The position sensitivity of retinal X- and Y-cells in cats

Summary We have devised a measure of a retinal ganglion cell's sensitivity to changes in the spatial position of a grating stimulus. At maximum, this relative position sensitivity is a scaled product of the stimulus spatial frequency and the cell's fundamental component of response to that spatial frequency. We obtained the relative position sensitivity as a function of spatial frequency for 13 X-cells and 14 Y-cells. X-cell functions peak at significantly higher spatial frequencies than do those of Y-cells. At their peaks, X-cells display significantly higher values of relative position sensitivity than do Y-cells. However, Y-cells have higher position sensitivity at lower spatial frequencies, but exhibit less of a range of variation from maximum to minimum than do X-cells. These results are consistent with a hypothesis that Y-cells provide the crucial substrate for form vision at lower spatial frequencies, while X-cells are important for details carried by the higher spatial frequencies.Supported by USPHS grants EY05241 and EY03038     

Development of neuronal response properties in the cat dorsal lateral geniculate nucleus during monocular deprivation

We measured response properties of X- and Y-cells from laminae A and A1 of the dorsal lateral geniculate nucleus of monocularly lid-sutured cats at 8, 12, 16, 24, and 52-60 wk of age. Visual stimuli consisted of small spots of light and vertically oriented sine-wave gratings counterphased at a rate of 2 cycles/s. In cats as young as 8 wk of age, nondeprived and deprived neurons could be clearly identified as X-cells or Y-cells with criteria previously established for adult animals. Nonlinear responses of Y-cells from 8- and 12-wk-old cats were often temporally labile; that is, the amplitude of the nonlinear response of nondeprived and deprived cells increased or decreased suddenly. A similar lability was not noted for the linear response component. This phenomenon rarely occurred in older cats. At 8 wk of age, Y-cell proportions (number of Y-cells/total number of cells) in nondeprived and deprived A-laminae were approximately equal. By 12 wk of age and thereafter, the proportion of Y-cells in deprived laminae was significantly lower than that in nondeprived laminae. At no age was there a systematic difference in response properties (spatial resolution, latency to optic chiasm stimulation, etc.) for Y-cells between deprived and nondeprived laminae. Spatial resolution, defined as the highest spatial frequency to which a cell would respond at a contrast of 0.6, was similar for nondeprived and deprived X-cells until 24 wk of age. In these and older cats, the mean spatial resolution of deprived X-cells was lower than that of nondeprived X-cells. This difference was noted first for lamina A1 at 24 wk of age and later for lamina A at 52-60 wk of age. The average latency of X-cells to optic chiasm stimulation was slightly greater in deprived laminae than in nondeprived laminae. No such difference was seen for Y-cells. Cells with poor and inconsistent responses were encountered infrequently but were observed far more often in deprived laminae than in nondeprived laminae. Lid suture appears to affect the development of geniculate X- and Y-cells in very different ways. Not only is the final pattern of abnormalities quite different between these cell groups, but the developmental dynamics of these abnormalities also differ.     

Properties of concentrically organized X and Y ganglion cells of macaque retina.

