Audiograms, gap detection thresholds, and frequency difference limens in cannabinoid receptor 1 knockout mice.

The cannabinoid receptor 1 (CB1R) is found at several stages in the auditory pathway, but its role in hearing is unknown. Hearing abilities were measured in CB1R knockout mice and compared to those of wild-type mice. Operant conditioning and the psychophysical Method of Constant Stimuli were used to measure audiograms, gap detection thresholds, and frequency difference limens in trained mice using the same methods and stimuli as in previous experiments. CB1R knockout mice showed deficits at frequencies above 8 kHz in their audiograms relative to wild-type mice. CB1R knockouts showed enhancements for detecting gaps in low-pass noisebursts relative to wild-type mice, but were similar for other noise conditions. Finally, the two groups of mice did not differ in their frequency discrimination abilities as measured by the frequency difference limens task. These experiments suggest that the CB1R is involved in auditory processing and lay the groundwork for future physiological experiments.

Discrimination of partial from whole ultrasonic vocalizations using a go/no-go task in mice.

Mice are a commonly used model in hearing research, yet little is known about how they perceive conspecific ultrasonic vocalizations (USVs). Humans and birds can distinguish partial versions of a communication signal, and discrimination is superior when the beginning of the signal is present compared to the end of the signal. Since these effects occur in both humans and birds, it was hypothesized that mice would display similar facilitative effects with the initial portions of their USVs. Laboratory mice were tested on a discrimination task using operant conditioning procedures. The mice were required to discriminate incomplete versions of a USV target from a repeating background containing the whole USV. The results showed that the mice had difficulty discriminating incomplete USVs from whole USVs, especially when the beginning of the USVs were presented. This finding suggests that the mice perceive the initial portions of a USV as more similar to the whole USV than the latter parts of the USV, similar to results from humans and birds.

Discrimination of ultrasonic vocalizations by CBA/CaJ mice (Mus musculus) is related to spectrotemporal dissimilarity of vocalizations.

The function of ultrasonic vocalizations (USVs) produced by mice (Mus musculus) is a topic of broad interest to many researchers. These USVs differ widely in spectrotemporal characteristics, suggesting different categories of vocalizations, although this has never been behaviorally demonstrated. Although electrophysiological studies indicate that neurons can discriminate among vocalizations at the level of the auditory midbrain, perceptual acuity for vocalizations has yet to be determined. Here, we trained CBA/CaJ mice using operant conditioning to discriminate between different vocalizations and between a spectrotemporally modified vocalization and its original version. Mice were able to discriminate between vocalization types and between manipulated vocalizations, with performance negatively correlating with spectrotemporal similarity. That is, discrimination performance was higher for dissimilar vocalizations and much lower for similar vocalizations. The behavioral data match previous neurophysiological results in the inferior colliculus (IC), using the same stimuli. These findings suggest that the different vocalizations could carry different meanings for the mice. Furthermore, the finding that behavioral discrimination matched neural discrimination in the IC suggests that the IC plays an important role in the perceptual discrimination of vocalizations.