Twelve healthy subjects in their 60s and 70s showed a different pattern of brain activations during thirst and satiation than did 10 healthy subjects in their 20s who drank the same amounts and underwent imaging with positron-emission tomography (PET).

Dysfunction in activated neural regions could help explain why older adults show the dangerous tendency toward reduced drinking in response to dehydration.

San Antonio and Australian researchers reported the PET study of thirst in this week's Proceedings of the National Academy of Sciences Online Early Edition.

The team has conducted a series of studies to catalog brain activations to basic physiologic necessities such as thirst, body temperature regulation, air hunger and pain relief.

“These are self-sensations that have very strong motivational power,” said co-author Peter T. Fox, M.D., professor and director of the Research Imaging Center at The University of Texas Health Science Center at San Antonio.

PET imaging measures brain function rather than picturing anatomical structure. In this latest PET study, researchers noted a less robust cerebral blood flow in a region called the anterior midcingulate cortex in the older study participants compared to the younger subjects.

The study is by researchers at the Health Science Center, the Southwest Foundation for Biomedical Research in San Antonio, the Howard Florey Institute at the University of Melbourne, Australia, and the Baker Heart Research Institute, also in Australia.

The University of Texas Health Science Center at San Antonio is the leading research institution in South Texas and one of the major health sciences universities in the world. With an operating budget of $576 million, the Health Science Center is the chief catalyst for the $15.3 billion biosciences and health care sector in San Antonio's economy. The Health Science Center has had an estimated $35 billion impact on the region since inception and has expanded to six campuses in San Antonio, Laredo, Harlingen and Edinburg. More than 22,000 graduates (physicians, dentists, nurses, scientists and allied health professionals) serve in their fields, including many in Texas. Health Science Center faculty are international leaders in cancer, cardiovascular disease, diabetes, aging, stroke prevention, kidney disease, orthopaedics, research imaging, transplant surgery, psychiatry and clinical neurosciences, pain management, genetics, nursing, allied health, dentistry and many other fields.