Dr. Boris P. Chagnaud

Research

General
I am broadly interested in sensory and motor systems and how both systems interact with each other. Motor activation often leads to reafferent stimulation of sensory systems, that can be detrimental to the sensory detection abilities of an animal. Thus for an optimal processing of sensory information during motor activity, mechanisms that counterbalance reafferent signalling are needed.
My sensory systems focus lies on hair cell sensory systems that are mechanical detectors of displacement. consequently, they are especially proned to reafferent signalling during motor tasks like walking or swimming. Fish and aquatic amphibians offer the unique ability to investigate the effect of motor systems on mechanosensory (hair cell) systems, due to the easy accessibility of their sensory systems and the variety of hair cell systems, i.e. lateral line, electrosensory and inner ear systems.

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Pattern generation of vocalization
Many different fish make sounds. There is a magnitude of different mechanisms to generate vocalizations in fishes (drumming, stridulation, tendon snapping) but up to date only few have been electrophysiologically characterized. I aim to investigate how different fish species generate sound at a neuronal level. A deeper understanding of these rather simple mechanisms would certainly lead to a better understanding of how vocal systems are organized in general and how different central pattern generators interact with sensory systems.

Fig 8
Hierarchical organization of the vocal pattern generator in toadfishes ( 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 focus to include peripheral sound producing organs as well.

Figure 7 summary - revised
Comparison between the vocal motor system of two toadfish species shows conserved organization
of the key neuronal elements (Chagnaud & Bass 2014 Brain Behavior Evolution)


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 06
Motor systems governing vocal, pectoral and breathing activity are coupled to each other (Figure adapted from Chagnaud & Bass 2012; PNAS)



Sensory motor integration

My long term goal is to understand how vertebrates make use of corollary discharges generated during vocalizations or locomotion in order to adapt their sensory systems to the new stimulus statistics. Due to the simple organization of the vocal pattern generators in fishes, I decided to study audio-vocal integration in vocalizing fishes. I therefore use a neurophysiological preparation in which rhythmic motor volley (fictive call) that directly establishes the temporal properties of natural calls can be elicited. I have used sharp electrode recordings coupled with neurobiotin injections to investigate the role of a several hindbrain nuclei in the pattern generation of vocalizations and have found a nucleus that projects not only to motor and premotor, but also to auditory nuclei. I am now investigating the role of these projection in auditory processing and prevention of reafferent signaling.

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 Audio-vocal coupling occurs at multiple level of the fish auditory system (asterisks) (also see Chagnaud & Bass 2013 J Neuroscience)

 
Neuronal control of superfast muscles
Besides my interest in sensory- motor integration I became interested in how superfast muscles, like the ones in toadfishes are neuronally controlled. Superfast muscles require a highly synchronous activation in order to generate enough force. In recent years, superfast muscles have also been discovered in birds and mamals. Together with the previously described superfast muscles in fish and reptiles, all major vertebrate lineages are now known to have this special kind of muscles. In a comparative project, I currently investigate the motor systems of different toadfish species in order to find common principles of superfast muscle motor activation. In addition I have started a collaborative project with Dr. Tobias Kohl (Technical University Munich) to investigate the neuronal control of the rattlesnake shaker muscles.

swimbladder 2


Midshipman swim bladder (white) with swim bladder muscles