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A J Vendrik

Publications and source records attributed to A J Vendrik.

At least 19 recordsLinked to original sources
PubMed1982

Reconstruction of cone-system contributions to responses of colour-opponent neurones in monkey lateral geniculate.

Responses of colour-opponent X-cells to intensity-modulation at various wavelengths were obtained in the lateral geniculate nucleus (LGN) of the anaesthetized (N2O/O2) rhesus monkey. The gaussian white noise (GWN) analysis method was used to describe the stimulus-response relationship. Two different methods were used to estimate sign and relative strength of the response contribution of each of the three known cone systems as a function of time. Both methods revealed that, in contrast to the well-known variability in gain and sign, the time course of the cone-type contributions was remarkably stereotyped in all cells. Surround-mediated cone-type contributions appeared to have a consistently longer delay than centre-mediated inputs. Response contributions from different types of cone appeared to add linearly in LGN neurones. Apart from rectification, it was possible to predict the response of the same neurone to step-modulation of intensity at various wavelengths successfully with the first-order Wiener kernel. This demonstrates that the cells behaved linearly under our stimulus conditions, which justifies the use of the first-order kernel as a means to characterize the system we wished to study.

Animals↗
PubMed1981

Characterization of spatial and temporal properties of monkey LGN Y-cells.

LGN Y-cells in 3 anaesthetized (N2O/O2) and paralyzed rhesus monkeys were investigated with stimuli, intensity modulated by gaussian white noise, and with moving and counterphase modulated spatial sine wave gratings. The results support the model, postulated on the base of electrophysiological recordings in the retina cat and mudpuppy, which consists of a linear centre and surround mechanism whose responses are modified in a frequency-selective multiplicative way by a nonlinear mechanism in the receptive field. This nonlinear mechanism is also held responsible for the second-order harmonic responses, which are the defining characteristic of Y-cells. The temporal and spatial characteristics of these mechanisms were determined. The responses obtained with the GWN stimulation and with modulated spatial sine wave gratings both indicate that the optimal temporal frequency of the linear mechanisms is near 7 Hz and 70 td and near 5 Hz for the nonlinear mechanism. The optimal spatial frequency for the linear mechanism is between 0.5--2 cycles/deg and between 6--12 cycles/deg for the nonlinear mechanism.

Action Potentials↗
PubMed1979

Responses of single units in the monkey superior colliculus to stationary flashing stimuli.

1. Responses of pan-directional cells in the superficial layers of the superior colliculus in paralysed anaesthetized rhesus monkeys to stationary flashing stimuli have been studied. 2. The receptive field centre response is always of the transient excitatory on-off type, while the surround response is transient inhibitory both at light-on and at light-off. The receptive field centres are circular or slightly elliptical. The average size of the receptive field centres is much larger than that of retinal ganglion cells. All units except those in the far temporal periphery receive binocular input. In each unit the on and off responses have the same latency times. With increasing stimulus area, the latency time at light-on and at light-off first decreases and then remains constant. In most units the number of spikes in the burst at light-on and at light-off first increases, reaches a maximum and then decreases with increasing stimulus area. This decrease demonstrates the presence of an inhibitory surround. 3. A model of spatial and temporal properties of centre and surround mechanisms is tested. Addition of excitatory centre input and inhibitory surround input, which have different spatial and temporal properties, determines the output of the neurone. The centre mechanism gets excitatory input from retinal ganglion cells and shows saturation. The inhibitory surround mechanism is made by an inhibitory interneurone. It could not be decided whether the excitatory input for this interneurone comes from retinal axon collaterals (forward inhibition) or from axon collaterals of "principal" cells in the superior colliculus (backward inhibition).

Animals↗
PubMed1979

Responses of single units in the monkey superior colliculus to moving stimuli.

1. Single unit responses of pan-directional cells to moving and stationary flashing stimuli were studied in the superficial layers of the superior colliculus in paralysed, anaesthetized rhesus monkeys. The aim of this study was to see how far cell responses to moving stimuli fit in with what would be expected from their responses to stationary flashing stimuli. 2. Both the leading and the trailing edge of a moving stimulus evoke a transient response. If the diameter of moving light spots is increased the strength of the leading edge response increases, reaches a maximum and decreases to a constant value which is similar to the behaviour of the on response when the diameter of flashing spots is increased. The strength of the trailing edge response increases and reaches the same strength as that of the leading edge response. If the width of a long moving slit is increased, the strength of the leading edge response is the same at all slit widths, while the strength of the trailing edge response shows a course similar to that of the trailing edge response if the spot diameter is increased. If the length of a wide moving slit is increased both the leading and the trailing edge responses decrease. These results indicate that the strength of both leading and trailing edge responses is dependent on the degree the inhibitory surround is activated. 3. The leading and the trailing edge of a stimulus evoke their responses at the same position in the receptive field independent of the direction of movement. 4. Increasing the velocity of a moving stimulus shows that in general the leading edge response is present up to higher velocities than the trailing edge response independent of the sign of contrast. The burst duration to moving stimuli decreases with increasing stimulus velocity and appears to be determined by the time a moving edge is present in the receptive field centre. When this time becomes shorter than 10--20 ms, the burst duration for moving stimuli is constant and about the same as for flashing stimuli. This indicates that, although spatial receptive field properties can vary considerably, temporal receptive field properties show a strong similarity among different units. 5. The response latencies to light and dark moving edges are the same, which in turn are about equal to the response latencies to stationary flashing stimuli. 6. Stimulation experiments show that the general response characteristics to moving stimuli can be predicted by using a set of receptive field parameters derived from responses to stationary flashing stimuli. The most important variable of moving stimuli appears to be the period of time a moving contour is present within the receptive field centre, besides the degree of activation of the inhibitory surround.

