Auditory steady-state responses in primary and non-primary regions of the auditory cortex in neonatal ventral hippocampal lesion rats.

Auditory steady-state responses (ASSRs) represent the electrophysiological activity of the auditory nervous system in response to a periodic acoustic stimulus. Spectrogram analysis can reveal the frequency and phase information entrained in ASSRs. Clinically, the ASSR is used to detect abnormalities in electroencephalographs obtained from schizophrenia patients, who show reduced power and phase locking of ASSRs. The neonatal ventral hippocampal lesion (NVHL) rat is a widely used model to investigate the neurodevelopmental mechanisms of schizophrenia. It has been established that NVHL rats exhibit several schizophrenia-like behavioral and molecular abnormalities. However, no clear abnormalities in ASSRs have been reported to date. The present study compared ASSRs of adult NVHL and sham-operated rats. We inserted microelectrodes into the primary auditory cortex (A1) or posterior auditory field (PAF) and recorded the local field potential (LFP) in response to 40- and 80-Hz click train stimuli. Spectrogram analysis was performed to obtain the mean trial power (MTP) and phase-locking factor (PLF) of the click train-evoked LFPs. We found that in the control animals, A1 showed a stronger MTP and PLF of ASSR than PAF, and NVHL operation mainly impaired the ASSR in PAF. Analysis of spike activity also indicated that NVHL operation extended the duration of tone-evoked responses in PAF neurons. Our results reveal, for the first time, that NVHL may distinctly influence the neural activities of primary and non-primary fields of the auditory cortex.

Engaging in a tone-detection task differentially modulates neural activity in the auditory cortex, amygdala, and striatum.

The relationship between attention and sensory coding is an area of active investigation. Previous studies have revealed that an animal's behavioral state can play a crucial role in shaping the characteristics of neural responses in the auditory cortex (AC). However, behavioral modulation of auditory response in brain areas outside the AC is not well studied. In this study, we used the same experimental paradigm to examine the effects of attention on neural activity in multiple brain regions including the primary auditory cortex (A1), posterior auditory field (PAF), amygdala (AMY), and striatum (STR). Single-unit spike activity was recorded while cats were actively performing a tone-detection task or passively listening to the same tones. We found that tone-evoked neural responses in A1 were not significantly affected by task-engagement; however, those in PAF and AMY were enhanced, and those in STR were suppressed. The enhanced effect was associated with an improvement of accuracy of tone detection, which was estimated from the spike activity. Additionally, the firing rates of A1 and PAF neurons decreased upon motor response (licking) during the detection task. Our results suggest that attention may have different effects on auditory responsive brain areas depending on their physiological functions.

Effect of chronic restraint stress on inhibitory gating in the auditory cortex of rats.

A fundamental adaptive mechanism of auditory function is inhibitory gating (IG), which refers to the attenuation of neural responses to repeated sound stimuli. IG is drastically impaired in individuals with emotional and cognitive impairments (i.e. posttraumatic stress disorder). The objective of this study was to test whether chronic stress impairs the IG of the auditory cortex (AC). We used the standard two-tone stimulus paradigm and examined the parametric qualities of IG in the AC of rats by recording the electrophysiological signals of a single-unit and local field potential (LFP) simultaneously. The main results of this study were that most of the AC neurons showed a weaker response to the second tone than to the first tone, reflecting an IG of the repeated input. A fast negative wave of LFP showed consistent IG across the sampled AC sites, whereas a slow positive wave of LFP had less IG effect. IG was diminished following chronic restraint stress at both, the single-unit and LFP level, due to the increase in response to the second tone. This study provided new evidence that chronic stress disrupts the physiological function of the AC. Lay Summary The effects of chronic stress on IG were investigated by recording both, single-unit spike and LFP activities, in the AC of rats. In normal rats, most of the single-unit and N25 LFP activities in the AC showed an IG effect. IG was diminished following chronic restraint stress at both, the single-unit and LFP level.