A directionally selective motion-detecting neurone in the brain of the locust: physiological and morphological characterization

The anatomy and physiology of a directionally selective motion-detecting (DSMD) neurone in the locust are described. The neurone was descending, with the cell body in the protocerebrum. The axon lay in the dorsolateral quadrant of the nerve cord and has been traced as far as the metathoracic ganglion. It arborized, ipsilateral to the cell body, from the dorsal intermediate tract (DIT) in the suboesophageal and thoracic ganglia.

The neurone was binocular and sensitive to motion in the horizontal plane. It had a preferred direction backwards over the ipsilateral eye and forwards over the contralateral eye. Motion in the opposite direction suppressed the discharge, which had a frequency of 5–20 spikes s⁻¹ at resting membrane potential.

The neurone showed a clear directional response to stimuli with temporal frequencies between 0.7 and 44Hz, with a peak response at 11–22 Hz. It responded with spikes to light ON and light OFF.

The neurone responded directionally to spatial frequencies of 0.28 cycles degree⁻¹ (3.7° stripe period) to above 0.025 cycles degree⁻¹ (40° stripe period). The maximum response was at around 0.035 cycles degree^-1 (29° stripe period).

No evidence of adaptation was seen in the responses of the neurone to real or apparent continuous horizontal motion in either the preferred or the null direction.