Long-term extracellular recordings from a spiking, movement-sensitive giant neuron (H1) in the third optic ganglion of the blowfly Calliphora vicina (L.) revealed periodic endogenous sensitivity fluctuations. The sensitivity changes showed properties typical of an endogenous circadian rhythm. This was true for the responses in reaction to intensity changes of visual patterns as well as for the responses elicited by pattern movement. For these two types of stimuli, the circadian fluctuations were comparable, but the envelope in the case of responses to movement was more robust. A circadian fluctuation in responses to movement is, therefore, present at the level of single elementary movement detectors. The tonic activity of the neuron was also shown to be under circadian control. In constant darkness (DD) the fluctuation was circadian, whereas in constant light it was not. The subjective light-dark (LD) transitions in the tonic activity in DD closely followed the LD transitions in the holding cages initially; that is, there was low activity at night and high activity during the daytime. The sensitivity fluctuations in response to visual stimuli led the tonic spike activity fluctuations by several hours.
The paper describes a low-cost, versatile, widely applicable digital display system in which a high-resolution, high-intensity display unit is driven by a real-time vector scan controller. The actual online display control of this device is preceded by an offline software stimulus-frame editor, designed to create and support a library of stimulus patterns (standard frames without any timing information and without any referencing to a special display co-ordinate system). The display times can be set individually for each single frame (containing at maximum 1023 pixels) with relative ease. Display frequency is set to 1 kHz. Writing time per pixel is less than 1 microsecond. A graphic display system like the one presented in this paper can be applied to generate a variety of real-time optical stimuli, such as intensity modulation of single spots or distinct display areas, abrupt displacements of a certain pattern, continuous movement or onset and offset of steady motion of a pattern.
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