Are the large monopolar cells of the insect lamina on the optomotor pathway?

Abstract

Evidence is presented here from experiments on the visual system of the fly that questions participation of the large monopolar cells (LMCs) in the optomotor response. 1. The response of a directionally-selective motion-detecting neuron (H1) in the lobula plate to small sudden jumps of a grating is directionally-selective (Fig. 1), indicating that at least one of the inputs to each of the elementary movement detectors (EMD) that feed into H1 must deliver a tonic signal. The responses of LMCs to the same stimulus are, however, entirely phasic (Fig. 2). 2. In dual electrode experiments on Eristalis, injection of current into an LMC does not change the spiking rate of H1. Induction of spiking activity, or injection of current into an LMC, which alters the cell's response to a flash of light from a point source, does not affect the response of H1 to the same flash (Figs. 3, 4). 3. The temporal properties of LMCs differ markedly from those of the optomotor response and of directionally-selective movement — detecting neurons in the lobula plate (Figs. 6, 9). 4. There is poor correlation between LMC degeneration and the strength of the optomotor response in a mutant of Drosophila (Fig. 8). 5. The optomotor response of Drosophila is strongly polarization sensitive, but Drosophila LMCs show no polarization sensitivity (Fig. 11).