A method for treating a subject having Parkinson's disease or Alzheimer'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 between about 10 mW/cm2 to about 10 W/cm2 and (ii) transmitting a portion of the light energy through the scalp and the skull to the brain, wherein the transmitted light energy has a power density of at least about 0.01 mW/cm2 at a depth of approximately 2 centimeters below the dura.