The diagnosis of psychiatric disorders is made complex by the overlap between normality and pathology, by the common symptoms shared between several diseases, and by the reliance of the diagnosis on (self-) reported abnormal thoughts and/or behaviors. This creates a need for more objective biomarkers (1).
Genetic biomarkers are promising. However, there is no one-to-one relationship between a genetic mutation and a disease, as numerous genes and environmental factors can be implicated in each disease. Genetic biomarkers should, therefore, be combined with structural, functional, neurophysiological, and cognitive ones, in an integrative approach (1). Imaging biomarkers are part of this arsenal. Functional MRI (fMRI) studies have made it possible to identify the key brain circuits affected by most psychiatric diseases (1), e.g., in a study realized by our group (2), the insular-striatal circuit in pathological gamblers.
However, although thousands of papers have been published on psychiatric imaging, the translation to clinical practice remains marginal. Results based on the mean effect observed on groups of subjects cannot, in most of the cases, be translated to single individuals because of the large overlap between the groups. Classification algorithms are a promising alternative, although some challenges still need to be addressed (1). Resting-State fMRI, identifying brain circuits in which the spontaneous fluctuations of the BOLD signal are correlated, is a promising alternative to conventional MRI, eliminating the influence of the stimuli on the results (1).
Pharmacologic MRI (phMRI) (3) is a technique in which a drug, which is not a radiological contrast agent, is injected in order to induce a variation in the signal. The technique is based on the fact that neurotransmitters, whose release is modulated by most psychiatric drugs, have a vasoactive effect, which can be detected by BOLD or perfusion MRI. The local hemodynamic changes can be correlated with the known spatial distribution of each neurotransmitter, making phMRI a potential molecular imaging technique for the release of neurotransmitters.
In psychiatry, neuroimaging-based prediction of a treatment’s efficacy would be a major step toward precision medicine (1). At an individual level, the techniques are not yet ready. However, in clinical trials, in which the effect of a new drug can be assessed at the group level, each patient having his/her own baseline scan, psychiatric imaging biomarkers are really promising.
(1) Gordon and Koslow, Integrative Neuroscience and Personalized Medicine. Oxford University Press 2011 (2) Brevers et al. Comfort for uncertainty in pathological gamblers: An fMRI study. Behav Brain Res. 2014 (3) Jenkins. Pharmacologic magnetic resonance imaging (phMRI): imaging drug action in the brain. Neuroimage 2012.
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