Blind subjects construct conscious mental images of visual scenes encoded in musical form.

Blind (previously sighted) subjects are able to analyse, describe and graphically represent a number of high-contrast visual images translated into musical form de novo. We presented musical transforms of a random assortment of photographic images of objects and urban scenes to such subjects, a few of which depicted architectural and other landmarks that may be useful in navigating a route to a particular destination. Our blind subjects were able to use the sound representation to construct a conscious mental image that was revealed by their ability to depict a visual target by drawing it. We noted the similarity between the way the visual system integrates information from successive fixations to form a representation that is stable across eye movements and the way a succession of image frames (encoded in sound) which depict different portions of the image are integrated to form a seamless mental image. Finally, we discuss the profound resemblance between the way a professional musician carries out a structural analysis of a musical composition in order to relate its structure to the perception of musical form and the strategies used by our blind subjects in isolating structural features that collectively reveal the identity of visual form.

The perception of visual images encoded in musical form: a study in cross-modality information transfer.

This study demonstrates the ability of blind (previously sighted) and blindfolded (sighted) subjects in reconstructing and identifying a number of visual targets transformed into equivalent musical representations. Visual images are deconstructed through a process which selectively segregates different features of the image into separate packages. These are then encoded in sound and presented as a polyphonic musical melody which resembles a Baroque fugue with many voices, allowing subjects to analyse the component voices selectively in combination, or separately in sequence, in a manner which allows a subject to patch together and bind the different features of the object mentally into a mental percept of a single recognizable entity. The visual targets used in this study included a variety of geometrical figures, simple high-contrast line drawings of man-made objects, natural and urban scenes, etc., translated into sound and presented to the subject in polyphonic musical form.

Myelin repair by Schwann cells in the regenerating goldfish visual pathway: regional patterns revealed by X-irradiation.

In the regenerating goldfish optic nerves, Schwann cells of unknown origin reliably infiltrate the lesion site forming a band of peripheral-type myelinating tissue by 1-2 months, sharply demarcated from the adjacent new CNS myelin. To investigate this effect, we have interfered with cell proliferation by locally X-irradiating the fish visual pathway 24h after the lesion. As assayed by immunohistochemistry and EM, irradiation retards until 6 months formation of new myelin by Schwann cells at the lesion site, and virtually abolishes oligodendrocyte myelination distally, but has little or no effect on nerve fibre regrowth. Optic nerve astrocyte processes normally fail to re-infiltrate the lesion, but re-occupy it after irradiation, suggesting that they are normally excluded by early cell proliferation at this site. Moreover, scattered myelinating Schwann cells also appear in the oligodendrocyte-depleted distal optic nerve after irradiation, although only as far as the optic tract. Optic nerve reticular astrocytes differ in various ways from radial glia elsewhere in the fish CNS, and our observations suggest that they may be more permissive to Schwann cell invasion of CNS tissue.

Myelination of regenerated axons in goldfish optic nerve by Schwann cells.

This study uses immunohistochemistry and EM to examine the site of injury in goldfish optic nerve during axonal regeneration. Within seven days of nerve crush axons begin to regrow and a network of GFAP+ reactive astrocytes appears in the nerve on either side of the injury. However, the damaged area remains GFAP-. By 42 days after nerve crush, the sheaths of new axons acquire myelin marker 6D2, and the crush area becomes populated by a mass of longitudinally-orientated S-100+ cells. Ultrastructurally, the predominant cells in the crush area bear a strong resemblance to peripheral nerve Schwann cells; they display a one-to-one association with myelinated axons, have a basal lamina and are surrounded by collagen fibres. It is proposed that these cells are Schwann cells which enter the optic nerve as a result of crush, where they become confined to the astrocyte-free crush area.

A polyclonal antibody to goldfish neuronal 145 kDa intermediate filament protein.

