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N V Swindale

Publications and source records attributed to N V Swindale.

At least 19 recordsLinked to original sources
PubMed1994

Comparison of receptive field properties of neurons in area 17 of normal and bilaterally amblyopic cats.

Receptive field properties of extracellularly recorded units in the visual cortex (area 17) of cats made bilaterally amblyopic by a variety of rearing conditions were measured and compared with the properties of units in normal cats. Properties studied included sensitivity to vernier offset, response facilitation to increasing bar length, receptive field size, responsiveness to moving and flashed stimuli, orientation tuning, the relation between mean firing rate and its variance, the amount of overlap of regions of on and off responsiveness in simple and complex cells, and, for flashed stimuli, latency to response onset, time to peak response, and response decay time constant. Behavioural testing of the amblyopic animals showed that spatial resolution was 2-4 times lower and vernier acuity thresholds 10-20 times greater than normal. Despite this, several neuronal response properties did not differ significantly from those in normal animals. These included peak responsiveness to moving stimuli, widths of orientation tuning curves, response variability, and latency to initial response for flashed stimuli. Other properties showed small but significant changes. Sensitivity to vernier offset (impulses per degree of offset) was reduced to nearly half its normal level; receptive field sizes increased by about 24% and an incomplete segregation of regions of on and off responsiveness was found in some cells, which made them hard to classify as simple or complex. Responses to flashed stimuli were smaller and more persistent. Their statistical significance notwithstanding, it seems unlikely that these relatively small response abnormalities in area 17 can fully account for the observed behavioural deficits.

Amblyopia↗
PubMed1994

Vernier acuity for edges defined by flicker.

We investigated the effects of contrast and temporal frequency on vernier edge alignment thresholds. Edges were defined by the presence of a 180 deg phase difference in the temporal modulation waveform of adjacent rectangles with spatially uniform luminances. Thresholds of 10 arc sec or less could be obtained at high contrasts, and flicker rates up to 8 Hz. Above this range, thresholds increased rapidly with decreasing contrast and increasing rates of flicker. Thresholds also increased with increasing temporal frequency over the range 0-20 Hz for contrasts normalized to thresholds for the detection of either flicker or the edge. Linear regression on log-log plots of threshold vs contrast at different temporal frequencies showed that the relationship between threshold and contrast was well described by a power law with an exponent of about -0.5 at temporal frequencies of 8 Hz or lower. About 8 Hz the slope more than doubled and thresholds increased. Thresholds also increased when the relative phase (i.e. the instantaneous sign of the contrast) of the upper and lower edges was reversed, and this effect was observed at all temporal frequencies. Measurements of threshold as a function of the size of a gap between the upper and lower edges suggested that the integration region was larger at 16 Hz or above than at 8 Hz. The results suggest that the channels which mediate vernier hyperacuity are phase sensitive and attenuate frequencies higher than 8 Hz.

Contrast Sensitivity↗
PubMed1993

Spectral motion produces an auditory after-effect.

Distortions of perception following prolonged exposure to an unvarying sensory stimulus have been observed since at least the third century BC. The motion after-effect is a familiar experience in which, after a few minutes of viewing objects moving in a single direction, a stationary object appears to move in the opposite direction. Similar after-effects have been observed for many visual stimuli, including tilted lines, colours, stereoscopic depth, curvature, spatial frequency, contrast, rotation and motion in depth. In contrast to the rich variety of visual after-effects reported since the 1960s, reports of analogous auditory adaptation effects only appeared in the 1970s, but have continued since then. Some effects of sound source spatial movement perception after adaptation to a spatially moving sound source have been reported. Here we report an auditory perceptual after-effect analogous to the visual motion after-effect, which is caused by adaptation to auditory spectral (frequency) motion. After a few minutes of listening to a simple spectral pattern moving upwards or downwards in frequency space, the same pattern sounds as though it is drifting in the opposite direction when it is stationary. The effect shows binaural transfer, implying that it is generated at the level after binaural interaction. After-effects produced by the motion of spectral peaks are independent of those produced by spectral notches, suggesting separate processing channels for spectral peaks and notches.

