Receptive field analysis and orientation selectivity of postsynaptic potentials of simple cells in cat visual cortex

Postsynaptic potentials (PSPs) were recorded from cat striate cortical cells by the whole-cell in vivo recording technique using patch-clamp electrodes. EPSPs and IPSPs evoked by flashing bars on the receptive field at different positions and orientations revealed the spatial structure of the excitatory and inhibitory inputs. The elongation of the excitatory input field (length:width ratio) was found to be minimal (mean ratio of 1.7) and much lower than those reported for spike discharges. Two-dimensional receptive field response profiles of early PSPs were recorded by flashing a small spot of light over a square matrix covering the receptive field. These recordings also showed only mild degrees of elongations of the receptive field. Such elongations could be the result of either an excitatory input from the geniculate that is already biased for orientation or an excitatory convergence from a limited number of LGN fields arranged in a row. In most first-order cells, we found that inhibition was contributing significantly to orientation selectivity. Often prominent IPSPs could be evoked by stimuli of nonoptimum orientations. Presence of inhibition could also be inferred by the way that EPSPs were sharply cut off by inhibition. When the amplitude of an EPSP was measured at different latencies after its onset, the EPSP was found to be very broadly tuned to orientation at the beginning, but showing increasing orientation selectivity with time. It is proposed that this progressive development of orientation selectivity is due to (1) inhibitory inputs arriving after the first wave of excitation, (2) intracortical excitatory inputs from other cells tuned to similar orientations, and (3) voltage-sensitive mechanisms such as NMDA channels.

Development of pattern ERG and pattern VEP spatial resolution in kittens with unilateral esotropia

PURPOSE

To follow the development of strabismic amblyopia longitudinally by comparing mean amplitudes and the visual spatial resolving ability of retinal and cortical pattern responses at various stages of postnatal development in unilateral iatrogenic convergent strabismic kittens.

METHODS

Surgery to produce iatrogenic convergent strabismus was performed on 20 kittens at 3 weeks of age; three kittens were used for controls. The monocular transient pattern electroretinogram (PERG) and pattern visual evoked potential (PVEP) were recorded simultaneously on the 23 kittens throughout development.

RESULTS

The PVEPs of the strabismic eyes were very reduced at 4 to 5 postnatal weeks (P < 0.01). The reduction increased at 6 to 16 weeks but was even worse at 17 to 30 weeks. The PERG of the squinting eye showed only a slight reduction in the first 4 to 5 weeks of age (P > 0.05), the decrease of responses was significant (P < 0.01) at 6 to 16 weeks and 17 to 30 weeks. At 4 to 8 weeks of age, the PVEP evoked through the unoperated eye in kittens consisted mainly of two positive components of similar amplitude. During development, the slow component decreased in comparison to the fast one, and its peak shifted forward until it merged into the fast (P100) component.

CONCLUSIONS

Esotropic amblyopia did affect the PERG and the PVEP in the amblyopic eye, but the effect on the PERG was less severe, had slower onset, and did not continue as long as for the PVEP.

Excitation and inhibition in orientation selectivity of cat visual cortex neurons revealed by whole-cell recordings in vivo

One striking transformation in response properties that occurs in the geniculo-cortical pathway is the appearance of a high degree of orientation selectivity in the cortex. This property may be conceived as arising purely from the excitatory inputs to the cell, as being structured largely by the inhibition a cortical cell receives or could be due to a combination of the two. We have studied the contributions of excitatory and inhibitory inputs to cortical cells' orientation selectivity by analyzing the postsynaptic potentials evoked in cat striate neurones by flashing stimuli of different orientations. We made these recordings using the in vivo whole-cell technique (Xing Pei et al., 1991), which provides more stable and reliable results than classical intracellular recording methods. Our results show that the cat striate cortex exhibits a variety of mechanisms to achieve orientation selectivity. Orientation selectivity of a particular cell can be created by excitatory, by inhibitory, or by a combination of both mechanisms.

