Positive self-perception and corticospinal excitability: Recalling positive behavior expands peripersonal space boundaries.

Converging evidence suggests that peripersonal space has dynamic properties, that can be influenced by motor and cognitive factors. Here, we investigated whether changes in self-perception may impact upon peripersonal representation. Specifically, employing non-invasive brain stimulation, we tested whether corticospinal excitability elicited by objects placed in the vertical peripersonal vs extrapersonal space can be influenced by changes in self-perception after recalling a personal experience inducing the feeling of high power (vs. positivity vs. low power). In a preliminary study (Study 1, N = 39) participants were presented with an object, whose position was manipulated in the horizontal vs vertical space. We assessed corticospinal excitability by measuring Motor Evoked Potentials (MEPs) using Transcranial Magnetic Stimulation with Electromyography co-registration (TMS-EMG). In the horizontal condition, we replicated the well-known motor facilitation induced by objects falling in the peri vs extrapersonal space, while in the vertical dimension MEPs were higher in the extrapersonal space. In the main experiment (Study 2), participants (N = 55) were randomly assigned to feel high power, low power, or a general positive emotion and were asked to observe the same object positioned either in the peripersonal or in the extrapersonal vertical space. Results showed that in the low power condition MEPs were higher in the extrapersonal vs peripersonal, as in Study 1, while in high power and positive conditions MEPs were not influenced by distance. Taken together, our findings suggest a dissociable pattern of motor facilitation underlying vertical vs horizontal space perception and, crucially, that changes in self-perception can influence such a representation.

Cerebellar magnetic stimulation decreases levodopa-induced dyskinesias in Parkinson disease.

BACKGROUND: The neural mechanisms and the circuitry involved in levodopa-induced dyskinesia (LID) are still partially obscure. LID can be considered the consequence of an abnormal pattern or code of activity that originates and is conveyed from the basal ganglia to the thalamus and the cortical motor areas. However, not only striatothalamocortical motor circuits but also other interconnected pathways could be implicated in its pathogenesis. METHODS: In a series of experiments, we applied repetitive transcranial magnetic stimulation (rTMS) over the lateral cerebellum in a group of patients with advanced Parkinson disease, to investigate whether modulation of cerebellothalamocortical circuits by means of rTMS may result in a modification of a dyskinetic state induced by levodopa ingestion. RESULTS: We found that a single session of cerebellar continuous theta burst stimulation (cTBS) was capable of transiently reducing LID. In the same patients, we observed that cerebellar cTBS changed the profile of activation of intracortical circuits in the contralateral primary motor cortex. Cerebellar cTBS reduced short intracortical inhibition and increased long intracortical inhibition, inducing a cortical reorganization that is associated with a reduction of LID. Furthermore, in another experiment, we observed that a 2-week course of bilateral cerebellar cTBS induced persistent clinical beneficial effects, reducing peak-dose LID for up to 4 weeks after the end of the daily stimulation period. CONCLUSIONS: Our study demonstrates that cerebellar continuous theta burst stimulation has an antidyskinetic effect in Parkinson disease patients with levodopa-induced dyskinesia, possibly due to modulation of cerebellothalamocortical pathways.