Efferent control of neuronal activity in the central nucleus of the inferior colliculus by the primary auditory cortex was studied using a novel photo-dynamic technique realizing direct and reversible inactivation of neuronal activity in focused areas of the brain in minutes. We used a near-infrared diode laser (wavelength, 830 nm; power density, 1.2-4.8 W/cm²) for the inactivation study. The laser-induced inactivation is thought to be brought about via reversible change of membrane property; hyperpolarization of membrane potential and decrease in membrane resistance. Laser irradiation to the primary auditory cortex through the dura mater reversibly depressed the spontaneous neuronal activity and auditory responses to the acoustic stimuli in the irradiated area within 5-10 minutes. The photo-dynamic inactivation of the primary auditory cortex synchronously changed neuronal activity in the central nucleus of the inferior colliculus; facilitation or inhibition of auditory responses and/or spontaneous (background) activity, and shortening or prolongation of latency period of auditory responses. This study demonstrated patterns in control of neuronal activity in the central nucleus of the inferior colliculus by the primary auditory cortex. [Jpn J Physiol 54 Suppl:S24 (2004)]