[Bacterial microcolony and its primary applications]

A new rapid and useful microcolony technique was developed by using cellulose-acetate membrane as a supporter. The bacteria were inoculated on the membrane and cultivated for 3-6h. Then the membrane was rendered, fixed and colored. The microcolonies were observed and counted under the microscope. By using this technique the microcolonies of 139 strains of bacteria were observed. 72 strains of Staphylococcus were differentiated by means of observing the characteristics of the microcolonies. The correlation rate between the microcolony method and the routine method was 90.28%. This technique was also first used to determine the bacteria numbers in urine within 6h, and the advantages of it were significant compared with the plate count method.

Postsynaptic potentials in cat visual cortex: dependence on polarization

During the investigation of visually evoked postsynaptic potentials (PSPs) of visual cortical neurons, we recorded cell activity under different levels of membrane potential. In some cases, however, dependence of these PSPs on the level of membrane polarization appears to be inconsistent with the conventional scheme. One disagreement was the reduction, instead of an increase, of excitatory potentials during hyperpolarization of the cell. The other point was that depolarization of the cell often leads to increase of the amplitude of both excitatory and inhibitory postsynaptic potentials. This inconsistency may suggest the involvement of voltage-dependent ion channels in generating PSPs to visual stimuli. A possible way of separating the excitatory and inhibitory components of the response by polarization of the cell in spite of the presence of voltage-dependent channels and possible implications of this mechanism in the visual cortex are discussed.

Extensive disinhibitory region beyond the classical receptive field of cat retinal ganglion cells

Forty-three single fibres were recorded from cat optic tract. They were tested with flashing lines of different lengths and/or spots of different dimensions. The area of centre excitation and of surround inhibition were represented in the length (or dimension)-response functions by the steep rising and falling phases, respectively. For most of the cells, a secondary gentle rise was seen when the stimulus extended beyond the inhibitory surround, indicating an extensive disinhibitory region (DIR) outside the classical receptive field (RF). Disinhibition appeared and developed concurrently with surround inhibition at stimulus intensities between 3 and 30 cd/m2, being represented in the phasic or the tonic component of responses depending on the cell type recorded.

The neurophysiological correlates of colour and brightness contrast in lateral geniculate neurons. II. Adaptation and surround effects

We report on experiments which were undertaken in an attempt to clarify mechanisms underlying the contrast effects of chromatic surround illumination on spectral responsiveness of cells in the parvocellular layers of the LGN (P-LGN-cells), that had been demonstrated under standard conditions in the preceding companion paper. The experiments were done in anesthetized macaques (Macaca fascicularis). In some neurons, S-potentials were recorded together with the post-synaptic action potentials, and all effects seen in P-LGN-cells were present already in their retinal afferents indicating their retinal origin. The responsiveness of the cells for center stimuli of different wavelengths and during illumination of the receptive field center or the outer surround was determined. Continuous outer surround illumination altered maintained discharge rate (MDR), sensitivity and gain of P-LGN and retinal ganglion cells in the same way and empirically not distinguishable from direct illumination of the receptive field. Responses to surround flashes showed the same dependence on spectral composition as those to center flashes. Adaptation and excitation caused by outer surround illumination (inner diameter 5 degrees, outer diameter 20 degrees) were, in the average, ten times weaker than those exerted by light of the same spectral composition shone directly into the receptive field. Surround effects decreased proportional to r-2. Excitation by outer surround flashes was reduced by adaptation of the receptive field center in the same manner as responses to center flashes. The findings indicate that outer surround light has a direct excitatory and adaptive effect on the excitatory or inhibitory cones feeding into the receptive field. This indicates that straylight from the surround into the center could be responsible for the adaptive and excitatory effects of surround illumination. The straylight fraction from the remote surround into the receptive field must be higher, however, than that estimated from the psychophysically determined point spread function. It comes closer to earlier direct straylight measurements in excised eyes, but may be enhanced by chromatic aberration. If a surround of excitatory colour is flashed simultaneously with an excitatory center stimulus, additivity of center and surround excitation is observed only at low center intensities, while at higher center intensities the gain for center excitation is reduced similar to adaptive gain control. This could be explained by lateral interaction through horizontal connections in the retina, which decays within seconds, while adaptation of the cones feeding into the receptive field center is fully effective only after about 3 s.(ABSTRACT TRUNCATED AT 400 WORDS)

