Award details

Motor control of auditory steering in crickets

Reference	BB/G018723/1
Principal Investigator / Supervisor	Professor Berthold Hedwig
Co-Investigators / Co-Supervisors
Institution	University of Cambridge
Department	Zoology
Funding type	Research
Value (£)	293,234
Status	Completed
Type	Research Grant
Start date	01/11/2009
End date	28/02/2013
Duration	40 months

Abstract

The project will forward our understanding of auditory processing in an insect nervous system by intracellular recording auditory responses in motoneurons and interneurons of actively walking and steering animals. Tethered crickets will be walking on a trackball and phonotactic steering will be elicited by computer generated song patterns presented from the left and right side. The prothoracic ganglion of the animals will be exposed to allow intracellular recordings from coxal and tibial motoneurons, which are involved in phonotactic steering. At the same time we will record the movement trajectories of the front legs with an optoelectronic camera and the overall steering direction of the animals with the trackball system. The motoneurons are the final elements of the auditory-to-motor pathway that processes the species-specific song pattern and generates the steering commands underlying auditory orientation. In the first part of the project the auditory evoked synaptic inputs to the motoneurons will be analysed. This will reveal the output of the auditory-to-motor pathway and the nature of the descending steering commands. We expect these commands to be tightly coupled to the sound pattern. The recordings will also demonstrate how the animals integrate the steering responses into the ongoing walking motor activity. We expect that the auditory evoked responses will depend on the phase of the leg movement. Next we will analyse the premotor network, to find out, if the descending steering signals impinge directly on the motoneurons or if they are mediated via local premotor interneurons like for other proprioceptive feedback. Based on the activity patterns encountered in the motoneurons we will finally systematically explore the axons in the connectives to identify those descending interneurons, which are central to the auditory-to-motor pathway and mediate the steering commands from the brain to the thorax.

Summary

Neuroscience has made enormous progress in understanding the function of neurons and neuronal networks. The analysis of motor systems or sensory pathways has revealed fundamental principles of how animals generate motor patterns or process sensory information from their environment. However, sensory-to-motor interfaces, the networks of the central nervous system where sensory signals are processed and appropriate motor commands are generated, have rarely been studied, as the focus is either on motor systems or on sensory systems. The aim of the project is to consider both aspects and to analyse the motor activity underlying auditory evoked steering responses in female crickets. These animals orient towards singing males using the male's calling song for orientation. In neurobiology they are model systems for analysing the neural mechanisms of auditory processing since many years. The neurons of the cricket auditory pathway are well described and we have a very good understanding, how the animals process sound patterns at the early stages of their nervous system. However, we still lack the crucial information, how they actually recognise the calling songs of the males and how they then manage to steer towards the singing mate. In many previous experiments auditory processing was generally analysed in restrained animals. In those experiments there was no indication, if the sensory signals were recognised and appropriate motor commands were generated. In our experiments tethered crickets will be walking on a trackball and will steer towards a sound pattern. The project will therefore overcome a fundamental experimental problem of previous approaches by monitoring the walking behaviour of the animals. This will be a reliable indicator that phonotaxis is elicited and that the corresponding processing of auditory signals has been initiated. This is crucial for our approach to demonstrate and understand the neural mechanisms underlying the auditory-to-motor pathway. Together with the walking behaviour we will record the activity of specific motoneurons, and interneurons, which control the steering movements of the front legs. These experiments will tell us, what type of auditory evoked commands are send to the motoneurons from the brain, in order to control the steering movements. They will also demonstrate how an auditory pattern recognition process, transforms responses of auditory interneurons into motor commands controlling leg movements. Analysing this model system will reveal principles of auditory processing and will contribute to a pivotal aim of behavioural neuroscience that is to understand the neural organisation of animal behaviour from sensory processing to motor pattern generation.

Committee	Closed Committee - Animal Sciences (AS)
Research Topics	Neuroscience and Behaviour
Research Priority	X – Research Priority information not available
Research Initiative	X - not in an Initiative
Funding Scheme	X – not Funded via a specific Funding Scheme

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