Monocular focal retinal lesions induce short-term topographic plasticity in adult cat visual cortex

Electrophysiological recording in primary visual cortex (Vl) was performed both prior to and in the hours immediately following the creation of a discrete retinal lesion in one eye with an argon laser. Lesion projection zones (LPZs; 21-64 mm2) were defined in the visual cortex by mapping the extent of the lesion onto the topographic representation in cortex. There was no effect on neuronal responses to the unlesioned eye or on its topographic representation. However, within hours of producing the retinal lesion, receptive fields obtained from stimulation of the lesioned eye were displaced onto areas surrounding the scotoma and were enlarged compared with the corresponding field obtained through the normal eye. The proportion of such responsive recording sites increased during the experiment such that 8-11 hours post-lesion, 56% of recording sites displayed neurons responsive to the lesioned eye. This is an equivalent proportion to that previously reported with long-term recovery (three weeks to three months). Responsive neurons were evident as far as 2.5 mm inside the border of the LPZ. The reorganization of the lesioned eye representation produced binocular disparities as great as 15 degrees, suggesting interactions between sites in VI up to 5.5 mm apart

Comparison of dendritic fields of layer III pyramidal neurons in striate and extrastriate visual areas of the marmoset: A lucifer yellow intracellular injection study

Basal dendritic field areas of layer III pyramidal neurons were compared between the first (V1), second (V2), dorsolateral (DL) and fundus of the superior temporal (FST) areas in marmoset monkey visual cortex. These areas correspond to early stages of visual processing (V1, V2) and to areas specialized for the analysis of shape (DL) and motion (FST). Neurons in fixed tangential cortical slices (250 μm) were injected with Lucifer Yellow and immunohistochemically processed for a diaminobenzidine reaction product. Dendritic field areas were calculated for layer III pyramidal cells whose complete basal projection was judged to be within the section (n = 189). Borders between different visual areas were established based on cytochrome oxidase immunohistochemistry and myelin patterns in the experimental hemisphere, and electrophysiological recordings in the contralateral hemisphere. Pyramidal neurons in V1 had a mean basal dendritic field area of 1.84 x 104 μm2 (SEM = 2.04 x 103 μm2; n = 21). Layer III pyramidal cells in V2 had a mean basal dendritic field 1.26 times larger (mean = 2.32 x 104 +/- 1.78 x 103 μm2; n = 42) than that of V1 neurons. The mean dendritic field area of layer III pyramidal cells in DL (n = 76) was 1.5 times larger than that in V1 (mean = 2.75 x 104 +/- 1.59 x 103 μm2). and that in FST (n = 50) was 2.3 times larger (mean = 4.26 x 104 +/- 2.79 x 103 μm2. Our results show that there is a correlation between tangential dendritic field area of basal dendrites of layer III pyramidal neurons and modality of visual processing. The increase in basal dendritic field area of layer III pyramidal cells may allow more extensive sampling of inputs as required by higher-order processing of visual information

Responsiveness of cat area-17 after monocular inactivation - limitation of topographic plasticity in adult cortex

