Segregation of callosal and association pathways during development in the visual cortex of the primate

The segregation of callosal and association pathways in the developing visual cortex of the monkey was studied using the retrograde tracers fast blue and diamidino yellow. Quantitative analysis of the laminar distribution of labeled callosal and association neurons made it possible to reveal the shifting pattern of connections that characterizes the development of these two pathways. In the adult, callosal neurons are restricted to supragranular layers, where they are concentrated at the bottom of layer 3. Association neurons are located both in infra- and supragranular layers. Supragranular layer association neurons are concentrated in layer 2, with limited spread into layer 3 so that there is little overlap with callosal neurons. In the immature brain, callosal neurons are characterized by a tangential distribution that is more widespread than in the adult, while their laminar distribution undergoes little developmental change. Association neurons show two types of changes in their laminar distribution: (1) in the early fetus, there is a large excess of association neurons in supragranular layers, the adult distribution being achieved some time after birth; and (2) during maturation there is a selective elimination of at least 50% of the projections originating from the lower part of layers 2/3. Hence, the adult radial segregation of association and callosal pathways is achieved in part by regressive phenomena. The developmental reduction of bihemispheric projections is largely independent of changes in the organization of association neurons. Quantitative analysis of the morphology and spatial location of neurons sending axon collaterals to both hemispheres suggests that they constitute a subset of callosal neurons and that their frequency is determined by factors that regulate directly this population. These results are discussed with respect to the specification of visual cortical pathways during ontogenesis.

The effects of bilateral enucleation in the primate fetus on the parcellation of visual cortex

Bilateral enucleation in the macaque fetus causes an areal reduction of an otherwise normal striate cortex. Here we show that in early operated animals this reduction is accompanied by a separation of striate and prostriate cortices which are normally contiguous. However this induced separation does not correspond to the areal reduction of striate cortex, indicating that extrinsic signals regulate either the proliferation and/or survival of striate cortical neurons.

Cost efficiency of bone scans in breast cancer

A total of 110 consecutive females who presented in 1987 with primary carcinoma of the breast were staged according to the UICC TNM staging system. Of these, 90 patients had bone scans at presentation, of which seven were positive. The rate of positive initial scans for Stages I-II was 3.5%. Of these only one patient subsequently had bone metastases confirmed, to diagnose which by bone scan, the estimated cost was pounds 1300. Follow-up information was obtained for 95 patients, repeat scans being performed in 22 who had symptoms suggestive of bone metastases. Ten patients with negative initial scans converted to scan-positive within a mean time of 15 months. Only four of these had radiological confirmation of bone metastases. The cost of detecting bone metastases by follow-up scan was approximately pounds 80 per patient. The false-positive rate and the false-negative rate were both calculated as 10%. The specificity of the test was calculated as 90%. It is recommended that bone scanning should be reserved for patients with Stages III and IV disease and to evaluate symptoms suggesting bone metastases.

Reflections on the aim of child analysis

Childhood disturbances can best be studied in a developmental frame of reference. Following Anna Freud, the authors distinguish between outcome aims and intermediary aims. They present the analyses of a child and an adolescent to demonstrate how these aims affect the nature and progression of treatment.

Incidence of visual cortical neurons which have axon collaterals projecting to both cerebral hemispheres during prenatal primate development

Fast blue was injected massively in extrastriate cortex of one hemisphere Diamidino yellow in area 17 of the other hemisphere, in adult and prenatal cynomolgus monkeys. After a suitable survival period the brains were processed for fluorescent dyes. Counts were made of the total number of labeled neurons and of those neurons which were labeled by both dyes and which project therefore to both hemispheres by means of bifurcating axon collaterals. At 122 and 135 days after conception (E122 and E135), shortly after cortico-cortical pathways are established, double-labeled neurons constituted 0.45% and 0.46% of the total population of labeled neurons in area V2. In V2 in the adult the range of values of double-labeled neurons was 0.03-0.08%.

