Title: The relationship between mirror movements and corticospinal tract connectivity in children with unilateral spastic cerebral palsy
Description: Unilateral Spastic Cerebral Palsy (USCP) is caused by an early brain lesion in which the Corticospinal Tract (CST), the primary pathway controlling upper extremity (UE) movements, is affected. The CST connectivity after early brain injury (i.e., an ipsilateral, contralateral, or bilateral connectivity) may influence treatment outcomes. Transcranial magnetic stimulation (TMS) is a common method to probe CST connectivity. However, TMS is limited to children without seizures. Mirror movements (MM), an involuntary imitation of movements by one limb during the contralateral limb voluntary movements, are common in USCP. MM may result when both UEs are controlled by the contralesional motor cortex. Here we investigated the relationship between MM and CST connectivity in children with USCP. We hypothesized that stronger MM were associated with an ipsilateral connectivity. Our secondary aim was to investigate whether the amount of MM was reduced after intensive therapy. Thirty-three children with USCP (mean age=9yrs 6mos; MACS: I-III) participated and were randomized to receive 90hrs of unimanual (n=16) or bimanual (n=17) intensive training.

Assessments were measured at baseline and immediately after training. We used TMS and diffusion tensor imaging (DTI) to determine the CST connectivity. We used three approaches to quantify MM: 1) behavioral MM assessment during contralateral movements, including hand opening/closing, finger opposition, finger individuation, and finger walking, 2) involuntary grip force oscillations recorded by force transducer (FT) when the contralateral hand performed repetitive pinching, and 3) involuntary muscle contractions measured by electromyography (EMG) when the contralateral hand performed pinching. Results showed that strong MM (scores ≥3) in the more-affected hand while hand opening/closing were associated with an ipsilateral pathway (Fisher's exact test, p= 0.02). This association was not found in the remaining tasks (Fisher’s exact test, opposition, p≥ 0.99; individuation, p≥ 0.99; finger walking, p≥ 0.99). Involuntary GF oscillations were measured in a subset of 16 children. Presence of FT-measured MM in the less-affected hand (> 0.3N) was not associated with TMS-probed connectivity (Fisher’s exact test, p= 0.59).

Nevertheless, presence of FT-measured MM was associated with DTI-assessed connectivity (Fisher’s exact test, p= 0.0498). Similarly, presence of EMG-measured MM in the more-affected hand was not associated with TMS-probed connectivity (Fisher’s exact test, p= 0.59). Nevertheless, presence of EMG-measured MM was associated with DTI-assessed connectivity (Fisher’s exact test, p= 0.03). The amount of MM did not change after training (p> 0.06 among all measures). In conclusion, strong MM in the more-affected hand while hand opening/closing may be indicative of an ipsilateral connectivity identified by TMS. Presence of MM measured by FT may be a predictor of DTI-assessed CST pattern. Findings of this study may help researchers and clinicians understand the relationship between the CST connectivity and its behavioral manifestation in children with USCP. Such relationship may further guide therapeutic strategies in a wider range of children with USCP.