Responses to magnetic stimuli recorded in peripheral nerves in the marine nudibranch mollusk Tritonia diomedea.

Prior behavioral and neurophysiological studies provide evidence that the nudibranch mollusk Tritonia orients to the earth's magnetic field. Earlier studies of electrophysiological responses in certain neurons of the brain to changing ambient magnetic fields suggest that although certain identified brain cells fire impulses when the ambient field is changed, these neuron somata and their central dentritic and axonal processes are themselves not primary magnetic receptors. Here, using semi-intact animal preparations from which the brain was removed, we recorded from peripheral nerve trunks.

Polarization vision in crayfish motion detectors.

Motion detector interneurons were examined to determine their responsiveness to the motion of polarized light images (i.e. images segmented by spatial variations in e-vector angle).

The distribution of polarization sensitivity in the crayfish retinula.

In many arthropod eyes the ommatidia contain two classes of retinular cells with orthogonally oriented microvilli. These receptors provide the basis for two-channel polarization vision. In several contexts such as navigation or the detection of polarization contrast, two channels may be insufficient.

Orientation by polarized light in the crayfish dorsal light reflex: behavioral and neurophysiological studies.

In decapod crustaceans, the dorsal light reflex rotates the eyestalk so that the dorsal retina faces the brightest segment of dorsal visual space. Stepwise displacements of white stripes elicit eyestalk rotations in the same direction as that of the stripe. Conversely, stepwise displacements of black stripes on a white background elicit eyestalk rotations in the opposite direction as that of the stripe.

Polarization contrast and motion detection.

Form and motion perception rely upon the visual system's capacity to segment the visual scene based upon local differences in luminance or wavelength. It is not clear if polarization contrast is a sufficient basis for motion detection. Here we show that crayfish optomotor responses elicited by the motion of images derived from spatiotemporal variations in e-vector angles are comparable to contrast-elicited responses.

Analysis and simulation of gain control and precision in crayfish visual interneurons.

Impulse trains in sustaining and dimming fibers of crayfish optic lobe (in situ) were elicited with sinusoidal extrinsic current and sine-wave illumination. Extrinsic currents and currents derived from postsynaptic potentials (PSPs) were used to compute the time course of the spike train with an adaptive integrate-and-fire model. The neurons exhibit variations in gain and spike timing precision related to the frequency of stimulation.

Encoder adaptation modulates the visual responses of crayfish interneurons.

The responses of sustaining and dimming fibers were characterized by the time varying firing rates elicited by extrinsic current and flashes of light. These data were simulated by an adaptive integrate-and-fire model. A postimpulse shunt conductance simulated spike-frequency adaptation.

Measuring information transfer in the spike generator of crayfish sustaining fibers.

We present a method based on information-theoretic distances for measuring the information transfer efficiency of voltage to impulse encoders. In response to light pulses, we simultaneously recorded the EPSP and spiking output of crayfish sustaining fibers. To measure the distance between analog EPSP responses, we developed a membrane noise model that accurately captures stimulus-induced nonstationarities.

Visual signals in an optomotor reflex: systems and information theoretic analysis.

Compensatory optomotor reflexes were examined in crayfish (Procambarus clarkii) with oscillating sine wave gratings and step displacements of a single stripe. A capacitance transducer was used to measure the rotation of the eyestalk about its longitudinal axis. System studies reveal a spatial frequency response independent of velocity and stimulus amplitude and linear contrast sensitivity similar to that of neurons in the visual pathway.