What Can Different Motor Circuits Tell Us About Psychosis? 

An RDoC Perspective

Vijay A. Mittal; Jessica A. Bernard; Georg Northoff

Disclosures

Schizophr Bull. 2017;43(5):949-955. 

In This Article

Conclusion

We pointed out the fruitfulness of the RDoC concept for exploring and understanding different motor functions in the context of psychiatric illnesses. First, we demonstrated how motor excitation/inhibition may provide important clues for understanding basal ganglia circuit pathology in psychosis. Secondly, the cerebello-thalamo-cortical circuits are relevant for motor timing and sensorimotor dynamics which, again, are abnormally altered in schizophrenia and perhaps other psychotic disorders. Finally, we determined cortico-motor or psychomotor circuits that appear relevant for (different forms of) psychomotor modulation such as psychomotor organization and speed which are abnormally altered in catatonia and BD. Though much works remains to be done in the future development of RDoC in the motor domain, our commentary supports the utility of such an approach for defining and determining the often neglected motor function and its various motor/psychomotor symptoms in psychiatric disorders.

More broadly, we need to view motor circuits as inter-related. At the same time, while each motor circuit is active during any given activity, it will be important to understand how dysfunction in a specific circuit may yield dissociable behavioral abnormalities. In addition, it will also be important to map the extent to which motor circuit abnormalities directly impact other systems such as cognition. There has been compelling evidence for such a link in schizophrenia.[59] The RDoC system, providing tools to look across systems in a mechanistically informed way, offers particular strengths in this regard.[60] Furthermore, although RDoC provides a theoretically and empirically informed Matrix, centered on brain-behavioral relationships, it will be informative to continue to view incoming studies within the context of prominent etiological models of psychosis. It is important to consider that motor "circuits" (central to any RDoC domain), speak to a variety of connected brain regions, and can therefore be interpreted through the lens of the disconnectivity hypothesis.[60–62] Indeed, there is already an accumulating body of studies indicating links between motor impairment and aberrant connectivity.[63] Future work evaluating relationships between RDoC motor constructs/subconstructs (eg, motor execution, action perception), will be particularly informative in this regard. The new RDoC Motor Systems constructs also show promise to fit well within developmental hypotheses,[64] cognitive dysmetria,[27] as well as DA and resource processing theories.[65,66] In addition, it will be important for future work to consider bi-directionality between healthy and psychiatric states. While understanding of the basal ganglia circuit is well developed on the basis of both animal and human research in the healthy brain, this is less the case in the second, cerebello-thalamo-cortical circuit, and even less so in the third circuit, the cortico-motor or psychomotor circuits. The latter in particular provides an example where we may want to start in the reverse. That is, from psychiatric symptoms and their motor alterations to the "normal" function of a circuit—the psychiatric abnormalities may thus pave the way and teach us a lesson about the "healthy brain."[67]

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