A content analysis of global and national policies, plans, and guidelines to integrate NCDs with HIV care in LMICs.

Self-motion is sensed by the vestibular system, contributing to reflexes, spatial perception, and motor coordination during everyday life [reviewed in ()]. Vestibular sensors detect head movement information, transmitting this information via afferents to the vestibular nuclei (VN). Vestibular-only neurons within the VN project to neurons in the thalamic ventral posteriolateral area (VPL) (, ). The VPL projects directly to multiple cortical areas that are involved in self-motion processing and perception, including the parietoinsular vestibular cortex (PIVC), the ventral intraparietal cortex (VIP), area 2v of the intraparietal sulcus, and area 3a in the sulcus centralis (–). Area PIVC further receives both visual inputs from the medial temporal (MT) via the dorsal medial superior temporal (MSTd) cortex (, –), projects to the VIP (), and is furthermore strongly interconnected with somatosensory cortex areas 3a and 2v (). Notably, PIVC is thought to play a central role in mediating self-motion perception: Stimulation of this area evokes vestibular sensations (), whereas lesions instead impair orientation perception (, ). The common wisdom is that neurons within ascending vestibular pathways exclusively transmit information through changes in firing rate that are linearly related to the self-motion stimulus [see (, ) for review]. However, the self-motion stimuli experienced during everyday behavior fundamentally differ from the artificial sinusoidal stimuli typically used in neurophysiological studies (, ). Subcortical vestibular neurons in both VN and VPL demonstrate strong nonlinearities () and respond with markedly different dynamics to natural versus artificial self-motion (–) [see (, ) for review]. This raises a fundamental question: Do cortical representations of vestibular input driven by artificial stimuli accurately generalize to natural self-motion? In particular, subcortical neurons respond to naturalistic stimuli using precise spike timing (), thereby suggesting that specific action potential patterns carry information. Perhaps one of the most commonly encountered action potential pattern is burst firing (i.e., the tendency of neurons to fire packets of action potentials followed by quiescence) (). This mode of activity is observed across diverse brain regions, including the hippocampus (–) and avian forebrain (, ) [see (, , ) for review], and arises from well-characterized somato-dendritic interactions (, ). Despite its ubiquity and mechanistic understanding, whether burst firing contributes to the encoding of self-motion within cortical pathways remains unknown. Accordingly, here we investigated how neurons in the macaque PIVC encode both natural and artificial self-motion. Consistent with prior results, PIVC neurons encoded the detailed time course of sinusoidal (artificial) motion. In notable contrast, during natural self-motion, cortical neurons adopted a fundamentally different coding strategy, reliably signaling distinct stimulus features through burst firing. This nonlinear transformation emerged within the cortex as the response of vestibular thalamic neurons in VPL continued to follow stimulus dynamics under both conditions. Computational modeling further revealed that this thalamic-cortical transformation emerges under richer self-motion stimulus statistics. Our modeling also predicted that PIVC representations of natural stimuli are distributed, requiring pooling across neurons to recover stimulus dynamics—a prediction that was confirmed experimentally. Together, these findings demonstrate that PIVC does not passively relay vestibular input to higher brain areas with little to no transformation. Rather, they identify the vestibular cortex as an essential site of thalamic-cortical transformation that recodes vestibular signals into distributed, feature-based population representations where each neuron signals a specific stimulus feature (e.g., upstroke) via burst firing thereby supporting perception of natural self-motion.