[The functional significance of the basal ganglia-thalamo-cortical loop in gait control in humans: a neuroimaging approach].

The basic locomotor modules located in the brainstem and the spinal cord can control elements of gait movement independently from other structures. Although these locomotor modules are considered to be acquired innately, their higher-level control is important in primates, especially in humans, who employ bipedal gait to adapt to the external environment. The basal ganglia-thalamo-cortical loops are involved in higher-leveled gait control. These loops are composed of several parallel, segregated, and functionally distinct, but homologous, neural circuits. The motor loop originates from the motor cortices, namely, the primary motor cortex, supplementary motor area (SMA), and lateral premotor cortex, and projects to the somatomotor region of the basal ganglia, thereby controlling voluntary movement. Dysfunction of the basal ganglia-thalamo-SMA loop results in gait disturbance in Parkinson disease and vascular parkinsonism. The dysfunction of the SMA loop could be compensated for by the activation of the lateral premotor cortex, the function of which appears to be preserved under appropriate external stimuli in parkinsonian patients.