Brain responses associated with consciousness of breathlessness (air hunger)

Little is known about the physiological mechanisms subserving the experienc e of air hunger and the affective control of breathing in humans. Acute hun ger for air after inhalation of CO2 was studied in nine healthy volunteers with positron emission tomography. Subjective breathlessness was manipulate d while end-tidal CO2-was held constant. Subjects experienced a significant ly greater sense of air hunger breathing through a face mask than through a mouthpiece. The statistical contrast between the two conditions delineated a distributed network of primarily limbic/paralimbic brain regions, includ ing multiple foci in dorsal anterior and middle cingulate gyrus, insula/cla ustrum, amygdala/periamygdala. lingual and middle temporal gyrus, hypothala mus, pulvinar, and midbrain, This pattern of activations was confirmed by a correlational analysis with breathlessness ratings. The commonality of reg ions of mesencephalon, diencephalon and limbic/paralimbic areas involved in primal emotions engendered by the basic vegetative systems including hunge r for air, thirst, hunger, pain, micturition, and sleep, is discussed with particular reference to the cingulate gyrus. A theory that the phylogenetic origin of consciousness came from primal emotions engendered by immediate threat to the existence of the organism is discussed along with an alternat ive hypothesis by Edelman that primary awareness emerged with processes of ongoing perceptual categorization giving rise to a scene [Edelman, C. M, (1 992) Bright Air, Brilliant Fire (Penguin, London)].