Auditory Perception↗
PubMed1992

A model for the coordinated development of columnar systems in primate striate cortex.

The existence of patchy regions in primate striate cortex in which orientation selectivity is reduced, and which lie in the centers of ocular dominance stripes is well established (Hubel and Livingstone 1981). Analysis of functional maps obtained with voltage sensitive dyes (Blasdel and Salama 1986) has suggested that regions where the spatial rate of change of orientation preference is high, tend to be aligned either along the centers of ocular dominance stripes, or to intersect stripe borders at right angles. In this paper I present results from a developmental model which show that a tendency for orientation selectivity to develop more slowly in the centers of ocular dominance stripes would lead to the observed relationships between the layout of ocular dominance and the map of orientation gradient. This occurs despite the fact that there is no direct connection between the measures of preferred orientation (from which the gradient map is derived) and orientation selectivity (which is independent of preferred orientation). I also show that in both the monkey and the model, orientation singularities have an irregular distribution, but tend to be concentrated in the centers of the ocular dominance stripes. The average density of singularities is about 3/lambda 2 theta, where lambda theta is the period of the orientation columns. The results are based on an elaboration of previous models (Swindale 1980, 1982) which show how, given initially disordered starting conditions, lateral interactions that are short-range excitatory and long-range inhibitory can lead to the development of patterns of orientation or ocular dominance that resemble those found in monkey striate cortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1991

Coverage and the design of striate cortex.

Hubel and Wiesel (1977) suggested that ocular dominance and orientation columns in the macaque monkey striate cortex might be bands of uniform width that intersected orthogonally. They pointed out that if this were the case, there would be an equal allocation of cells of different orientation preference to each eye and to each point in visual space. However, orientation and ocular dominance columns have a more complex structural organization than is implied by this model: for example, iso-orientation domains do not intersect ocular dominance stripes at right angles and the two columnar systems have different periodicities. This raises the question as to how well the striate cortex manages to allocate equal numbers of neurons of different orientation preference to each eye and to each region of visual space, a factor referred to here as coverage. This paper defines a measure of uniformity of coverage, c', and investigates its dependence on several different parameters of columnar organisation. Calculations were done first using a simplified one-dimensional model of orientation and ocular dominance columns and were then repeated using more realistic two-dimensional models, generated with the algorithms described in the preceding paper (Swindale 1991). Factors investigated include the relative periodicities of the two columnar systems, the size of the cortical point image, the width of orientation tuning curves, whether columns are spatially anisotropic or not, and the role of the structural relationships between columns described by Blasdel and Salama (1986). The results demonstrate that coverage is most uniform when orientation hypercolumns are about half the size of ocular dominance hypercolumns. Coverage is most uneven when the hypercolumns are the same size, unless they are related in the way described by Blasdel and Salama, in which case coverage gets only slightly worse as the size ratio (ori/od) increases above 0.5. The minimum diameter of cortical point image that ensures reasonably uniform coverage is about twice the size of an ocular dominance hypercolumn i.e. about 1.5-2.0 mm.

Animals↗
PubMed1990

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.

Animals↗
PubMed1990

Is the cerebral cortex modular?

Two types of modular subunit, differing in size, have been hypothesized to exist in the cerebral cortex. The first, known as a mini-column, consists of a group of 110 +/- 10 cells which form a fascicle about 30 micrograms in diameter oriented perpendicular to the cortical surface. Mini-columns are believed to be organized into larger modular groupings, referred to here as macro-columns, with a diameter of about a millimetre or less. Nicholas Swindale argues in this article that there is very little real evidence in favour of either type of module. As an alternative, he suggests that the diversity of types of columnar organization, both within and between different cortical areas, may reflect the diversity of types of information stored in the cortex. Consequently, columnar organization can be expected to vary within and between species, and even between different individuals of the same species. This new interpretation is in line with current neural network theories, which do not demand the existence of structural modularity, but show how complex forms of organization can result from the existence of simple processing rules between the elements of a structure given complex structured inputs.

Animals↗
PubMed1989

Vernier acuities of neurons in area 17 of cat visual cortex: their relation to stimulus length and velocity, orientation selectivity, and receptive-field structure.

