Visual modulation of auditory evoked potentials in the cat.

Visual modulation of the auditory system is not only a neural substrate for multisensory processing, but also serves as a backup input underlying cross-modal plasticity in deaf individuals. Event-related potential (ERP) studies in humans have provided evidence of a multiple-stage audiovisual interactions, ranging from tens to hundreds of milliseconds after the presentation of stimuli. However, it is still unknown if the temporal course of visual modulation in the auditory ERPs can be characterized in animal models. EEG signals were recorded in sedated cats from subdermal needle electrodes. The auditory stimuli (clicks) and visual stimuli (flashes) were timed by two independent Poison processes and were presented either simultaneously or alone. The visual-only ERPs were subtracted from audiovisual ERPs before being compared to the auditory-only ERPs. N1 amplitude showed a trend of transiting from suppression-to-facilitation with a disruption at ~ 100-ms flash-to-click delay. We concluded that visual modulation as a function of SOA with extended range is more complex than previously characterized with short SOAs and its periodic pattern can be interpreted with "phase resetting" hypothesis.

Visually evoked potentials (VEPs) across the visual field in hearing and deaf cats.

Introduction: Congenitally deaf cats perform better on visual localization tasks than hearing cats, and this advantage has been attributed to the posterior auditory field. Successful visual localization requires both visual processing of the target and timely generation of an action to approach the target. Activation of auditory cortex in deaf subjects during visual localization in the peripheral visual field can occur either via bottom-up stimulus-driven and/or top-down goal-directed pathways. Methods: In this study, we recorded visually evoked potentials (VEPs) in response to a reversing checkerboard stimulus presented in the hemifield contralateral to the recorded hemisphere in both hearing and deaf cats under light anesthesia. Results: Although VEP amplitudes and latencies were systematically modulated by stimulus eccentricity, we found little evidence of changes in VEP in deaf cats that can explain their behavioral advantage. A statistical trend was observed, showing larger peak amplitudes and shorter peak latencies in deaf subjects for stimuli in the near- and mid-peripheral field. Additionally, latency of the P1 wave component had a larger inter-sweep variation in deaf subjects. Discussion: Our results suggested that cross-modal plasticity following deafness does not play a major part in cortical processing of the peripheral visual field when the "vision for action" system is not recruited.

Differences in auditory associative memory between younger adults and older adults.

Aging impairs visual associative memories. Up to date, little is known about whether aging impairs auditory associative memories. Using the head-related-transfer function to induce perceived spatial locations of auditory phonemes, this study used an audiospatial paired-associates-learning (PAL) paradigm to assess the auditory associative memory for phoneme-location pairs in both younger and older adults. Both aging groups completed the PAL task with various levels of difficulty, which were defined by the number of items to be remembered. The results showed that compared with younger participants' performance, older participants passed fewer stages and had lower capacity of auditory associative memory. For maintaining a single audiospatial pair, no significant behavioral differences between the two aging grous werefound. However, when multiple sound-location pairs were required to be remembered, older adults made more errors and demonstrated a lower working memory capacity than younger adults. Our study indicates aging impairs audiospatial associative learning and memory.

Looming Effects on Attentional Modulation of Prepulse Inhibition Paradigm.

In a hazardous environment, it is fundamentally important to successfully evaluate the motion of sounds. Previous studies demonstrated "auditory looming bias" in both macaques and humans, as looming sounds that increased in intensity were processed preferentially by the brain. In this study on rats, we used a prepulse inhibition (PPI) of the acoustic startle response paradigm to investigate whether auditory looming sound with intrinsic warning value could draw attention of the animals and dampen the startle reflex caused by the startling noise. We showed looming sound with a duration of 120 ms enhanced PPI compared with receding sound with the same duration; however, when both sound types were at shorter duration/higher change rate (i.e., 30 ms) or longer duration/lower rate (i.e., more than 160 ms), there was no PPI difference. This indicates that looming sound-induced PPI enhancement was duration dependent. We further showed that isolation rearing impaired the abilities of animals to differentiate looming and receding prepulse stimuli, although it did not abolish their discrimination between looming and stationary prepulse stimuli. This suggests that isolation rearing compromised their assessment of potential threats from approaching objects and receding objects.

The limited capacity of visual temporal integration in cats.

It has been long known that prolonging stimulus duration may increase the perceived brightness of a visual stimulus. The interaction between intensity and duration generally follows a rule, such as that described in Bloch's law. This visual temporal integration relationship has been identified in human subjects and in non-human primates. However, although auditory temporal integration has been extensively studied in the cat, visual temporal integration has not. Therefore, the goal of this study was to examine visual temporal integration in the cat. We trained five cats to respond when a brief luminance change was detected in a fixation dot. After training, we measured the success rate of detecting the luminance change with varying durations at threshold, subthreshold, and suprathreshold luminance levels. Psychometric functions showed that prolonging stimulus duration improved task performance, more noticeably for stimuli below 100 ms than beyond. Most psychometric functions were better fit to an exponential model than to a linear model. The gradually saturated performance observed here, as in previous studies, can be explained by the "leaky integrator" hypothesis, that is, temporal integration is only valid below a critical duration. Overall, we developed a task whereby visual temporal integration was successfully demonstrated in the cat. The effect of stimulus duration on detection success rate displayed a pattern generally consistent with previous human and non-human primate findings on visual temporal integration.

Both Val158Met Polymorphism of Catechol-O-Methyltransferase Gene and Menstrual Cycle Affect Prepulse Inhibition but Not Attentional Modulation of Prepulse Inhibition in Younger-Adult Females.

