Auditory-to-motor interface of phonotaxis
During phonotactic walking the movements of the front legs play a major role for auditory steering. Especially the front legs contralateral to the acoustic stimulus are rotated and extended towards the sound source and the activity pattern of the tibia muscles is modulated. Contributing to the sound induced steering movements are the tibia extensor and flexor muscles and motoneurons that control the angle of the femur-tibia joint. We identified the corresponding tibial motoneurons which are located in the prothoracic ganglion. There is no direct auditory input to these motoneurons in resting crickets but as they contribute to auditory steering they will receive sound induced steering commands during phonotaxis. Since pattern recognition of the male song occurs in the brain, we assume that descending neurons forward auditory steering commands to the thoracic motor system. The objective of the project is to identify and describe the pathway involved in steering response by answering two central questions:
- What is the nature of the auditory evoked descending steering commands as revealed by analyzing the synaptic inputs to motoneurons during phonotaxis?
- Which descending and local interneurons forward the steering commands from the brain to the thoracic networks?
To answer these questions we use a preparation developed by Klaus Hensler (1986). In crickets that are walking on a trackball the prothoracic ganglion is exposed for intracellular recording and labeling of leg motoneurons. We also monitor the EMG of tibial muscles, the movements of the front leg and the phonotactic walking behaviour of the animals.
Female crickets show clear phonotactic steering during intracellular recordings of tibial motoneurons. During sound presentations from the ipsi- or contralateral side typical changes in the rhythmic membrane potential oscillations and spike activity of the motoneurons occur. The activity pattern of the motoneurons depends on the direction of walking but the synaptic inputs appears not to be coupled to the acoustic stimuli when sound is presented from one-side only.
We now test the motoneuron response to split-song paradigms in which sound is presented alternating from opposite directions. We also look for descending axons that mediate sound evoked activity patterns that could be candidates to forward auditory steering commands to tibial motoneuron.
Group Members
Dr Berthold Hedwig (Group Leader)
bh202@cam.ac.uk
Dr Fabienne Dupuy
Research: Auditory motor interface
fyd20@cam.ac.uk
Dr Kostas Kostarakos
Research: Auditory brain neurons
kk437@cam.ac.uk
Dr Stefan Schoeneich
Research:Song pattern generation
ss817@cam.ac.uk
Kelly Seagraves
Research: Directional sensitivity
ks584@cam.ac.uk
Part II Zoology Project Students
Tanya Gunnarsdottir
Gemma Longson