The neurophysiological correlates of colour and brightness contrast in lateral geniculate neurons. I. Population analysis

The colour of an object is changed by surround colours so that the perceived colour is shifted in a direction complementary to the surround colour. To investigate the physiological mechanism underlying this phenomenon, we recorded from 260 neurons in the parvo-cellular lateral geniculate nucleus (P-LGN) of anaesthetized monkeys (Macaca fascicularis), and measured their responses to 1.0-2.0 degrees diameter spots of equiluminant light of various spectral composition, centered over their receptive field (spectral response function, SRF). Five classes of colour opponent neurons and two groups of light inhibited cells were distinguished following the classification proposed by Creutzfeldt et al. (1979). In each cell we repeated the SRF measurement while an outer surround (inner diameter 5 degrees, outer diameter 20 degrees) was continuously illuminated with blue (452 nm) or red (664 nm) light of the same luminance as the center spots. The 1.0-1.5 degree gap between the center and the surround was illuminated with a dim white background light (0.5-1cd/m2). During blue surround illumination, neurons with an excitatory input from S- or M-cones (narrow- and wide-band/short-wavelength sensitive cells, NS- and WS-cells, respectively) showed a strong attenuation of responses to blue and green center spots, while their maintained discharge rate (MDR) increased. During red surround illumination the on-minus-off-responses of NS- and WS-cells showed a clear increment. L-cone excited WL-cells (wide-band/long-wavelength sensitive) showed a decrement of on-responses to red, yellow and green center spots during red surround illumination and, in the majority, also an increment of MDR. The response attenuation of narrow-band/long-wave-length sensitive (NL)-cells was more variable, but their on-minus-off-responses were also clearly reduced in the average during red surrounds. Blue surround illumination affected WL-cell responses little and less consistently than those of NL-cells, but often broadened the SRF also in the WL-cells towards shorter wavelengths. The M-cone excited and S-cone suppressed WM-cells were strongly suppressed by blue but only little affected by red surround illumination. The changes of spectral responsiveness came out clearly in the group averages of the different cell classes, but showed some variation between individual cells in each group. The zero-crossing wavelengths derived from on-minus-off-responses were also characteristically shifted towards wavelengths complementary to those of the surround.(ABSTRACT TRUNCATED AT 400 WORDS)

Whole cell recording and conductance measurements in cat visual cortex in-vivo

Long and stable recordings of post-synaptic, action and membrane potentials from visual cortical neurons in-vivo, are possible with the patch-clamp technique. These are comparable to the whole-cell configuration, but with an incomplete seal. EPSPs and IPSPs of normal time course and up to several mV can be recorded. DC potentials ranged from - 30 to - 60 mV and input resistances from 50 to 150 M omega. Injected currents have the same effect as if applied intracellularly. Membrane conductance after electrical stimulation of the lateral geniculate nucleus is increased during the first 20 ms, but decreases from 60 to about 130 ms, during return of the membrane potential to its resting level. The recording method is compared to other intracellular recording techniques in-vivo and in-vitro.

Role of the extensive area outside the X-cell receptive field in brightness information transmission

Stimulus area-response functions of retinal ganglion cells show an extensive disinhibitory region (DIR) outside the classical receptive field (RF). The DIR has a wide summation area but low sensitivity. Spatial responses of the retinal ganglion cells have been simulated in a model which takes into account also the properties of the DIR. By scanning the RF and its DIR with a visual image and reconstructing the transferred image for single cells, it is shown that these properties of the DIR are beneficial in the transmission of area brightness and image grey scales.