Transient projection from the superior temporal sulcus to area 17 in the newborn macaque monkey

Area 17 in the neonate of numerous species receives projections from cortical areas that do not project to area 17 in the adult. To investigate if this were the case in the developing primate, we have made injections of retrograde tracers in area 17 of newborn monkeys (Macaca irus) and examined the areal distribution of labeled neurons. Neurons projecting to area 17 were found to be restricted to those cortical regions that project to area 17 in the adult. The projection to area 17 in the neonate did appear to be very different in that in the superior temporal sulcus there was a large contingent of labeled neurons in supragranular layers. This constitutes a transient projection because in the adult area 17 projecting neurons in this cortical region originate almost exclusively from infragranular layers. To test if a change in the laminar distribution of area 17 projecting neurons in extrastriate cortex is a general feature of postnatal development, we have computed in neonates and adults the proportion of area 17 afferent neurons in infra- and supragranular layers for each cortical region that projects to area 17. This revealed (i) that in the adult the laminar distribution of area 17 afferents is characteristic for each cortical area and (ii) that this distribution emerges during development from an immature state in which labeled neurons are more numerous in supragranular layers. These results show that there is an extensive remodeling of the neuronal circuitry connecting visual cortical areas during postnatal development in the monkey and that the transient connectivity of primate area 17 is very different from that observed in other mammalian species.

Studies on calcium absorption from milk using a double-label stable isotope technique

Calcium absorption was measured in ten male volunteers from skimmed milk, Ca-enriched skimmed milk or watercress (Nasturtium officinale) soup. The foods were labelled extrinsically with 30 mg 44Ca. Shortly after consuming the labelled meal, each subject was given an intravenous injection of 3 mg 42Ca. Fractional absorption from the oral dose was determined from plasma and urine samples collected 24-72 h later, using fast atom bombardment mass spectrometry to measure isotope ratios. The values for urine and plasma were in good agreement. Mean percentage absorption was 45.5 (SEM 1.9)% from the skimmed milk, 35.7 (SEM 4.7)% from the Ca-enriched milk and 27.4 (SEM 1.9)% from the watercress soup. The effect of consuming 568 ml (1 pint) Ca-enriched milk each day for 4 weeks on the efficiency of absorption of Ca was studied. Although there was no statistically significant difference between Ca absorption before and after the supplementation period, the results were considered to be somewhat inconclusive due to the small number of subjects and wide individual variation in Ca absorption.

A double-labeling investigation of the pretectal visuo-vestibular pathways

The projections of the nucleus of the optic tract were studied in the cat by simultaneous use of two distinct retrograde tracers (Fast Blue and Diamidino Yellow) injected in the inferior olive and the prepositus hypoglossi nucleus. Following injections of diamidino yellow in one structure and fast blue in the other, a significant number of retrogradely labeled neurons projecting to either target were observed dispersed in the nucleus of the optic tract. Three populations of labeled cells were found: one which projected to the inferior olive, a second to the nucleus prepositus hypoglossi, and a third which projected by means of a bifurcating axon to both of these structures. Quantification of these results reveals that 72% of the total number of labeled neurons are labeled by the IO injection, the remaining cells being labeled by the NPH injection. Double-labeled neurons represent more than 7% of the total number of the labeled cells. Tentative inferences as to the electrophysiological properties of the nucleus of the optic tract are discussed in the context of the optokinetic system.

