Brain activation patterns underlying upper limb bilateral motor coordination in unilateral cerebral palsy: an fNIRS study

Aim To explore cortical activation during bimanual tasks and functional correlates in unilateral cerebral palsy (CP). Method This cross-sectional study included eight participants with unilateral CP (six females, two males; mean age [SD] 20y 10mo [5y 10mo], 13y 8mo-31y 6mo) in Manual Ability Classification System levels II to III and nine age-matched participants with typical development (seven females, two males; mean age [SD] 17y 8mo [5y 7mo], 9y 4mo-24y 2mo). They performed bimanual symmetric squeezing (BSS) and bimanual asymmetric squeezing (BAS) tasks at 1Hz, and a pouring task with dominant hand (DPour) and a pouring task with non-dominant hand (NDPour) at 0.67Hz, all while a custom array of functional near-infrared spectroscopy (fNIRS) optodes were placed over their sensorimotor area. Mixed-effects were used to contrast groups, tasks, and hemispheres (corrected p-values [q] reported). Analysis of variance and t-tests compared performance measures across groups and tasks. Results Participants with unilateral CP showed greater activation in both hemispheres during BAS (non-lesioned: qq<0.001), and in the lesioned hemisphere during BSS (q<0.001), DPour (q=0.02), and NDPour (q=0.02) than those with typical development. The lesioned hemisphere in unilateral CP showed more activity than the non-lesioned one (BSS: q=0.01; BAS: q=0.009; NDPour: q=0.04). During BAS, higher cortical activity correlated with more synchronous arm activation (r=0.79; p=0.02); activity lateralized towards the non-lesioned hemisphere correlated with better Pediatric Evaluation of Disability Inventory computer adaptive test scores (r=0.81; p=0.03). Interpretation Results suggest abnormally increased sensorimotor cortical activity in unilateral CP, with implications to be investigated. What this paper adds Cortical activity in manual tasks is described with functional near-infrared spectroscopy in typical and atypical cohorts. Activation levels in unilateral cerebral palsy appear to escalate with task difficulty. Increased brain activity may be associated with poorer selective manual control. Specific patterns of brain activity may be related to impaired bimanual function.