Neuroimaging of Primal Drives Air Hunger

The arousal accompanying the primal drive of hunger for air or breathlessness is possibly one of the most powerful evolutionary subjective states. While there are well-defined medullary, mesencephalic, hypothalamic, and thalamic functions in the basic mechanisms of respiratory regulation, knowledge of cortical and affective control of breathing and the elements subserving the consciousness of breathlessness and air hunger is limited. A recent series of PET studies (Brannan et al., 2001; Liotti et al., 2001; Parsons et al., 2001) investigated such mechanisms in nine young adults, where air hunger was produced acutely by 8 percent CO2 inhalation. Comparisons were made with inhalation of a N2/O2 gas mixture with the same apparatus, with paced breathing, and with ECR. Both respiratory parameters and subjective ratings were recorded for each condition. Independent of the control state (ECR, O2 breathing, paced breathing), CO2 stimulation activated a distributed network including pons, midbrain, hypothalamus, limbic and paralimbic areas (amygdala and periamygdalar region), ventral cingulate, parahippocampal and fusiform gyrus, caudate nuclei, and pulvinar. Strong deactivations were seen in dorsal cingulate, posterior cingulate, and prefrontal cortex (Brannan et al., 2001; see Fig. 2.5, left). In the same subjects, subjective breathlessness was manipulated while end-tidal CO2 was held constant. Subjects experienced a significantly greater sense of air hunger breathing through a face mask

CO2 Stimulation CO2 FM vs. O2 FM

Breathlessness CO2 FM vs. CO2 MP

CO2 Stimulation CO2 FM vs. O2 FM

D ACg midbrain pons

D ACg midbrain pons

Breathlessness CO2 FM vs. CO2 MP

Amygdala

Figure 2.5. PET changes during CO2 stimulation and air hunger. Left: CO2 stimulation activates the amygdalae, pons-midbrain, cerebellum (bottom) and deactivates the dorsal anterior and posterior cingulate and prefrontal cortex (top). Right: Breathlessness is accompanied by increases in anterior and midcingulate cortex (top) and with minimal or no effects in amygdalae and pons/midbrain. [These data are adapted from Brannan et al. (2001) and Liotti et al. (2001).] See ftp site for color image.

than through a mouthpiece. The statistical contrast between the two CO2 inhalation conditions delineated a distributed network of primarily limbic/paralimbic brain regions, including multiple foci in dorsal anterior and middle cingulate gyrus, insula/claustrum, lingual, and anterior temporal poles (see Fig. 2.5, right). This pattern of activations was confirmed by a correlational analysis with breathlessness ratings (Liotti et al., 2001).

Anxiety and Depression 101

Anxiety and Depression 101

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