Convergence and divergence in the afferent projections to cat area 17

We have examined the topography of the afferent connections to area 17 in the cat by means of double retrograde label tracing techniques. Injections of two fluorescent retrograde tracers, diamidino yellow and fast blue, were made with variable separations in area 17 and the spatial distributions of the resulting populations of labeled cells examined in afferent cortical areas and subcortical structures. When injections were separated rostrocaudally, the topographic organizations of the projections were characterized quantitatively with two graphic methods: the labeling density curve and the connectivity graph. The labeling density curve measures labeled neuron density in successive rostrocaudal sections, whereas the connectivity graph provides a two-dimensional model of the topography of a given connectivity. The connectivity graph makes it possible to define two parameters that characterize the topography of the connection: the convergence and the divergence. The convergence is defined as the extent of an afferent structure that contains neurons converging on a line normal to the cortical surface in area 17. The divergence is the extent of area 17 that is innervated by neurons contained in an infinitely small region of the afferent structure. The results show that a number of subcortical structures project to area 17 in a nontopographic manner, i.e., that in each of these structures neurons contained in an infinitely small region send projections to the whole of area 17 and that a line normal to the surface of area 17 is innervated by neurons distributed throughout the afferent structure in question. Nontopographic projections are found from the intralaminar nuclei, the ventral mesencephalic tegmental region, the diagonal band of Broca, and the locus coeruleus. All remaining subcortical structures and cortical areas send topographically organized projections to area 17. The extent of the convergence and divergence, however, varies between structures. Only the projection from the A laminae of the LGN was found to approximate a point-to-point projection with a convergence of 0.4 mm and 2 mm in divergence. Much larger convergence and divergence values are found in the projections from the claustrum and the cortical areas. For example, the divergence reaches 20 mm for the projections from area 20 or from the anterior part of the lateral suprasylvian sulcus. Knowing the convergence and divergence values and the retinotopic organizations of area 17 and a number of its afferents, it becomes possible to test whether connections in the visual system link regions representing the same zone of the visual field.(ABSTRACT TRUNCATED AT 400 WORDS)

Maturation and connectivity of the visual cortex in monkey is altered by prenatal removal of retinal input

In several species, the peripheral input from the eyes partly determines the pattern of interconnections between the visual areas of the two cerebral hemispheres through the fibre tract termed the corpus callosum. In the macaque monkey, the neurons projecting through the callosum are largely restricted to area 18 throughout ontogeny, whereas area 17 is characterized by few or no callosal projections. Here, we show that suppressing the peripheral input by prenatal removal of the eyes leads to a marked reduction in the extent of area 17, resulting in a large shift in the position of the histologically identifiable boundary between the two areas. Even so, the boundary continues to separate an area rich with callosal connections (area 18) from one poor in such projections (area 17), indicating there is no effect on the callosal connectivity of area 17. In contrast, in area 18, eye removal results in many more neurons with callosal projections than in normal animals. The results suggest that the factors that determine the parcellation of cortical areas also specify their connectivity.

Experimental myopia in cats reared in stroboscopic illumination

Spectacle refraction of eyes of strobe-reared animals was compared to that of normal cats. Strobe reared cats were found to be significantly more myopic than normal cats.

The maturational status of thalamocortical and callosal connections of visual areas V1 and V2 in the newborn monkey

Cytochrome oxidase (CytOx) is known to preferentially stain those regions of the visual cortex which receive direct projections from the thalamus. The pattern of CytOx stain has been used to investigate the maturation of thalamic input to areas V1 and V2 in the newborn monkey. In both areas, the intensity of CytOx activity was similar in newborns and adults. The distribution of CytOx in area V2 was not found to vary with age. In area V1, the only difference in CytOx activity in newborns was a relative immaturity of staining in layer 4C. The callosal connections of visual areas V1 and V2 were investigated by the axonal transport of wheat germ agglutinin conjugated to horseradish peroxidase and free horseradish peroxidase. In the adult, V1 was found to be reciprocally callosally connected for a distance of 1-2.5 mm from the V1/V2 border, whilst V2 was connected for a distance of 3-8 mm from the border. In both areas, callosal connections showed a certain degree of clustering, particularly in V2 which contained 97-98% of the total number of callosal connections of these two areas. In the newborn, the number, tangential extent and clustered distribution of callosal connections were as in the adult. In the newborn, as in the adult, callosal connections coincided with regions of high CytOx activity in area V2. The results showing a relative maturity of the tangential distribution of callosal projecting neurons on the one hand, and an immaturity of thalamic projections on the other, are discussed in terms of: (1) the maturational status of the newborn monkey compared to other mammals at the moment of birth and (2) the possible role of visual experience in shaping cortical connections.

