The Evolution of Neural Circuits
We are interested both in the underlying causes and consequences of changes in both the physiology and anatomy of neural circuits. Almost nothing is known about the types of changes that have occurred during evolution in neural circuits. Even less is know about how changes in neural circuits affect the behaviours these circuits generate. To assess the diversity of neural circuits our studies concentrate on two circuits in which it is possible to relate the activity of neurons to specific behaviours - the photoreceptors of insects (and in particular flies) and the neural circuits that control the movements of the legs in grasshoppers, crickets and bush crickets. By assessing changes in both the anatomy and physiology of species and relating them to behavioural differences and the known evolutionary relationships between these species we can begin to understand the patterns of change.
How do neural circuits combine parallel datastreams from different types of sensor to produce a compound signal that is suitable for motor control? This question is particularly pertinent in systems where extreme speed and accuracy are critical. One such model system is the reflexive flight control system of the fly, where necessary reaction times approach timescales comparable to the refractory period of a spiking neuron. The fly combines inputs from two visual systems, the ocelli and the compound eyes, to stabilise its head in flight. Working with Holger Krapp, we have discovered that an exceptionally well characterised set of visually driven neurons, the large tangential neurons of the fly lobula plate, are driven by both sensory systems. We are exploiting this opportunity to analyse sensor fusion in circuits that are specialised for sensorimotor coordinate transformation using behavioural, electrophysiological and computational methods.