Prepulse inhibition (PPI) can be modulated by both the Val158Met (rs4680) polymorphism of the Catechol-O-Methyltransferase (COMT) gene and the menstrual-cycle-related hormone fluctuations, each of which affects the subcortical/cortical dopamine metabolism. PPI can also be modulated by attention. The attentional modulation of PPI (AMPPI) is sensitive to psychoses. Whether the Val158Met polymorphism affects the AMPPI in female adults at different menstrual-cycle phases is unknown. This study examined whether AMPPI and/or PPI are affected by the Val158Met polymorphism in 177 younger-adult females whose menstrual cycles were mutually different across the menstruation, proliferative, or secretory phases. The AMPPI was evaluated by comparing PPI under the condition of the auditory precedence-effect-induced perceptual spatial separation between the prepulse stimulus and a masking noise (PPIPSS) against that under the condition of the precedence-effect-induced perceptual spatial co-location (PPIPSC). The results showed that both the menstrual cycle and the COMT Val158Met polymorphism affected both PPIPSC and PPIPSS, but not the AMPPI (difference between PPIPSS and PPIPSC). Moreover, throughout the menstrual cycle, both PPIPSC and PPIPSS decreased monotonously in Val/Val-carrier participants. However, the decreasing pattern was not overserved in either Met/Met-carrier or Met/Val-carrier participants. Thus, in healthy younger-adult females, PPIPSC and PPIPSS, but not the AMPPI, is vulnerable to changes of ovarian hormones, and the COMT Val158Met polymorphism also has a modulating effect on this menstrual-cycle-dependent PPI variation. In contrast, the AMPPI seems to be more steadily trait-based, less vulnerable to ovarian hormone fluctuations, and may be useful in assisting the diagnosis of schizophrenia in female adults.

Emotionally conditioning the target-speech voice enhances recognition of the target speech under "cocktail-party" listening conditions.

Under a noisy "cocktail-party" listening condition with multiple people talking, listeners can use various perceptual/cognitive unmasking cues to improve recognition of the target speech against informational speech-on-speech masking. One potential unmasking cue is the emotion expressed in a speech voice, by means of certain acoustical features. However, it was unclear whether emotionally conditioning a target-speech voice that has none of the typical acoustical features of emotions (i.e., an emotionally neutral voice) can be used by listeners for enhancing target-speech recognition under speech-on-speech masking conditions. In this study we examined the recognition of target speech against a two-talker speech masker both before and after the emotionally neutral target voice was paired with a loud female screaming sound that has a marked negative emotional valence. The results showed that recognition of the target speech (especially the first keyword in a target sentence) was significantly improved by emotionally conditioning the target speaker's voice. Moreover, the emotional unmasking effect was independent of the unmasking effect of the perceived spatial separation between the target speech and the masker. Also, (skin conductance) electrodermal responses became stronger after emotional learning when the target speech and masker were perceptually co-located, suggesting an increase of listening efforts when the target speech was informationally masked. These results indicate that emotionally conditioning the target speaker's voice does not change the acoustical parameters of the target-speech stimuli, but the emotionally conditioned vocal features can be used as cues for unmasking target speech.

The role of N-methyl-D-aspartate receptors and metabotropic glutamate receptor 5 in the prepulse inhibition paradigms for studying schizophrenia: pharmacology, neurodevelopment, and genetics.

Treatments for the positive and negative symptoms of schizophrenia have been explored for decades, but no completely successful therapy has been found as yet. Metabotropic glutamate receptor 5 (mGluR5), which potentiates N-methyl-D-aspartate receptors in brain regions implicated in schizophrenia, has become a novel drug target in the treatment of schizophrenia, especially for the mGluR5-positive allosteric modulators. Individuals with schizophrenia show deficits in prepulse inhibition (PPI), which is an operational measurement of sensorimotor gating. In this review, we focus on pharmacological, neurodevelopmental, and genetic animal models of disrupted PPI, with the aim of showing the potential role of mGluR5 in modulating the activity of N-methyl-D-aspartate receptors and their contributions toward the treatment of schizophrenia. As, the impairment of attentional modulation of PPI, but not that of baseline PPI, in individuals with schizophrenia is correlated with their symptom severity, this review also highlights that investigation of attentional modulation of PPI is critical for studying both cognitive impairments and glutamatergic dysfunctions of schizophrenia.

The role of the temporal pole in modulating primitive auditory memory.

Primitive auditory memory (PAM), which is recognized as the early point in the chain of the transient auditory memory system, faithfully maintains raw acoustic fine-structure signals for up to 20-30 milliseconds. The neural mechanisms underlying PAM have not been reported in the literature. Previous anatomical, brain-imaging, and neurophysiological studies have suggested that the temporal pole (TP), part of the parahippocampal region in the transitional area between perirhinal cortex and superior/inferior temporal gyri, is involved in auditory memories. This study investigated whether the TP plays a role in mediating/modulating PAM. The longest interaural interval (the interaural-delay threshold) for detecting a break in interaural correlation (BIC) embedded in interaurally correlated wideband noises was used to indicate the temporal preservation of PAM and examined in both healthy listeners and patients receiving unilateral anterior temporal lobectomy (ATL, centered on the TP) for treating their temporal lobe epilepsy (TLE). The results showed that patients with ATL were still able to detect the BIC even when an interaural interval was introduced, regardless of which ear was the leading one. However, in patient participants, the group-mean interaural-delay threshold for detecting the BIC under the contralateral-ear-leading (relative to the side of ATL) condition was significantly shorter than that under the ipsilateral-ear-leading condition. The results suggest that although the TP is not essential for integrating binaural signals and mediating the PAM, it plays a role in top-down modulating the PAM of raw acoustic fine-structure signals from the contralateral ear.