Functional implications of the anatomical organization of the callosal projections of visual areas V1 and V2 in the macaque monkey

The efferent and afferent connections of the V1/V2 border with the contralateral hemisphere have been examined using anatomical tracers. The V1/V2 border was found to exchange connections with the contralateral V2 area as well as a restricted strip of V1 lying adjacent to the V1/V2 border. Besides these homotopic projections, two heterotopic projections were found to V3/V3A and V5. Anterograde tracing of callosal connections showed that terminals in these heterotopic sites were focused in layer 4, the recipient layer of projections originating from the ipsilateral V1/V2 border. Bilateral injections of fluorescent dyes showed that these heterotopic targets of the V1/V2 border are connected to the homologous ipsilateral V1/V2 border region. The laminar location of callosal projecting neurons as well as their terminals were characteristic for each cortical region. The laminar pattern of callosal connectivity was found to differ markedly from that of associational visual pathways. Two principal hypotheses are suggested by these results. First, the fact that V1 in part is reciprocally callosally connected in all mammals supports the notion that this interhemispheric pathway completes long-range intrinsic cortical connections. Second, the convergence of inter- and intrahemispheric pathways could provide the anatomical basis for the modulation of the sensory processing within one hemisphere by ongoing activity in the contralateral hemisphere.

Characterization of transient cortical projections from auditory, somatosensory, and motor cortices to visual areas 17, 18, and 19 in the kitten

We have examined the anatomical features of ipsilateral transient cortical projections to areas 17, 18, and 19 in the kitten with the use of axonal tracers Fast Blue and WGA-HRP. Injections of tracers in any of the three primary visual areas led to retrograde labeling in frontal, parietal, and temporal cortices. Retrogradely labeled cells were not randomly distributed, but instead occurred preferentially at certain loci. The pattern of retrograde labeling was not influenced by the area injected. The main locus of transiently projecting neurons was an isolated region in the ectosylvian gyrus, probably corresponding to auditory area A1. Other groups of transiently projecting neurons had more variable locations in the frontoparietal cortex. The laminar distribution of neurons sending a transient projection to the visual cortex is characteristic and different from that of parent neurons of other cortical pathways at the same age. In the frontoparietal cortex, transiently projecting neurons were located mainly in layer 1 and the upper part of layers 2 and 3. In the ectosylvian gyrus, nearly all the neurons are located in layers 2 and 3. In addition, a few transiently projecting neurons are found in layer 6 and in the white matter. Transiently projecting neurons have a pyramidal morphology except for the occasional spindle-shaped cell of layer 1 and multipolar cells observed in the white matter. Anterograde studies were used to investigate the location of transient fibers in the visual cortex. Injections of WGA-HRP at the site of origin of transient projections gave rise to few retrogradely labeled cells in areas 17, 18, and 19, demonstrating that transient projections to these areas are not reciprocal. Although labeled axons were found over a wide area of the posterior cortex, they were more numerous over certain regions, including areas 17, 18, and 19, and absent from other more lateral cortical regions. Transient projecting fibers were present in all cortical layers at birth. Plotting the location of transient fibers in numerous sections and at all ages showed that these fibers are not more plentiful in the white matter than they are in the gray matter. We found no evidence that the white/gray matter border constituted a physical barrier to the growth of transient axons. Comparison of the organization of this transient pathway to that of other transient connections is discussed with respect to the development of the cortex.

