Directionally selective motion detection in the sustaining fibers of the crayfish optic nerve: linear and nonlinear mechanisms

Abstract

1. Directional selectivity of crayfish sustaining fibers was examined with drifting sine wave gratings and with intracellular and extracellular recordings. Directionality was measured for variations in stimulus contrast, spatial frequency, and temporal frequency. 2. Sustaining fibers exhibit directional selectivity in the magnitude of the compound postsynaptic potential (PSP), the impulse frequency modulation response, and the mean firing rate. The mean synaptic potential is insensitive to direction. The directionality of the mean impulse rate appears to arise by rectification in the voltage-to-impulse transduction. 3. The preferred directions of three identified sustaining fibers are similar to those of head-down optomotor neurons to which these sustaining fibers project. 4. The modulatory response, elicited by gratings drifting in the preferred direction, increased linearly with contrast until saturation (typically at a contrast of 0.5), where maximum directional selectivity obtains. 5. The magnitude of the directional response is a band-pass function of spatial and temporal frequency and exhibits reversal of directionality (i.e., aliasing) at high spatial and temporal frequencies. The results imply a spatial sampling interval of 4.5 degrees and a temperature-dependent inhibitory delay of 40-90 ms. The PSP modulation response shares several features with that of neighboring tangential (Tan1) neurons. 6. A qualitative model is proposed for the transformation of a phase-sensitive, linear directional response to a phase-insensitive and nonlinear time-averaged response, based on the functional connections from Tan1 neurons to sustaining fibers to optomotor neurons. The model includes a threshold rectification, a synaptic band-pass filter, and differences in temporal phase among converging modulatory signals.

Neuronal processing of translational optic flow in the visual system of the shore crabCarcinus maenas

“…They are additionally directionally selective to movement (Glantz et al, 1995) (Fig.7A) and the response to light pulses (Fig.9A) are identical to those described above for such fibres. Additionally, our evidence that there are a number of these neurones, with receptive fields that together cover the whole visual field of the crab, is compatible with the 14 members of the sustaining fibre ensemble identified by Kirk et al (Kirk et al, 1983).…”

Encoder Adaptation Modulates the Visual Responses of Crayfish Interneurons

“…Adult crayfish, Pacifasticus leniusculus, of both sexes were prepared as in Glantz et al (1995). The eyestalks were cemented into their sockets with cyanoacrylate adhesive and chilled to 8°C.…”

“…In crayfish visual interneurons (i.e., sustaining fibers and dimming fibers, Glantz et al 1995;Kirk et al 1983;Pfeiffer and Glantz 1989) and a number of other interneurons (Fohlmeister et al 1977;Galarreta and Hestrin 2001;Poliakov et al 1997;Powers and Binder 1996), the time course of the discharge may be quite distinct from that of the PSP, and the discharge may exhibit a higher temporal frequency response than the PSP (French et al 2001;Glantz et al 1995;Knight et al 1970). Following an illumination increment (or decrement for dimming fibers), response adaptation in the sustaining fiber PSP is on the order of 15-50%, while the concurrent sustaining fiber discharge may decline by Յ95 or 100%.…”

Computer-aided studies of vision in crabs

“…Glantz and co-workers (e.g. Glantz et al, 1995) have overcome this problem in their work on visual interneurones in the optic ganglia of crayfish by opening the pericardial sinus and replacing the blood with oxygenated Ringer. Our approach was broadly similar.…”