This is a prospective interventional study involving young children who will all receive non-invasive, passive assessments of sensory and motor function. In addition a subpopulation of young children with cerebral palsy will participate in a randomized controlled trial of constraint-induced movement therapy, a routinely prescribed therapy used in clinical practice for children with motor difficulties. The study attempts to apply a rigorous scientific approach to study a widely used but poorly studied practice. The design is an RCT with wait-list controls to allow all children to benefit from the therapy, even if they are randomized to the control group. All children, regardless of group allocation will continue with their standard of care occupational and physical therapy throughout the study.

Cerebral palsy (CP) is the most common physical disability in childhood.1 It affects 3.6/100 children in the US2 with ~10,000 new diagnoses every year. The prevalence of CP in developing countries is estimated to be ~5-10 times greater. CP is a disorder resulting from sensory and motor impairments due to perinatal brain injury, with lifetime consequences that range from poor adaptive and social function to communication and emotional disturbances,9 all contributing to a shortened life expectancy. The societal costs are difficult to estimate but the financial burden is well over $1 M per life affected. A growing number of evidence-based therapies aim to improve gross motor function through changes in body structures and function in children with CP (e.g. hip surveillance, surgery). However, infants with CP have a fundamental disadvantage in recovering motor function: they do not receive accurate sensory feedback from their movements, leading to neglect of an affected extremity and difficulty learning new movements, a process called developmental disregard (DD). As a consequence, even children who receive time- and resource-intensive standard therapies have stable or declining motor function and developmental trajectories that do not "catch up" to those of typically developing children. DD can then lead to school-age learning problems, decreased participation in physical and social activities and costly long-term mental and physical morbidities.

Constraint-Induced Movement Therapy (CIMT) is one of the few effective neurorehabilitative strategies shown to improve upper extremity motor function in adults and older children with CP, potentially overcoming developmental disregard. It is mainly applicable to CP patients who are diagnosed with asymmetric or hemiparetic forms of the disorder, in which one side of the body is more affected than the other. CIMT is based on the premise that preferential use of an affected upper extremity (by constraining the less affected one), and shaping with repetition of movement by skilled therapists, can overcome neglect and restore function of that extremity.

The investigators are conducting a randomized trial of CIMT in children with CP using a wait-list control group. This design allows every child with CP to eventually receive the treatment and avoids issues of equipoise. The RCT portion of the study extends only for a 7-month period, from baseline to 6 months after the 1-month CIMT ends. For CP wait-listed controls, the study continues for 6 months following the CMIT intervention, separate from the completed RCT. We will reference data from both groups to a cohort of typically developing (TD) children to determine developmental trajectories.

Inclusion Criteria:

• CP children (n=72): Inclusion criteria will be diagnosis of hemiparetic or asymmetric CP as determined by published algorithms and neurologic exam.
• TD children (n=144): Inclusion criteria will be GA and sex-matched compared to the CP group, with CA at assessment matched to the CP group at baseline (72 children) and at the 7-month assessment (72 children). Exclusion criteria will be any motor or sensory impairment as defined by neurologic exam and/or scaled motor scores below 8 for CA on the Bayley III and cognitive impairment or delays as described for the CP group.

Exclusion Criteria:

• CP children: exclusion criteria will be CP with Gross Motor Function Classification Score (GMFCS) of 4-5, corresponding to poor or absent mobility and neck control; receipt of Botox to the affected extremity within 3 months of study entry; or scores of <70 on the Bayley Scales of Infant Development (Bayley III) cognitive composite.
• TD children: Exclusion criteria will be any motor or sensory impairment as defined by neurologic exam and/or scaled motor scores below 8 for CA on the Bayley III and cognitive impairment or delays as described for the CP group.