Nonlinear Spatial Summation Research Articles

Properties of ganglion cells with atypical receptive-field organization in retina of macaques.

1. About 10% of a sample of 436 cells recorded in the retina of macaques had receptive fields lacking a center-surround organization. These cells had a diffuse extrafoveal distribution, they were less frequently found in the foveal region, and their conduction latencies overlapped with those of cells (types I, III, and IV) having a center-surround organization. Three groups were distinguished. 2. Type II cells had spectrally opponent responses mediated by mechanisms having similar or identical distributions and response latency; these cells did not respond to white light. They predominated in the central retina, they usually received input from all three types of cone, they had a linear spatial summation of incomming photo-receptor signals, they lacked rod input, they had conduction latencies that were intermediate between those of the other two groups, and they could be antidromically activated by electrical stimulation of the lateral geniculate body but not of the superior colliculus. 3. Type V cells were neurons whose common characteristic was the presence of on-off responses to both small and large stimuli. One subgroup had either excitatory or inhibitory on-off responses and a silent inhibitory surround that tended to suppress cell responses and maintained activity. They were observed throughout the central retina, including the fovea; they received input from green- and red-sensitive cones, but not from blue-sensitive cones; they had a non-linear spatial summation; they had comparatively long conduction latencies; and they could be antidromically activated by electrical stimulation of either the lateral geniculate body or superior colliculus. Another subgroup lacked spontaneous activity and any type of surround. They were encountered at a retinal depth more sclerad than that of other neurons and could not be antidromically driven from the optic tract or more central structures; these cells also lacked input from blue-sensitive cones and had a nonlinear spatial summation. 4. Type VI cells were predominantly inhibited by moving stinuli in any direction of motion and failed to respond to stationary flashing stimuli; they appeared to predominate toward the perifovea and had comparatively short conduction latencies.

Spatial summation in the receptive fields of simple cells in the cat's striate cortex.

1. We have examined the responses of simple cells in the cat's atriate cortex to visual patterns that were designed to reveal the extent to which these cells may be considered to sum light-evoked influences linearly across their receptive fields. We used one-dimensional luminance-modulated bars and grating as stimuli; their orientation was always the same as the preferred orientation of the neurone under study. The stimuli were presented on an oscilloscope screen by a digital computer, which also accumulated neuronal responses and controlled a randomized sequence of stimulus presentations. 2. The majority of simple cells respond to sinusoidal gratings that are moving or whose contrast is modulated in time in a manner consistent with the hypothesis that they have linear spatial summation. Their responses to moving gratings of all spatial frequencies are modulated in synchrony with the passage of the gratings' bars across their receptive fields, and they do not produce unmodulated responses even at the highest spatial frequencies. Many of these cells respond to temporally modulated stationary gratings simply by changing their response amplitude sinusoidally as the spatial phase of the grating the grating is varied. Nonetheless, their behavior appears to indicate linear spatial summation, since we show in an Appendix that the absence of a 'null' phase in a visual neurone need not indicate non-linear spatial summation, and further that a linear neurone lacking a 'null' phase should give responses of the form that we have observed in this type of simple cell. 3. A minority of simple cells appears to have significant non-linearities of spatial summation. These neurones respond to moving gratings of high spatial frequency with a partially or totally unmodulated elevation of firing rate. They have no 'null' phases when tested with stationary gratings, and reveal their non-linearity by giving responses to gratings of some spatial phases that are composed partly or wholly of even harmonics of the stimulus frequency ('on-off' responses). 4. We compared simple receptive fields with their sensitivity to sinusoidal gratings of different spatial frequencies. Qualitatively, the most sensitive subregions of simple cells' receptive fields are roughly the same width as the individual bars of the gratings to which they are most sensitive. Quantitatively, their receptive field profiles measured with thin stationary lines, agree well with predicted profiles derived by Fourier synthesis of their spatial frequency tuning curves.

On the characteristic of nonlinear spatial summation observed in the lateral geniculate cells of cats.

The spatial summation characteristic in the receptive fields of cat lateral geniculate cells were investigated. First, the central area of the receptive field was determined using a spot of light. Then the response of the cell were obtained using disc-shaped stimuli of various radii located in the middle point of the receptive field center. When the radius was increased gradually, the response tended to increase, at first, until it reached a peak value and began to decrease thereafter. The radius where the peak response took place was generally less than that of the receptive field center. Furthermore, this radius decreased when the intensity of the stimulus light was increased. These neurophysiological findings could be simulated by a model. The model consists of two parts. The first part receives the input from the photoreceptors. It is of homogeneous structure with shunting inhibition. The second part receives the input from the first part. The structure is characterized by the conventional center-surround type lateral interaction.

On the characteristic of nonlinear spatial summation observed in the lateral geniculate cells of cats

On the characteristic of nonlinear spatial summation observed in the lateral geniculate cells of cats