The H1 neuron measures change in velocity irrespective of contrast frequency, mean velocity or velocity modulation frequency

Abstract

The H1 neuron of the fly Lucilia cuprina is one of the wide-field motion-perception interneurons of the lobula plate. The response, measured as the mean spike rate over many repetitions of the same stimulus sequence, is initially large at the onset of a movement, quickly falling to a plateau and then continuing to adapt slowly when the stimulus is a steady motion of a pattern. Modulation of the velocity of the moving pattern (velocity contrast) causes a modulation of the mean spike rate, which adapts more slowly than the adaptation to the mean velocity. The modulation of the spike rate and the average maximum spike rate are both measures of the velocity modulation irrespective of the contrast frequency, mean velocity, or velocity modulation frequency up to 12 Hz. The responses are in phase with the sine-wave modulated stimulus velocity; suggesting that HI measures Δω/2ω not Δω/Δt. If the responses of the H1 neuron are representative of their properties, the unit motion detectors are specialized for high resolution, high gain, short latency, and transient detection of direction of velocity change. These features are those required in controlling errors in stability while flight is already in progress and other aspects of insect vision presumably are carried in other neurons.