Central auditory metabolic activity induced by intense noise exposure

Neural activity in the central auditory system was mapped by measuring 2-deoxyglucose (2-DG) uptake during a one hour exposure to a two-octave (1414-5656 Hz) band of noise. Gerbils were exposed to 100, 110 or 120 dB SPL, intensities which can produce only temporary (100 dB) or both temporary and permanent (120 dB) hearing loss. Exposure to 100 dB SPL evoked high levels of neural activity throughout responsive regions of auditory nuclei. At 110 dB SPL, a central region of low neural activity was surrounded by areas exhibiting increased activity. At 120 dB SPL, neural activity was low in almost all areas of auditory nuclei. To study the effects of permanent hearing loss on auditory neuronal activity, other animals were given 2-DG during exposure to 65 dB SPL broad band noise as a test stimulus, two months after exposure to the noise band at 110 dB SPL. Central auditory nuclei showed a tonotopic region of low neural activity corresponding to an approximately 3 kHz pure tone, surrounded by regions of evoked activity. The deficits in evoked metabolic activity observed both during and long after noise exposure appear to exceed those predicted from the degree of temporary and permanent threshold shift produced by the same noise exposures.