Absence of interhemispheric connections of area 17 during development in the monkey

Our understanding of the development of cortical connectivity largely stems from studies of the ontogeny of interhemispheric pathways in carnivores, rodents and lagomorphs. Early in development, cortical neurons projecting to the contralateral hemisphere through the corpus callosum (callosal projection neurons) have a widespread distribution. As maturation proceeds, callosal projection neurons become restricted to those cortical regions that are connected in the adult. In newborn cats and rats, for example, callosal projection neurons are not restricted to the 17-18 border as in the adult, but are found throughout areas 17 and 18. The macaque monkey is an exception, because at birth it has an adult-like distribution of callosal projection neurons in area 18, with practically none in area 17. Here we show that whereas area 17 is devoid of interhemispheric connections throughout prenatal development, the distribution of callosal projection neurons in area 18 shows the common sequence of an early widespread distribution followed by regression. The absence of callosal projection neurons in area 17 throughout ontogeny may well be a feature unique to Old World primates.

Restenosis after multilesion percutaneous transluminal coronary angioplasty

Experience and new technical advances have resulted in an increasing number of patients with multivessel coronary disease who can be considered for percutaneous transluminal coronary angioplasty (PTCA). In selected patients with multivessel coronary disease, PTCA is a safe and effective procedure for the immediate relief of anginal symptoms. However, many questions remain regarding the long-term therapeutic benefit of the procedure. Few data are available on the incidence and clinical significance of restenosis after multilesion PTCA. Clearly, there is the potential for a higher rate of restenosis in patients who undergo dilatation of more than 1 lesion. Determination of restenosis rates after multilesion PTCA is important in the definition of expanded indications for this procedure. Because of the variations in definitions of restenosis and in patient selection factors, reported recurrence rates after multilesion PTCA are not easily compared between patient series. After multilesion dilatation the risk of developing at least 1 recurrent lesion ranges from 26% to 53% and appears to be greater than that reported for single lesion PTCA. Multilesion restenosis occurs in 7% to 21% of patients who undergo multilesion PTCA and is frequently observed in patients with recurrent symptoms. "Silent" multilesion restenosis (i.e., multiple lesion restenosis without symptoms) is rare. A higher risk of restenosis at one of several dilatation sites in a patient with extensive coronary disease should not be a deterrent in recommending multilesion PTCA to selected patients with multivessel coronary disease because the procedure provides important symptomatic relief to most. Further, recurrent narrowings are usually amenable to a second dilatation attempt if clinically indicated.

Callosal connectivity of areas V1 and V2 in the newborn monkey

The callosal connectivity of areas V1 and V2 in the newborn monkey has been investigated with the neuroanatomical tracers wheat germ agglutinin conjugated to horseradish peroxidase and free horseradish peroxidase. In the adult, callosal projecting neurons in cortex subserving the lower parafoveal visual field were found to extend from the V1/V2 border for a distance of 1-2.5 mm into V1 and 8 mm into V2. In the newborn, the tangential extent and total number of callosal projecting neurons were the same as in the adult. Within area V1, callosal projecting neurons in the adult and newborn were limited to supragranular layers. In the adult, axon terminals of callosal projections were located in layers 4B and 5 and were excluded from layer 4C. In the newborn, axon terminals were more extensively distributed than in the adult and invaded layer 4C. In area V2, the laminar distribution and the patchy location of callosal connections in regions of high cytochrome oxidase activity were similar in the newborn and adult animals. In both newborns and adults, the patchy distribution of callosal projections persisted when the neuroanatomical tracers were injected over extensive regions of the contralateral striate and extrastriate cortex. In the adult, area V1 and V2 project contralaterally to two heterotopic sites located in the fundus of the lunate sulcus and the superior temporal sulcus. This was also found to be the case in the newborn. In the adult the terminals of these heterotopic projections were focused in layer 4. This was not the case in the newborn, where after injection limited to the contralateral V1/V2 border they were more evenly distributed among the different cortical layers. Following extensive contralateral injection of tracer, terminals in cortex anterior to V2 were focused over layer 5 and the bottom of layer 4.

