Motion detection by interneurons of optic lobes and brain of the flies Calliphora phaenicia and Musca domestica.

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Abstract
Three general classes of interneurons were investigated in the medulla, lobula and central brain of the insects Calliphora phaenicia and Musca domestica. The 2 classes in the lobula and brain combined visual properties of form and selective motion. The visual fields of the lobula region cells are monocular, but units with ipsilateral and contralateral fields exist in each lobe. These units responded maximally to patterns with lateral motion in one preferred direction and were inhibited for motion in the opposite direction. Four principal directions were found along approximately the horizontal and vertical axes of the head. Units typified by contralateral field, horizontal periphery to center motion detection, dominated in terms of ease of detection. The visual fields of the lobula units extended over the full geometrical fields of the individual eyes but their sensitivity to moving patterns varied greatly over the field and had a single peak in the forward part of the field. Detailed optical and histological studies of the eyes show that the retinula cell field axes are aligned along 3 major axes that are determined by the fact that individual facets are 6-sided. These axes referred to a spherical coordinate system which varies about 20 degrees over the whole eye. Tests with small striped patterns showed that the directions of maximum responses to motion also varied in the same manner and thus maintained the same geometrical relationship to the ommatidia in differ -ent portions of the eye. The responses, recorded from units in the 3rd region, either replicated the lobula unit responses or were binocular and summed the stimulus responses of a pair of the monocular units. Units summing horizontal periphery to center motion from both eyes are the dominant binocular class. Pertinent correlations are presented between the properties of these unit classes and earlier work on the anatomical structure of the eyes, generator potentials obtained in the retina cells, and optokinetic responses.

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