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Imaging the Brain by mapping Activity Based pH Changes

Normal brain activity results in localized pH fluctuations. Moreover, low brain pH has been linked to depression, anxiety and different panic disorders. This is because certain receptors present in the brain are activated by the reduced pH. Studies conducted in mice show that learning and memory, as well as fear responses are regulated by acid sensing proteins present in the brain. Therefore, mapping the brain based on activity based pH changes can be a novel method of brain imaging, different from the usual MRI using contrast mediums. However, until now, measuring the pH changes in the brain had been a difficult proposition. A team of researchers, led by Dr. John Wemmie from the University of Iowa, have come up with a new imaging technique that detects activity based pH changes in the brain. The results of the study have been published in the latest issue of the journal Proceedings of the National Academy of Sciences (PNAS).

According to the neuroscientists, by constantly manipulating the carbon dioxide or bicarbonate levels, it is possible to detect pH changes during T1 relaxation in the rotating frame (T1ρ) during magnetic resonance imaging. Lowering the pH by breathing carbon dioxide increased the signal, whereas bicarbonate injections increased the pH and decreased the strength of the MRI signal. Flashing a checkerboard induced localized acidosis in the visual cortex. T1ρ was successful in detecting this localized acidosis. A drop in the pH of the visual cortex was also confirmed by lactate measurements and pH sensitive 31P spectroscopy. While a functional MRI is dependent upon the blood oxygen levels, T1ρ is not directly sensitive to it. On the contrary, it depends upon the pH changes in specific areas in the brain.

According to the researchers, further experiments are required to establish whether the pH is altered in human psychiatric conditions and if so, whether its manipulation can offer a way of treating these conditions.


Wednesday, May 23, 2012