Topography of the afferent connectivity of area 17 in the macaque monkey: a double-labelling study

The various structures afferent to area 17 (or V1) of the macaque monkey have widely differing retinotopic organizations. It is likely that these differences are reflected in the topographic organizations of the projections from these structures to area V1. We have investigated this issue by placing side-by-side injections of two retrograde fluorescent tracers, fast blue and diamidino yellow, in V1. By examining the extent of mixing of the two populations of singly labelled cells and the presence of doubly labelled cells, in different structures, we have characterized the topography of each projection in terms of the size of its axonal arborization and the amount of convergence and divergence. The afferents from the lateral geniculate nucleus (LGN) and from the pulvinar are organized in a point-to-point fashion. The maximum extent of axonal arborization of these afferents is 0.5 mm and these projections demonstrate little scatter (i.e., neighboring LGN neurons project to adjacent regions of V1). The other two subcortical structures examined, the claustrum and the intralaminar nuclei, demonstrate a much larger scatter and wider axonal arborizations in their projections to V1 than do the LGN and pulvinar. Two-dimensional reconstructions were made of the distribution of labelled neurons in extrastriate cortical areas. Using the separation between patches of labelled cells and transitions in myelin-stained sections, we have identified seven separate cortical regions containing labelled cells. Two of these can be identified as area V2 and the middle temporal visual area (MT). Three other regions correspond to areas V3, V3A and V4t. Finally, two more regions of labelling have been distinguished that belong to area V4. These results demonstrate that, at least within the central 6 degrees of visual field, all the presently known extrastriate visual cortical areas project to V1. This result is interesting in view of the fact that only a few extrastriate cortical areas are reported to receive afferents from V1. Three groups of cortical areas can be distinguished on the basis of the characteristics of their cortical connections to V1. The first group contains area V2, V3, and the posterior region of V4. These areas project to V1 with infra- as well as supragranular layer neurons and show limited axonal arborization and scatter in the projection. The second group consists of two regions of labelling in the superior temporal sulcus corresponding to V4t and MT and another on the annectant gyrus (V3A). These regions contain almost exclusively infragranular labelling and show wide axonal arborization and scatter in their projections to V1.(ABSTRACT TRUNCATED AT 400 WORDS)

Velocity sensitivity and direction selectivity of neurons in areas V1 and V2 of the monkey: influence of eccentricity

One hundred and forty two neurons in V1 and V2 were quantitatively tested using a multihistogram technique in paralyzed and anesthetized macaque monkeys. V1 neurons with receptive fields within 2 degrees from the fixation point (central V1 sample) and V1 neurons with eccentric receptive fields (15-25 degrees eccentricity, peripheral V1 sample) were compared to assess changes in velocity sensitivity and direction selectivity with eccentricity. The central V1 sample was compared with V2 neurons with receptive fields in the same part of the visual field (central V2 sample) to compare the involvement of both areas in the analysis of motion. Velocity sensitivity of V1 neurons shifts to faster velocities with increasing eccentricity. V1 and V2 neurons subserving central vision have similar preference for slow movements. All neurons could be classified into three categories according to their velocity-response curves: velocity low pass, velocity broad band, and velocity tuned. Most cells in parts of V1 and V2 subserving central vision are velocity low pass. As eccentricity increases in V1, velocity low-pass cells give way to velocity broad-band cells. There is a significant correlation between velocity upper cutoff and receptive field width among V1 neurons. The change in upper cutoff velocity with eccentricity depends both on temporal and spatial factors. Direction selectivity depends on stimulus velocity in most V1 cells. Neurons in the central V1 sample retain their direction selectivity at lower speeds than do neurons in the peripheral V1 sample. The proportion of direction-selective cells is low in both V1 and V2. In V1, direction selectivity decreases with eccentricity. In V1, both velocity upper cutoff and direction selectivity correlate more with laminar position than with receptive field type. The similarity between V1 of the monkey and area 17 of the cat, and the dissimilarity between V2 of the monkey and area 18 of the cat, are discussed.