1. Recordings were made from neurones in the splenial sulcus of normal adult cats and adult cats which had one eye inactivated by enucleation or photocoagulation of the optic disc. Two visually responsive regions were observed, corresponding to the peripheral representation of visual area 1 (V1) and the splenial visual area. In normal animals, responses to the ipsilateral eye in V1 were restricted to the medial half of the splenial sulcus, up to 45-50 deg eccentricity. Thus, by inactivating the eye contralateral to the experimental hemisphere, rye created a region in V1, 1-2 mm wide, that lacked normal inputs. 2. In contrast to results from previous experiments where lesions were placed in the central retina, neurones in the deprived peripheral representation remained unresponsive to light stimuli for up to 12 h after deactivation of the contralateral eye. 3. In animals that were allowed to recover from the monocular deactivation for periods of 2 days to 16 months, there was rearrangement of the retinotopic maps. Receptive fields in regions of cortex that normally represented the monocular crescent were displaced to the temporal border of the binocular field of vision. However, most neurones in the deprived peripheral representation remained unresponsive to visual stimuli even more than 1 year after treatment. This is also in marked contrast with the extensive reorganization that is observed in the central representation of Vi after restricted retinal lesions. Analysis of the cortical magnification factor demonstrates that the change in visual topography is local, and does not involve an overall centro-peripheral shift of the retinotopic map. 4. Among the neurones that did show displaced receptive fields, the response properties were clearly abnormal. They showed a notable lack of spontaneous activity, low firing rates and rapid habituation to repeated stimulation. 5. The low potential for reorganization of the monocular sector of Vl demonstrates that the capacity for plasticity of mature sensory representations varies with location in cortex. Even relatively small pieces of cortex, such as the monocular crescent representations, may not reorganize completely if certain conditions are not met. These results suggest the existence of natural boundaries that may limit the process of reorganization of sensory representations

Retinal-detachment induces massive immediate reorganization in visual-cortex

Large inactive regions of the retina of adult cats were produced by the novel method of inducing monocular retinal detachment. Within a few hours, neurones throughout the detachment projection zone in primary visual cortex (55-136 mm2), including some \u3e 4.5 mm from its boundary, were found to have large receptive fields displaced onto intact retina. The new receptive fields of some neurones represented shifts of up to 9 mm across the retinotopic representation. For these rapid changes to occur pre-existing viable circuits must provide a cortical locus with inputs from a wide extent of the retina. Receptive fields, and the retinotopic map, for stimulation of the other eye were unchanged

Contrast and luminance adaptation alter neuronal coding and perception of stimulus orientation

Sensory systems produce stable stimulus representations despite constant changes across multiple stimulus dimensions. Here, the authors reveal dynamic neural coding mechanisms by testing how coding of one dimension (orientation) changes with adaptations to other dimensions (luminance and contrast)

Visuotopic reorganization in the primary visual cortex of adult cats following monocular and binocular retinal lesions

The effect of discrete monocular retinal lesions on the representation of the visual field in the primary visual area (V1) was investigated in adult cats. Lesions were created using argon lasers, 8 d to 4 1/2, months prior to electrophysiological recording. This produced lesion projection zones (LPZs) in V1, 1.6-9.5 mm wide, that were deprived of their normal input from one eye, but that received a normal input from the other eye, Nevertheless, at the majority of recording sites within these zones neuronal responses were elicited by stimulation of the lesioned eye, with receptive fields being displaced onto regions of retina surrounding the lesion, while receptive fields determined through stimulation of the normal eye followed the normal visuotopic organization of V1. However, neuronal responses to stimulation of the lesioned eye within the LPZs were characterized by rapid habituation and unusually low firing rates in comparison with responses to stimulation of the normal eye, Stimulation of the normal eye temporarily masked the responsiveness of neurons within the LPZ to stimulation of the lesioned eye, The proportion of neurons responsive to stimulation of the lesioned eye was higher just inside the borders of the LPZs than at the centers of these zones. However, neurons responsive to stimulation of the test eye were found up to 3.6 mm from the perimeter of the LPZs, and therefore the shifts in the visuotopic map caused by retinal lesions cannot he explained solely on the basis of the normal scatter of receptive fields and point-image size in V1. The proportion of cells responsive to stimulation of the lesioned eye was highest in the infragranular layers, and lowest in the supragranular layers, By combining a restricted lesion of one eye with laser photocoagulation of the optic disc of the other eye, the effects of deactivation of the normal eye on the lesion-induced visuotopic reorganization were also investigated. Neither chronic nor acute deactivation produced any discernible further changes in visuotopy or in the characteristics of neuronal responses to stimulation of the eye with the discrete lesions. Our findings show that the representations of the two eyes in adult visual cortex are capable of independent reorganization, These findings parallel those of work in auditory cortex, suggesting that topographic reorganization in primary sensory areas of adult cortex may be governed by similar mechanisms