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Vestibular loss causes hippocampal atrophy and impaired spatial memory in humans. Brain

Department of Neurology, Ludwig-Maximilians University, Munich, Germany.
Brain (Impact Factor: 10.23). 12/2005; 128(Pt 11):2732-41. DOI: 10.1093/brain/awh617
Source: PubMed

ABSTRACT The human hippocampal formation plays a crucial role in various aspects of memory processing. Most literature on the human hippocampus stresses its non-spatial memory functions, but older work in rodents and some other species emphasized the role of the hippocampus in spatial learning and memory as well. A few human studies also point to a direct relation between hippocampal size, navigation and spatial memory. Conversely, the importance of the vestibular system for navigation and spatial memory was until now convincingly demonstrated only in animals. Using magnetic resonance imaging volumetry, we found that patients (n = 10) with acquired chronic bilateral vestibular loss (BVL) develop a significant selective atrophy of the hippocampus (16.9% decrease relative to controls). When tested with a virtual variant (on a PC) of the Morris water task these patients exhibited significant spatial memory and navigation deficits that closely matched the pattern of hippocampal atrophy. These spatial memory deficits were not associated with general memory deficits. The current data on BVL patients and bilateral hippocampal atrophy revive the idea that a major--and probably phylogenetically ancient--function of the archicortical hippocampal tissue is still evident in spatial aspects of memory processing for navigation. Furthermore, these data demonstrate for the first time in humans that spatial navigation critically depends on preserved vestibular function, even when the subjects are stationary, e.g. without any actual vestibular or somatosensory stimulation.

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    • "It is likely that participants imagined self-motion by means of visual flow, and, indeed, there was a deactivation of vestibular areas such as the inferior parietal lobule during imagery. Vestibular deactivation has been reported repeatedly during visually induced self-motion (e.g., Brandt et al., 2002). This discrepancy illustrates that subtle changes in how people perform mental imagery tasks can substantially change brain activation, and it will be a challenge for future research to narrow down the cognitive processes. "
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    ABSTRACT: A growing number of studies in humans demonstrate the involvement of vestibular information in tasks that are seemingly remote from well-known functions such as space constancy or postural control. In this review article we point out three emerging streams of research highlighting the importance of vestibular input: (1) Spatial Cognition: Modulation of vestibular signals can induce specific changes in spatial cognitive tasks like mental imagery and the processing of numbers. This has been shown in studies manipulating body orientation (changing the input from the otoliths), body rotation (changing the input from the semicircular canals), in clinical findings with vestibular patients, and in studies carried out in microgravity. There is also an effect in the reverse direction; top-down processes can affect perception of vestibular stimuli. (2) Body Representation: Numerous studies demonstrate that vestibular stimulation changes the representation of body parts, and sensitivity to tactile input or pain. Thus, the vestibular system plays an integral role in multisensory coordination of body representation. (3) Affective Processes and Disorders: Studies in psychiatric patients and patients with a vestibular disorder report a high comorbidity of vestibular dysfunctions and psychiatric symptoms. Recent studies investigated the beneficial effect of vestibular stimulation on psychiatric disorders, and how vestibular input can change mood and affect. These three emerging streams of research in vestibular science are-at least in part-associated with different neuronal core mechanisms. Spatial transformations draw on parietal areas, body representation is associated with somatosensory areas, and affective processes involve insular and cingulate cortices, all of which receive vestibular input. Even though a wide range of different vestibular cortical projection areas has been ascertained, their functionality still is scarcely understood.
    Frontiers in Integrative Neuroscience 05/2014; 8:44. DOI:10.3389/fnint.2014.00044
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    • "Presumably, the intrinsic stimulus during physical activity essentially consists of proprioception and vision. Likewise, there are numerous reports on links between the vestibular system and hippocampal function [(Brandt et al. 2005); see Ref. Smith et al. (2010) for review] even though effects on adult neurogenesis have not yet been specifically addressed. In order to identify relevant sensory stimuli independent of locomotion , we here focused on auditory input as a potential signal to affect adult hippocampal neurogenesis. "
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    Brain Structure and Function 12/2013; DOI:10.1007/s00429-013-0679-3 · 4.57 Impact Factor
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    • "Indeed, although incorporating only a small sample, Soza Ried and Aviles (2007) found that the vestibular system of people suffering from depression is functionally affected in the sense that they have a hypoactive right vestibular nucleus. Interestingly, not only depressed subjects display reduced hippocampus volume size (McKinnon et al., 2009), patients with vestibular dysfunction also do so (Brandt et al., 2005; Smith et al., 2005) and this leads to disturbed cognitive function in both groups. Physiotherapeutic vestibular rehabilitation has been reported to alleviate symptoms of anxiety and depression (Whitney et al., 2005; Meli et al., 2007). "
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