Syozo Yasui

Spatio-Temporal Receptive Field Measurement of Retinal Neurons by Random Pattern Stimulation and Cross Correlation

A method is developed for the measurement of the spatio-temporal receptive field (STRF) of neurons in the retina. The test input is an unsteady visual pattern randomly modulated in both space and time, and the output is the stochastic time course of the intracellular response. The STRF is expressed in terms of the spatio-temporal Wiener kernels calculated through a special cross-correlation algorithm between the response and the stimulus-related information. The method is an extension of existing white-noise identification techniques to include the spatial domain. Consideration is given to the practical implementation of the required stimulus pattern, and has led to several alternative approaches.

H1 horizontal cells of carp retina have different postsynaptic mechanisms to mediate short-versus long-wavelength visual signals

SummaryVertebrate photoreceptors release neuro-transmitter substance(s) tonically in the dark and this release is curtailed by light. Recently, we have become increasingly aware of the possibility that short- and long-wavelength visual signals are mediated differently during the synaptic transmission to second-order retinal neurons. The experiment described here advances this notion further by demonstrating a postsynaptic difference. Treatment of the carp retina by dopamine reduced the gap-junctional coupling of horizontal cells, and we made use of this known effect to measure the input resistance (Rin) of H1-type horizontal cells. Flashes of light increased Rin. This increase, however, was found to be smaller with short wavelengths, even though the comparison was made when voltage responses were equal in amplitude. Often, Rin was even found to decrease at the blue end of spectrum. No single postsynaptic mechanism can account for any equal-voltage Rin difference such as this. The synaptic spectral segregation thus revealed is probably subserved by a dual scheme wherein the transmitter from blue-sensitive cone photoreceptors acts to decrease the membrane conductance of H1 cells whereas the synapses made by red-and green-sensitive cones are of a classical excitatory type.

Asymmetric Temporal Properties in the Receptive Field of Retinal Transient Amacrine Cells

The speed of signal conduction is a factor determining the temporal properties of individual neurons and neuronal networks. We observed very different conduction velocities within the receptive field of fast-type On-Off transient amacrine cells in carp retina cells, which are tightly coupled to each other via gap junctions. The fastest speeds were found in the dorsal area of the receptive fields, on average five times faster than those detected within the ventral area. The asymmetry was similar in the On- and Off-part of the responses, thus being independent of the pathway, pointing to the existence of a functional mechanism within the recorded cells themselves. Nonetheless, the spatial decay of the graded-voltage photoresponse within the receptive field was found to be symmetrical, with the amplitude center of the receptive field being displaced to the faster side from the minimum-latency location. A sample of the orientation of varicosity-laden polyaxons in neurobiotin-injected cells supported the model, revealing that ∼75% of these processes were directed dorsally from the origin cells. Based on these results, we modeled the velocity asymmetry and the displacement of amplitude center by adding a contribution of an asymmetric polyaxonal inhibition to the network. Due to the asymmetry in the conduction velocity, the time delay of a light response is proposed to depend on the origin of the photostimulus movement, a potentially important mechanism underlying direction selectivity within the inner retina.

Horizontal cell signal is smaller with texture-like nonuniform patterns than with uniform fields of the same space-average illuminance.

While measurement of the pertinent response as a function of flash intensity has been a standard procedure in vision research, we ask here what happens to horizontal cells in the vertebrate retina if the flash energy is varied through the density of a large number of small light spots rather than through the intensity of uniform illumination. The experiment described here demonstrates that the electrical response of horizontal cells in the turtle retina is consistently smaller with the present dot-density modulation than with the usual intensity modulation, even though the comparison is made when the mean irradiance per photoreceptor is equal in the two methods of modulation. Thus, the spatial summation, an important retinal function often thought to provide a base signal level for contrast detection, is affected significantly by how the visual pattern is structured at a level of microscopic dimension far smaller than the receptive field. The present finding, which seems to be a new form of area-intensity effect, can be explained if the dendritic membrane conductance of horizontal cells at each synaptic site increases at a progressively higher rate with decreases of the corresponding local illuminance. This possibility is discussed in the light of relevant photoreceptor response data, the presumed sigmoidal trend of the postsynaptic chemosensitivity and a simple electrical analog of contiguous horizontal cells.

The use of clipped input information in multidimensional cross-correlation for estimating Wiener-like kernels of non-linear systems

While the measurement of Wiener-like kernels by multidimensional input-output cross-correlation is a well-known non-parametric approach to non-linear system identification, we propose here a simplifying kernel estimation scheme; rather than using the white-noise signal that is actually applied to stimulate the system, the present method uses a clipped information (that is, two- or three-level quantization) of the continuous-level test input for computing the cross-correlation. This greatly reduces the computational requirement without disturbing the generality of actual test input which may be gaussian. The statistical variance of the kernel estimation is discussed in comparison with other algorithms. Certain non-statistical errors may be incurred using this approach, but are thought to be minor in most applications. A special emphasis is given to the problem of choosing optimal procedural parameters for ternary quantization in the case of white gaussian input.

Transmission of array data by multivariate convolution and cross-correlation using white-noise reference signal

Abstract An information-transmission scheme with holographic-like properties is described for encoding and decoding multidimensional imagery data. An m-dimensional message pattern is mapped into an mth order Wiener kernel, creating a non-linear system. The sender stimulates this system with a gaussian white-noise input and the response is transmitted to the receiving end. Thus, the encoding algorithm is a convolutional operation. The white-noise input serves as a reference signal which may be also transmitted, or alternatively may be conveyed a priori to the intended receiver. The message pattern is decoded by performing an m -dimensional cross-correlation between the stimulus and response signals. The method is particularly suitable when the transmission is subject to severe extraneous noise disturbances including periods of complete signal loss. This is demonstrated by making comparisons with the photographic telecommunication operating on a point-by-point basis, as well as through a computer-simulated ...