Adaptation of PMLS neurons to prolonged optic flow stimuli.

Changes in neuronal responses during and after adaptation to prolonged optic flow stimulation were investigated by extracellular single-unit recording in the posteromedial lateral suprasylvian area (PMLS) of the cat. In comparison with translation stimuli, the complex optic flow patterns (radiation and rotation) produced more pronounced adaptation and after-effects by inducing larger response reduction, and altered the direction selectivity of many neurons obviously as well. Generally, the adaptation effects were direction-specific for radiation/rotation, but independent of the direction of test stimulus for translation. These results suggest that PMLS may play an important role in the perception of motion after-effects to complex optic flow fields, while the adaptation to simple translation might be generated at a relatively earlier level of the visual system.

Pattern and component motion selectivity in cortical area PMLS of the cat.

Visual motion perception is one of the most prominent functions performed by the mammalian cerebral cortex. The moving images are commonly considered to be processed in two stages. The first-stage neurons are sensitive to the motion of one-dimensional orientated components, and their outputs are combined at the second stage to perceive the global motion of the whole pattern. Alternatively, the pattern motion may be signalled by monitoring a distinctive feature of the image, such as a line-end or a corner. In the present study, a series of 'random-line' patterns were used to measure the direction-tuning responses of 138 neurons in the posteromedial lateral suprasylvian area of the cat. The novel stimuli comprised identical thin line segments, with a length : width ratio no less than 10 : 1, which were moved perpendicularly or obliquely to their common orientation during the recordings. When the component lines were much shorter than the size of receptive field, the majority of cells were selective to the direction of pattern motion while only a small subset was sensitive to the direction of component motion. However, the response profiles of most cells became more component-motion selective with the increment of orientation element in stimulus by elongating the component lines in the patterns. These findings imply that the two-stage theory might be incomplete for modelling the visual motion analysis. Even at relatively low levels of the visual system, some kind of nonorientation-based processing may coexist with the orientation-sensitive processing in a dynamic competition, where one rises as the other falls depending upon the strength of the orientation element in the stimulus, so that under some circumstances it becomes possible to signal the veridical direction of pattern motion.

Response properties of PMLS and PLLS neurons to simulated optic flow patterns.

The processing of optic flow information has been extensively investigated in the medial superior temporal area (MST) of the macaque. In the cat, the posteromedial area and the posterolateral area in the lateral suprasylvian cortex (PMLS and PLLS, respectively) have been suggested as likely participants according to their direction preferences to moving objects. In the present study, 203 PMLS and 123 PLLS neurons were tested with simulated optic flow patterns composed of random dots (including expansion and contraction, clockwise and counter-clockwise rotation, and translation) and moving bar stimuli. About 90% of the neurons were found to be excited by the optic flow stimuli and most of them were multiple-responsive to different flow patterns. Only 20-25% of the cells were selective to different optic flow modes, and in general, the direction preference was fairly modest. The selective cells showed stronger directionality to both flow field and moving bar than nonselective cells. However, the optic flow response properties in the PMLS and PLLS were not well correlated with the direction preference to moving bars. In accordance with previous findings, the PMLS was analogous to the middle temporal area of the macaque in many respects. As for the PLLS cells, they were sensitive to fewer types of stimuli, but responded better and more selectively to radial motion. All these results suggest that the two lateral suprasylvian areas are unlikely to be specialized for the analysis or discrimination of different flow patterns, but may play some kind of relay role in optic flow information processing.

Synergistic effect of optic and peripheral nerve grafts on sprouting of axon-like processes of axotomized retinal ganglion cells in adult hamsters.

We investigated the sprouting response of retinal ganglion cells (RGCs) following the transplantation of peripheral nerve (PN) and/or optic nerve (ON) into the vitreous of the eye and the intraorbital transection of the optic nerve in hamsters. Our previous results showed that an intravitreal PN graft could induce sprouting of axon-like processes in axotomized RGCS [3] (Cho, E.Y. and So, K.F., Characterization of the sprouting response of axon-like processes from retinal ganglion cells after axotomy in adult hamsters: a model using intravitreal implantation of a peripheral nerve, J. Neurocytol., 21 (1992) 589-603). In this model, we have examined the effect of intravitreal ON graft on the sprouting of RGCs both following a co-transplantation of PN and ON into the vitreous and transplantation of ON alone. The present results show that sprouting is increased by more than two-fold in retinas having PN and ON grafts than a PN graft alone. However, the ON graft by itself rarely induced sprouting in RGCs. These results suggest that the ON graft enhance the number of RGCs to sprout axon-like processes in the presence of PN graft by exerting a synergistic rather than an additive effect, since ON graft alone did not induce sprouting. In addition, no diffusible inhibitory effect of ON graft on PN induced sprouting was observed.