The sensitivity of neurons in area 17 of the cat's visual cortex to vernier offset was expressed as the percentage reduction in response caused by the introduction of a given offset into a bar stimulus moving across the receptive field. There was a wide variation in sensitivity: in some cells response could be halved by an offset equal to a fifth receptive-field width (defined as twice the standard deviation of a Gaussian curve fitted to the response profile), while other cells showed no sensitivity. The highest absolute sensitivities of complex and simple cells were similar, although most cells with poor sensitivity were complex. Sensitivity was largely unaffected by changes in stimulus velocity and stimulus length, although there was a tendency for sensitivity to increase with decreasing bar length. Comparisons of orientation tuning curves with vernier tuning curves showed that the response to a vernier stimulus approximated the response to a single bar of the same overall length and an orientation equal to that of a line joining the midpoints of each bar. This was true for a wide range of sensitivity values. Vernier sensitivity was correlated with a measure of length summation H, which is positive when there is net facilitation between the bars, and negative when there is net inhibition. Vernier sensitivity was highest in cells with large values of H, and least in cells where H was negative. We examined a linear model of the simple cell receptive field which, together with a variable response threshold, was able to explain the correlation between vernier acuity and length summation. Although this model accounted qualitatively for many of our findings, the majority of simple cells had tuning curves that were sharper than the predicted ones. This suggests that there are nonlinearities in the behavior of many simple cells whose effect is to increase the sharpness of orientation tuning and consequently vernier sensitivity.

Animals↗
PubMed1988

Role of visual experience in promoting segregation of eye dominance patches in the visual cortex of the cat.

Transneuronal autoradiography was used to study the role of visual experience in the development of ocular dominance patches in the cat. In order to assess quantitatively the effects of visual deprivation, image analysis was used to measure the profiles of grain density in layer IV. Fourier power spectra of these profiles were computed to give a measure of the amplitudes and frequencies of the fluctuations in grain density that were present. Deprivation of normal patterned vision by binocular lid suture or by rearing in total darkness from shortly after birth abolished the dominant periodicity (of about 1.1 mm) in the distribution of left and right eye afferents in layer IV of area 17. A dominant periodicity of about 2.2 mm was, however, present in area 18 of both normal and dark-reared animals. Visual deprivation was not able to reverse segregation. One animal reared normally for 6 weeks was placed in the dark for a further 28 weeks and showed normal periodicities in the distribution of geniculate inputs to area 17. Another animal given 128 hours of experience and kept in the dark for the rest of the time until it was 12 weeks old also showed normal segregation. To determine the minimum amount of visual experience necessary for segregation to occur, four animals were given 8-, 24-, 48-, and 128-hour periods of visual experience and were studied at 12 weeks of age. Eight hours of experience had no detectable effect on segregation; periodicities of intermediate amplitude were present in animals that received 24 and 48 hours of experience, while 128 hours of experience resulted in periodicities of normal amplitude. Recovery from visual deprivation was studied by rearing kittens from birth in the dark for varying periods and then returning them to the normally lit colony room for periods of 6 to 22 weeks. Recovery from 6 weeks of dark rearing was found to be complete; much less recovery occurred following periods of 8 to 25 weeks of initial deprivation, and no recovery at all occurred after 30 weeks of deprivation. It is concluded that the spontaneous activity present in the geniculocortical afferents of dark-reared and lid-sutured cats is not adequate to drive normal periodic segregation in area 17, though it can do so in area 18. Between 48 and 128 hours of visual experience, given before 8 weeks of age, appears to be necessary and sufficient for normal periodic segregation of geniculate afferents in area 17 of the cat.

Animals↗
PubMed1987

Anatomical properties and physiological correlates of the intrinsic connections in cat area 18.

