Cerebral palsy (CP) is the most common childhood-onset motor disorder, with Unilateral Cerebral Palsy (UCP)- motor impairment predominantly impacting one side of the body-representing the most frequent form of CP. Among available rehabilitation programs, Action Observation Treatment (AOT) has gained increasing attention for its demonstrated effectiveness in improving manual motor function. AOT involves the systematic observation of goal-directed actions followed by their execution/imitation and is thought to leverage the mirror mechanism and its role in motor learning. Specifically, it relies on the neurophysiological principle that observing others' actions activates the same neural structures involved in executing those actions, reflecting the engagement of the mirror neuron system (MNS). In children with CP, the feasibility and effectiveness of AOT have been shown functionally (Sgandurra et al., 2013, Buchignani et al., 2019). However, despite its theoretical grounding in MNS functioning, the neurophysiological correlates of this system in children with CP remain less characterized, with only limited investigations using functional neuroimaging (e.g., Sgandurra et al., 2020) or neurophysiological methods such as electroencephalography (EEG; e.g., Demas et al., 2019).

This observational study aims to characterize the neurophysiological signatures of action execution and action observation in children aged 5-15 years with a diagnosis of UCP compared to a group of age-matched typically developing (TD) peers. To this end, non-invasive high-density EEG (hdEEG) will be used to quantify sensorimotor cortex modulation through mu-rhythm reactivity-specifically event-related desynchronization (ERD) and synchronization (ERS)-and its topographical distribution during an active visuo-motor task involving upper limbs. Mu-rhythm desynchronization (or suppression) over sensorimotor regions is a well-established marker of MNS engagement. A secondary objective is to examine the relationship between EEG measures and participants' attention, upper-limb kinematics, and manual motor function. To this purpose, participants will wear non-invasive wearable sensors to capture arm/hand kinematics, and attention will be monitored with a non-invasive eye-tracking system. Validated scales will be used to assess manual motor function.

Participants will take part in one single visit of about 1.5 hours. During the EEG acquisition session, children will wear a 128-channel EEG net and complete an active visuo-motor paradigm including the observation and execution of unimanual and bimanual goal-directed actions (e.g., reaching-grasping). In the observation condition, children will watch videos depicting these actions on a computer screen while refraining from movement. In the subsequent execution condition, they will interact themselves with the same objects as in the observation condition. Throughout the same session, children's attention/gaze will be tracked via eye-tracking, and upper-limb kinematics will be recorded using wearable inertial measurement unit (IMU) sensors. Before or after EEG acquisition, manual motor function will be assessed using two standardized scales: the Assisting Hand Assessment (AHA) and the Melbourne Assessment-2 (MA-2).

Data analysis will characterize the mu rhythm ERD topography and temporal dynamics during both action execution and action observation, within and between groups. Correlation analyses will explore associations between neurophysiological measures, gaze and attentional patterns, kinematic data, and motor assessments scores to elucidate how motor and attentional factors modulate sensorimotor cortical activation.

Children with Unilateral Cerebral Palsy

Inclusion Criteria:

• Children with confirmed diagnosis of Unilateral Cerebral Palsy,
• Manual ability levels from I to III in the Manual Ability Classification System (MACS);
• Children's age from 5 to 15 years old.

Exclusion Criteria:

• Severe Upper Limb (UpL) impairment (MACS ≥ level IV: inability to grasp),
• UpL surgery within 12 months prior to study entry and botulinum toxin injection within 6 months prior to study entry,
• Severe comobordities,
• Severe cognitive disability, clinically assessed by the cognitive scales Wechsler, Preschool and Primary Scale of Intelligence (WPPSI-IV) or Wechsler Intelligence Scale for Children (WISC-IV or V).

Typically Developing children:

Inclusion Criteria

• 5 to 15 year-old children with typical development,
• No documented clinically relevant disorders

Children with Unilateral CP (study group) - recruited at the IRCCS Fondazione Stella Maris Typically developing children (control group) - community sample