Vestibular brain changes within 70 days of head down bed rest

Abstract

Head-down-tilt bed rest (HDBR) is frequently utilized as a spaceflight analog research environment to study the effects of axial body unloading and fluid shifts that are associated with spaceflight in the absence of gravitational modifications. HDBR has been shown to result in balance changes, presumably due to sensory reweighting and adaptation processes. Here, we examined whether HDBR results in changes in the neural correlates of vestibular processing. Thirteen men participated in a 70-day HDBR intervention; we measured balance, functional mobility, and functional brain activity in response to vestibular stimulation at 7 time points before, during, and after HDBR. Vestibular stimulation was administered by means of skull taps, resulting in activation of the vestibular cortex and deactivation of the cerebellar, motor, and somatosensory cortices. Activation in the bilateral insular cortex, part of the vestibular network, gradually increased across the course of HDBR, suggesting an upregulation of vestibular inputs in response to the reduced somatosensory inputs experienced during bed rest. Furthermore, greater increase of activation in multiple frontal, parietal, and occipital regions in response to vestibular stimulation during HDBR was associated with greater decrements in balance and mobility from before to after HDBR, suggesting reduced neural efficiency. These findings shed light on neuroplastic changes occurring with conditions of altered sensory inputs, and reveal the potential for central vestibular-somatosensory convergence and reweighting with bed rest.

Functional and/or structural brain changes in response to resistance exercises and resistance training lead to cognitive improvements – a systematic review

“…Interventional studies (or cross-sectional studies) investigating the relationship of resistance exercises (or strength, muscle function/structure) and cognition should utilize different neuroimaging methods during standardized cognitive testing and assess neurochemical substances (e.g., neurotransmitters, neurotrophic factors) to elucidate underlying neurobiological mechanisms. Bed rest studies, which reported a worsening of executive functions [395][396][397], profound brain changes [397][398][399], and a decrease in muscle mass as well as muscle strength [400][401][402][403][404][405][406][407][408], could be an interesting model to study the relationship between the muscular system, functional and structural brain changes, and cognition.…”

Neural Correlates of Vestibular Processing During a Spaceflight Analog With Elevated Carbon Dioxide (CO2): A Pilot Study

“…fMRI images were collected at seven time points: two times pre-, three times during, and two times post-HDBR (Figure 1). As we have previously reported neural vestibular changes with this intervention (Yuan et al, 2018b), here we use these fMRI data only for group comparisons with the HDBR + CO 2 group. We examine only the fMRI scans from BDC 8, HDT 8, and HDT 50, as these points fell closest in time to those collected pre-and during bed rest for the HDBR + CO 2 group and allowed us to compare slopes of change over time in the two groups.…”

“…In our past HDBR work, using this skull tap technique, we identified longitudinal brain changes suggestive of upregulation of vestibular processing in response to reduced somatosensory input during 70 days of HDBR (Yuan et al, 2018b). We also found associations between increased frontal, parietal, and occipital brain activity and greater HDBR-related mobility and balance declines, suggestive of reduced neural efficiency post-HDBR (Yuan et al, 2018b). Further, we identified post-HDBR increases in resting state connectivity for a network including the vestibular cortex and the cerebellum (Cassady et al, 2016).…”

“…However, the most commonly activated regions across several different vestibular stimulation methods were the parietal opercular area ("OP2") and retroinsular cortex; consequently, these regions are sometimes referred to as "vestibular cortex, " and considered to be the core regions responsible for vestibular processing. In the present work, we stimulated the vestibular system during fMRI using pneumatic skull taps, which we have previously validated in young (Noohi et al, 2017) and older adults (Noohi et al, 2019), and successfully employed in our past HDBR work (Yuan et al, 2018b). Pneumatic skull taps elicit both activation in the vestibular cortex and deactivation in cross-modal sensory regions.…”

“…Subjects remain in bed with their head tilted down six degrees to mimic a subset of spaceflight consequences including headward fluid shifts, arterial pressure changes, axial body unloading, and reduced somatosensory input. Although gravitational vector input does not change during HDBR, there is evidence that, similar to spaceflight, axial body unloading contributes to sensory reweighting (Moore et al, 2010;Mulavara et al, 2018;Yuan et al, 2018b). Even though HDBR does not directly affect vestibular inputs, sensory reweighting is thought to affect neural vestibular processing during HDBR; more specifically, the vestibular nuclei receive inputs from the vestibular organs, in addition to proprioceptive signals from the limbs (Fredrickson et al, 1966;Rubin et al, 1979;Yates et al, 2000;Jian et al, 2002).…”