Biomedical subjects

M G Rosa

Publications and source records attributed to M G Rosa.

At least 19 recordsLinked to original sources

PubMed2001

The dorsomedial visual areas in New World and Old World monkeys: homology and function.

The extrastriate cortex near the dorsal midline has been described as part of an 'express' pathway that provides visual input to the premotor cortex. This pathway is considered important for the integration of sensory information about the visual field periphery and the skeletomotor system, especially in relation to the control of arm movements. However, a better understanding of the functional contributions of different parts of this complex has been hampered by the lack of data on the extent and boundaries of its constituent visual areas. Recent studies in macaques have provided the first detailed view of the topographical organization of this region in Old World monkeys. Despite differences in nomenclature, a comparison of the visuotopic organization, myeloarchitecture and connections of the relevant visual areas with those previously studied in New World monkeys reveals a remarkable degree of similarity and helps to clarify the subdivision of function between different areas of the dorsomedial complex. A caudal visual area, named DM or V6, appears to be important for the detection of coherent patterns of movement across wide regions of the visual field, such as those induced during self-motion. A rostral area, named M or V6A, is more directly involved with visuomotor integration. This area receives projections both from DM/V6 and from a separate motion analysis channel, centred on the middle temporal visual area (or V5), which detects the movement of objects in extrapersonal space. These results support the suggestion, made earlier on the basis of more fragmentary evidence, that the areas rostral to the second visual area in dorsal cortex are homologous in all simian primates. Moreover, they emphasize the importance of determining the anatomical organization of the cortex as a prerequisite for elucidating the function of different cortical areas.

Animals↗

PubMed2001

Somatotopic organization and cortical projections of the ventrobasal complex of the flying fox: an "inverted" wing representation in the thalamus.

The present study investigates the somatotopic representation in the somatosensory thalamus of a megachiropteran bat. Using standard microelectrode mapping techniques, representational maps were generated for the ventrobasal (Vb) and posterior (Po) thalamic complexes of the Grey-headed flying fox. Anatomical tracing from neocortical injections provided additional data confirming the somatotopy found physiologically. A full representation of the body surface innervated by the trigeminal and spinal nerves was found. However, in contrast with other mammals, the representations of the forelimb and adjacent thoracic trunk within the thalamus were inverted. This means that the distal portions of the wing membrane and the tips of the digits were represented dorsally in Vb, and the thoracic trunk was represented ventrally. In Po the digit tips were represented in the ventral most portion and the thoracic trunk in the dorsal portion of the nucleus. These results are discussed in relation to similarities of megachiropteran somatosensory thalamic nuclei to those of other mammalian species and in relation to the formation of thalamic somatotopic maps and fiber sorting.

Animals↗

PubMed2001

An architectonic comparison of the ventrobasal complex of two megachiropteran and one microchiropteran bat: implications for the evolution of Chiroptera.

The architectonic features of the thalamic ventrobasal complex (Vb) of two species of Megachiropteran (Grey-headed flying fox, Pteropus poliocephalus, and the Eastern tube-nosed bat, Nyctimene robinsoni) are compared with those of a Microchiropteran (Australian ghost bat, Macroderma gigas). The somatosensory system was chosen for comparison as it represents a sensory system that has undergone analogous modifications in both Chiropteran lineages (the evolution of the wing). The components of Vb were examined as there are taxon-specific features in this region of the brain. Within the Megachiropteran Vb, four subnuclei were recognized: the ventral posterior medial (VPM), the ventral posterior lateral (VPL), the ventral posterior inferior (VPI), and the basal ventral medial (VMb). In the ghost bat only VPM and VPL were identified with certainty. No VPI was evident in the ghost bat, however a putative VMb was observed. Vb of the ghost bat also lacked the arcuate lamina, which distinguishes VPM from VPL in the Megachiropterans and many other mammals. These taxon-specific differences lend support to the proposal that the order Chiroptera has a diphyletic origin.

Animals↗

PubMed2000

Pyramidal cells, patches, and cortical columns: a comparative study of infragranular neurons in TEO, TE, and the superior temporal polysensory area of the macaque monkey.

