The cerebellum is increasingly recognized for its crucial role in high-level cognitive processes, particularly in the domain of social cognition and action prediction. Disruptions in cerebellar circuits can lead to significant impairments in anticipating others' intentions and behaviors, affecting daily social interactions. This randomized, double-blind, sham-controlled trial protocol investigates the combined effects of personalized cerebellar High-Definition transcranial Alternating Current Stimulation (HD-tACS) and Immersive Virtual Reality (IVR) training on social prediction abilities. The study involves two clinical populations: adolescents and young adults with congenital cerebellar malformations (CM) and adults with acquired neurodegenerative cerebellar atrophy (CA). Participants undergo eight daily sessions of IVR training designed to enhance internal models of social events through interactive scenarios. Simultaneously, they receive either active or sham HD-tACS delivered at their Individual Gamma Frequency (IGF), determined via baseline EEG. The primary outcomes include behavioral responses to context-based social prediction tasks (action intentions, emotions, and personality traits). Secondary outcomes encompass electrophysiological measures, neuropsychological functioning, and adaptive behavior. By integrating neuromodulation with embodied virtual experiences, the project aims to facilitate cerebello-cerebral plasticity and provide a novel transdiagnostic rehabilitative approach for socio-cognitive impairments.
Documented malformations confined to the cerebellum confirmed by a 3T brain MRI scan;
Age ranging from 12 to 32 years old;
IQ >= 50;
Absence of extra-cerebellar malformations on conventional brain MRI scan.
Presence of severe motor and visual impairments, as well as neurodevelopmental (i.e., autism), neurological or psychiatric disorders that could interfere with task execution and protocol compliance;
Presence of any contraindication for tACS.
Parallel
EEg-guided High-Definition transcranial alternate current stimulation (HD-tACS)
DeviceEEG-guided HD-tACS is delivered via a CE-marked Starstim® 8-channel device using a multifocal montage with the active ring electrode centered over the left cerebellar hemisphere (2 cm below and 3 cm left of the inion) and four equidistant references (4 cm). This configuration, validated by SimNIBS 4.1 electric field modeling, targets cerebellar regions linked to mentalizing connectivity. Stimulation is applied for 20 minutes daily at 1 mA peak-to-peak intensity-selected for its safety and efficacy in younger participants-including 30-second ramp-up/down phases. In the sham condition, current is deactivated after the initial ramp-up to maintain blinding through transient tingling. The stimulation frequency is individually tailored to each participant's Individual Gamma Frequency (IGF), identified as the peak power within the 30-80 Hz band via Welch's PSD estimation of 19-channel EEG data (10/10 system) recorded at 500 Hz and processed using FIR filtering.
Immersive Virtual Reality (IVR) Social Prediction training
BehavioralThe protocol employs age-matched, immersive virtual scenarios developed in Blender and Unity, delivered via Meta Quest 2 HMD (120 Hz, 110° FOV) to ensure a high sense of presence. To maximize ecological validity through personalized settings, adolescents interact with school-based environments (library/playground), while adults use a supermarket or restaurant. From a first-person perspective with synchronous hand-tracking, participants observe three objects on a counter as an avatar approaches. Each session (40 mins) includes 88 trials where participants must infer and predict the avatar's preferred object category (e.g., beverages, books) and grasp it first. Three avatars follow specific preferences, while a fourth acts randomly; mappings are pseudo-randomized across eight sessions to ensure identity-based learning. Feedback is provided via auditory cues.
Context-based social prediction task
Behavioral responses (accuracy and reaction times) to three ad-hoc computer-assisted social prediction tasks and one non-social control task. The three social prediction tasks measure the ability to use contextual information to infer and predict others' mental states or traits, including action intentions, emotional states, and personality traits. All tasks share a priming-target procedure where participants select between two interpretations of a target stimulus following a congruent or incongruent situational context. Specifically, the Action Intention task requires predicting if a hand-grasp is for using or moving an object; the Emotion task involves identifying happiness or fear in facial expressions; and the Personality Trait task assesses trustworthiness judgments based on moral or immoral behaviors. A Non-social Control task requiring the classification of natural or artificial objects in indoor/outdoor environments is used as a control.
Cognitive discrimination response task (DRT)
This computer-assisted task is used as an index of perceptual and cognitive control, such as inhibition, a core executive function supporting social cognition. Participants respond quickly to target stimuli and withhold responses to non-target stimuli.
High-density event-related potentials (ERPs) recording
ERPs are measured during the DRT, to examine pre- and post-stimulus activity, capturing reactive sensory-motor processes, proactive motor preparation, and cognitive anticipation
Cortical rhythms
EEG recordings are collected at rest (5 minutes) and during the DRT (15 minutes) to assess changes in delta, alpha, beta, and gamma power across time points, focusing on regions linked to socio-cognitive functions
NEPSY-II: Social Perception
For participants ≤16 years, a domain-specific Composite Score is calculated as the arithmetic mean of the age-standardized scaled scores (Mean=10, SD=3; range 1-19) of the administered subtests. It assesses the ability to recognize facial affect and understand mental states (Theory of Mind).
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I.R.C.C.S. Fondazione Santa Lucia
Lead sponsor
IRCCS National Neurological Institute "C. Mondino" Foundation
Collaborator
