Pattern adaptation of relay cells in the lateral geniculate nucleus of binocular and monocular vision-deprived cats.

To test whether the pattern adaptation in thalamus is dependent upon postnatal visual experience during early life, the responses of relay cells to prolonged drifting grating stimulation were recorded extracellularly from the dorsal lateral geniculate nucleus (dLGN) of cats reared with binocular and monocular lid suture. In binocular vision-deprived cats, 68% of cells recorded showed significant adaptation to prolonged grating stimuli within 30 s, with a mean response decrease of 33%, and then stabilized gradually. This adaptation was stronger than that of relay cells in normal cats. In monocular vision-deprived cats, 53% of the cells driven by the deprived eye showed similar adaptation as did 44% of the cells driven by the non-deprived eye. These results indicate that pattern adaptation could be maintained or even enhanced after visual deprivation in early life. It is suggested that pattern adaptation is a general and intrinsic property of the dLGN cells, which may be mainly determined by genetic factors.

[Spatial frequency tuning characteristics of cat primary visual cortex at different topological locations by optical imaging].

Using optical imaging based on intrinsic signals, we studied spatial frequency tuning characteristics of cat primary visual cortex at different visual topological locations. We found that the areas representing the peripheral visual field had null or very weak responses to high spatial frequency grating stimuli, whereas the areas representing the central visual field responded to the stimuli of a wide range of spatial frequencies with greater responses to high spatial frequencies. The more centered the corresponding visual field of the cortical area, the higher the cutoff spatial frequency. The spatial frequency tuning curves also tended to have a smooth shift along the cortical surface. The results above demonstrate that spatial frequency tuning characteristics of the primary visual cortex change according to different visual topological locations of the cortical areas, in addition to the existence of spatial frequency columns. It is suggested that the distribution of spatial frequency columns may be related to visual topology.

[The oblique effect revealed by optical imaging in primary visual cortex of cats].

The oblique effect is a ubiquitous visual psychological effect. To explore its underlying neural basis, we quantitatively analyzed the proportion and response amplitude of the cardinal preferred areas and the oblique preferred areas in a fairly large region of the primary visual cortex of cats, using optical imaging based on intrinsic signals. The results show that cardinal preferred areas were larger than oblique preferred areas, with a mean difference of 4.7%. Overall, the responses evoked by cardinal stimuli were generally greater than those by oblique stimuli. The present work provides an explanation for the differences in electrophysiological results reported for this issue, and gives a new insight into the neural basis of the oblique effect.

[Orientation and direction sensitivity of cells in subcortical structures of the visual system].

Since the work of Hubel and Wiesel, it is generally accepted that visual orientation and direction selectivity are achieved by processes in the visual cortex in the higher mammals. This view seems to require revision in views of more recent experimental finding that both relay cells in the lateral geniculate nucleus (LUN) and the ganglion cells in the retina do show some orientation and direction sensitivities. Such selective sensitivities in the LGN which are genetically determined and not affected by post-nated environment, would furnish a basis for further architectural fabrication in the visual cortex for orientation/direction detection. Relativiely segregated grouping in the LGN plays an important role in the formation of parallel processing pathways of the visual system. In the course of post-natal development of the visual system, the emergence of orientation/direction sensitive cells in the subcortical level would contribute to enhance intracortical mechanisms to achieve more refined orientation/direction detectability.

[Topographic relationship of orientation sensitive relay cells in lateral geniculate nucleus (LGN) of dark-reared cats].

The orientation sensitivity of the LGNd neurons of dark-reared cats were investigated. As in normal cats, most of the cells studied were significantly sensitive to the orientations of grating stimuli (Bias > 0.1), and preferred horizontal and/or radial orientations. Also the adjacent cells tended to assume similar preferred orientations. These results indicate that visual deprivation in cats neither affect the distribution properties of preferred orientations, nor the clustering of cells with similar preferred orientations in the LGN.

[Binocular competitive mechanisms in the visual cortex in early developing kittens of monocular deprivation and reverse suture revealed by pattern visual evoked potential].

