Identified target-selective visual interneurons descending from the dragonfly brain

Summary

• 1. Eight large interneurons descending in the dragonfly (Aeshna umbrosa, Anax junius) ventral nerve cord from the brain to the thoracic ganglia were identified anatomically with intracellular dye injection (Fig. 3). All eight were strictly visual and responded only to movements of small patterns, such as black squares, ‘targets’, moving on a white background.

• 2. The target interneurons all projected from the protocerebrum at least as far as the metathoracic ganglion. Within the protocerebrum they arborized in the posterodorsal neuropil region, near the base of the circumesophageal connectives (Fig. 3).

• 3. The receptive fields of six of the cells were large, including most of the forward hemisphere of vision. For five of these, spiking responses were often restricted to a much smaller region within the receptive field, with stimulation of other areas yielding only subthreshold responses (Figs. 4 and 5, Table 1).

• 4. The pattern of selectivity for target size varied, with some neurons responding only to small targets, some showing consistent responses over a wide range of target sizes, and one preferring larger targets (Fig. 6, Table 1).

• 5. Five of the interneurons were directionally selective. Movement in the antipreferred direction elicited hyperpolarizing responses in two of them. Movements of large patterns, such as a checkerboard pattern covering the forward hemisphere, elicited opposite directional responses, i.e., hyperpolarizations in the preferred target direction and subthreshold depolarizations in the antipreferred direction (Fig. 7). A large pattern moving in any direction inhibited the response to target movement (Fig. 8).

• 6. These neurons mediate, in part, the visual control of flight orientation. I propose that they convey turning signals to the wing motor in response to objects moving relative to the animal.