Neuroimaging of cerebral activations and deactivations associated with hypercapnia and hunger for air

There are defined medullary, mesencephalic, hypothalamic, and thalamic func tions in regulation of respiration, but knowledge of cortical control and t he elements subserving the consciousness of breathlessness and air hunger i s limited. In nine young adults, air hunger was produced acutely by CO2 inh alation. Comparisons were made with inhalation of a N-2/O-2 gas mixture wit h the same apparatus, and also with paced breathing, and with eyes closed r est. A network of activations in pens, midbrain (mesencephalic tegmentum, p arabrachial nucleus, and periaqueductal gray), hypothalamus. limbic and par alimbic areas (amygdala and periamygdalar region) cingulate, parahippocampa l and fusiform gyrus, and anterior insula were seen along with caudate nucl ei and pulvinar activations. Strong deactivations were seen in dorsal cingu late, posterior cingulate, and prefrontal cortex. The striking response of limbic and paralimbic regions points to these structures having a singular role in the affective sequelae entrained by disturbance of basic respirator y control whereby a process of which we are normally unaware becomes a sali ent element of consciousness. These activations and deactivations include p hylogenetically ancient areas of allocortex and transitional cortex that to gether with the amygdalar/periamygdalar region may subserve functions of em otional representation and regulation of breathing.