Frequency Tuning Of Auditory Neurons Research Articles

Bottom-Up Driven Involuntary Auditory Evoked Field Change: Constant Sound Sequencing Amplifies But Does Not Sharpen Neural Activity

The capability of involuntarily tracking certain sound signals during the simultaneous presence of noise is essential in human daily life. Previous studies have demonstrated that top-down auditory focused attention can enhance excitatory and inhibitory neural activity, resulting in sharpening of frequency tuning of auditory neurons. In the present study, we investigated bottom-up driven involuntary neural processing of sound signals in noisy environments by means of magnetoencephalography. We contrasted two sound signal sequencing conditions: "constant sequencing" versus "random sequencing." Based on a pool of 16 different frequencies, either identical (constant sequencing) or pseudorandomly chosen (random sequencing) test frequencies were presented blockwise together with band-eliminated noises to nonattending subjects. The results demonstrated that the auditory evoked fields elicited in the constant sequencing condition were significantly enhanced compared with the random sequencing condition. However, the enhancement was not significantly different between different band-eliminated noise conditions. Thus the present study confirms that by constant sound signal sequencing under nonattentive listening the neural activity in human auditory cortex can be enhanced, but not sharpened. Our results indicate that bottom-up driven involuntary neural processing may mainly amplify excitatory neural networks, but may not effectively enhance inhibitory neural circuits.

Vibrotactile suppression of tinnitus

At the Society’s 142nd meeting, the efficacy of high frequency bone conducted stimulation in suppressing tinnitus was presented. The hypothesized mechanism was the reprogramming of frequency tuning of auditory neurons in the central nervous system, secondarily to peripheral hearing loss. This mechanism is unlikely in cases of tinnitus in the presence of normal audiometric sensitivity. There is the possibility that hearing loss above 10 kHz can play a role in tinnitus, an association not thoroughly explored. Somatomotor stimulation influencing the quality of tinnitus has been reported, as have interconnections of the auditory and somatosensory systems. There would appear to be an evolutionary advantage of linking the sensorimotor organization of the external ear and the auditory function of the brainstem in sound localization. Thus, stimulation of the pinna and post auricular area may be a means of suppressing tinnitus. To that end a thin aluminum ceramic bimorph was constructed to fit on the inner surface of the pinna. When driven by low (<100 Hz) and high (>10 kHz) frequencies multiplied by MHz carriers, demodulation in the skin resulted in vibrotactile stimulation. Tactile stimulation was an adjunct to the high frequencies resulting in a multimodal suppressive effect in a small pilot study.

Altered activity patterns during development reduce neural tuning.

Neonatal mice were reared in an acoustic environment that repetitively entrained activity in a large proportion of primary auditory afferents during the period when the frequency tuning of auditory neurons normally develops. The tuning curves obtained from these mice were significantly broader than those of normally reared mice of the same age. This suggests that the normal frequency tuning of neurons was prevented or delayed by synchronizing the pattern of activity imposed on the auditory pathway.