After making a map of response properties of neurons in a roughly 3 X 4 mm region of area 18 in the cat, we injected wheat-germ agglutinin horseradish peroxidase (WGA-HRP) and succinylated concanavalin A (Con A) into physiologically identified regions of the map. We observed up to 10 patches of retrogradely labeled cells surrounding each injection site. The majority of the patches occurred within 1.4 mm of the center of the injection site, but rare patches were found as far as 3.4 mm from the injection site. The mean center-to-center spacing of the intrinsic patches was about 1 mm, while the mean distance between the center of the injection site and the nearest patches was less than 1 mm. The labeled cells included both nonpyramidal and pyramidal types and were found in all layers, although they were usually most dense in layers II-IV. Between 2% and 9% of the cells within a cortical column were labeled after a single injection of WGA-HRP or Con A into area 18. Injections of different tracers into 2 neighboring areas resulted in a uniform and less patchy distribution of labeled cells, which suggests that the patches observed after a single injection were only a portion of a continuous horizontal system of interconnections. The patterns and positions of the intrinsic patches were compared to the distribution of the following receptive-field properties: preferred orientation, receptive-field location, and eye preference. The preferred orientations of the recording sites within the injected and labeled areas were different and, most frequently, orthogonal to each other. This is a highly specific projection, since regions with orientation values like those of the injection site were "within range," yet not labeled. We were unable to detect any relationship between the ocular preferences of the injected and labeled cell regions. Injections into areas predominantly driven by the contralateral eye resulted in labeled regions exhibiting varied eye preference distributions. In some animals they were like the injection site and in others there were equal numbers of contra- and ipsilateral eye-dominated regions. The overall distribution of the patches around the injection site was elongated along the anterior-posterior cortical axis of the brain. The patches extended further in the posterior than the anterior direction. These observations appear to be related to the finding that the cortical magnification factor is greater along the anterior-posterior than the medial-lateral axis of area 18.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1987

Functional topography in cat area 18.

Using closely spaced microelectrode penetrations, we have mapped the representation of the visual field and of several functional response properties on the surface of cat area 18. The representation of the visual field was anisotropic, with the magnification factor for vertical visual space being about 2-5 times greater than that for horizontal. The topographic anisotropy was paralleled by an anisotropy in the cortical point-spread function, a measure of the distribution in the cortex of cells with overlapping receptive-field centers. The spread of this distribution (measured as twice the standard deviation) was positively correlated with the magnification factor anisotropy, averaging about 0.6 mm along the mediolateral (M-L) axis and 1.2 mm along the anteroposterior (A-P) axis. Units with similar response properties were clustered across the cortical surface, but different response features were laid out in different ways. For units with orientations within a 90 degrees range, the clusters took the form of branching bands, with a center to center spacing of 1.25 +/- 0.13 mm. These bands ran from postero-medial to anterolateral across the cortical surface, roughly perpendicular to the 17/18 border. Units with similar preferred eye input were laid out in patches without a well-defined direction of elongation, and with a less well-defined periodicity that averaged 1.86 +/- 0.75 mm. Local correlations in direction preference extending over distances of 300 micron were found, together with frequent 180 degrees differences in the direction preferences of units close together. The organization of the map of orientation preference, and the way in which direction selectivity is overlaid on this map, is discussed in more detail in the accompanying paper (Swindale et al., 1987). No obvious structural relationships between the ocular dominance patches and the pattern of iso-orientation domains were observed. There were, however, obvious interrelationships between the topographic map and other functional response properties. The iso-orientation bands ran approximately perpendicular to the direction in which both the point-spread function and magnification factor were elongated. This will have the effect of maximizing the allocation of a full range of orientations by the cortex to each location in visual space.

Action Potentials↗
PubMed1987

Surface organization of orientation and direction selectivity in cat area 18.