1. Macaque retinal ganglion cells having concentrically organized receptive fields were classified as X- or Y-cells on the basis of the linearity or nonlinearity of their spatial summation to a "null" test of alternating contrast and drifting gratings. 2. When an alternating-phase, bipartite field positioned at the middle of the receptive field was used as a stimulus, X-cells had a null position, whereas Y-cells showed a doubling of the response frequency. When drifting sine-wave gratings of low contrast were used as a stimulus, X-cells showed a periodic modulation of their discharge having the same mean value for different spatial frequencies, whereas Y-cells showed a large increase in the mean value of their discharges. 3. X-cells had opponent-color responses that received cone-specific signals, i.e., center and surround responses were mediated by input from spectrally different types of cone, whereas Y-cells had broad-band spectral responses receiving mixed-cone signals, i.e., center and surround responses were totally or partly mediated by input from the same type(s) of cone. In most Y-cells, the spatially opponent responses from the center and the surround were mediated by the same types of cone and were thus spectrally nonopponent; other Y-cells showed spectral opponency, since one of the types of cone mediating responses of one region of the receptive field (e.g., center) was absent in the responses of the other region (e.g., surround). 4. X- and Y-cells projected to the lateral geniculate body. Opponent-color X- and Y-cells did not project to the superior colliculus, whereas a fraction of spectrally non-opponent Y-cells projected to this structure. 5. X-cells tended to have longer conduction latencies, less transient responses to small stimuli, and a more central retinal distribution than Y-cells; these differences, however, represented tendencies and not invariant properties. 6. The results show that the X/Y dichotomy of ganglion cells is present in the retina of macaques and indicate that the degree of the linearity of spatial summation of incoming cone signals to the cells is related to the degree of cone specificity of spectral inputs to the receptive-field mechanisms.     

Velocity tuning of cells in dorsal lateral geniculate nucleus and retina of the cat

Velocity tuning curves were measured for on-center cells in the dorsal lateral geniculate nucleus of the cat using a stimulus approximately the height and one-fourth the width of the hand-plotted receptive-field center. The standard stimulus strength was 1 log unit above the mesopic background luminance. Lateral geniculate Y-cells had significantly higher preferred velocities than geniculate X-cells when cells with receptive fields having the same range of retinal eccentricities were compared. Preferred velocity increased for both classes of cells as a function of retinal eccentricity. For all geniculate cells, preferred velocity increased with stimulus strength, showing an approximately threefold increase in preferred velocity for each log unit of stimulus strength. Preferred velocity was measured for on-center retinal ganglion cells with receptive fields at the same range of retinal eccentricities as the geniculate sample and under the same stimulus conditions. Preferred velocities of retinal ganglion Y-cells were significantly higher than those of ganglion X-cells, and as for geniculate cells, preferred velocities increased with increasing stimulus strength. However, the classes were better separated in the geniculate than in the retina; with geniculate X-cells having lower preferred velocities than retinal X-cells, and the geniculate Y-cells having higher preferred velocities than retinal Y-cells. For retinal ganglion cells, smaller receptive-field center sizes of the X-cells than the Y-cells could account in large part for the lower preferred velocities of the X-cells. However, for geniculate cells, differences in receptive-field center size could not account as well for the differences in preferred velocity between X- and Y-cells. Furthermore, field size differences could not account for the differences in preferred velocity between ganglion and geniculate cells of the same functional class. Experiments comparing responses to moving stimuli and flashed stationary stimuli show that stimuli moving at high velocities are in effect equivalent to brief-duration flashes, and responses are governed by the same laws of temporal summation in both cases. When velocity tuning curves were measured with long bars that enhanced peripheral inhibition, geniculate X- and Y-cells were better separated than ganglion X- and Y-cells, not only with respect to preferred velocity but also, with respect to velocity selectivity (width of the velocity tuning curve) and differential velocity sensitivity (slope of the leg of the velocity tuning curves ascending from low velocities to the peak).(ABSTRACT TRUNCATED AT 400 WORDS)     

Evidence of input from lagged cells in the lateral geniculate nucleus to simple cells in cortical area 17 of the cat.

