['Olfactory and gustatory hallucinations (phantosmias and phantageusias, respectively) are sensory distortions that commonly follow losses of olfactory and gustatory acuity (hyposmia and hypogeusia, respectively). The biochemical basis of these hallucinations is unclear. Functional magnetic resonance imaging has been used previously to demonstrate widespread and robust central nervous system (CNS) activation to memories of these sensory distortions in patients with these symptoms. In this study, possible CNS mechanisms responsible for these distortions were evaluated using magnetic resonance spectroscopy, because this technique has been used to measure various CNS metabolites in patients with neurologic disorders.', 'Forty-seven subjects were studied: 28 normal volunteers (13 men and 15 women) and 19 patients (8 men and 11 women) with persistent oral global phantageusia and/or birhinal phantosmia studied before any treatment. Four patients (1 man and 3 women) were studied before and after pharmacologic treatment that reduced the severity of their sensory distortions. All subjects were studied in a Signa 1.5-T magnetic resonance scanner with a quadrature head coil using a modified standard 2-dimensional J-point resolved excitation in the steady state (PRESS) sequence by which gamma-aminobutyric acid (GABA), glutamic acid, choline, N-acetylaspartate, and creatine (Cre) were measured in various CNS regions. Results were expressed using Cre as a denominator to determine ratios for each measurement. Differences were defined between normal subjects and patients before treatment and in patients before and after successful pharmacologic treatment.', 'Before treatment, GABA levels in several CNS regions were lower in patients than in normal volunteers and were the only biochemical changes found; significantly lowered GABA levels were found in the cingulate, right and left insula, and left amygdala. No differences between patients and normal volunteers were found in any of the metabolites in the posterior occipital region. After treatment that inhibited sensory distortions, CNS GABA levels increased in the cingulate, insula, and amygdala but significantly only in the left insula and in the right and left amygdala. After this successful treatment, no change in any biochemical parameter was found in the posterior occipital region.'] Are brain gamma-aminobutyric acid levels decreased in patients with phantageusia and phantosmia demonstrated by magnetic resonance spectroscopy?