The basal dendritic arbors of layer III pyramidal neurons are known to vary systematically among primate visual areas. Generally, those in areas associated with "higher" level cortical processing have larger and more spinous dendritic arbors, which may be an important factor for determining function within these areas. Moreover, the tangential area of their arbors are proportional to those of the periodic supragranular patches of intrinsic connections in many different areas. The morphological parameters of both dendritic and axon arbors may be important for the sampling strategies of cells in different cortical areas. However, in visual cortex, intrinsic patches are a feature of supragranular cortex, and are weaker or nonexistent in infragranular cortex. Thus, the systematic variation in the dendritic arbors of pyramidal cells in supragranular cortex may reflect intrinsic axon projections, rather than differences in columnar organization. The present study was aimed at establishing whether cells in the infragranular layers also vary in terms of dendritic morphology among different cortical areas, and whether these variations mirror the ones demonstrated in supragranular cortex. Layer V pyramidal neurons were injected with Lucifer yellow in flat-mounted cortical slices taken from cytoarchitectonic areas TEO and TE and the superior polysensory area (STP) of the macaque monkey. The results demonstrate that cells in STP were larger, had more bifurcations, and were more spinous than those in TE, which in turn were larger, had more bifurcations and were more spinous than those in TEO. These results parallel morphological variation seen in layer III pyramidal neurons, suggesting that increasing complexity of basal dendritic arbors of cells, with progression through higher areas of the temporal lobe, is a general organizational principle. It is proposed that the differences in microcircuitry may contribute to the determination of the functional signatures of neurons in different cortical areas. Furthermore, these results provide evidence that intrinsic circuitry differs across cortical areas, which may be important for theories of columnar processing.

Analysis of Variance↗

PubMed2000

Visual responses of neurons in the middle temporal area of new world monkeys after lesions of striate cortex.

In primates, lesions of striate cortex (V1) result in scotomas in which only rudimentary visual abilities remain. These aspects of vision that survive V1 lesions have been attributed to direct thalamic pathways to extrastriate areas, including the middle temporal area (MT). However, studies in New World monkeys and humans have questioned this interpretation, suggesting that remnants of V1 are responsible for both the activation of MT and residual vision. We studied the visual responses of neurons in area MT in New World marmoset monkeys in the weeks after lesions of V1. The extent of the scotoma in each case was estimated by mapping the receptive fields of cells located near the lesion border and by histological reconstruction. Two response types were observed among the cells located in the part of MT that corresponds, in visuotopic coordinates, to the lesioned part of V1. Many neurons (62%) had receptive fields that were displaced relative to their expected location, so that they represented the visual field immediately surrounding the scotoma. This may be a consequence of a process analogous to the reorganization of the V1 map after retinal lesions. However, another 20% of the cells had receptive fields centered inside the scotoma. Most of these neurons were strongly direction-selective, similar to normal MT cells. These results show that MT cells differ in their responses to lesioning of V1 and that only a subpopulation of MT neurons can be reasonably linked to residual vision and blindsight.

Animals↗

PubMed2000

Visual areas in lateral and ventral extrastriate cortices of the marmoset monkey.

The representation of the visual field in visual areas of the dorsolateral, lateral, and ventral cortices was studied by means of extracellular recordings and fluorescent tracer injections in anaesthetised marmoset monkeys. Two areas, forming mirror-symmetrical representations of the contralateral visual field, were found rostral to the second visual area (V2). These were termed the ventrolateral posterior (VLP) and the ventrolateral anterior (VLA) areas. In both areas, the representation of the lower quadrant is located dorsally, between the foveal representation of V2 and the middle temporal crescent (MTc), whereas the representation of the upper quadrant is located ventrally, in the supratentorial cortex. A representation of the vertical meridian forms the common border of areas VLP and VLA, whereas the horizontal meridian is represented both at the caudal border of area VLP (with V2) and at the rostral border of area VLA (with multiple extrastriate areas). The foveal representations of areas VLP and VLA are continuous with that of V2, being located at the lateral edge of the hemisphere. The topographic and laminar patterns of projections from dorsolateral and ventral cortices to the primary (V1) and dorsomedial (DM) visual areas both support the present definition of the borders of areas VLP and VLA. These results argue against a separation between dorsolateral and ventral extrastriate areas and provide clues for the likely homologies between extrastriate areas of different species.

