A Study of the Afferent Pathways of the Dragonfly Lateral Ocellus From Extracellularly Recorded Spike Discharges

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Abstract
The lateral ocellar nerve of adult dragonflies contains at least two kinds of afferent nerve fibres: the ‘giant’ afferent and small afferents. Efferent fibres are also present, but are not described here. The afferent fibres and receptor axons were studied by extracellular recording of their spike discharges. Experiments using light and electrical (D.C.) stimulation and the application of magnesium were performed. Responses of the giant afferent were analysed into a number of exponential components. The number could be altered experimentally. The giant afferent shows the phenomenon of ‘delayed response’, a delayed onset of the off-response to brief light stimuli. A qualitative model for delayed responses, incorporating the exponential components, is described. It is concluded that the small afferents behave in accordance with Ruck ‘s model of ocellar of functioning but that the giant afferent does not. It is proposed that inhibion in the giant afferent fibre is produced electrotonically, but there may be a synaptic contribution also."

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