Neuroimaging evidence implicating cerebellum in the experience of hypercapnia and hunger for air

Recent neuroimaging and neurological data implicate cerebellum in nonmotor sensory, cognitive, vegetative, and affective functions. The present study assessed cerebellar responses when the urge to breathe is stimulated by inh aled CO2. Ventilation changes follow arterial blood partial pressure CO2 ch anges sensed by the medullary ventral respiratory group (VRG) and hypothala mus, entraining changes in midbrain, pens, thalamus, limbic, paralimbic, an d insular regions. Nearly all these areas are known to connect anatomically with the cerebellum. Using positron emission tomography, we measured regio nal brain blood flow during acute CO2-induced breathlessness in humans. Sep arable physiological and subjective effects (air hunger) were assessed by c omparisons with Various respiratory control conditions. The conjoint physio logical effects of hypercapnia and the consequent air hunger produced stron g bilateral, near-midline activations of the cerebellum in anterior quadran gular, central, and lingula lobules, and in many areas of posterior quadran gular, tonsil, biventer, declive, and inferior semilunar lobules. The prima l emotion of air hunger, dissociated from hypercapnia, activated midline re gions of the central lobule. The distributed activity across the cerebellum is similar to that for thirst, hunger, and their satiation. four possible interpretations of cerebellar function(s) here are that: it subserves impli cit intentions to access air; it provides predictive internal models about the consequences of CO2 inhalation; it modulates emotional responses; and t hat while some cerebellar regions monitor sensory acquisition in the VRG (C O2 concentration), others influence VRG to adjust respiratory rate to optim ize partial pressure CO2, and others still monitor and optimize the acquisi tion of other sensory data in service of air hunger aroused vigilance.