Vestibular agnosia is a cognitive disability that prevents a patient from detecting body motion that includes the head during periods of imbalance (Calzolari et al. 2020; Hadi et al. 2022), which can lead to falls that are denied by the patient. Consequently, this dysfunction is under reported (Hadi et al. 2024). It is suspected that this disorder is due to a degeneration of the interior longitudinal fasciculus of the right hemisphere, as evidenced by diffusion tensor imaging (Hadi et al. 2024). This fasciculus interconnects the occipital cortex along with the medial temporal cortex (MT) and medial superior temporal cortex (MST) with anterior regions of the temporal lobe including the insular cortex (see Fig. 1), all of which are part of the cortico-vestibular network (Gogolla 2017; Guldin and Grüsser 1998). Electrical stimulation of the inferior longitudinal fasciculus induces a plethora of vestibular sensations (Kahane, Berthoz et al. 2003): the sensation of head and body rotation with mainly a contralateral bias, the sensation of head and body translation either forward or backward, and the sensation of gravitational force either of heaviness or lightness. Returning astronauts are very aware of these feelings when they must adapt to 1G (Carriot et al. 2021; Demontis et al. 2017; Lawson et al. 2016). See Figure 2 to understand how distance from the earth’s surface affects our experience of gravity.
Volitional behaviors such as reading, writing, speaking, walking, or running are accompanied by theta activity (i.e., 6 to 10 Hz; Tehovnik 2017; Vanderwolf 1969), which is omnipresent in the brain including both cortical and subcortical regions (Tehovnik, Hasanbegović, Chen 2024). As well, for both human and non-human mammals, theta activity is potentiated as subjects learn and acquire new skills (Asaka, Berry et al. 2005; Berry and Thompson 1978; Griffin, Berry et al. 2004; Hoffman and Berry 2009; Pu, Johnson et al. 2017). Of late, it has been discovered that before human subjects are cued to rotate the head and body (whether real or virtual) there is a burst of theta activity that precedes the start of rotation in the frontal and parietal lobes (as measured at Fz, F3, F4, C3, Cz, C4, P3, and P4; Hadi et al. 2024). This concurs with the observation that when there are changes in the stream of consciousness, as assessed with binocular rivalry, there is a burst of theta activity in the neocortex that precedes a transition in perception (Dwarkanath, Logothetis et al. 2023).
Figure 1: The inferior longitudinal fasciculus projecting between the occipital cortex and temporal cortex of a human subject. Image from figure 3 of Sobhani et al. (2015).
Figure 2: Acceleration is plotted as a function of distance from the earth’s surface (distance = 1) plotted as a function of the earth’s radius. Notice that at the center of the earth, the gravitational force is zero since all the forces cancel each other out. Plot derived from John Wo, an aircraft and spacecraft designer, as made available on Google on June 22, 2024.
Vestibular agnosia, a disorder where individuals cannot detect body motion and balance, is linked to damage in the inferior longitudinal fasciculus (ILF) in the brain. This pathway connects regions involved in processing vestibular information. Conscious awareness of balance involves integrating sensory inputs through these neural networks. Theta activity, which precedes changes in sensory perception, further supports the role of these brain regions in conscious awareness. While vestibular agnosia does not "prove" that the vestibular sense is solely mediated by consciousness, it demonstrates that disruptions in specific neural pathways can affect conscious sensory experiences, highlighting the interconnected nature of sensory processing and conscious awareness.
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