1. The visual cortex receives several types of afferents from the lateral geniculate nucleus (LGN) of the thalamus. In the cat, previous work studied the ON/OFF and X/Y distinctions, investigating their convergence and segregation in cortex. Here we pursue the lagged/nonlagged dichotomy as it applies to simple cells in area 17. Lagged and nonlagged cells in the A-layers of the LGN can be distinguished by the timing of their responses to sinusoidally luminance-modulated stimuli. We therefore used similar stimuli in cortex to search for signs of lagged and nonlagged inputs to cortical cells. 2. Line-weighting functions were obtained from 37 simple cells. A bar was presented at a series of positions across the receptive field, with the luminance of the bar modulated sinusoidally at a series of temporal frequencies. First harmonic response amplitude and phase values for each position were plotted as a function of temporal frequency. Linear regression on the phase versus temporal frequency data provided estimates of latency (slope) and absolute phase (intercept) for each receptive-field position tested. These two parameters were previously shown to distinguish between lagged and nonlagged LGN cells. Lagged cells generally have latencies > 100 ms and absolute phase lags; nonlagged cells have latencies < 100 ms and absolute phase leads. With the use of these criteria, we classified responses at discrete positions inside cortical receptive fields as lagged-like and nonlagged-like. 3. Both lagged-like and nonlagged-like responses were observed. The majority of cortical cells had only or nearly only nonlagged-like zones. In 15 of the 37 cells, however, the receptive field consisted of > or = 20% lagged-like zones. For eight of these cells, lagged-like responses predominated. 4. The distribution of latency and absolute phase across the sample of cortical simple cell receptive fields resembled the distribution for LGN cells. The resemblance was especially striking when only cells in or adjacent to geniculate recipient layers were considered. Absolute phase lags were almost uniformly associated with long latencies. Absolute phase leads were generally associated with short latencies, although cortical cells responded with long latencies and absolute phase leads slightly more often than LGN cells. 5. Cells in which a high percentage of lagged-like responses were observed had a restricted laminar localization, with all but two being found in layer 4B or 5A. Cells with predominantly nonlagged-like responses were found in all layers. 6. Lagged-like zones can not be easily explained as a result of stimulating combinations of nonlagged inputs.(ABSTRACT TRUNCATED AT 400 WORDS)     

Velocity selectivity in the cat visual system. I. Responses of LGN cells to moving bar stimuli: a comparison with cortical areas 17 and 18

Velocity selectivity of 92 LGN cells was measured quantitatively using long, narrow light or dark bars of high contrast in N2O-anesthetized and paralyzed cats. The optimal velocities of the main responses to a moving light bar, representing center responses (i.e., due to entering the ON center or leaving the OFF center) were significantly lower for X-cells than for Y-cells. The velocity upper cutoffs were significantly higher for Y-cells than for X-cells, whereas responses to slow movement were significantly stronger in X-cells than in Y-cells. The velocity range over which secondary responses were found was significantly lower for X-cells than for Y-cells. The velocity characteristics of LGN cells were compared with those measured under precisely the same experimental conditions in areas 17 and 18. Overall, the LGN cells were sensitive to much faster velocities than cortical cells. The differences between these cortical areas were found to be much larger than the differences in velocity selectivity observed in the LGN between X- and Y-cells or within the X and Y classes. In particular, the ubiquitous presence of cells responding only to very low velocities (less than 10 degrees/s) in area 17 subserving central vision cannot directly reflect LGN velocity selectivity, since such extreme preference for low velocities was not found in the LGN sample. Changes in eccentricity had much less effect on the velocity characteristics in the LGN than in the cortex. The latency of responses to a moving light bar as estimated using a spatial lag-velocity method was on average 46 and 37 ms for X-ON and Y-ON cells as opposed to 75 and 68 ms for X-OFF and Y-OFF cells, respectively. These latencies were slightly shorter than the ON and OFF latencies (time to peak) measured with stationary presentations of the same light bar (averages 61 and 53 ms for X-ON and Y-ON, 113 and 93 ms for X-OFF and Y-OFF). For a moving dark bar the average latency was 35 and 29 ms for X-OFF and Y-OFF cells, respectively, whereas it was 47 and 54 ms for X-ON and Y-ON cells. There were no significant differences in response strength between ON and OFF cells nor between X- and Y-cells. Many Y-OFF cells had nonlinear spatial lag-velocity relationships. This indicates a shift in response origin from distal to more proximal parts of the receptive field when going from low to high velocities.(ABSTRACT TRUNCATED AT 400 WORDS)     

