Although widely believed to be silent, many species of fishes are very vocal. Fish vocalize in various different contexts such as territorial defense, predator escape and for mate attraction. For a sample on how a fish vocalization sounds like click here.
Fish use a variety of mechanisms to produce vocalizations such as drumming, tendon snapping or teeth grinding and thus offer a unique opportunity to investigate the evolution of the neuronal circuits underlying vocal behavior independent of the structures used in sound production. Using a combination of different electrophysiological and anatomical/immunohistological methods the lab is centered around 4 major research topics but is always open for novel projects and collaborations:
Neuronal basis of vocal patterning
One of our major research interests is to understand the basis of vocal patterning. Using a variety of vocal fishes we aim to decipher how vocal pattern generators code for the command signal to the vocal muscles. We have deciphered the basic vocal pattern generator in two species of toadfish and are currently pursuing these studies on other toadfish species to understand neuronal adaptations that lead to different vocal behaviors. Toadfishes offer tremendous advantages to study these circuits as a single set of muscle is used in the generation of sound, thereby reducing the complexity of the motor patterning.
Figure legend: Hindbrain vocal network used in the temporal patterning of vocalizations in fishes. The vocal pattern generator is organized in distinct nuclei coding each for a specific call attribute, namely frequency, duration and amplitude (Figure adapted from Chagnaud et al. 2011; Nature Communications)
Evolution of vocal motor behavior
To understand the driving force underlying the formation of neuronal circuits generating vocal behavior, a comparative approach is needed. Only by comparing the differences within and between families with similar and different peripheral sound producing structures can one gain an understanding of the conserved neuronal features in vocal pattern generation. Such a comparative approach, however, includes not only the neuronal circuits, but also the peripheral sound producing structures, as both are adapted to each other and thus need to co-evolve. The lab is investigating the evolution of vocal pattern generation by comparing the neuronal circuits within and across different fish families. Currently we are extending our approach to include peripheral sound producing organs.
Figure legend: Anatomical and physiological comparision of gulf toadfish and midshipman fish vocal pattern generators reveals a similar neuronal organization that leads to different call types
During vocal behavior one unwillingly stimulates his auditory system. In order to prevent this so called reafferent stimulation various mechanisms have evolved among vertebrates. One if not the most important among these mechanisms are vocal corollary discharges. Vocal corollary discharges originate from vocal areas and inform the auditory system at different levels (periphery hind- and midbrain) about impending or ongoing vocal activity. We aim to understand how and where this interaction takes place at a single neuron level.
Figure legend: The vocal system interacts with the auditory system at different levels. Asterisks indicated the auditory processing centers that recieve vocal corollary discharge inputs.
Mechanisms of neuronal synchrony
Many vocal systems including some in vocal fishes make use of highly adapted muscles, so called superfast muscles, that can contract at fast frequencies (up to 250Hz). The motoneuronal command signals that drive theses muscles need to be highly synchronous in order to generate short and fast contractions of the vocal muscles. We are studying the adaptations of motoneuronal and premotoneuronal populations in the generation of neuronal synchrony that drives these superfast muscles.
Figure legend: The vocal nerve motor signal can be used as a direct readout of a natural call. Vocal nerve readout (fictive grunt) is composed of synchronous activity of up to 4000 vocal motor neurons making it one of the most synchronously active nuclei known (Figure adapted from Chagnaud &Bass 2013, J Neuroscience)
Evolution of vocal gestural coupling
Humans and animals alike show a strong coupling between vocal behavior and gestural coupling. Humans for instance permanently wave with their hands while they try to explain something to each other. The neuronal basis of this coupling may have originated in fishes, as fishes show coupling of various motor systems (e.g., breathing, pectoral and fin movements) to their vocal behavior. We aim at elucidating how these motor systems interact with each other in order to understand how vocal gestural coupling evolved.
Figure legend: Motor systems governing vocal, pectoral and breathing activity are coupled to each other (Figure adapted from Chagnaud & Bass 2012; PNAS)
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