Abstract
Cortical representation of time-varying features of acoustic signals is a fundamental issue of acoustic processing remaining unresolved. The rat is a widely used animal model for auditory cortical processing. Though some electrophysiological studies have investigated the neural responses to temporal repetitive sounds in the auditory cortex (AC) of rats, most of them were conducted under anesthetized condition. Recently, it has been shown that anesthesia could significantly alter the temporal patterns of neural response. For this reason, we systematically examined the single-unit neural responses to click-trains in the core region of rat AC under awake condition. Consistent with the reports on anesthetized rats, we confirmed the existence of characteristic tonotopic organizations, which were used to divide the AC into anterior auditory field (AAF), primary auditory cortex (A1) and posterior auditory field (PAF). We further found that the neuron's capability to synchronize to the temporal repetitive stimuli progressively decreased along the anterior-to-posterior direction of AC. The median of maximum synchronization rate was 64, 32 and 16 Hz in AAF, A1 and PAF, respectively. On the other hand, the percentage of neurons, which showed non-synchronized responses and could represent the stimulus repetition rate by the mean firing rate, increased from 7% in AAF and A1 to 20% in PAF. These results suggest that the temporal resolution of acoustic processing gradually increases from the anterior to posterior part of AC, and thus there may be a hierarchical stream along this direction of rat AC.
Highlights
Both human speech and animal vocalizations are characterized by a low-frequency temporal modulation [1]
Some previous studies investigated the neural responses to temporal modulated sounds in the auditory cortex (AC) of rats. They found that the majority of AC neurons exhibited a sequence of transient discharges synchronized with the temporal envelope of sound stimulus, and the maximum repetition rate that can evoked the synchronous neural responses was generally lower than 20 Hz [5,6,7]
According to the reports of anesthetized rats, the reversals of BF gradient could be used to define the boundaries between anterior auditory field (AAF), A1 and posterior auditory field (PAF) [5,6,7,12,13,14,15]
Summary
Both human speech and animal vocalizations are characterized by a low-frequency temporal modulation [1]. The representation of temporal information by auditory cortex (AC) neurons has been studied in various animal models and different animal preparations (for reviews see [2,3]). The laboratory rat is a kind of important animal model for studies of auditory cortical function. Some previous studies investigated the neural responses to temporal modulated sounds in the AC of rats. They found that the majority of AC neurons exhibited a sequence of transient discharges synchronized with the temporal envelope of sound stimulus, and the maximum repetition rate that can evoked the synchronous neural responses was generally lower than 20 Hz [5,6,7]. It is necessary to examine the temporal processing of AC neurons in the awake rats
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