Behavioural physiology: Motion capture and ground reaction force measurements in freely walking insects
Electrophysiology: Intra- and extracellular recordings of nerves, muscles and individual neurons
Neurobionics: Modelling of bio-inspired control algorithms in both software and hardware, linking artificial neural networks and biorobotics
Our lab is broadly interested in sensory-guided control of behaviour in insects and bio-inspired robotic systems. Our research focus is on the function of active tactile sensing (touch) and distributed proprioception (the sense of posture).
Our main model systems are stick insects. These nocturnal insects rely heavily upon sensory feedback to control locomotion. Stick insects have been used as study organisms in animal physiology and neurobiology for about a century - accordingly, we can build on a lot of detailed knowledge regarding anatomy, physiology and behaviour. Methodologically, their relatively low speed and large size makes them amenable to many electrophysiological techniques, and allows detailed analyses of natural, unrestrained movement behaviour.
Load-dependent control of locomotion
During walking, legs undergo cyclic changes in load - step after step. In a parallel research effort we study how stick insects integrate feedback from load sensors on their legs (campaniform sensilla) to control locomotion. In collaboration with the Zill Lab in Huntington/WV and the Büschges Lab in Cologne, we use extracellular recording methods to study how different groups of campaniform sensilla encode the loading and unloading of leg segments. In a complementary approach, we study how individual leg segments are loaded and unloaded in freely walking animals. Here we take advantage of the relatively long legs of stick insects to simultaneously record 3D joint kinematics, single leg ground reaction forces and multi-channel electromyograms.
Picture: Campaniform sensilla on the tibia of a stick insect.
Role of proprioceptors and body models in locomotion
This modelling study aims at identifying the relative importance of proprioceptive feedback and internal body models for estimating the posture and motion of animals during locomotion. We use detailed natural whole-body movement data of walking stick insects to model sensory feedback from different proprioceptors on the legs. How well are body posture and movements estimated from distributed proprioceptors alone? Does an internal body model, which takes the geometry of the animal into account, improve purely sensor-based estimates?
Picture: Schematic of a hairfield model.
Active tactile exploration and goal-directed movement
Stick insects live nocturnally and many species are obligatory walkers (none of the ones we study can jump or fly). As a consequence, many stick insect species use their antennae (or feelers) for tactile near-range orientation. During locomotion, they actively move their antennae as if to search the ambient space for obstacles. Once an antenna touches an object, the animal typically responds to this contact event by directed movements. For example, it may move a front leg to reach for the obstacle touched. In a number of recent and ongoing projects, we study (i) how the animals adapt their tactile exploration behaviour to spontaneous and induced changes in speed and walking direction, (ii) whether and how the tactile contact sequence predicts the forthcoming movements, and (iii) how the coordinate-transfer may work by which the antenna "tells" the leg when and where to grasp an obstacle.
Picture: Movement trajectory of a stick insect antenna during walking.
Descending interneurons involved in tactile sensing
Stick insects show tactually induced behaviours that require spatial and temporal coordination of the antenna (the tactile sensor organ) and subsequent reaching movement of a leg. To understand what is encoded in the antennal mechanosensory system and how behaviourally relevant information is transferred to the legs, we study descending interneurons that mediate tactile and proprioceptive information from the antennae to thoracic neural networks. In particular, we focus on the role of an identified giant interneuron, cONv, as the animal interacts with its environment. cONv belongs to a group of neurons that encode antennal movement velocity, an important cue in active tactile sensing. Owing to its specific properties cONv can be identified by means of extracellular nerve recordings.
Picture: cONv in the prothoracic ganglion of a stick insect.
Bio-inspired tactile sensors for object localisation
Compared to vision, active tactile sensing enables animals to perform unambiguous object localisation, segmentation and shape recognition. In this project we develop a bio-inspired CPG-based control model of the stick insect antenna. Using both simulated and robotic antennae we study how antennal movement strategies are integrated with sensory information such as antennal vibration to localise objects effectively in 3D space.
Picture: Model of a bio-inspired antenna.
Marker-less motion capture of insect antennae
In this project we develop a marker-less motion tracking system for hinged insect antennae with a geniculate morphology, as is typical for Hymenopteran insects (honeybees, bumblebees, wasps and ants). The tracking system is being designed to investigate the role of antennal movements in active tactile exploration, pattern recognition and tactile learning.
Picture: Top view of a honeybee with tracked antennae overlaid in green.