Cervelletto e memorie traumatiche: un’ipotesi neuro-funzionale sul Disturbo Post Traumatico da Stress e sulla terapia EMDR

The role of the cerebellum in modulating our emotional experience is a fairly recent acquisition of neuroscience. The existence of a so-called limbic cerebellum has been hypothesized based on anatomical and functional connectivity findings. In our study, through a non-invasive transcranial stimulation (transcranial Direct Current Stimulation - tDCS) we modulated the cerebellar excitability in order to investigate the involvement of this structure in the maintaining of posttraumatic stress disorder (PTSD). In particular, we investigated the effect of stimulation on the quality of emotional states induced by the recall of negative memories and of traumatic memories. In the first case, which involved 51 subjects, we evaluated the effect of cerebellar stimulation, comparing it with sham stimulation and the stimulation of the right dorsolateral prefrontal cortex (DLPFC). The effect of stimulation was measured on the intensity of arousal generated by an unpleasant memory. In this experiment, we observed a reduction of tonic skin conductance level, probably linked to a reduction in the implicit emotional level triggered by the negative memory, even in the absence of explicit changes of emotional experience. The second experiment involved patients with traumatic memories compatible with PTSD. In this experiment we assessed, by self-report questionnaires, the intensity of emotions linked to the recall of the traumatic memory before and after either real or sham cerebellar stimulation. Following a single session of real tDCS stimulation a significant reduction of symptoms related to the disorder was observed. These results suggest the involvement of cerebellum in the construction of the emotional content of mnestic events, at least of traumatic ones. Given the speed of therapeutic response and the anatomical location of this structure, the hypothesis is that early bottom-up mechanism or implicit pre-processing of emotional stimuli take place. If we consider the world of trauma therapy and in particular the well-known therapy based on eye movements (Eye Movement Desensitization and Reprocessing – EMDR), we can notice how both tDCS stimulation and EMDR similarly reduces the malaise connected to a traumatic memory by reducing the possibility to generate unpleasant emotions connected with the trauma. In addition, some studies document further overlap between these two techniques in the ability to decrease arousal, what could be of further help in decreasing the intrusiveness and unpleasantness connected to traumatic memories. The results of this study opens the field to new hypotheses on the role of the cerebellum as a key structure in the maintenance of trauma, suggesting that a modulation of activity of this structure, which may occur more directly through the tDCS and perhaps more indirectly through EMDR, could lead to the critical restructuring of traumatic memories that represents the endpoint of most recent therapeutic approaches to PTSD.