Animals↗
PubMed1975

Spectral and temporal characteristics of activation and suppression of units in the cochlear nuclei of the anaesthetized cat.

1. The responses are described of cochlear nucleus neurons of anaesthetized cats as a function of time in dependence on intensity and frequency of tonal stimuli. Depending on spectral properties three types are distinguished in the group of spontaneously active units: A type (activation only) AS type (activation and suppression) and S type (suppression only). The A(S) neurons have insufficient spontaneous activity to judge presence or absence of suppression. 2. Four temporal patterns of response are distinguished: transient, sustained, build up and complex. Units of the A type display a sustained time course of activation and have properties similar to those of auditory nerve fibres. S type units show sustained suppression. Temporal patterns of activation other than sustained were found only in the AS and A(S) units. 3. The recordings indicate that on suppression and off suppression are present more frequently in VCN neurons than previously found. The suppression phenomena in the DCN are, however, still more wide spread and more dramatic in appearance. 4. In contrast to earlier findings, off suppression was always observed and never seen to extent beyond the on activation band in A neurons. Data from AS neurons indicate that off suppression is neither simply an affect of high firing rates nor simply a continuation of on suppresion. 5. The relations between off suppression and spectral and temporal characteristics of on activation and suppression can be matched with a model featuring overlapping antagonistic inputs and postexcitatory inhibition.

Anesthesia, General↗
PubMed1975

Neurons in the cochlear nucleus investigated with tone and noise stimuli.

1. Responses of cochlear nucleus neurons to stationary and amplitude modulated noise stimulation are investigated and compared with responses to tonal stimuli. 2. Cross-correlation functions, computed from responses to stationary noise stimulation, showing a clear oscillation could be most easily obtained from low CF fibres presumed to be auditory nerve fibres and low CF cochlear nucleus neurons showing only activation response and a primarylike temporal pattern of response to tone bursts. This reflects good quality of phase locking in these neurons. 3. The CCF reflects strongly the frequency selectivity of the neuron as revealed in its response area but not the temporal pattern of response to tone bursts. 4. Responses to noise bursts are correlated with the responses to tone bursts of many different frequencies in both their sign (i.e. activation or suppression) and their temporal pattern. 5. The concept of two independently operating mechanisms, one depending on the fine time structure of the stimulus (the carrier) and the other on its amplitude, and determining respectively the fine time structure of the response pattern and its magnitude, is introduced. Experimental data are presented which lend support to the adequacy of the description in the majority of cases and reveal its shortcomings in others.

Animals↗
PubMed1975

Statistical analysis and interpretation of the initial response of cochlear nucleus neurons to tone bursts.

1. Subject of investigation is the initial response of cochlear nucleus neurons and units presumed to be auditory nerve fibres to CF tone burst stimulation. 2. The initial response is characterized by computing the distribution of the latency of the first spike and of the duration of the first interval in the ensemble of responses to a large number of stimuli. 3. In many of the neurons the properties of both distributions appear to be related. The presumed auditory nerve fibres and spontaneously active cochlear nucleus neurons showing only activation responses to tonal stimuli (A type) exhibit irregularity in both response onset and intervals. Minimum latency and minimum first intervals are short. On the other hand, spontaneously active neurons with both activation and suppression in the response area (AS type) and silent neurons showing only activation (A(S) type) often show a more precisely timed onset of response and narrow interval distributions. In many neurons this leads to oscillations in the PSTH (chopping). In these neurons minimum latency and minimum first interval have higher values. The longer minimum latency cannot be attribute-d to longer pure time delays in these neurons. 4. The results are interpreted as speaking in favour of temporal integration as an important mechanism in many of the AS and A(S) neurons, particularly those in the DCN. The firing patterns of A neurons are thought to indicate virtual absence of this mechanism. 5. Using pure time delay estimates derived from cross-correlation functions, computed from the responses to stationary noise, an attempt is made to estimate the integration time in the cochlear and in the cochlear nucleus neurons.

Animals↗