Non-linear spatial summation in cat retinal ganglion cells at different background levels

Summary Cat retinal ganglion cells were identified as X-cells (linear) or Y-cells (non-linear) on the basis of the spatial summation properties of their receptive fields. For each cell, the degree of non-linearity in spatial summation was assessed at a number of different mean luminance levels in order to determine how spatial linearity depended on mean luminance. The stimuli were counterphase sinusoidal gratings whose contrast was sinusoidally modulated in time. A grating with one bar centered on the receptive field was used to measure the contrast sensitivity of the mechanisms which produced responses at the stimulus frequency. A grating with a zero crossing centered on the receptive field was used to measure the contrast sensitivity of mechanisms responsible for the non-linear frequency doubled responses of Y-cells. As the mean luminance was reduced from low photopic to scotopic, the contrast sensitivity decreased for both the linear and non-linear responses. The ratio of non-linear to linear sensitivity in Y-cells changed less with background than did either contrast sensitivity. In some Y-cells this ratio decreased slightly at low luminance levels, but in others it did not. X-cells appeared to sum signals linearly at all levels of illumination. X-cells and Y-cells could still be distinguished on the basis of their spatial summation properties in the scotopic range.     

Nonlinear measurement and classification of receptive fields in cat retinal ganglion cells

Originally, modeling of ganglion-cell responses in cat was based mainly on linear analysis. This is satisfactory for those cells in which spatial summation of excitation is approximately linear (X-cells) but it fails for Y-cells, where summation has strong nonlinear components. Others have shown the utility of using sinusoidal analysis to study harmonic and intermodulation nonlinearities in the temporal frequency domain. We have used Wiener-kernel analysis to obtain directly both temporal and spatial impulse responses and their nonlinear interactions. From these, we were able to predict accurately the responses that a counterphase modulated grating elicited in both X-cells and Y-cells. In addition, we show that the first-order responses can measure the two-dimensional spatial features of the receptive field with high resolution. Thus, nonlinear analysis of responses to white-noise stimuli may be sufficient to both classify and measure the receptive fields of many different types of ganglion cells.     

Classification of cat retinal ganglion cells into X- and Y-cells with a contrast reversal stimulus

Summary A contrast reversal (alternating phase) stimulus was used to study the responses of 150 retinal ganglion cells from 15 adult cats. Because the majority of the cells did not show perfect linear spatial summation, a ratio of the firing rates at two time periods was used to express the degree of nonlinearity. Y-cells showed a high degree of nonlinearity, and their mean null ratio was significantly lower than that of X-cells. With the stimulus at the null position, X-cells had an unmodulated discharge rate which was significantly higher than maintained activity, while the firing rate of Y-cells was lower than maintained activity. With the stimulus placed at an eccentric position in the receptive field, X-cells responded in a sustained manner, while Y-cells respond transiently. Because of these observations, we conclude that X-cells correspond to the sustained cells, while Y-cells correspond to the transient cells.     

Neurotransmitter receptors mediating excitatory input to cells in the cat lateral geniculate nucleus. I. Lagged cells

