Neuroimaging of genesis and satiation of thirst and an interoceptor-driventheory of origins of primary consciousness

There are defined hypothalamic functions in the genesis of thirst, but litt le is known of the cortical processes subserving consciousness of thirst no twithstanding the medical disorders that occur in psychiatric illness, addi ction, and the attested decline of thirst with aging. In 10 adult males, po sitron emission tomography scans were made (i) during genesis of moderate t hirst by infusion of i.v. hypertonic saline 0.51 M, (ii) after irrigation o f the mouth with water to remove the sensation of dryness, and (iii) 3, 14, 45, and 60 minutes after drinking water to fully satiate thirst. The corre lation of regional cerebral blood flow with thirst score showed the major a ctivation to be in the posterior cingulate. Maximum thirst sensation evoked 13 highly significant activations and 9 deactivations in cingulate and par ahippocampal gyri, insula, thalamus, amygdala, and mesencephalon. It is pos sible that cingulate sites (Brodmann's areas 32, 24, and 31) that persisted with wet mouth but disappeared immediately after drinking to satiation may have an important role in the consciousness of thirst. Consciousness of th irst, a primal vegetative emotion, and satiation of thirst appear to be sub served by phylogenetically ancient brain regions. This is salient to curren t discussion on evolutionary emergence of primary consciousness.