Electrophysiology of the Insect Dorsal OceUus III. Responses to j ckering light of the dragonfly oceUus

The ERG of the dragonfly ocellus has been analyzed into four components, two of which originate in the photoreceptor cells, two in the ocellar nerve fibers (Ruck, 1961 a). Component 1 is a sensory generator potential, component 2 a response of the receptor axons. Component 3 is an inhibitory postsynaptic potential, component 4, a discharge of afferent nerve impulses in ocellar nerve fibers. Responses to flickering light are examined in terms of this analytic scheme. It has been found that the generator potential can respond to higher rates of flicker--up to 220/sec.--than can the receptor axon responses, the postsynaptic potential, or the ocellar nerve impulses. The maximum flicker fusion frequency as measured by fusion of the ERG is that of the sensory generator potential itself. I N T R O D U C T I O N Two previous papers (Ruck, 1961 a, b) were concerned with analysis of the ocellar E R G and the mechanisms controlling the discharge of ocellar nerve impulses. This paper is concerned with responses to flickering light. The dragonfly ocellus contains two kinds of neural elements, photoreceptor cells and ocellar nerve fibers. Synapses between the two occur in the distal end of the ocellar nerve in the region where it joins the ocellar cup. The E R G is complex. I t can be resolved into a generator potential (component 1), a receptor axon response (component 2), an inhibitory postsynaptic potential (component 3), and ocellar nerve impulses (component 4). Responses of each component to flickering light have been studied. The generator potential can follow higher rates of flicker than any of the other components. The maximum flicker fusion frequency of the ERG, therefore, is that of the generator potential itself.