Cerebellum and Neurorehabilitation in Emotion with a Focus on Neuromodulation.

More and more research has focused on the role of the cerebellum in emotions and social cognition. Structural cerebellar and cerebello-cerebral connectivity abnormalities have been identified in several prevalent neuropsychiatric conditions, which have in some cases even been linked to the severity of the emotional disorder.Non-invasive brain stimulation (NIBS) techniques are currently used to modulate neuronal excitability and tune the connectivity within and between neuronal networks. Targeting the cerebellum with NIBS in order to improve emotions and social behavior in neuropsychiatric conditions seems to be a very interesting and innovative approach. Several studies have already explored the effect of cerebellar vermis stimulation in patients with schizophrenia with promising results. Other neuropsychiatric disorders such as bipolar disorder (BD), obsessive-compulsive disorder (OCD), major depressive disorder, or generalized anxiety disorder (GAD) have received less attention with respect to cerebellar stimulation, although the cerebellum has been implicated in these disorders. We will address NIBS and neuropsychiatric disorders in this chapter. Future research should focus on combining cerebellar NIBS with neuroimaging to unravel the specific role of the cerebellum in emotional disorders. Such studies will be very valuable in establishing causal relationships between the structural and functional abnormalities that can be observed in these disorders, and in the search for neurophysiological biomarkers for emotions. However, it is still unclear which stimulation parameters are optimal. Moreover, an important factor to consider when applying cerebellar NIBS in order to improve emotional or other functioning is cerebellar reserve. Although the cerebellum has a wide variety of plasticity mechanisms and its structural organization intrinsically incorporates a lot of redundancy, this redundancy can be depleted. A certain amount of cerebellar reserve should be preserved to successfully apply NIBS.Systematic studies are therefore needed to clarify the optimal stimulation parameters, and methods should be developed to quantify cerebellar reserve in order to estimate the possible added value of NIBS in the rehabilitation of emotions.