Noise Degrades Listening Processes And Learning & Memory

The impacts on health of chronic exposure to moderate,nontraumatic level of noise(at ～60-80 d B SPL),which is commonplace in modern home and workplace environments,are not well characterized and often ignored.Earlier studies have shown that this nontraumatic noise has potential negative effects on auditory and learning-memory systems,the underlying synaptic mechanisms,however,remain largely unknown.In this study,rats were exposed to moderate-level noise(～65 d B SPL)for 10 hours each day between postnatal 9(p9)and p56.Using the rat model of moderate-level noise exposure,we found that: 1)While noise exposure had little effect on peripheral auditory function,it significantly impaired the performance of rats in the auditory discrimination task.Nosie exposure also degraded the temporal and spectral responses of neurons in the primary auditory cortex.These changes were attributed to the persistently altered inhibitory synaptic input as a result of noise exposure.2)Noise exposure significantly degraded hippocampus-related learning and memory function as shown by the performance in the Morris water maze,Y-maze test and the new object recognition test.The synaptic transmission efficiency in hippocampus was also persistently decreased for at least 8 weeks.In parallel,the total or phosphorylation levels of certain LTP-related key signaling molecules in synapses of the hippocampus were down-regulated after the high frequency stimulation.However,no measurable changes in the stress-related process were found for the noise-exposed animals.These results in a rodent model suggest that even moderate-intensity noise with little effect on peripheral hearing and stress status can substantially impair auditory-related and hippocampus-related function.They argue strongly for the importance of more completely defining these possible hitherto-unappreciated hazards of noise pollution in modern human environments.