[Integration of visual signals in the brain: mechanisms and functional significance of synchronous oscillation].

How are the functions performed by one part of the nervous system integrated with those of others? One possible way is by synchronous oscillation. We have reviewed recent advances in visual system, where synchronous oscillations have been intensively observed and investigated. This article is concentrated on discussing theoretical reasoning, experimental evidence, possible mechanisms underlying the generation and the functional significance of visual synchronous oscillations. Predictions on several prosperous areas were also outlined.

A morphological study of neurons expressing NADPH diaphorase activity in the visual cortex of the golden hamster.

The distribution of the enzyme nicotinamide adenine dinucleotide phosphate (NADPH) diaphorase, which is identical to nitric oxide synthase (NOS), was examined in cortical area 17 and the 17/18a border region in the brain of the golden hamster. The activity of the enzyme was present as a network of processes and in special populations of neurons in the visual cortex. The dense enzyme-positive network exhibited numerous varicosities distributed throughout the cortex. The prominent orientation of the processes in layer I and the white matter are parallel to the surface of the brain, but those in layers II-IV are perpendicular to the surface of the brain. However, the processes in layers V and VI seem to run randomly. The NADPH diaphorase-positive cells could be divided into two classes: heavily stained neurons and lightly stained neurons. For the lightly stained NADPH diaphorase-positive neurons, only the cell bodies could be observed, whereas for the heavily stained neurons, the cell bodies and their varicosity-carrying dendrites and, occasionally, the smooth, thin and weakly stained axons were visible. The heavily stained neurons were morphologically diverse, but no pyramidal or spiny neurons were found. Multipolar and bipolar neurons were located throughout the depth of the cortex, including the white matter, more frequently in layers V and VI. Occasionally, monopolar neurons were found in layer VI. Callosal projecting neurons in the visual cortex were labeled retrogradely with the use of FluoSpheres applied at the opposite visual cortex, but these neurons did not co-localize with the NADPH diaphorase-positive neurons, suggesting that the callosal projecting neurons and NADPH diaphorase-positive neurons belong to two populations of cells in the visual cortex.

How is direction selectivity organized in the extrastriate visual area PMLS of the cat?

Although most neurones in the PMLS of the cat are selective for direction of motion, whether the preferred directions are organized into cortical columns, as they are in the MT area of the monkey, is not certain. We have quantitatively investigated the organization of direction selectivity of PMLS neurones. The results showed that adjacent neurones have similar direction selectivity. The preferred direction of neurones sampled successively in a tangential penetration changed continually, occasionally with an approximately 180 degrees reversal, and neurones with bidirectional selectivity tended to be located in the reversal region. It is spectulated that direction selectivity in the PMLS is organized on the basis of preferred axis of motion in such a way that one column with bidirectional preference lies between two columns with opposite unidirectional preferences, a unidirectional column is always adjacent to a bidirectional column and these adjacent columns share a common preferred axis-of-motion.

Transcallosal circuitry revealed by blocking and disinhibiting callosal input in the cat.

The purpose of this study was to obtain quantitative measures of the influence of callosal input to cells at the area 17/18 border region where transcallosal axons terminate most densely. Single-cell recordings were performed at the area 17/18 border region of the right hemisphere, while gamma-aminobutyric acid (GABA) or its antagonist, bicuculline, were applied to the transcallosal projecting regions of the left hemisphere to either block or overactivate the cells which projected to the neurons at the recording site. The results showed that visually evoked responses of the cells at the area 17/18 border were affected by administration of GABA or bicuculline to the contralateral hemisphere. Blockade of transcallosal input by application of GABA in the left hemisphere diminished the visually evoked responses of 51% of the neurons in the right hemisphere, and led to an increase in response magnitude for 17% of the neurons. Disinhibition of transcallosal input by application of bicuculline increased the evoked activity of 40% of the neurons and diminished the response magnitude of 20% of the neurons in the right hemisphere. GABA and bicuculline failed to show antagonistic effects on some cells. Thirty-two percent of the cells were affected by only one type of drug administration, and 13% of the cells showed either an increase or a decrease in responses after both GABA and then bicuculline administration. This study demonstrated complex interactions between neurons connected by the transcallosal pathway. A model of the transcallosal circuitry was proposed to explain the results.

[Effects of GABA and bicuculline on the properties of visual superior colliculus neurons in golden hamsters].

