Flowering plants in Australia have been geographically isolated for more than 34 million years. In the Northern Hemisphere, previous work has revealed a close fit between the optimal discrimination capabilities of hymenopteran pollinators and the flower colours that have most frequently evolved. We collected spectral data from 111 Australian native flowers and tested signal appearance considering the colour discrimination capabilities of potentially important pollinators. The highest frequency of flower reflectance curves is consistent with data reported for the Northern Hemisphere. The subsequent mapping of Australian flower reflectances into a bee colour space reveals a very similar distribution of flower colour evolution to the Northern Hemisphere. Thus, flowering plants in Australia are likely to have independently evolved spectral signals that maximize colour discrimination by hymenoptera. Moreover, we found that the degree of variability in flower coloration for particular angiosperm species matched the range of reflectance colours that can only be discriminated by bees that have experienced differential conditioning. This observation suggests a requirement for plasticity in the nervous systems of pollinators to allow generalization of flowers of the same species while overcoming the possible presence of non-rewarding flower mimics.

To define the number and limits of the visual areas in the primate extrastriate cortex, the visuotopy of the dorsal convexity and medial wall was studied by electrophysiological recordings in five marmosets anaesthetised with sufentanil and nitrous oxide and paralysed with pancuronium bromide. We identified five visuotopic representations in and around the densely myelinated zone between visual area 2 (V2) and the posterior parietal cortex. Most of the densely myelinated zone is formed by the homologue of the owl monkey's dorsomedial area (DM); thus, we also termed this area DM in the marmoset. Within DM, the lower quadrant representation is continuous, with central vision represented laterally, peripheral vision medially, the horizontal meridian caudally, and the vertical meridian rostrally. In contrast, the upper quadrant representation is split, with the central portion represented at the lateral edge of DM on the dorsal surface, and the periphery along the midline. Two other visual field representations, corresponding to the dorsointermediate area (DI) and to a new subdivision termed the dorsoanterior area (DA), are also densely myelinated but can be distinguished from DM based on the separation of the bands of Baillarger and visual topography. In addition, a homologue of the medial visual area (M) was identified. Our results reveal a highly complex visuotopy in primate cortex, with local discontinuities in representation and borders between areas that are often not coincident with either the horizontal or the vertical meridian. The topography of the dorsal extrastriate cortex in the marmoset strongly suggests that both visual area 3 (V3) and the parietooccipital area (PO) of other primates are portions of a single visuotopic representation, DM, and calls into question the existence of visual areas with partial or quadrantic representations of the visual field.

We describe the organization of the dorsolateral frontal areas in marmoset monkeys using a combination of architectural methods (Nissl, cytochrome oxidase, and myelin stains) and injections of fluorescent tracers in extrastriate areas (the second visual area [V2], the dorsomedial and dorsoanterior areas [DM, DA], the middle temporal area and middle temporal crescent [MT, MTc], and the posterior parietal cortex [area 7]). Cytoarchitectural field 8 comprises three subdivisions: 8Av, 8Ad, and 8B. The ventrolateral subdivision, 8Av, forms the principal source of frontal projections to the "dorsal stream," having connections with each of the injected visual areas. The cytoarchitectural characteristics of 8Av suggest that this subdivision corresponds to the marmoset's frontal eye field. The intermediate subdivision of area 8 (8Ad) has efferent projections to area 7, while the dorsomedial subdivision (8B) has few or no connections with extrastriate cortex. Area 46, located rostrolateral to area 8Av, has substantial connections with the medial extrastriate areas (DM, DA, and area 7) and with MT, while the cortex lateral to 8Av (area 12/45) projects primarily to MT and to the MTc. The rostromedial prefrontal (area 9) and frontopolar (area 10) regions have very few extrastriate projections. Finally, cells in dorsal area 6 (6d) have sparse projections to DM, MT, and the MTc, as well as strong projections to DA and to area 7. These results illuminate aspects of the evolutionary development of the primate frontal cortex, and serve as a basis for further research into cognitive functions using a marmoset model.

The dendritic morphology of pyramidal cells located at the base of layer III in the primary visual area (V1), the second visual area (V2), the middle temporal area (MT), the ventral portion of the lateral intraparietal area (LIPv) and in the portion of cytoarchitectonic area 7a within the anterior bank of the superior temporal sulcus was revealed by injecting neurons with Lucifer Yellow in fixed, flattened slices of macaque monkey visual cortex. These areas correspond to different levels of the occipitoparietal cortical 'stream', which processes information related to motion and spatial relationships in the visual field. The tissue was immunocytochemically processed to obtain a light-stable diaminobenzidine reaction product, revealing the dendritic morphology in fine detail. Retrogradely labelled MT-projecting neurons in supragranular V1 (layer IIIc of Hassler's nomenclature, corresponding to Brodmann's layer IVb) were predominantly pyramidal, although many spiny multipolar (stellate) cells were also found. The average basal dendritic field area of pyramidal neurons in sublamina IIIc of V1 was significantly smaller than that in the homologous layer of V2, within the cytochrome oxidase-rich thick stripes. Furthermore, the average basal dendritic field areas of V1 and V2 pyramidal neurons were significantly smaller than those of neurons in MT, LIPv and area 7a. There was no difference in basal dendritic field area between layer III pyramidal neurons in areas MT, LIPv and 7a. While the shape of most basal dendritic fields was circularly symmetrical in the dimension tangential to the cortical layers, there were significant biases in complexity, with dendritic branches tending to cluster along particular axes. Sholl analysis revealed that the dendritic fields of neurons in areas MT, LIPv and 7a were significantly more complex (i.e. had a larger number of branches) than those of V1 or V2 neurons. Analysis of basal dendritic spine densities revealed regional variations along the dendrites, with peak densities being observed 40-130 microns from the cell body, depending on the visual area. The peak spine density of layer III pyramidal neurons in V1 was lower than that observed in V2, MT or LIPv, which were all similar. Pyramidal neurons in area 7a had the greatest peak spine density, which was on average 1.7 times that found in V1. Calculations based on the average spine density and number of dendritic branches at different distances from the cell body demonstrated a serial increase in the total number of basal dendritic spines per neuron at successive stations of the occipitoparietal pathway. Our observations, comparing dendritic fields of neurons in the homologous cortical layer at different levels of a physiologically defined 'stream', indicate changes in pyramidal cell morphology between functionally related areas. The relatively large, complex, spine-dense dendritic fields of layer III pyramidal cells in rostral areas of the occipitoparietal pathway allow these cells to sample a greater number of more diverse inputs ...

