My group currently focuses on the behaviour of the Mediterranean field cricket Gryllus bimaculatus. By rubbing their front wings together male crickets produce a calling song to attract females. Singing male crickets rhythmically open and close their front wings. Each closing movement scratches the wings against each other and generates a short sound pulse. Several pulses are grouped into chirps. They are repeated 2-3 times per second in a calling song that may last for many hours. Females are mute but if they are ready to mate they walk towards the singing males - this behaviour is called phonotaxis. Ears in crickets are located in the front legs. The animals house a well known auditory pathway in their central nervous system in which many neurons have been identified. Thus crickets can be used as an insect model system to study sound processing and sound production at the cellular level. Our research currently is dominated by the following central questions:
1. How is singing controlled by the nervous system?
2. Which peripheral and neural mechanisms underlie sound localisation?
3. What are the neuronal networks that recognize a species-specific signal?
4. How is pattern recognition linked to phonotaxis?
We address these questions by measuring the animals’ phonotactic and singing behaviour, by intracellular recording the activity of neurons in the auditory and motor networks and by analysing the calcium dynamics in neurons during signal processing.
In order to analyze the neural networks underlying the singing motor pattern, we use micro-injections of neuroactive substances into the brain. This activates descending command neurons and singing is released even in de-afferented preparations, with the CNS exposed for intracellular recordings.
Phonotactic walking behavior is analyzed by placing the tethered females on a sensitive track ball system, that records the movements of the trackball, when the crickets walk and orient towards computer controlled acoustic paradigms. This allows a systematic behavioural analysis of the pattern recognition system and its directional sensitivity. We also developed preparations, in which intracellular recordings of auditory brain neurons and thoracic motoneurons are obtained in walking females to understand the neural control of phonotaxis.
Finally we link the calcium dynamics of auditory neurons to signal processing with an optical imaging system. Neurons are loaded with a calcium sensitive indicator and changes in the intracellular calcium dynamics are measured during auditory processing.