Visual response properties of single neurons in the superior colliculus of golden hamsters could be altered by iontophoretically applied gamma-aminobutyric acid (GABA) and its antagonist, bicuculline (Bicu). GABA decreased the responses of the superficial cells to stationary flashing stimuli, while Bicu increased the responses and suppressed the inhibition exerted by the surround. The number of spikes evoked by a moving bar/spot decreased after applying GABA in 76.6% of the cells (n = 60) and increased in 90.0% (n = 60) of the cells after Bicu. Similar effects on the spontaneous activities were observed. In addition, 65.0% of the 60 cells recorded have enlarged movement receptive fields after application of Bicu. GABA and Bicu have some effects on the orientation selectivity of the collicular cells too.

Dendritic morphology of visual callosal neurons in the golden hamster.

The visual callosal neurons and the connections between the two cerebral hemispheres in hamsters have been shown to be important for visual functions, but little is known about the detailed morphology of these neurons. In this study, we have used techniques based on retrograde transport of a fluorescent tracer, Granular Blue, and intracellular injection of Lucifer Yellow in fixed brain slices to identify the laminar distribution and dendritic morphology of the visual callosal neurons in the 17/18a border region of the adult golden hamster. The cells giving rise to the callosal projections were morphologically heterogeneous, although they were all spiny neurons. Most were pyramidal cells, but some were stellate cells. They were located in layers II-VI, with cells concentrating in three bands: (1) in the middle three fifths of layer II/III; (2) in layer IV, and (3) in the middle three fifths of layer V. In layer II/III and layer V, the great majority of the cells were pyramidal or star pyramidal neurons. In layer IV, about half were stellate neurons and the rest pyramidal or star pyramidal neurons. In layer VI, they consisted mostly of modified pyramidal cells. The soma areas of the pyramidal and star pyramidal neurons in all the layers ranged from 52 to 335 micron 2 with a mean of 148 micron 2 (n = 92; SD = 64.4). In general, these cells gave rise to 3-5 basal dendrites.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional organization of the cortical 17/18 border region in the cat.

The representation of the visual field in the 17/18 border region of the cat's visual cortex, and the layout of orientation and ocular dominance columns, were studied by making many closely spaced electrode penetrations into the superficial layers of the flattened dorsal region of the marginal gyrus and recording response properties at each location. The 17/18 border region was defined by measuring the change in the horizontal component of receptive field position within the gyrus: as the position of the recording electrode moved from medial to lateral, the receptive fields moved towards the vertical midline, indicating that the electrode was in area 17; as penetrations were made in increasingly lateral positions, the trend reversed, and receptive field positions moved away from the midline, indicating that the electrode was in area 18. The receptive fields of cells close to the border straddled, or lay within 2 degrees-3 degrees on either side of the vertical midline. In addition, patches of cortex were sometimes encountered in which cells had receptive field centers located up to 7 degrees in the ipsilateral visual field. Experiments in which maps were made in the left and right hemispheres of a single animal showed that these patches had a complementary distribution in the two hemispheres. Cells within the patches behaved as though driven by Y-cell inputs: they usually had large receptive fields and responded to rapidly-moving stimuli. They were broadly tuned for orientation and strongly dominated by the contralateral eye. Fourier spectral analysis of orientation selectivity maps showed that iso-orientation bands had an average spacing of 1.14 +/- 0.1 mm and tended to be elongated in a direction orthogonal to the 17/18 border. Individual bands crossed the border without obvious interruption, although singularities (points of discontinuity in the layout of orientations) were more frequently observed in the border region than in adjacent areas. Two dominant periodicities could be measured in the maps of ocular dominance, one at around 0.8 +/- 0.2 mm and a second at 2.0 +/- 0.3 mm. No constant direction of elongation was noted. These are close to the periods present within areas 17 and 18 respectively.

Callosal projections in the visual cortex and the vertical meridian of the visual field in the albino rat.

Studies using electrophysiological and HRP-labeling techniques showed that the lateral border of physiologically determined primary visual cortex coincides with the cytoarchiectonically defined area 17/18a border. The dense callosal projections are distributed in a zone, about 1.5 mm wide, along this border, which lies in the callosal zone, about 1/4-1/3 of the zone width from its lateral limit. There are two representations of the vertical meridian of the visual field, one in the proper of area 17, about 1/3 of the zone width from its medial limit, the other in area 18a, at about the lateral zone limit.

Effects on the growth of damaged ganglion cell axons after peripheral nerve transplantation in adult hamsters.