Two-dimensional maps of orientation and direction preference were made in area 18 of the cat's visual cortex using multiple electrode penetrations 150-300 micron apart. The maps were then analyzed by autocorrelation and Fourier transformation. The power spectrum of the orientation map was sharply peaked below the theoretical cutoff frequency for the sampling function (the pattern of electrode penetrations) used to obtain the map. This suggested that it would be possible to interpolate orientation values between the sample points in the cortex. This was done and the resulting fine-grain maps of orientation preference were studied. Empirical testing showed that the interpolated orientation values were accurate to within +/- 30 degrees. Study of the fine-grain maps showed that iso-orientation domains for broad orientation ranges (0 degrees-90 degrees) were branching bands running from an anterolateral to a posteromedial direction across the surface of the cortex with a periodicity of 1.25 +/- 0.13 mm. Domains for smaller orientation ranges (0 degrees-30 degrees) were periodically spaced, but somewhat irregularly shaped patches. The orientation maps contained numerous point singularities where orientation changed discontinuously. These were spaced about 750 micron apart and most were surrounded by a single 180 degrees cycle of orientations. Autocorrelation analysis of the maps of preferred direction revealed local clustering that extended over a distance of 250-300 micron, but spectral analysis failed to reveal any evidence of periodicity. The absence of periodicity was probably due to a relatively large number of 180 degrees reversals in the map of direction preference, which do not affect the continuity of the orientation map and are not sufficiently numerous to destroy local continuity in the direction map. It is shown that the direction map, if it is to be as continuous as possible, must nevertheless contain lines across which direction preference reverses by 180 degrees. These lines run from one orientation singularity to another. Evidence that the direction map approaches this degree of continuity is presented.

Action Potentials↗
PubMed1986

Physiological segregation of geniculo-cortical afferents in the visual cortex of dark-reared cats.

Transneuronal autoradiography in cats dark-reared from birth shows that geniculate terminals from left and right eyes are spread throughout layer IV in area 17 of the visual cortex. In area 18 however, segregation into alternating left and right eye ocular dominance patches appears to be normal. We attempted to correlate this difference between the two areas with the ocular dominance distribution of physiological activity of the geniculate afferents. To do this, microelectrode recordings of multi-unit activity, believed to represent the activity of a number of geniculate terminal axons in the vicinity of the electrode tip, were made in layer IV of areas 17 and 18 in dark-reared cats. The ocular dominance distribution of this activity was predominantly monocular in area 18, as the anatomical results predicted, but surprisingly there were also many regions in area 17 where activity could only be elicited by stimulation of one eye. This has to be reconciled with the anatomical results showing that inputs from both eyes are present throughout layer IV in area 17 of dark-reared cats. Reasons for the discrepancy are discussed.

Afferent Pathways↗
PubMed1985

Intrinsic projections within visual cortex: evidence for orientation-specific local connections.

The functional organization of intrinsic connections within area 18 of cat visual cortex was studied using combined electrophysiological and anatomical techniques. Physiological recordings were first used to map the distribution of orientation preference, ocular dominance, and receptive-field location relative to the cortical surface. Next, localized injections of lectin-conjugated horseradish peroxidase were made into physiologically identified regions within area 18. We found that (i) the local cortical interconnections are made preferentially between cell populations with orthogonal preferred orientations and are independent of the ocular dominance of the cortical cells, (ii) the map of visual space in the cortex is anisotropic with the magnification factor for vertical at least twice that for horizontal visual space, and (iii) the pattern of cortical projections compensates for the functional asymmetry so that a population of interconnected cells represents a roughly circular region of visual space.

Animals↗
PubMed1982

A model for the formation of orientation columns.

A mathematical model is proposed to describe the formation of orientation columns in mammalian visual cortex. The model is similar in concept to that proposed for ocular dominance column formation (Swindale 1980), the essential difference being that orientation is a vector rather than a scalar variable. It is assumed that initially orientation selectivity is weak and randomly distributed, and that selectivity develops in such a way that the orientation preferences of neurons less than about 200 microns apart tend to change in a similar direction, whereas the preferences of cells further apart tend to develop in opposite directions. No hypotheses are made about the anatomical or physiological basis of these interactions, and it is not necessary to assume that they are the result of environmental stimulation, as with existing models for the development of orientation selectivity (see, for example, von der Malsburg, 1973). The model reproduces the experimental data on orientation columns: roughly linear sequences of orientation change are produced, and these alternate unpredictably between clockwise and anticlockwise directions of change. Continuous sequences may span several 180 degrees cycles of rotation. The sequences are generally smooth, but abrupt discontinuities of up to 90 degrees also occur. The iso-orientation domains for large orientation ranges (60-90 degrees) are periodically spaced branching stripes that resemble those demonstrated in animals by the 2-deoxyglucose technique. The domains for narrower orientation ranges are periodically spaced but are more irregular in shape, though sometimes thin and elongated. The model makes a number of predictions that can be tested experimentally. Of particular interest are the discontinuities in the orientation sequences: these should be distributed with a spacing roughly equal to, or half, that of the iso-orientation domains. Each should be surrounded by one or two complete sets of iso-orientation domains, and each may be associated with regions where cells are not orientation selective. These regions may be more extensive in younger animals, when the columns are at an intermediate stage of formation, and less numerous where the columns run parallel and unbranched over large areas.