Animals↗

PubMed2000

Does the visual system of the flying fox resemble that of primates? The distribution of calcium-binding proteins in the primary visual pathway of Pteropus poliocephalus.

It has been proposed that flying foxes and echolocating bats evolved independently from early mammalian ancestors in such a way that flying foxes form one of the suborders most closely related to primates. A major piece of evidence offered in support of a flying fox-primate link is the highly developed visual system of flying foxes, which is theorized to be primate-like in several different ways. Because the calcium-binding proteins parvalbumin (PV) and calbindin (CB) show distinct and consistent distributions in the primate visual system, the distribution of these same proteins was examined in the flying fox (Pteropus poliocephalus) visual system. Standard immunocytochemical techniques reveal that PV labeling within the lateral geniculate nucleus (LGN) of the flying fox is sparse, with clearly labeled cells located only within layer 1, adjacent to the optic tract. CB labeling in the LGN is profuse, with cells labeled in all layers throughout the nucleus. Double labeling reveals that all PV+ cells also contain CB, and that these cells are among the largest in the LGN. In primary visual cortex (V1) PV and CB label different classes of non-pyramidal neurons. PV+ cells are found in all cortical layers, although labeled cells are found only rarely in layer I. CB+ cells are found primarily in layers II and III. The density of PV+ neuropil correlates with the density of cytochrome oxidase staining; however, no CO+ or PV+ or CB+ patches or blobs are found in V1. These results show that the distribution of calcium-binding proteins in the flying fox LGN is unlike that found in primates, in which antibodies for PV and CB label specific separate populations of relay cells that exist in different layers. Indeed, the pattern of calcium-binding protein distribution in the flying fox LGN is different from that reported in any other terrestrial mammal. Within V1 no PV+ patches, CO blobs, or patchy distribution of CB+ neuropil that might reveal interblobs characteristic of primate V1 are found; however, PV and CB are found in separate populations of non-pyramidal neurons. The types of V1 cells labeled with antibodies to PV and CB in all mammals examined including the flying fox suggest that the similarities in the cellular distribution of these proteins in cortex reflect the fact that this feature is common to all mammals.

Animals↗

PubMed2000

"Third tier" ventral extrastriate cortex in the New World monkey, Cebus apella.

The ventral extrastriate cortex adjacent to the second visual area was studied in the New World monkey Cebus apella, using anaesthetised preparations. The visuotopic organisation and myeloarchitecture of this region demonstrate the existence of a distinct strip of cortex, 3-4 mm wide, with an ordered representation of the contralateral upper visual quadrant, up to 60 degrees eccentricity. This upper-quadrant representation is probably homologous to the ventral subdivision of the third visual complex (V3v) of Old World monkeys, also known as the ventral posterior area. The representation of the horizontal meridian in V3v forms its posterior and medial border with V2, while the upper vertical meridian is represented anterior and laterally, forming a congruent border with the fourth visual area (V4). Central visual fields are represented in posterior and lateral portions of V3v, in the inferior occipital sulcus, while the periphery of the visual field is represented anteriorly, on the tentorial surface. Cortex anterior to V3v, at the ventral occipitotemporal transition, had neurones that had poor visual responses. No representation of the lower quadrant was found adjacent to V3v in ventral cortex. However, we observed cells with perifoveal receptive fields centred in the lower quadrant immediately dorsal to V3v, around the junction of the inferior occipital and lunate sulci. These observations argue against the idea that V3v is an area restricted to the ventral cortex in New World monkeys and support the conclusions of previous anatomical studies in Cebus that showed a continuity of myeloarchitecture and connectional patterns between ventral and lateral extrastriate cortices. Together, these data suggest that V3v may be part of a larger area that extends into dorsolateral extrastriate cortex, overlapping to some extent with the caudal subdivision of the dorsolateral area described in other New World monkeys.