After transplantation of autologous sciatic nerve segments into the retina of adult hamsters for 1-2 months, retrograde labelling with horseradish peroxidase demonstrated a population of ganglion cells situated peripheral to the graft. If an additional lesion was placed between the insertion of the graft and the optic disc at the same time as transplantation, in addition to labelled cells situated peripheral to the graft, retrograde labelling with horseradish peroxidase demonstrated a population of labelled neurons located between the graft and the optic disc which was not observed in animals without the additional lesion. Since the axons of this population of cells would have to turn around away from their normal course towards the optic disc and travel for about 1.5 mm in order to grow into the graft, it suggests that the peripheral nerve graft might play an active role in attracting and/or guiding damaged ganglion cell axons to grow into it.

Binocular responses in the superior colliculus of the albino rat.

The retinotopic map for the contralateral eye is similar to that found in the pigmented rats and in other rodents. Cells which had ipsilateral responses were recorded in a fairly large area in the rostral portion of the tectum. Their receptive fields lay from about 40 degrees in the contralateral hemifield to about 40 degrees in the ipsilateral hemifield. The ipsilateral response of a binocular cell is similar in almost every respect to its counterpart in the opposite eye except being very weak and that the receptive field is usually smaller. Most binocular cells are distributed in the Stratum griseum superficiale (SGS) and the Stratum opticum (SO). Less binocular cells recorded in the Stratum griseum intermediale (SGI) have more scattered distribution both in the size and in the position of the receptive field.

Correlation between the visual callosal connections and the retinotopic organization in striate-peristriate border region in the hamster: an anatomical and physiological study.

The correlation between the retinotopic organization of receptive fields in the striate-peristriate border region and the distribution pattern of the visual callosal projections was investigated in hamsters with corpus callosum transected 2 days before recording. The results showed that in all the animals studied, the V1/V2 border defined by reversal of receptive fields at the vertical meridian was located in the dense central portion of the visual callosal projection which terminated in cortical regions bordering areas 17 and 18a. These results indicate that there is a close relationship between the striate-peristriate border determined by anatomical and physiological methods. In addition, these data strengthen the suggestion that the pattern of visual callosal projections is a useful and reliable reference system for delineating boundaries of different visual areas in the golden hamster.

Possible functions of the interhemispheric connexions between visual cortical areas in the cat.

The functions of interhemispheric axons linking the borders between cortical areas 17 and 18 on the two sides of the brain were investigated by two techniques. A well-matched sample of neurones was recorded in the 17/18 border region before and after an extensive lesion was made in the corresponding part of the other hemisphere. The proportion of binocularly driven cells fell from 96% to 67%, confirming the results of Dreher & Cottee (1975). Orientation-and direction-selectivity, as well as the responsiveness of the population of neurones, seemed unaltered. The reduction in binocularity was much less convincing for cells in the body of area 17, even very close to the callosal-recipient zone. Reversible cooling of the 17/18 border had no effect on the few cells recorded outside the callosal zone in the other hemisphere nor on eighteen of the thirty-five cells recorded in the callosal zone. However, in ten cells the receptive field disappeared completely in one eye; in five cells there was a general reduction in responsiveness; two cells lost a portion of the receptive field, on the ipsilateral side, in both eyes. The receptive fields that were apparently transmitted via the corpus callosum lay around the vertical meridian of the visual field and were not restricted to the visual hemifield ipsilateral to the receiving hemisphere: their distribution overlapped that provided by the direct geniculo-cortical input. The principal function of the callosal projection between the 17/18 borders may be to contribute to binocular convergence on cortical cells and perhaps to play a part in stereoscopic vision.

Representation of the binocular visual field in the superior colliculus of the albino rat.

Electrophysiological mapping techniques were used to determine the representation of the central field of vision in the superior colliculus of the albino rat. The retinotopic map for the contralateral eye is similar to that found in other mammals. There is an unexpected extensive binocular segment subserving the central 40 degrees of the ipsilateral hemifield as well as the central 40 degrees of the contralateral hemifield in the rostrolateral portion of the tectum.

Binocular responses of cortical cells and the callosal projection in the albino rat.

Four hundred and fifteen cells were recorded in the binocular segment of the visual cortex in the albino rat. Cells encountered were mainly dominated by the contralateral eye. The percentage of binocularly-driven cells increased as the electrode was moved towards the border between areas 17 and 18a. Ninety percent of the cells studied in the region of the border could be driven by electrical stimulation applied at the corresponding site in the opposite hemisphere. Within area 17, however, there were only about 30% of such cells. Through the combined use of electrical stimulation and reversible cortical cooling, two types of contributions by callosal fibres were revealed. One is that the callosal fibres constitute the only inputs from the ipsilateral eye to a cell. The other is that the callosal input provides ipsilateral reinforcement to a binocular cell. These results are compatible with neuroanatomical findings and show that binocularity of visual cortical cells in this animal depends, to a great degree, on the function of callosal fibres.