1. Synaptic mechanisms that might explain the functional properties of the recently discovered class of lagged cells in the dorsal lateral geniculate nucleus (LGN) were analyzed with electrophysiological and pharmacologic techniques. To study the type of excitatory amino acid (EAA) receptor that mediates visual responses of lagged cells, we recorded the response of single cells to a stationary flashing light spot before, during, and after microiontophoretic application of antagonists and agonists to EAA receptors. 2. The visual response of the lagged cells could be almost completely blocked by an antagonist to the N-methyl-D-aspartate (NMDA) receptor. The degree of suppression was dose dependent, and the average maximum degree of suppression for all the cells was 94%. NMDA enhanced the response, and this enhancement was antagonized by NMDA antagonists. A quisqualate/kainate receptor antagonist had no significant effect on the lagged cells. 3. These findings indicate that the visual response in lagged cells is dependent upon activation of NMDA receptors, which may directly result from activation of retinal inputs. 4. No pharmacologic difference was seen between lagged X- and Y-cells, or between lagged ON- and OFF-center cells. 5. gamma-Aminobutyric acid-A (GABA-A) receptor antagonists were used to study whether the characteristic lag of the visual response and the suppression of the initial transient response component of the lagged cells are dependent on geniculate inhibition. Beside enhancement of the visual response, the GABA antagonists strongly reduced the lag of the visual response, and an initial transient response component occurred instead of the initial suppression. The lag remained slightly longer than for nonlagged cells, and the peak firing rate of the transient was below values typical for nonlagged cells, indicating that the lagged cell properties are dependent on other factors beside GABA-A receptor-mediated inhibition. 6. The enhanced visual response during iontophoresis of GABA antagonists could be completely blocked by simultaneous iontophoresis of an NMDA-receptor antagonist. This gives further support to the hypothesis that the retinal input to these cells is mediated by NMDA receptors. 7. The NMDA-receptor/ionophore complex mediates excitatory postsynaptic potentials (EPSPs) characterized by slow rise and decay times and long duration. The ionophore is characterized by a voltage-dependent blockade that makes these receptors particularly sensitive to inhibitory input. The temporal interplay between the slow NMDA receptor-mediated EPSPs and the fast GABA receptor-mediated inhibitory postsynaptic potentials (IPSPs) may explain the characteristic response properties of the lagged cells.     

Properties of X- and Y-cells in the rabbit retina

Bevelled glass microelectrodes were used to record spike potentials extracellularly from the ganglion cells of the rabbit retina. Good responses were obtained from the isolated retina or eye-cup preparation for at least 12 hr. Using a contrast reversal stimulus, 63.8% (67/105) of the units showed linear spatial summation (X-cells), and 21.0% (22/105) showed nonlinear spatial summation (Y-cells). The X- and Y-cells in the rabbit retina had physiological properties which were similar to those in cat retina. Directionally selective cells (15.2%) were found to respond poorly, if at all, to the contrast reversal stimulus.     

Spatial properties of neurones in the lateral geniculate nucleus of the pigmented ferret

Summary We used quantitative electrophysiological techniques to study the spatial properties of single units recorded extracellularly in the lateral geniculate and perigeniculate nuclei of the adult pigmented ferret. All neurones examined had approximately circular receptive fields, whose central regions gave responses antagonistic to those elicited from the surrounds. We presented sinusoidally modulated grating patterns, either drifting or counterphased, to obtain spatial frequency tuning curves, contrast sensitivity functions and to assess linearity or non-linearity of each neurone's response. In the ferret, as in other species, two types of lateral geniculate neurone could be distinguished, and we have termed these X-cells and Y-cells; both groups responded briskly to visual stimulation but X-cells gave sustained and linear responses whereas Y-cells responded transiently and non-linearly. Perigeniculate cells gave linear responses. For neurones in the lateral geniculate and perigeniculate nuclei, both the limit of spatial resolution (acuity) and optimum spatial frequency were inversely related to receptive field eccentricity and the diameter of the receptive field centre. We recorded geniculate neurones in the ferret with acuities up to 3 cycles deg^-1 and contrast sensitivities up to 114, values that are lower than those found previously for many geniculate cells in the cat.     