A polyclonal antibody raised to a protein from goldfish optic tectum recognises, immunohistochemically, axons throughout normal goldfish visual pathway. In goldfish with injured optic nerve, this antibody recognises degenerating neuronal debris as well as regenerating fibres. On immunoblot, the antibody recognises, primarily, a neuronal intermediate filament protein in the region of 145 kDa. Such an antibody should prove useful in studies pertaining to goldfish visual pathway.

Preferential histochemical staining of protoplasmic and fibrous astrocytes in rat CNS with GFAP antibodies using different fixatives.

Serial sections of rat brain and spinal cord were fixed in either acid-alcohol or 4% paraformaldehyde, and stained for visualization of astrocytes using GFAP antibodies. With paraformaldehyde, GFAP-positive astrocytes were visualised almost exclusively in the grey matter of all above tissues. In sharp contrast, acid-alcohol treatment gave intensely stained GFAP-containing astrocytes in the white matter. Since fibrous astrocytes are mainly located in the white matter and protoplasmic astrocytes are located in the grey matter, it is concluded that acid-alcohol is a good fixative for fibrous astrocytes while paraformaldehyde is a better fixative for protoplasmic astrocytes.

Expression of glial fibrillary acidic protein (GFAP) in goldfish optic nerve following injury.

By using an antibody to goldfish glial fibrillary acidic protein (GFAP), the reaction of goldfish optic nerve to injury has been studied by immunoblotting and immunohistochemical methods. Goldfish optic nerve, which normally lacks GFAP immunoreactivity (Nona et al.: Glia, 2:189-200, 1989), expresses GFAP following injury. This immunoreactivity, which is observed as early as 10 days after crush and which is still evident at 30 days after crush, all but disappears by 150 days after crush. Since it is well established that functional restoration of synaptic connections and the recovery of vision takes place in goldfish following optic nerve injury, our results indicate that reactive astrocytes do not represent an impediment to regeneration in goldfish visual system.

Anti-goldfish glial fibrillary acidic protein (GFAP) recognises astrocytes from rat CNS.

A polyclonal antibody to goldfish GFAP recognises, immunohistochemically, astrocyte populations in rat brain, spinal cord and optic nerve. The pattern of staining compares favourably with that obtained using a polyclonal anti-human GFAP or a monoclonal anti-porcine GFAP. These results are consistent with the notion that GFAP is well conserved in vertebrate phylogeny.

Identification of astrocyte- and oligodendrocyte-like cells of goldfish optic nerves in culture.

Fish glial cells were obtained from cultivated segments of the optic nerve and raised in vitro. Two types of cells were identified as astrocyte- and oligodendrocyte-like glia by the monoclonal antibody Mab O1 (specific for oligodendrocytes) and the rabbit serum anti-goldfish glial fibrillary acidic protein (anti-G-GFAP). Cells of compact morphology were rare, and anti-G-GFAP positive and O1 negative. Multipolar cells in 5-day-old cultures were anti-G-GFAP but rarely O1 positive. In 5-week-old cultures, however, roughly 75% of the multipolar cells were double-labeled with both anti-G-GFAP and O1; 10% were single labeled with Mab O1 and 15% with anti-G-GFAP, respectively.

Glial fibrillary acidic protein (GFAP) from goldfish: its localisation in visual pathway.

An intermediate filament fraction, isolated from goldfish brain, contains a prominent protein having a molecular weight of 51 kDa. In normal goldfish visual pathway, this protein is present in tectum and tract, but not in optic nerve. A polyclonal antibody raised to this protein clearly labels ependymal glial profiles in tectum and parallel processes in the tract, whereas optic nerve is unlabelled; Müller fibres in the retina are also labelled. A similar, but less prominent, pattern of staining is observed with antibodies, raised elsewhere, against glial fibrillary acidic protein from human and porcine. These results suggest that the 51 kDa protein is a GFAP, demonstrate the heterogeneity of astrocytes in goldfish visual pathway, and are consistent with the idea that GFAP is well conserved in vertebrate phylogeny.

Goldfish retina and tectum influence each other's growth activity during regrowth of the retinotectal projection.

