Abstract
While bipedalism is a fundamental evolutionary adaptation thought to be essential for the development of the human brain, the erect body is always an inch or two away from falling. Although the neural mechanism for automatically detecting one's own body instability is an important consideration, there have thus far been few functional neuroimaging studies because of the restrictions placed on participants' movements. Here, we used functional magnetic resonance imaging to investigate the neural substrate underlying whole body instability, based on the self-recognition paradigm that uses video stimuli consisting of one's own and others' whole bodies depicted in stable and unstable states. Analyses revealed significant activity in the regions which would be activated during genuine unstable bodily states: The right parieto-insular vestibular cortex, inferior frontal junction, posterior insula and parabrachial nucleus. We argue that these right-lateralized cortical and brainstem regions mediate vestibular information processing for detection of vestibular anomalies, defensive motor responding in which the necessary motor responses are automatically prepared/simulated to protect one's own body, and sympathetic activity as a form of alarm response during whole body instability.
Highlights
Bipedalism is the fundamental evolutionary adaptation that sets hominids – and humans – apart from other primates
In the self-condition, the brain regions activated during perception of a dynamically unstable state are involved in extracting and processing unstable components of whole body movement
parieto-insular vestibular cortex (PIVC) activity during vestibular stimulation is stronger in the right hemisphere in right-handers [34], in concordance with the present findings
Summary
Bipedalism is the fundamental evolutionary adaptation that sets hominids – and humans – apart from other primates. Body Instability vertically, such that the head, trunk, legs, and feet, as well as their links in the neck, spine, pelvis, knees, and ankles, dynamically balance together to form an upright ‘‘antigravity pole’’. Because these segments and their points of articulation are not fixed, and given that the downward force of gravity never stops, the erect body always exists an inch or two away from falling. Investigations of the neural mechanism that prevents us from falling would seem to be important for improving our understanding of basic evolutionary brain structures that support survival, brain scanning technologies such as functional magnetic resonance imaging (fMRI) place major restrictions on participants’ movements and do not permit study of in-vivo brain activity during falls, near-falls, or other instances of body instability. We explored the possibility of measuring such brain activity by having participants view images of their own bodies in unstable states
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