Precision, reliability, and information-theoretic analysis of visual thalamocortical neurons

High-order statistics of neural responses allow one to gain insight into neural function that may not be evident from firing rate alone. In this study, we compared the precision, reliability, and information content of spike trains from X- and Y-cells in the lateral geniculate nucleus (LGN) and layer IV simple cells of area 17 in the cat. To a stochastic, contrast-modulated Gabor patch, layer IV simple cells responded as precisely as their primary inputs, LGN X-cells, but less reliably. LGN Y-cells were more precise and reliable than LGN X-cells. Also, within each LGN cell type, 1) responses to the same stimulus were nearly identical if they shared the same center sign and 2) responses of neurons with the same center sign were nearly identical to the responses of neurons of opposite center sign if the stimulus' contrasts were inverted. These results suggest simple cells receive highly precise and synchronous LGN input, resulting in precise responses. Nonetheless, the response precision of simple cells was greater than expected. Finally, information-theoretic calculations of our cell responses revealed that 1) LGN X-cells encoded information at half the rate of LGN Y-cells but 2.5 times the rate of layer IV simple cells; 2) LGN cells encoded information in their responses using temporal patterns, whereas simple cells did not; and 3) simple cells used more of their information capacity than LGN X-cells. We propose mechanisms that simple cells might use to ensure high precision.     

W-and Y-cells in the C layers of the cat's lateral geniculate nucleus: normal properties and effects of monocular deprivation

1. Previous studies have shown that rearing with monocular visual deprivation (MD) produces a loss of Y-cells and a reduction in spatial resolution among X-cells in layers A and A1 of the cat's dorsal lateral geniculate nucleus (dLGN). However, there have been no studies of the effects of visual deprivation on the function of the retinogeniculate W-cell pathway, which terminates in the C layers of the dLGN. It also is not known if Y-cells in the C layers are affected by MD in the same way as Y-cells in the A layers. These questions were addressed by the present experiment. 2. Single-cell recordings were made from the C layers of 5 normal adult cats (112 cells) and from the nondeprived (94 cells) and deprived (95 cells) C layers in 10 cats monocularly deprived by lid suture for 3-7 yr. The cells were classified as X, Y, or W on the basis of their receptive-field properties and responses to electrical stimulation of the optic chiasm. In addition, quantitative measures were made of responses to sine-wave gratings of different spatial frequencies. 3. Receptive-field organization, receptive-field center size, spatial and temporal linearity to counterphased sine-wave gratings, and latency to optic chiasm stimulation were similar for C-layer cells in normal cats and in the deprived and nondeprived layers of MD cats. On the basis of these properties, 23% of normal layer-C cells were classified as Y-cells and 72% were classified as W-cells. The Y-cells tended to be located in the magnocellular division of layer C and most (though not all) W-cells were in the parvocellular division. Normal layers C1 and C2 contained almost exclusively W cells. The incidence of Y and W cells was similar to normal in the nondeprived and deprived C-layers of MD cats. 4. In normal cats, W cells typically had the lowest amplitude first-harmonic (F1) response rates to drifting sine-wave gratings. However, many W cells gave quite brisk responses and, overall, there was no significant difference between F1 response amplitudes of Y and W cells. Response amplitudes of Y- and W-cells in the deprived and nondeprived C-layers of MD cats were not significantly different from normal. 5. Normal Y- and W-cells tended to have low optimal spatial frequencies (0.2 c/deg or lower) and spatial resolutions (generally 0.4-1.6 c/deg) to drifting sine-wave gratings.(ABSTRACT TRUNCATED AT 400 WORDS)     

Adaptation and dynamics in X-cells and Y-cells of the cat retina

Summary On the basis of the spatial summation properties of their receptive fields, cat retinal ganglion cells were classified as either X-cells (linear) or Y-cells (non-linear). Responses were then obtained to a small, centered spot, square-wave modulated in time and superimposed on various levels of diffuse, steady background illumination. When fully dark-adapted, both X-cells and Y-cells produced responses that were entirely sustained. When well lightadapted but still in the scotopic range, both cell types produced largely transient responses with only a very small sustained component. The sustained or transient nature of responses is, therefore, not an invariant characteristic of X-cells and Y-cells in the scotopic range. We also conclude that the mechanism which controls the center's sensitivity in the scotopic range is similar though not identical in the two types of cells.     