Using contrast reversing square- wave gratings as stimuli the pattern visual evoked potentials (P-VEP) and pattern electroretinograms (P-ERG) were simultaneously recorded to determine the spatial frequency tuning curves for kittens of monocular deprivation (from 8th to 12th postnatal week) and reverse suture (from 12th to 15th postnatal week), as compared with those of normal kittens of the same age and adult cats. The results showed that in the range from spatial frequency 0.12 to 1.5 c/d the amplitudes of P-VEP responses driven respectively by the left and the right eyes in normal kittens were similar but clearly smaller than those driven binocularly. For kittens with one eye deprived, the P-VEP amplitudes driven by the deprived eye decreased markedly. In contrast, the P-VEP amplitudes driven by the undeprived eye increased significantly, while the P-VEP amplitudes driven by simultaneous stimulation of both eyes were intermediate between the two monocular responses. For the reversely sutured kittens, the P-VEP amplitudes driven by the formally deprived eye recovered to some extent, while the P-VEP amplitudes driven by the reversely sutured eye decreased, and their amplitudes tended to be quite close. The P-VEP amplitude driven by both eyes was the biggest. Neither such shift of spatial frequency tuning curves of the P-VEP in adult cats, nor such functional competition between the two eye in P-ERG responses during early development of kittens of monocular deprivation and reverse suture was found.(ABSTRACT TRUNCATED AT 250 WORDS)

Organized arrangement of orientation-sensitive relay cells in the cat's dorsal lateral geniculate nucleus.

We studied the physiological orientation biases of over 700 relay cells in the cat's dorsal lateral geniculate nucleus (LGNd). Relay cells were sampled at regular intervals along horizontally as well as vertically oriented electrode penetrations in a fashion analogous to that used previously in studies of visual cortex (Hubel and Wiesel, 1962). The strengths of the orientation biases and the distributions of the preferred orientations were determined for different classes of relay cells, relay cells in different layers of the LGNd, and relay cells subserving different parts of the visual field. We find that, at the population level, LGNd cells exhibit about the same degree of orientation bias as do the retinal ganglion cells providing their inputs (see also Soodak et al., 1987). Also, as in the retina (Levick and Thibos, 1982; Leventhal and Schall, 1983), most LGNd cells tend to prefer stimuli oriented radially, i.e., parallel to the line connecting their receptive fields to the area centralis projection. However, the radial bias in the LGNd is weaker than in the retina. Moreover, there is a relative overrepresentation of cells preferring tangentially oriented stimuli in the LGNd but not in the retina. As a result of the overrepresentation of cells preferring radial and tangential stimuli, the overall distribution of preferred orientations varies in regions of the LGNd subserving different parts of the visual field. Reconstructions of our electrode penetrations provide evidence that, unlike in the retina, cells having similar preferred orientations are clustered in the LGNd. This clustering is apparent for all cell types and in all parts of laminae A and A1. The tendency to cluster according to preferred orientation is evident for cells preferring radially, intermediately, and tangentially oriented stimuli and thus is not simply a reflection of the radial bias evident among retinal ganglion cells at the population level. It is already known that cells having inputs from different eyes, on-center, off-center, X-, Y-, W-type, and color-sensitive ganglion cells are distributed nonrandomly in the LGNd of cats and monkeys (for review, see Rodieck, 1979; Stone et al., 1979; Lennie, 1981; Stone, 1983). The finding that relay cells having similar preferred orientations are also distributed nonrandomly suggests that the initial sorting of virtually all properties segregated in visual cortex may begin in the LGNd.

Y cells in the cat retina are more tolerant than X cells to brief elevation of IOP.

The responses of X and Y type retinal ganglion cells were extracellularly recorded from the cat optic chiasm or tract before and during brief intraocular pressure (IOP) elevation. The responses of both X and Y cells to stimulus flashes decreased monotonically with increase of IOP. Y cells had significantly higher tolerance to IOP than did X cells. This systematic difference was independent of the cell's retinal position. The findings support the conclusion that during brief IOP elevation pressure-induced ischemia is the main factor causing a decrease in ganglion cell responsiveness. Our findings also suggest a means of selectively eliminating the contribution of X cells to visual function. At moderate levels of IOP elevation X cells, but not Y cells, virtually cease to function.

Two types of change in sensitivity during light adaptation in cat retina.

The electroretinograms (ERG) were recorded during light adaptation at various levels of background in the urethane-anaesthetized cat. Our previous assumption that for a fixed background all the stimulus strength-response amplitude curves at any moment during light adaptation were similar in slope[1] has been confirmed experimentally. It thus offers a method to deduce the transient sensitivity from b-wave amplitude. Two kinds of change in retinal sensitivity were observed during light adaptation according to the strength of adapting light. When a dim adapting light was used the sensitivity decreased suddenly and then remained at a low level, as soon as the adapting light was over 10(3) scotopic td the initial decrease in sensitivity was followed by a partial recovery within 10 min after the onset of adapting light. It is suggested that the sensitivity recovery is related to the degree in which cones are released from rod suppression and participate in the generation of the b-wave.