Blood flow and oxidative metabolism of the brain in patients with schizophrenia

Prospects for quantitative fMRI: investigating the effects of caffeine on baseline oxygen metabolism and the response to a visual stimulus in humans

Functional magnetic resonance imaging (fMRI) provides an indirect reflection of neural activity change in the working brain through detection of blood oxygenation level dependent (BOLD) signal changes. Although widely used to map patterns of brain activation, fMRI has not yet met its potential for clinical and pharmacological studies due to difficulties in quantitatively interpreting the BOLD signal. This difficulty is due to the BOLD response being strongly modulated by two physiological factors in addition to the level of neural activity: the amount of deoxyhemoglobin present in the baseline state and the coupling ratio, n, of evoked changes in blood flow and oxygen metabolism. In this study, we used a quantitative fMRI approach with dual measurement of blood flow and BOLD responses to overcome these limitations and show that these two sources of modulation work in opposite directions following caffeine administration in healthy human subjects. A strong 27% reduction in baseline blood flow and a 22% increase in baseline oxygen metabolism after caffeine consumption led to a decrease in baseline blood oxygenation and were expected to increase the subsequent BOLD response to the visual stimulus. Opposing this, caffeine reduced n through a strong 61% increase in the evoked oxygen metabolism response to the visual stimulus. The combined effect was that BOLD responses pre- and post-caffeine were similar despite large underlying physiological changes, indicating that the magnitude of the BOLD response alone should not be interpreted as a direct measure of underlying neurophysiological changes. Instead, a quantitative methodology based on dual-echo measurement of blood flow and BOLD responses is a promising tool for applying fMRI to disease and drug studies in which both baseline conditions and the coupling of blood flow and oxygen metabolism responses to a stimulus may be altered.

Comorbid mood, psychosis, and marijuana abuse disorders: a theoretical review

There is a need to bridge the gap between the fields of addiction psychiatry and general psychiatry to effectively treat co-morbid substance abuse and psychiatric disorders. This alarming epidemic transcends communities and severely impacts healthcare worldwide, yielding poor treatment outcomes and prognoses for afflicted patients. Because substance abuse can exacerbate or trigger psychosis and mood disorders, it is important to keep these issues in the forefront when evaluating patients. To address some of the complications stemming from not enough interactions between various groups of practitioners, this review addresses the neurobehavioral effects of cannabis use and their impact on patients who suffer from psychotic or affective disorders. The hope is that this article will serve as a spring board for further discussions among practitioners who treat these patients. Greater interactions between caretakers are bound to impact the care of our patients in a very positive way.