title: Neural correlates of the emergence of consciousness of thirst.
abstract: Thirst was induced by rapid i.v. infusion of hypertonic saline (0.51 M at 13.4 ml/min). Ten humans were neuroimaged by positron-emission tomography (PET) and four by functional MRI (fMRI). PET images were made 25 min after beginning infusion, when the sensation of thirst began to enter the stream of consciousness. The fMRI images were made when the maximum rate of increase of thirst occurred. The PET results showed regional cerebral blood flow changes similar to those delineated when thirst was maximal. These loci involved the phylogenetically ancient areas of the brain. fMRI showed activation in the anterior wall of the third ventricle, an area that is key in the genesis of thirst but is not an area revealed by PET imaging. Thus, this region plays as major a role in thirst for humans as for animals. Strong activations in the brain with fMRI included the anterior cingulate, parahippocampal gyrus, inferior and middle frontal gyri, insula, and cerebellum. When the subjects drank water to satiation, thirst declined immediately to baseline. A precipitate decline in intensity of activation signal occurred in the anterior cingulate area (Brodmann area 32) putatively related to consciousness of thirst. The intensity of activation in the anterior wall of the third ventricle was essentially unchanged, which is consistent with the fact that a significant time (15-20 min) would be needed before plasma Na concentration changed as a result of water absorption from the gut.
authors.affiliation: The Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3010, Australia. g.egan@hfi.unimelb.edu.au
authors.forename: Gary
authors.initials: G
authors.lastname: Egan
authors.forename: Tim
authors.initials: T
authors.lastname: Silk
authors.forename: Frank
authors.initials: F
authors.lastname: Zamarripa
authors.forename: John
authors.initials: J
authors.lastname: Williams
authors.forename: Paolo
authors.initials: P
authors.lastname: Federico
authors.forename: Ross
authors.initials: R
authors.lastname: Cunnington
authors.forename: Leonie
authors.initials: L
authors.lastname: Carabott
authors.forename: John
authors.initials: J
authors.lastname: Blair-West
authors.forename: Robert
authors.initials: R
authors.lastname: Shade
authors.forename: Michael
authors.initials: M
authors.lastname: McKinley
authors.forename: Michael
authors.initials: M
authors.lastname: Farrell
authors.forename: Jack
authors.initials: J
authors.lastname: Lancaster
authors.forename: Graeme
authors.initials: G
authors.lastname: Jackson
authors.forename: Peter
authors.initials: P
authors.lastname: Fox
authors.forename: Derek
authors.initials: D
authors.lastname: Denton
mesh_terms: D000328:Adult; D001931:Brain Mapping; D002531:Cerebellum / Q000473:pathology; D002540:Cerebral Cortex; D002560:Cerebrovascular Circulation; D005260:Female; D006179:Gyrus Cinguli / Q000473:pathology; D006801:Humans; D007091:Image Processing, Computer-Assisted; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D010104:Oxygen Radioisotopes; D010802:Phylogeny; D012462:Saline Solution, Hypertonic; D012964:Sodium / Q000097:blood; D013894:Thirst; D014055:Tomography, Emission-Computed / Q000379:methods*; D014867:Water / Q000378:metabolism
chemical_list: D010104:Oxygen Radioisotopes; D012462:Saline Solution, Hypertonic; D014867:Water; D012964:Sodium