The Neuronal Responses to Repetitive Acoustic Pulses in Different Fields of the Auditory Cortex of Awake Rats

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.

Auditory response properties of neurons in the putamen and globus pallidus of awake cats

“…More than 60% of thalamic neurons in marmosets could synchronize to 200-Hz repetition rate (Bartlett and Wang 2007). It was also reported that some of thalamic and cortical neurons show nonsynchronized discharge throughout the entire duration of repetitive stimulus (Bartlett and Wang 2007;Dong et al 2011;Lu et al 2001;Ma et al 2013b). Such sustained responses were rarely found in our data.…”

The Role of Inhibition in a Computational Model of an Auditory Cortical Neuron during the Encoding of Temporal Information

“…While non-synchronized responses have been reported in several different species (e.g. monkey [ 14 , 17 – 18 ], cat [ 19 ], and rat [ 51 ]), many previous studies have only reported stimulus-synchronized responses in auditory cortex. Our model provides several suggestions why this may be the case.…”

Predictive cues for auditory stream formation in humans and monkeys

“…There is some evidence that at least two different processes can affect neuronal responses to isochronous stimuli: repetition‐following (Wang & Scheich, ) or an increase in baseline activity (Heinemann et al ., ; Keceli et al ., ). How can our finding of no main effect of isochrony be reconciled with evidence that modulation rate (Kilgard & Merzenich, ) and repetition time (Phillips et al ., ; Bendor & Wang, ; Dong et al ., ; Ma et al ., ; Recasens et al ., ) are encoded in the auditory cortex and can affect neuronal activity? One solution to this apparent paradox is that not all neurons encode all stimuli and the sparseness of the representation of repetition rate in the primary auditory cortex might preclude any global effects of predictable isochronous sequences across the entire population of neurons.…”