RESEARCH

Neuronal basis of motor control

One of our major research interests is to understand the basis of neuronal pattern generation. Vocal patterning is in this aspect especially interesting, as it requires high degrees of precision. Although widely believed to be silent, many species of fishes are very vocal and offer a multitude of advantages to study such patterning, one factor being the rather simple sound producing apparatus. Using a variety of vocal fishes we thus aim to decipher how vertebrate vocal pattern generators generate the command signals to generate social vocal behaviors. We have deciphered the basic vocal pattern generator in two species of toadfish and are currently pursuing these studies on other fish species to understand neuronal adaptations that lead to different vocal behaviors.

Hindbrain vocal network used in the temporal patterning of vocalizations in toadfishes. 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)

Sensory – motor  interactions

During motor behaviors one unwillingly stimulates his sensory systems. In order to prevent this so called reafferent stimulation various mechanisms have evolved among vertebrates, one being corollary discharges. One example of such corollary discharges are Vocal corollary discharges (VCD). VCDs 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.

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

The correct activation of neurons is essential for motor patterning. One aspect to coordinate neuronal firing is synchronous activation. Many motor systems take advantage of synchronous activation patterns. Most vocal systems in fishes necessitate highly synchronous motoneuronal command signals to generate short and precise contractions of their vocal muscles to generate high frequency vocal patterns. To better understand the mechanisms that lead to such neuronal activity we are studying the adaptations of motoneuronal and premotoneuronal populations in the generation of neuronal synchrony that vocal motor systems.

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 neuronal circuits

To understand the driving force underlying the formation of neuronal circuits generating behavior, a comparative approach is needed. Only by comparing the differences within and between circuits that originate from the same neuronal substrate can one fully understand how neuronal networks get adapted to a particular behavior. The lab is investigating the evolution of pattern generation by comparing the neuronal circuits within and across different motor behaviors ranging from locomotion, to vocal system to electric organs. 

VOCAL CIRCUITS


Anatomical and physiological comparision of gulf toadfish and midshipman fish vocal pattern generators reveals a similar neuronal organization that leads to different call types

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.

Motor systems governing vocal, pectoral and breathing activity are coupled to each other (Figure adapted from Chagnaud & Bass 2012; PNAS)