The conduction velocity in retino geniculate afferent fibers in the rabbit

We have recorded X- and Y-like cells in the rabbit lateral geniculated nucleus (LGN) and found a small but statistically significant difference between the latencies of the two cell types to stimulation of the chiasm. The relative frequency of recordable Y-cells was equal in pigmented and in albino rabbits. No relative increase in the recording probability of Y-cells versus X-cells was found with increasing eccentricity of the receptive field (RF) locations with respect to the visual streak in either breed.     

Receptive-field properties of adult cat’s retinal ganglion cells with regenerated axons

Receptive-field properties of retinal ganglion cells (RGCs) that had regenerated their axons were studied by recording single-unit activity from strands teased from peripheral nerve (PN) grafts apposed to the cut optic nerve in adult cats. Of the 286 visually responsive units recorded from PN grafts in 20 cats, 49.7% were classified, according to their receptive-field properties, as Y-cells, 39.5% as X-cells, 6.6% as W-cells, and 4.2% were unclassified. The predominant representation of Y-cells is consistent with a corresponding morphological study (Watanabe et al. 1993a), which identified α-cells as the RGC type with the largest proportion of regenerating axons. Among the X-cells, we only found ON-center types, whereas both ON-center and OFF-center Y-cells were found. As in intact retinas, the receptive-field center sizes of Y-cells and W-cells were larger than those of X-cells at corresponding displacements from the area centralis. Within the 10° surrounding the area centralis, the receptive fields of X-cells with regenerated axons were larger than those in intact retinas, suggesting that some rearrangement of retinal circuitry occurred as a consequence of degeneration and regeneration. Receptive-field center responses of Y-, X-, and W-type units with regenerated axons were similar to those found in intact retinas, but the level of spontaneous activity of Y- and X-type units was, in general, less than that of intact RGCs. Receptive-field surrounds were weak or not detected in more than half of the visually responsive RGCs with regenerated axons. Received: 17 November 1997 / Accepted: 19 June 1998     

A comparison between Y-cells in A-laminae and lamina C of cat dorsal lateral geniculate nucleus

Extracellular responses of Y-cells in the A-laminae and in lamina C of the cat dorsal lateral geniculate nucleus were recorded and compared for several sine-wave grating presentations. Both spatial and temporal contrast sensitivity functions were determined for these cells as well as suprathreshold response functions at 0.2 and 0.4 contrast. Qualitatively, the responses of the lamina C Y-cells were very similar to Y-cells of the A-laminae; differences were of a quantitative nature. At threshold, lamina C Y-cells were more sensitive at all spatial and temporal frequencies tested. Suprathreshold results showed no major differences in fundamental response amplitude between laminar Y-cells. Interlaminar differences were found with respect to second harmonic response amplitude. Lamina C Y-cells gave the largest overall second harmonic response for all stimulus conditions. A trend was observed for these laminar Y-cells such that the second harmonic responses were highest for Y-cells of lamina C, intermediate for lamina A Y-cells, and lowest for those of lamina A1. Based on differences in projection pattern and present electrophysiological results, we conclude that the lamina C Y-cells may represent a population of cells that is distinct from A-laminae Y-cells. These lamina C Y-cells provide a significant input to visual cortex.     

