Neural correlates of the emergence of consciousness of thirst.
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.
Egan
Gary
G
The Howard Florey Institute of Experimental Physiology and Medicine, University of Melbourne, Parkville, Victoria 3010, Australia. g.egan@hfi.unimelb.edu.au
Silk
Tim
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Zamarripa
Frank
F
Williams
John
J
Federico
Paolo
P
Cunnington
Ross
R
Carabott
Leonie
L
Blair-West
John
J
Shade
Robert
R
McKinley
Michael
M
Farrell
Michael
M
Lancaster
Jack
J
Jackson
Graeme
G
Fox
Peter
P
Denton
Derek
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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
D010104:Oxygen Radioisotopes; D012462:Saline Solution, Hypertonic; D014867:Water; D012964:Sodium