocampus has been known as one of the limited areas in the adult mammalian brain where neurogenesis normally occurs [39], and it is widely acknowledged that hippocampal neurogenesis is impaired in AD, which plays a role in cognitive decline [40, 41].
On the other hand, recent evidence suggests that reactive adult neurogenesis occurs in sensory systems following damages to the sensory nerve, and in fact this mechanism promotes balance recovery after vestibular loss [42]. Thus, it is conceivable that some common disorder related to neurogenesis in AD might underlie the link between inner ear dysfunction and hippocampal atrophy.
Although currently this is just a hypothesis and further investigation is needed to prove it, this hypothesis might be related to the fact that AD is also strongly associated with olfactory dysfunction [43,44,45,46], given that olfactory bulb is another area of the adult brain where neurogenesis occurs vigorously [39] and people with AD exhibit smaller olfactory bulb volumes [47].
MCI is not just a prodrome to dementia, but a very important intervention point to treat AD. Recently, aducanumab, an antibody drug targeting Aβ [48], was approved by FDA in the US [49]. This decision made aducanumab the first new drug to be approved for the treatment of AD since 2003 and the first drug to ever be approved for modification of the course of AD. Since the drug is targeting MCI and early AD, the demand for efficient screening of MCI will become larger in the near future.
Because we started this project to realize an inexpensive and easy-to-use MCI screening system, we focused on WBB, a very popular Nintendo game machine, and successfully showed that it can be used as a good stabilometer that has the same performance as an authentic apparatus approved for the medical use. Nintendo has so far sold out more than 37 million WBB worldwide (https://www.nintendo.co.jp/ir/pdf/2009/091030.pdf). It means a huge potential for the novel approach to diagnose MCI at an earlier stage.