Effects of strabismus on responsivity, spatial resolution, and contrast sensitivity of cat lateral geniculate neurons

Rearing cats with esotropia is known to cause a number of deficits in visual behavior tested through the deviated eye. These include a loss of orienting response to stimuli presented in the nasal visual field of the deviated eye, a reduction in visual acuity, and a general reduction in contrast sensitivity at all spatial frequencies. To assess the involvement of the lateral geniculate nucleus (LGN) in these deficits, we measured the following: 1) the visual responsiveness of lamina A1 cells with peripheral (more than 10 degrees from area centralis) receptive fields in three esotropic and three normal cats and 2) the spatial resolution and contrast sensitivity of lamina A X-cells with central (within 5 degrees of the area centralis) receptive fields in six esotropic and six normal cats. For comparison, we also measured LGN X-cell spatial resolutions in four exotropic cats and in two cats raised with an esotropia in one eye and the lids of the other eye sutured shut (MD-estropes). Recordings from the lateral portion of lamina A1 in esotropic cats yielded similar numbers of visually responsive cells with far nasal receptive fields as were seen in normal animals. Peak and mean response rates to a flashing spot also were normal. In addition, no differences were found between esotropes and normals in the percentages of X- and Y-cells encountered. These results suggest that the loss of orienting response to stimuli presented in the nasal field (12, 20) is not due to a loss of neural responses in the LGN of esotropic cats. In addition, they suggest that decreases in cell size in lamina A1 of esotropic cats (13, 36; R. E. Kalil, unpublished observations) are not accompanied by marked functional abnormalities of the cells and that cortical abnormalities ipsilateral to the deviated eye (22) are likely to have their origin within striate cortex itself. Recordings from lamina A cells with receptive fields near area centralis revealed that the average X-cell spatial resolution in esotropes (2.1 cycles/deg) was significantly lower than that in normal cats (3.1 cycles/deg). This reduction was seen in all esotropic cats tested and was due both to an increase in the proportion of X-cells with very low spatial resolution and to a loss of X-cells responding to high spatial frequencies (greater than 3.25 cycles/deg). The average spatial resolution of X-cells driven by the deviated eye in MD-esotropes fell midway between those of esotropes and normals. In exotropes, mean X-cell spatial resolution was normal.(ABSTRACT TRUNCATED AT 400 WORDS)     

Two classes of single-input X-cells in cat lateral geniculate nucleus. I. Receptive-field properties and classification of cells

Cells in the cat's dorsal lateral geniculate nucleus (LGN) were studied by presentation of visual stimuli and also by simultaneous recording of their ganglion cell inputs in the retina. This paper describes receptive-field properties and a new system of classification for LGN X-cells that appear to receive essentially only one excitatory retinal input. These X-cells were of two distinct classes. The visual responses of one class of cell (XS, single) replicated the basic form of the responses of a retinal X-cell. The other class of cell (XL, lagged) had responses with two remarkable features: their firing lagged 40-80 ms behind that of XS-cells or ganglion cells at response onset, and they fired anomalously at times when XS-cells or ganglion cells would not be firing. Thus, for a flashing spot, XL-cells were inhibited from firing after stimulus onset, during the time when XS-cells or retinal X-cells had an initial transient peak in firing; XL-cells generally had an anomalous peak in firing after stimulus offset, after XS-cells or retinal X-cells had stopped firing. For a moving bar, XS-cells or retinal X-cells responded primarily while the bar was in the receptive-field center, whereas most of a typical XL-cell's response occurred after the bar had left the receptive-field center. The latencies of various features in the visual responses were analyzed. For several visual response latencies, the distribution was clearly bimodal, thus objectively demonstrating the existence of two cell classes. Using only the latencies from spot and bar responses, over 90% of these single-input cells could be reliably identified as belonging to one of the two classes. The remaining cells (7 of 128) were intermediate between the two classes in some but not all respects; because they had some properties in common, these cells were kept in a separate group (XPL, partially lagged). The axons of both XS- and XL-cells could be antidromically activated from visual cortex. Cortical latencies were typically 0.7-2.0 ms for XS-cells but much longer, typically 2.4-5.0 ms, for XL-cells. It is possible that XL-cells have not previously been recognized as a separate class because cells with such long latencies have been recorded infrequently in the past. Responses to central flashing spots were more transient than those of retinal X-cells for most XS-cells and more sustained for most XL-cells.(ABSTRACT TRUNCATED AT 400 WORDS)