Objective: Little is known about the effects of reduced sensory input and motor output in the human brain. Therefore, we conducted a longitudinal study to investigate whether limb immobilization after unilateral arm injury is reflected in structural plastic changes in gray matter (cortical thickness) and white matter (fractional anisotropy [FA]).
Methods: We examined 10 right-handed subjects with injury of the right upper extremity that required at least 14 days of limb immobilization. Subjects underwent 2 MRI examinations, the first within 48 hours postinjury and the second after an average time interval of 16 days of immobilization. Based on the MRI scans, we measured cortical thickness of sensorimotor regions and FA of the corticospinal tracts.
Results: After immobilization, we revealed a decrease in cortical thickness in the left primary motor and somatosensory area as well as a decrease in FA in the left corticospinal tract. In addition, the motor skill of the left (noninjured) hand improved and is related to increased cortical thickness and FA in the right motor cortex.
Conclusions: The present study illustrates that cortical thickness of the sensorimotor cortex and FA of the corticospinal tract changed during right arm immobilization and that these changes are associated with skill transfer from the right to the left hand. Thus, immobilization induces rapid reorganization of the sensorimotor system. Given that limb immobilization is a standard intervention technique in constraint-induced therapy, therapists should be aware of both the positive and negative effects of this intervention.