Deoxyglucose mapping of nervous activity induced inDrosophila brain by visual movement

SummaryLocal metabolic activity was mapped in the brain ofDrosophila by the radioactive deoxyglucose technique. The distribution of label in serial autoradiographs allows us to draw the following conclusions concerning neuronal processing of visual movement information in the brain ofDrosophila.1.The visual stimuli used (homogeneous flicker, moving gratings, reversing contrast gratings) cause only a small increase in metabolic activity in the first visual neuropil (lamina).2.In the second visual neuropil (medulla) at least four layers respond to visual movement and reversing contrast gratings by increased metabolic activity; homogeneous flicker is less effective.3.With the current autoradiographic resolution (2—3 μm) no directional selectivity can be detected in the medulla.4.In the lobula, the anterior neuromere of the third visual neuropil, movement-specific activity is observed in three layers, two of which are more strongly labelled by ipsilateral front-to-back than by back-to-front movement.5.In its posterior counterpart, the lobula plate, four movement-sensitive layers can be identified in which label accumulation specifically depends on the direction of the movement: Ipsilateral front-to-back movement labels a superficial anterior layer, back-to-front movement labels an inner anterior layer, upward movement labels an inner posterior layer and downward movement labels a superficial posterior layer.6.A considerable portion of the stimulus-enhanced labelling of medulla and lobula complex is restricted to those columns which connect to the stimulated ommatidia. This retinotopic distribution of label suggests the involvement of movement-sensitive small-field neurons.7.Certain axonal profiles connecting the lobula plate and the lateral posterior protocerebrum are labelled by ipsilateral front-to-back movement. Presumably different structures in the same region are labelled by ipsilateral downward movement. Conspicuously labelled foci and commissures in the central brain cannot yet be associated with a particular stimulus. The results are discussed in the light of present anatomical and physiological knowledge of the visual movement detection system of flies.