Animals↗

PubMed1999

Cellular heterogeneity in cerebral cortex: a study of the morphology of pyramidal neurones in visual areas of the marmoset monkey.

The morphological characteristics of the basal dendritic fields of layer III pyramidal neurones were determined in visual areas in the occipital, parietal, and temporal lobes of adult marmoset monkeys by means of intracellular iontophoretic injection of Lucifer yellow. Neurones in the primary visual area (V1) had the least extensive and least complex (as determined by Sholl analysis) dendritic trees, followed by those in the second visual area (V2). There was a progressive increase in size and complexity of dendritic trees with rostral progression from V1 and V2, through the "ventral stream," including the dorsolateral area (DL) and the caudal and rostral subdivisions of inferotemporal cortex (ITc and ITr, respectively). Neurones in areas of the dorsal stream, including the dorsomedial (DM), dorsoanterior (DA), middle temporal (MT), and posterior parietal (PP) areas, were similar in size and complexity but were larger and more complex than those in V1 and V2. Neurones in V1 had the lowest spine density, whereas neurones in V2, DM, DA, and PP had similar spine densities. Neurones in MT and inferotemporal cortex had relatively high spine densities, with those in ITr having the highest spine density of all neurones studied. Calculations based on the size, number of branches, and spine densities revealed that layer III pyramidal neurones in ITr have 7.4 times more spines on their basal dendritic fields than those in V1. The differences in the extent of, and the number of spines in, the basal dendritic fields of layer III pyramidal neurones in the different visual areas suggest differences in the ability of neurones to integrate excitatory and inhibitory inputs. The differences in neuronal morphology between visual areas, and the consistency in these differences across New World and Old World monkey species, suggest that they reflect fundamental organisational principles in primate visual cortical structure.

Animals↗

PubMed1999

Variation in the spatial relationship between parvalbumin immunoreactive interneurones and pyramidal neurones in rat somatosensory cortex.

The morphology of pyramidal neurones was revealed by intracellular injection of Lucifer Yellow (LY) in fixed tangential cortical slices taken from rat primary somatosensory cortex. Slices were processed with a combination of antibodies to allow visualization of both the LY-injected neurones and parvalbumin immunoreactive (PV-ir) cell bodies, by confocal microscopy. Basal dendritic fields of pyramidal neurones in layer V were larger and more complex than those of layer III. Furthermore, the number of PV-ir cell bodies contained within the basal dendritic territories of pyramidal neurones in layer V was significantly greater than in layer III (mean +/- s.e.m., 36.3 +/- 3.0 and 20.9 +/- 1.6, respectively). These findings have functional implications both in terms of physiological characteristics, and inhibitory modulation of receptive field properties, of cortical neurones.

Animals↗

PubMed1999

Topographic organisation of extrastriate areas in the flying fox: implications for the evolution of mammalian visual cortex.

The organisation of extrastriate cortex was studied in anaesthetised flying foxes (Pteropus poliocephalus) by using multiunit recording techniques. Based on the visuotopic organisation and response characteristics, the cortex immediately rostral to the second visual area (V2) was subdivided into two fields: visual area 3 (V3) laterally and the occipitoparietal area (OP) medially. Area V3 is a 1.0-1.5 mm wide strip of cortex that represents the entire contralateral hemifield as a mirror image of the representation found in V2. The representation of the vertical meridian and the area centralis form the rostral border of V3. In area OP, receptive fields are much larger than those of V3 and form a separate visuotopic map, with the upper quadrant represented rostral to the lower quadrant. Multiunit clusters in the cortex rostral to area OP (posterior parietal area) respond to both visual and somatosensory stimuli. Farther laterally, in the cortex rostral to V3, the occipitotemporal area (OT) was found to form yet another map of the visual field. Similar to the middle temporal area in primates, area OT in the flying fox forms a first-order representation of the visual field, with the lower quadrant represented medially, the upper quadrant represented laterally, the area centralis represented caudally, and the visual field periphery represented rostrally. The cortex surrounding area OT rostrally and ventrally is also visually responsive but could not be subdivided due to the large receptive fields. Finally, visual responses were elicited from an area adjacent to the peripheral representation in the first visual area (V1) in the splenial sulcus. These results demonstrate that nearly half of the flying fox cortex is related to vision, which contrasts with that of microchiropteran bats, in which auditory areas predominate. A comparison of the flying fox with other mammals suggests that several areas, including homologues of V1, V2, V3, OT, and the splenial area, may have originated early in mammalian evolution and have been inherited by most present-day eutherians. However, studies in other species will be needed to distinguish patterns of common ancestry from parallel evolution.

