By Marcello Cherchi, MD PhD
For patients
An individual suffering with disequilibrium from any cause often complains of “brain fog,” feeling “not with it,” or noting problems with memory, follow-through and other “thinking” activities. The relationship between disequilibrium and these cognitive deficits is still poorly understood.
For clinicians
Overview
The relationship between the symptom of disequilibrium and cognitive deficits is still poorly understood, but research is beginning to delineate potential mechanisms of this connection. A variety of visuo-spatial, non-spatial, and emotional deficits appear to be associated with vestibular dysfunction. While cognitive deficits may co-occur with the symptom of disequilibrium itself, it appears that some cognitive deficits may persist even in between discrete episodes of disequilibrium. Some literature suggests that different vestibular diseases are associated with specific patterns of cognitive dysfunction.
How do we measure the cognitive deficits associated with disequilibrium?
Some investigators suspect that standard psychometric testing may not be adequate to capture the cognitive deficits associated with disequilibrium (Donaldson, Yan et al. 2021). Other research concludes that standard “dizziness questionnaire” metrics, such as the Dizziness Handicap Inventory (Jacobson and Newman 1990), do not elicit sufficient information to draw conclusions about cognitive deficits (Dornhoffer, Liu et al. 2021).
Consequently, some investigators have developed psychometric tests specific to the cognitive deficits occurring in the context of disequilibrium (Lacroix, Deggouj et al. 2016, Jacobson, Piker et al. 2020).
What sorts of cognitive deficits occur with disequilibrium?
Some investigators conclude that the predominant adverse cognitive effects of disequilibrium lie in the domain of visuospatial abilities (Xie, Bigelow et al. 2017, Zhang, Huang et al. 2022); for example, “The strongest evidence exists in connecting vestibular function to the cognitive domain of visuospatial ability, which includes spatial memory, navigation, mental rotation, and mental representation of three-dimensional space” (Bigelow and Agrawal 2015).
One study observed that cognitive deficits involve spatial and non-spatial tasks (Risey and Briner 1990, Smith, Zheng et al. 2005), and that these deficits are more pronounced in patients with bilateral vestibular loss compared with unilateral vestibular loss (Popp, Wulff et al. 2017). Surprisingly, some investigators identified different degrees of cognitive deficits depending on the lateralization of vestibular weakness (Hufner, Hamilton et al. 2007).
Cognitive deficits from disequilibrium appear to be independent of age and emotional distress
Although normal healthy aging is known to be associated with declines in vestibular function (Agrawal, Van de Berg et al. 2019) and cognition, research suggests that vestibular disease can cause cognitive dysfunction beyond what is expected for age (Rizk, Sharon et al. 2020).
Disequilibrium from any cause appears to have the potential to cause emotional disorders (Brandt and Dieterich 2020, Beh 2021), disturbances of sleep and wakefulness (Smith, Wilkinson et al. 2019), and cognitive deficits. Some investigators have concluded that the cognitive deficits are beyond what would be expected from emotional distress alone (Xie, Welgampola et al. 2021).
Are these cognitive deficits only present when perceiving disequilibrium?
Some investigators have noted that patients suffering from episodic vestibular disorders may exhibit cognitive deficits inter-ictally — meaning deficits even during “dizzy-free” periods between discrete episodes of disequilibrium (Chari, Liu et al. 2021), suggesting that disequilibrium may cause longer-term neurological changes.
Can different “dizzy diseases” cause different patterns of cognitive deficits?
Some literature discusses cognitive impairment from disequilibrium caused by specific diseases, such as migraine associated vertigo (Wang, Huang et al. 2016). In a similar vein, some literature identifies different degrees of cognitive impairment in different vestibular diseases (Liu, Locklear et al. 2019).
What is the mechanism by which disequilibrium causes cognitive deficits?
Concerning the underlying mechanism of the reported cognitive deficits, some research identifies neuroanatomical projections from the vestibular nuclei to the cerebral cortex (Hanes and McCollum 2006), hippocampus and amygdala (Bigelow, Semenov et al. 2016). One study showed that in patients with chronic bilateral vestibular loss exhibit hippocampal atrophy on MRI (Brandt, Schautzer et al. 2005).
Some research observes significant variability in cognitive deficits associated with disequilibrium, and postulates that this variability is due to the fact that vestibular compensation progresses through different stages, each of which places different demands on attention, and thus proposes “the idea of a limited quantity of cognitive resources that can be allocated to cognitive tasks during the compensation stages. This basic mechanism of attentional limitations may lead to different compensation profiles in patients, with or without cognitive dysfunction, depending on the compensation stage” (Lacroix, Deggouj et al. 2021).
References
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