Animals of most species emit vocalizations to communicate each other and to convey
their emotional states. Intraspecific communication consists of the transfer of information
from one or more animals [sender(s)] to one or more conspecifics [receiver(s)] in
order to affect the current or future behaviors of the receiver(s). Vocal communication
may occur both in the audible and ultrasonic frequency ranges and it is subjected
by a complex brain modulation involving multiple areas and neural circuits. Communication
is also impaired in a variety of pathological conditions, such as neurodevelopmental
disorders (autism spectrum disorders, ASD, in particular), and these alterations can
be tackled by pharmacological therapeutic strategies that have been proposed in several
preclinical studies.
One of the most ambitious challenges of animal vocal communication concerns the study
of ultrasonic vocalizations (USVs) in rodents and it consists of fully automatizing
the procedures for spectrographic USV analysis. This would allow bypassing the operator-dependent
and time-consuming analyses that are necessary for the quantitative and qualitative
studies of USVs. This challenge was successfully faced by de Chaumont et al. in this
special issue, as they developed one open-access software to automatically study mouse
USVs. Their system also allowed coupling the spectrographic analysis of USVs with
the automatic labeling of several behaviors scored over a long time-period (i.e.,
3 days), thus providing an additional evaluation of the behavioral value of USVs in
laboratory mice. The method was validated in C57BL/6J mice and also in mutants lacking
the Shank3 gene, i.e., a mouse model of autism, in both sexes and at multiple ages.
Also Goussha et al. developed a new software, the HybridMouse, that is an audio analysis
tool for automatically identifying, labeling, and extracting recorded USVs. The methodological
challenges of automatic processing a large amount of data from audio files does not
concern only mouse ultrasonic communication. Here Marck et al. developed an automatic
system based on audio signal processing algorithms and deep learning and applied to
the vocal repertoire of the White Spectacled Bulbul (Pycnonotus xanthopygos), a bird
species with a complex vocal communication system. Other modern computational methods
for bioacoustics have been developed for the analysis of vocal communication in several
animal species (including fish, amphibians, and insects), as described in detail in
the review by Sainburg and Gentner.
Beside the analysis of the vocalizations emitted by the sender, the response of the
receiving animal to vocalizations deserves to be studied. In rats, two main types
of vocalizations are typically distinguished (Brudzynski, 2013; Wöhr and Schwarting,
2013): vocalizations with frequencies around 22 kHz, that are referred to as aversive
or distress calls, presumably representing a negative affective state (Blanchard et
al., 1991; Fendt et al., 2018), and vocalizations with frequencies around 50 kHz,
that are thought to represent a positive affective state usually emitted during appetitive
situations like play or mating (Knutson et al., 1998; Panksepp, 2005). In this context,
Berz et al. investigated the emission of USVs in response to the playback of natural
50 kHz USVs in male juvenile rats of different strains. Their data demonstrated that
most rats emitted response calls specifically linked to 50-kHz USV playback and these
response calls were mostly characterized by a frequency range of 20–32 kHz and a mean
duration of approximately 300 ms in all rat strains. The possible function of these
type of calls has yet to be clarified, although it was unaffected by the pharmacological
blockade of dopamine D2 receptors by haloperidol administration. In rats, the emission
of USVs can be also promoted by operant conditioning during multiple weeks: this approach
was employed in the study by Johnson et al. where a semi-automated method for training
rats to increase their rate of USV production was introduced.
The impact of social context on animal communication is an issue of critical relevance
that is far from being fully elucidated. Here, Warren et al. studied the ontogeny
of prairie vole pup ultrasonic vocalizations when isolated or when the mother was
present, but physically unattainable. They demonstrated a developmental maturation
in all features of pup vocalizations and the impact of the different social contexts
in modifying vocal emission. Capas-Peneda et al. reviewed instead the role of mouse
USVs in the reproductive context; indeed, they summarized the most recent evidence
demonstrating that USVs have an important role in parental cooperation, inducing both
maternal and paternal behaviors. Bouguiyoud et al. investigated the effects of visual
deprivation in acoustic communication and social behaviors using a mouse model of
congenital blindness. They demonstrated here that congenital visual deprivation had
no effect on the number of USVs emitted in pups and juveniles, but affected the USV
emission in adult males and the social behaviors in juvenile and adult mice. The role
of social isolation on adult USVs and social behaviors was instead assessed in both
male and female mice by Premoli et al. Their study contributed to provide new guidelines
for assessing ultrasonic communication in inbred mice, demonstrating also several
sex differences in ultrasonic communication and social behaviors that were mostly
unaffected by pre-testing social isolation.
Finally, another interesting aspect that has been investigated in a study included
in this special issue concerns the molecular mechanisms underlying vocal communication.
In particular, Aamodt and White examined whether microRNA-128 is behaviorally regulated
in Area X (the striatopallidal song control nucleus) in juvenile zebra finches and
found that its levels decline with singing. Furthermore, they demonstrated that inhibition
of miR-128 in young birds enhanced the organization of learned vocal sequences, thus
suggesting an important role for miR-128 in vocal communication and as a potential
therapeutic target for autism spectrum disorders.
Author contributions
All authors listed have made a substantial, direct, and intellectual contribution
to the work and approved it for publication.
Funding
SP received funding from Bordeaux University, CNRS, Association Autour de Williams
and Fondation pour l'Audition (FPA-RD-2020-8). SAB received funding from the University
of Brescia.
Conflict of interest
The authors declare that the research was conducted in the absence of any commercial
or financial relationships that could be construed as a potential conflict of interest.
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