Organization of the callosal connections of visual areas V1 and V2 in the macaque monkey

The interhemispheric efferent and afferent connections of the V1/V2 border have been examined in the adult macaque monkey with the tracers horseradish peroxidase and horseradish peroxidase conjugated to wheat germ agglutinin. The V1/V2 border was found to have reciprocal connections with the contralateral visual area V1, as well as with three other cortical sites situated in the posterior bank of the lunate sulcus, the anterior bank of the lunate sulcus, and the posterior bank of the superior temporal sulcus. Within V1, callosal projecting cells were found mainly in layer 4B with a few cells in layer 3. Anterograde labeled terminals were restricted to layers 2, 3, 4B, and 5. In extrastriate cortex, retrograde labeled cells were in layers 2 and 3 and only very rarely in infragranular layers. In the posterior bank of the lunate sulcus, labeled terminals were scattered throughout all cortical layers except layers 1 and 4. In the anterior bank of the lunate sulcus and in the superior temporal sulcus, anterograde labeled terminals were largely focused in layer 4. Callosal connections in all contralateral regions were organized in a columnar fashion. Columnar organization of callosal connections was more apparent for anterograde labeled terminals than for retrograde labeled neurons. In the posterior bank of the lunate sulcus, columns of callosal connections were superimposed on regions of high cytochrome activity. The tangential extent of callosal connections in V1 and V2 was found to be influenced by eccentricity in the visual field. Callosal connections were denser in the region of V1 subserving foveal visual field than in cortex representing the periphery. In V1 subserving the fovea, callosal connections extended up to 2 mm from the V1/V2 border and only up to 1 mm in more peripheral located cortex. In area V2 subserving the fovea, cortical connections extended up to 8 mm from the V1/V2 border and only up to 3 mm in peripheral cortex.

Optokinetic response and visual suppression of the vestibulo-ocular reflex in the open loop condition in the cat

Optokinetic nystagmus (OKN), vestibulo-ocular reflex (VOR) and the visual suppression of the VOR were investigated before and after elimination of retinal image motion following monocular surgical paralysis. Monocular paralysis gave rise to an instability of eye position in the dark which was abolished during the illumination of the mobile but not the immobile eye. In the open-loop condition there was a substantial increase in the monocular OKN gain and a large asymmetry with respect to temporo-nasal and naso-temporal stimulation. Viewing a head-fixed world through a completely paralysed eye suppressed the VOR. This visual suppression was asymmetric and the asymmetry was consistent with that found in the open-loop OKN. These results imply that in the cat visual system, cancellation models of visual suppression of the VOR need to be expanded to accommodate signals generated by stable retinal images.

Cytochrome oxidase activity in the striate cortex and lateral geniculate nucleus of the newborn and adult macaque monkey

The laminar location of cytochrome oxidase staining has been compared in the lateral geniculate nucleus and area 17 in newborn and adult macaque monkeys. In area 17 of the adult, the distribution of cytochrome oxidase activity confirmed published findings. In the newborn animals, the tissue reacted as strongly for cytochrome oxidase as in the adult but the pattern of labelling was different in two respects. Firstly in layer 1 activity was stronger and occupied a wider portion of this layer. Secondly, cytochrome oxidase staining in layer 4C occupied two separate bands, a small narrow band at the bottom of 4C beta and a wider one occupying the full width of 4C alpha and spilling over into 4B. The pattern of cytochrome oxidase activity did not appear to be influenced by eccentricity in the newborn whereas, in the adult, label in 4C was more intense in cortex subserving central vision. In the lateral geniculate nucleus of the adult, the magnocellular layers and the most dorsal parvocellular layer reacted most strongly for cytochrome oxidase. In the newborn, parvocellular layers were more uniformly labelled and the difference between parvo- and magnocellular layers more pronounced. These results are discussed in relationship to the development of thalamo-cortical projections in the monkey.