A method for treating a subject having Parkinson's disease is provided. The method includes noninvasively delivering light energy having a wavelength of about 630 nanometers to about 904 nanometers to the brain of the subject. Delivering the light energy can include (i) irradiating the scalp with light energy having an incident power density less than 1000 mW/cm2 and (ii) transmitting a portion of the light energy through the scalp and the skull to the brain.