Animals↗

PubMed1999

Cortical integration in the visual system of the macaque monkey: large-scale morphological differences in the pyramidal neurons in the occipital, parietal and temporal lobes.

Layer III pyramidal neurons were injected with Lucifer yellow in tangential cortical slices taken from the inferior temporal cortex (area TE) and the superior temporal polysensory (STP) area of the macaque monkey. Basal dendritic field areas of layer III pyramidal neurons in area STP are significantly larger, and their dendritic arborizations more complex, than those of cells in area TE. Moreover, the dendritic fields of layer III pyramidal neurons in both STP and TE are many times larger and more complex than those in areas forming 'lower' stages in cortical visual processing, such as the first (V1), second (V2), fourth (V4) and middle temporal (MT) visual areas. By combining data on spine density with those of Sholl analyses, we were able to estimate the average number of spines in the basal dendritic field of layer III pyramidal neurons in each area. These calculations revealed a 13-fold difference in the number of spines in the basal dendritic field between areas STP and V1 in animals of similar age. The large differences in complexity of the same kind of neuron in different visual areas go against arguments for isopotentiality of different cortical regions and provide a basis that allows pyramidal neurons in temporal areas TE and STP to integrate more inputs than neurons in more caudal visual areas.

Animals↗

PubMed1999

Supragranular pyramidal neurones in the medial posterior parietal cortex of the macaque monkey: morphological heterogeneity in subdivisions of area 7.

Pyramidal neurones were injected with Lucifer Yellow in cortical slices taken from layer III of the medial subdivision of cytoarchitectonic area 7 (7m) of the macaque monkey. Cross-sectional area, branching complexity and spine density of the basal dendritic fields were determined and compared with those of neurones in other areas of the dorsal processing stream. Layer III pyramidal neurones in area 7m have an average basal dendritic field area of 109.57 +/- 13.03 x 10(3) microm2, which is significantly greater than that obtained for neurones in the lateral intraparietal area (LIP) and area 7a. Moreover, Sholl analyses revealed that neurones in area 7m are significantly more complex in their branching patterns than those in LIP and area 7a. These results reinforce the view that, behind the apparent architectural uniformity of Brodmann's area 7, there is a significant diversity of neuronal structure and function.

Animals↗

PubMed1999

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

Electrophysiological recording in primary visual cortex (VI) 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.

Animals↗

PubMed1999

The evolution of visual cortex: where is V2?

A comparative analysis of the area of the cortex that is adjacent to the primary visual area (V1), indicates that the lateral extrastriate cortex of primitive mammals was likely to contain only a single visuotopically organized field, the second visual area (V2). Few, if any, other visual areas existed. The opposing hypothesis, that primitive mammals had a 'string' of small visual areas in the cortex lateral to V1 (as in some rodents), is not supported by studies of the organization of extrastriate cortex in other mammals, nor by the variability in this organization among extant rodents. A critical re-analysis of published evidence on the presence of multiple areas adjacent to V1 in some rodents has led to alternative interpretations of the organization of the areas in these regions.

Anatomy, Comparative↗

PubMed1999

Organization of visual cortex in the northern quoll, Dasyurus hallucatus: evidence for a homologue of the second visual area in marsupials.

