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Biomedical subjects

R B Pinter

Publications and source records attributed to R B Pinter.

12 recordsLinked to original sources
PubMed1991

An identifiable molluscan neuron responds to changes in earth-strength magnetic fields.

Diverse animals can orient using geomagnetic cues, but little is known about the neurophysiological mechanisms that underlie magnetic field detection. The marine mollusc Tritonia diomedea (Bergh) has a magnetic sense and its nervous system is amenable to cellular-level electrophysiological analysis. In a semi-intact whole-animal preparation, intracellular recordings from the large, visually identifiable neurons left pedal 5 (LPe5) and right pedal 5 (RPe5) in the brain of Tritonia revealed enhanced electrical activity in response to changes in ambient earth-strength magnetic fields. No such changes in activity were observed in approximately 50 other neurons subjected to identical magnetic stimuli. The responses of LPe5 were characterized by increases in spiking frequency occurring about 6-16 min after the ambient magnetic field had been rotated to a new position. The response was abolished when the brain had been isolated from the periphery of the animal by severing nerves, a procedure that also transected prominent neurites of LPe5. We hypothesize that LPe5 is one component of a neural circuit mediating detection of the earth's magnetic field or orientation to it.

Animals↗
PubMed1990

Shift of edge-taxis to scototaxis depends on mean luminance and is predicted by a matched filter theory on the responses of fly lamina LMC cells.

The strength of the flanking inhibitory regions of the receptive fields of fly lamina cells (LMC) decreases as the mean luminance is lowered. Simultaneously, the biphasic temporal flash (impulse) response of the lamina cells becomes monophasic on lowering luminance. For a moving-edge stimulus at high mean luminance, this implies that the spatial integration by the lamina cell yields a temporal waveform which is congruent to the waveform of the temporal impulse response of the lamina cell. In other words, the temporal waveform generated by the moving edge is matched to the temporal waveform most preferred by the lamina cell. The edge is the stimulus causing the largest amplitude response at high (above 1 cd/m2) levels of luminance. On lowering luminance, the now monophasic nature of the spatial and temporal impulse responses of the lamina gives a preference not for the edges but for the center of a uniform region. We describe this theory and its behavioral corroboration in walking flies (Lucilia cuprina).

Animals↗
PubMed1990

What causes edge fixation in walking flies?

The orientation of freely walking flies (female Lucilia cuprina) to lines and stripes in a circular arena is described. The following observations were made. 1. The flies walked straight towards a dark line using the frontal eye region, but a pale line on a dark background was only weakly attractive. 2. In bright conditions flies walked in a curved line towards a black-white edge, the path being convex towards the dark side of the border. The curves indicated that the flies were heading for a point about 5-10 degrees to the dark side of the edge. 3. In dim conditions the edge of a dark region was not especially attractive and flies headed towards any point in the dark area. These observations can be accounted for by assuming that the fly walks towards the darkest region in its visual field (scototaxis). In bright conditions the edges of a dark region become more attractive than its centre. This change could be explained if lateral inhibition creates a 'Mach-band' effect, making the edges appear darker than the centre. Thus, fixation behaviour in walking Lucilia females seems to be a simple taxis.

Animals↗
PubMed1985

Adaptation of spatial modulation transfer functions via nonlinear lateral inhibition.

Adaptation, or change of shape of spatial modulation transfer functions (MTFs) on change of mean luminance level, occurs in visual interneurone and human psychophysical observations. Generally the bandwidth decreases and relative low frequency attenuation decreases as mean luminance decreases. Here it is shown how these changes in MTFs can be accounted for by nonlinear lateral inhibition based on spatial distributions of efficacy of voltage controlled synaptic conductance variation.

Adaptation, Physiological↗
PubMed1984

Adaptation of receptive field spatial organization via multiplicative lateral inhibition.

The interactions among electrically independent neurons via synapses mediating voltage controlled conductance become primarily multiplicative lateral inhibition. This nonlinear lateral inhibition among members of an array of neurons causes adaptation of the organization of the spatial receptive field. A proof of the adaptation is given and applications of the results to studies on insect visual interneurons are discussed. Given a simple hypothesis of spatial gradient of order of conductance dependence on neighboring cell voltage, a sharpening of spatial tuning of the receptive field is predicted with increased background level along with an increased linearization of the neuronal response function.

Adaptation, Physiological↗
PubMed1983

The electrophysiological bases for linear and for nonlinear product term lateral inhibition and the consequences for wide field textured stimuli.

The electrophysiological bases of linear, and of nonlinear product term recurrent lateral inhibition are defined and the general equations derived. Defining texture as sinusoidal spatial luminance functions, the response characteristics of nonlinear product term lateral inhibitory arrays to wide field textured stimuli are derived, and applications to locust DCMD and Y retinal ganglion cells discussed.

Animals↗
PubMed1981

Temporal and spatial response characteristics of the cat superior colliculus.

We have examined the responses of 72 cells of the cat superior colliculus to drifting gratings of sinusoidal luminance profile as a function of spatial frequency velocity and contrast. Of 72 cells, 66 responded to gratings either by change in mean firing rate only (58/72) or in a temporally modulated pattern in addition to the change in mean firing rate (8/72). The remaining 6 showed no change in discharge rate in response to any of the gratings tested. Many cells (24/72) were inhibited or excited by particular combinations of spatial and temporal frequencies. Some (8/72) demonstrated selective inhibition or excitation to a particular temporal frequency independent of spatial frequency and velocity and could therefore be said to be tuned specifically to temporal frequency. No cells were tuned only to a constant spatial frequency or a constant velocity. (24/72) cells displayed maximum inhibition or excitation only at a particular combination of spatial and temporal frequencies. Some cells (8/72) demonstrated a temporal modulation synchronous with the drifting grating in addition to an elevated mean discharge rate. The change in discharge rates evoked by gratings are generally less than those evoked by presentation of moving small slits or spots of light. Collicular cells often demonstrate a center-surround organization in their response to gratings. The center and surround often differ in their spatial frequency and velocity preferences. Compared to cortical and retinal ganglion cells, individual collicular cells are extremely non-linear. On a cell population basis, however, a linear Fourier analysis on grating response predicts the collicular cells' preference for movement of small objects.

Animals↗
PubMed1966

Sinusoidal and delta function responses of visual cells of the Limulus eye.

Dynamic responses of visual cells of the Limulus eye to stimuli of sinusoids and narrow pulses of light superimposed on a nonzero mean level have been obtained. Amplitudes and phase angles of averaged sinusoidal generator potential are plotted with respect to frequency of intensity modulation for different mean levels of light adaptation. At frequencies above 10 CPS, generator potential amplitudes decrease sharply and phase lag angle increases. At frequencies below 1 CPS, amplitude decreases. A maximum of amplitude in the region of 1 to 2 CPS is apparent with increased mean intensity. The generator potential responses are compared with those of differential equation models. Variation of gain with mean intensity for incremental stimuli is consistent with logarithmic sensitivity of the photoreceptor. Frequency response of the photoreceptor derived from narrow pulses of light predicts the frequency response obtained with sinusoidal stimuli, and the photoreceptor is linear for small signals in the light-adapted state.

Animals↗