Animals↗
PubMed1981

Recovery from monocular deprivation in the monkey. III. Reversal of anatomical effects in the visual cortex.

Transneuronal autoradiography was used to study the effects of visual deprivation on the ocular dominance stripes in layer IVc of the striated cortex of Erythrocebus patas (Old World) monkeys. The animals were studied after: (a) 21-28 days of monocular deprivation starting at, or within, a few days of birth; (b) the same treatment followed by a further 3, 6, 15 or 126 days of monocular vision through both eyes (reopening). One other monkey was monocularly deprived from birth to 1890 days. In most cases the behaviour of the ocular dominance stripes formed by the initially closed eye was studied. After 24 days of monocular deprivation from birth, the input from the normal eye was distributed uniformly within layer IVc, with no periodicity evident. After 21 days of deprivation, the deprived eye's input formed narrow stripes occupying about 38% of layer IVc in the operculum. Seven months of monocular deprivation reduced this to about 29%. Opening the closed eye after the deprivation produced no change in the area innervated: when periods of 15 or 96 days of binocular vision followed the deprivation, the areas innervated by the initially deprived eye were 26 and 30% respectively. However, in both cases the deprived eye's input formed blobs and spots, rather than uniformly narrow stripes. In contrast to reopening, reverse suturing increased the fraction of layer IVc occupied by input form the initially deprived eye. In the operculum, the effects of reverse suturing appeared to be fully developed after only 6 days of reversal: the initially deprived eye's stripes having expanded to occupy about 50% of layer IVc. A further 9 days' reversal produced little change in this. In the visual cortex in the calcarine fissure, the effect of the initial deprivation ws more severe, and the expansion induced by reverse suturing more pronounced. The initial deprivation caused the stripes to shrink to occupy 24% of layer IVc; after 6 days of reverse sulture the proportion increased to 52%, while after 15 days of reverse suture about 88% of IVc was occupied. These results show that reverse suturing can cause fresh growth of afferent axons in regions of layer IVc from which they had been at least partially removed, either by the normal process of segregation, or as a consequence of monocular deprivation. Taken in conjuction with the findings of the accompanying two papers (Blackemore et al...

Animals↗
PubMed1981

Absence of ocular dominance patches in dark-reared cats.

If a young monkey or kitten is monocularly deprived for a period of days of weeks, the ocular dominance stripes or patches formed in layer IV of the visual cortex by the geniculo-cortical afferents driven by that eye become smaller, while the patches formed by afferents from the other, experienced eye, spread out and increase in size. One explanation for this effect is that it results from a disturbance of competitive process which, during the first weeks of life, guides a "sorting out" of the initially intermixed right and left eye inputs into complementary, largely non-overlapping territories. One feature of this process may be a local interaction between right and left eye synapses in which like synapses reinforce each other's growth rates and cause rejection of the other eye's synapses. If this is the case, then the effect of monocular deprivation on the relative sizes of the two sets of columns can be explained by supposing that the strengths of the effects exerted by the deprived eye are reduced. This explanation has a testable consequence: if both eyes are deprived of vision then each eye should be made less effective in eliminating the other eye's inputs, and the overall rate at which the ocular dominance columns form should be decreased. Although LeVay et al. found that columns were present in a 7-week old monkey reared in the dark from the age of 3 days, this result does not necessarily imply that the rate of column formation had been normal, because in normal monkeys the columns are well developed by 3 or more weeks of age. I report here the results of transneuronal autoradiography in cats, which show that columns, as revealed anatomically, are undetectable in most parts of the visual cortex of cats reared in the dark for periods of up to 20 weeks, implying that visual experience is necessary for their proper formation.

Animals↗