Variations in retinal and tectal growth activity, during regrowth of the goldfish retinotectal projection, were monitored by measuring the rates of incorporation of [14C]leucine into soluble protein and tubulin-enriched fractions at different times after crushing the optic nerves. Other experiments tested for growth-modulating interactions between tectum and retina. Here we studied how the absence of one of these structures (i.e. tectal ablation or eye removal) affected the profile of biosynthetic activity in the other. Experiments were also conducted on groups of fish in which the tectum was reinnervated by a half-retina (either half-nasal (1/2 N) or half-temporal (1/2 T) retina). This was done to ascertain if growth interactions between retina and tectum display any position-dependent differences that may be relevant to retinotopic ordering during regeneration. Our studies have revealed that: the retina and tectum of 1/2 T and 1/2 N groups differ in their growth responses during regeneration of the visual pathway: the tectum may exert a stimulatory and at other times an inhibitory influence on retinal protein synthesis; and retina and tectum display a bimodal profile of biosynthetic activity during regeneration that coincides with two stages of increased cell division (primarily glia) which other workers have found occurs in the tectum and tract during regeneration of the retinotectal projection. Indeed it seems there may be a link between this glial proliferation and the neurotrophic and guiding influences which tectum and retina exert upon one another during regeneration.

Postnatal developmental profiles of filamentous actin and of 200 kDa neurofilament polypeptide in the visual cortex of light- and dark-reared rats and their relationship to critical period plasticity.

The concept of critical period plasticity in rat visual cortex has been studied in terms of changes in the level of filamentous actin and of the 200 kDa neurofilament polypeptide. Our results suggest that the postnatal developmental profile of filamentous actin is affected by visual experience, as a consequence of eye-opening. No such correlation, however, is detected for the 200 kDa neurofilament polypeptide. The significance of these findings in relationship to neuronal plasticity is discussed in terms of changes in the state and equilibrium conditions of the cytoskeletal proteins.

Effect of visual experience on tubulin synthesis during a critical period of visual cortex development in the hooded rat.

1. In some species, restriction of visual experience in early life may affect normal functional development of visual cortical cells. The purpose of the present study was to determine if visual deprivation during post-natal development in the hooded rat also affects the production in brain cells of certain molecular components such as tubulin, that are needed for growth and maintenance of synapses and neurites. 2. Norwegian black hooded rats were reared under a variety of conditions of visual deprivation. At various stages of development the animals were killed and the rate of synthesis of tubulin in visual and motor cortex determined. Tritiated colchicine was used to assay tubulin and L-[14C]leucine injected into the brain ventricles 2 hr before death was used to measure rate of tubulin synthesis. 3. In rats reared in normal light there is a marked elevation in visual cortex tubulin synthesis that spans the period from eye-opening (13 days) until approximately 35 days. This elevation in tubulin synthesis is absent in animals reared in darkness from birth or deprived of pattern vision by eyelid suture. Also the effect of visual deprivation on tubulin synthesis was specifically confined to visual cortex and was not found for the motor cortex. Similarly, the incorporation of L-[14C]leucine into total protein in visual cortex was unaffected by dark rearing. Hence the stimulation of tubulin synthesis by visual experience in rat visual cortex is not attributable to a general non-specific stimulation of protein synthesis. 4. Rats that were dark-reared from birth and then exposed to a lighted environment for 24 hr during a certain critical period that extends from eye-opening (13 days) until approximately 35 days, displayed a significant increase in visual cortex tubulin rats that were brought into the light later than 35 days showed no significant increase in tubulin synthesis when compared with their continuously dark-rearer controls. 5. It is suggested that the number of synapses and cytoplasmic processes that a developing cell can maintain depends on the size of the tubulin pool available to that cell. Tubulin in brain only has a half-life of about 4 days, so when the level of tubulin drops this could result in competition between different synapses for the limited supply of tubulin needed for their maintenance, a factor which may contribute to the structural plasticity of the visual cortex during the critical period.