Understanding how communication sounds are processed and encoded in the central auditory system is critical to understanding the neural bases of acoustic communication. Here, we examined neuronal representations of species-specific vocalizations, which are communication sounds that many species rely on for survival and social interaction. In some species, the evoked responses of auditory cortex neurons are stronger in response to natural conspecific vocalizations than to their time-reversed, spectrally identical, counterparts. We applied information theory-based analyses to single-unit spike trains collected in the auditory cortex (n ϭ 139) and auditory thalamus (n ϭ 135) of anesthetized animals as well as in the auditory cortex (n ϭ 119) of awake guinea pigs during presentation of four conspecific vocalizations. Few thalamic and cortical cells (Ͻ10%) displayed a firing rate preference for the natural version of these vocalizations. In contrast, when the information transmitted by the spike trains was quantified with a temporal precision of 10 -50 ms, many cells (Ͼ75%) displayed a significant amount of information (i.e., Ͼ2SD above chance levels), especially in the awake condition. The computed correlation index between spike trains (R corr , defined by Schreiber et al., 2003) indicated similar spike-timing reliability for both the natural and time-reversed versions of each vocalization, but higher reliability for awake animals compared with anesthetized animals. Based on temporal discharge patterns, even cells that were only weakly responsive to vocalizations displayed a significant level of information. These findings emphasize the importance of temporal discharge patterns as a coding mechanism for natural communication sounds, particularly in awake animals.

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This prospective study demonstrated that direct-drive stimulation provided by the VSB allows better speech performances than acoustic stimulation for rehabilitation of patients with steeply sloping high-frequency hearing losses.

Hemispheric fine-grain maps of primary auditory cortex (AI) were derived from microelectrode penetrations in the temporal gyrus of the common marmoset (Callithrix jacchus) to 1) compare the functional organization of AI in the marmoset with other mammalian species and 2) compare the right and left AI maps in individual monkeys. Frequency receptive fields (FRFs) were recorded with pure tones. Five FRF parameters were analyzed: characteristic frequency, threshold, sharpness of tuning 10 dB and 40 dB above threshold, and minimum response latency. The present study confirms that the functional organization of AI is characterized by a robust tonotopic frequency gradient overlaid with spatially clustered distributions of other FRF parameters. Globally, this functional organization of AI in the common marmoset is similar to that in other mammalian species. With respect to within-subject hemispheric comparisons of the five FRF parameters, a coherent pattern of asymmetry is not evident in marmoset AI. The overall results indicate that the basic functional organization between hemispheres is similar but not identical.

Objective-Auditory processing diYculties have been reported in schizophrenia. This study explores peripheral auditory function in patients with schizophrenia in whom certain early disturbances of auditory message filtering have been found and may be associated with certain abnormalities which are particularly localised in the left temporal lobe. Methods-Otoacoustic emissions, including click evoked and spontaneous emissions and measurements of functioning of the medial olivocochlear eVerent system were obtained from 12 chronic schizophrenic patients and compared with normative data recorded from 12 normal controls. Results-Otoacoustic emission amplitudes and medial olivocochlear functioning were similar between the normal controls and schizophrenic patients; the schizophrenic patients did, however, diVer from the normal controls in otoacoustic emission intensity and in medial olivocochlear asymmetry. A tendency to a higher number of spontaneous peaks, and a significantly higher click evoked otoacoustic emission response amplitude were found in the right ear compared with the left ear of schizophrenic patients. For the medial olivocochlear system, whereas normal controls showed greater attenuation in the right than in the left ear, schizophrenic patients lacked such an asymmetry. Conclusion-In the absence of any attention task, the findings show disturbed peripheral lateralisation in schizophrenia of mechanisms involved in auditory information filtering. Such a lack of right ear advantage in medial olivocochlear functioning may thus be a peripheral reflection of central lateralisation anomalies. (J Neurol Neurosurg Psychiatry 2001;70:88-94)

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