Two visual areas, V1 and V2 (first and second visual areas), appear to be present in the posterior neocortex of all eutherian mammals investigated so far. However, previous studies have not established whether an area homologous to V2 also exists in metatherian mammals (marsupials). Using electrophysiological techniques, we mapped the visual receptive fields of neurons in the striate and peristriate cortices of the northern quoll, an Australian marsupial. We found that neurons in a 2-mm-wide strip of cortex rostrolateral to V1 form a single, relatively simple representation of the complete contralateral hemifield. This area resembles V2 of eutherians in several respects: (i) neurons in the medial half of the peristriate area represent the lower visual quadrant, whereas those in the lateral half represent the upper visual quadrant; (ii) the vertical meridian of the visual field is represented adjacent to V1, while the visual field periphery is represented along the lateral and rostrolateral borders of the peristriate area; (iii) there is a marked anisotropy in the representation, with a larger magnification factor parallel to the V1 border than perpendicular to this border; and (iv) receptive fields of multiunit clusters in the peristriate cortex are much larger than those of cells in V1 at comparable eccentricities. The cortex immediately rostral and lateral to V2 did not respond to visual stimulation under our recording conditions. These results suggest that V1 and V2 together form a 'core' of homologous visual areas, likely to exist in all therian mammals.

Animals↗

PubMed1998

Visual responses of neurones in the second visual area of flying foxes (Pteropus poliocephalus) after lesions of striate cortex.

1. The first (V1) and second (V2) cortical visual areas exist in all mammals. However, the functional relationship between these areas varies between species. While in monkeys the responses of V2 cells depend on inputs from V1, in all non-primates studied so far V2 cells largely retain responsiveness to photic stimuli after destruction of V1. 2. We studied the visual responsiveness of neurones in V2 of flying foxes after total or partial lesions of the primary visual cortex (V1). The main finding was that visual responses can be evoked in the region of V2 corresponding, in visuotopic co-ordinates, to the lesioned portion of V1 ('lesion projection zone'; LPZ). 3. The visuotopic organization of V2 was not altered by V1 lesions. 4. The proportion of neurones with strong visual responses was significantly lower within the LPZs (31.5 %) than outside these zones, or in non-lesioned control hemispheres ( > 70 %). LPZ cells showed weak direction and orientation bias, and responded consistently only at low spatial and temporal frequencies. 5. The data demonstrate that the functional relationship between V1 and V2 of flying foxes resembles that observed in non-primate mammals. This observation contrasts with the 'primate-like' characteristics of the flying fox visual system reported by previous studies.

Animals↗

PubMed1998

Visuotopic organisation and neuronal response selectivity for direction of motion in visual areas of the caudal temporal lobe of the marmoset monkey (Callithrix jacchus): middle temporal area, middle temporal crescent, and surrounding cortex.

On the basis of extracellular recordings in marmoset monkeys, we report on the organisation of the middle temporal area (MT) and the surrounding middle temporal crescent (MTc). Area MT is approximately 5-mm long and 2-mm wide, whereas the MTc forms a crescent-shaped band of cortex 1-mm wide. Neurones in area MT form a first-order representation of the contralateral hemifield, whereas those in the MTc form a second-order representation with a field discontinuity near the horizontal meridian. The representation of the vertical meridian forms the border between area MT and the MTc. In both areas, the fovea is represented ventrocaudally, and the visual field periphery is represented dorsorostrally. Analysis of single units revealed that 86% of cells in area MT show a strong selectivity for the direction of motion of visual stimuli. The proportion of direction-selective cells in the MTc (53%), whereas lower than that in area MT, is much higher than that observed in most other visual areas. Neurones in the cortex immediately rostral to area MT and the MTc are direction selective, with receptive fields predominantly located in the visual field periphery. In contrast, only a minority of the cells in the cortex ventral to the MTc are direction selective, and their receptive fields emphasise central vision. The results suggest that the MTc is functionally closely related to area MT, and distinct from the areas forming the dorsolateral complex. The MTc may have a role in combining information about motion in the visual field, processed by area MT, with information about stimulus shape, processed by the dorsolateral complex.

Animals↗