In this paper, we review evidence from comparative studies of primate cortical organization, highlighting recent findings and hypotheses that may help us to understand the rules governing evolutionary changes of the cortical map and the process of formation of areas during development. We argue that clear unequivocal views of cortical areas and their homologies are more likely to emerge for "core" fields, including the primary sensory areas, which are specified early in development by precise molecular identification steps. In primates, the middle temporal area is probably one of these primordial cortical fields. Areas that form at progressively later stages of development correspond to progressively more recent evolutionary events, their development being less firmly anchored in molecular specification. The certainty with which areal boundaries can be delimited, and likely homologies can be assigned, becomes increasingly blurred in parallel with this evolutionary/developmental sequence. For example, while current concepts for the definition of cortical areas have been vindicated in allowing a clarification of the organization of the New World monkey "third tier" visual cortex (the third and dorsomedial areas, V3 and DM), our analyses suggest that more flexible mapping criteria may be needed to unravel the organization of higher-order visual association and polysensory areas.

Rosa, Marcello G. P., Vivien A. Casagrande, Todd Preuss, and Jon H. Kaas. Visual field representation in striate and prestriate cortices of a prosimian primate ( Galago garnetti). J. Neurophysiol. 77: 3193–3217, 1997. Microelectrode mapping techniques were used to study the visuotopic organization of the first and second visual areas (V1 and V2, respectively) in anesthetized Galago garnetti, a lorisiform prosimian primate. 1) V1 occupies ∼200 mm2 of cortex, and is pear shaped, rather than elliptical as in simian primates. Neurons in V1 form a continuous (1st-order) representation of the visual field, with the vertical meridian forming most of its perimeter. The representation of the horizontal meridian divides V1 into nearly equal sectors representing the upper quadrant ventrally, and the lower quadrant dorsally. 2) The emphasis on representation of central vision is less marked in Galago than in simian primates, both diurnal and nocturnal. The decay of cortical magnification factor with increasing eccentricity is almost exactly counterbalanced by an increase in average receptive field size, such that a point anywhere in the visual field is represented by a compartment of similar diameter in V1. 3) Although most of the cortex surrounding V1 corresponds to V2, one-quarter of the perimeter of V1 is formed by agranular cortex within the rostral calcarine sulcus, including area prostriata. Although under our recording conditions virtually every recording site in V2 yielded visually responsive cells, only a minority of those in area prostriata revealed such responses. 4) V2 forms a cortical belt of variable width, being narrowest (∼1 mm) in the representation of the area centralis and widest (2.5–3 mm) in the representation of the midperiphery (>20° eccentricity) of the visual field. V2 forms a second-order representation of the visual field, with the area centralis being represented laterally and the visual field periphery medially, near the calcarine sulcus. Unlike in simians, the line of field discontinuity in Galago V2 does not exactly coincide with the horizontal meridian: a portion of the lower quadrant immediately adjacent to the horizontal meridian is represented at the rostral border of ventral V2, instead of in dorsal V2. Despite the absence of cytochrome oxidase stripes, the visual field map in Galago V2 resembles the ones described in simians in that the magnification factor is anisotropic. 5) Receptive field progressions in cortex rostral to dorsal V2 suggest the presence of a homologue of the dorsomedial area, including representations of both quadrants of the visual field. These results indicate that many aspects of organization of V1 and V2 in simian primates are shared with lorisiform prosimians, and are therefore likely to have been present in the last common ancestor of living primates. However, some aspects of organization of the caudal visual areas in Galago are intermediate between nonprimates and simian primates, reflecting either an intermediate stage of differentiation or adaptations to a nocturnal niche. These include the shape and the small size of V1 and V2, the modest degree of emphasis on central visual field representation, and the relatively large area prostriata.

It has been suggested that the development of the cerebral cortex reflects its hierarchical organization, with the primary sensory areas being the first to reach structural and functional maturity, and higher-order association areas being the last. In the present study, we labelled the cortex of New World marmoset monkeys of late fetal and early postnatal ages with an antibody to non-phosphorylated neurofilament, a marker of structural maturation of a subset of pyramidal cells. Supporting the concept of hierarchical maturation, we found that at birth labelled cells were found in the primary visual, auditory and somatosensory areas, but not in most other cortical fields. The exception was visual area MT, which revealed an infragranular pattern of labelling comparable to the one observed in the primary areas, as well as some supragranular staining. In MT, an adult-like pattern of labelled cells, including both supragranular and infragranular layer neurons, emerged within the first postnatal month. In comparison, the development of other extrastriate areas was delayed, with the first signs of neurofilament staining not present until the third week. The present results support the concept of MT as another primary visual area, an idea previously advanced on the basis of functional and anatomical evidence.

Humans are set apart from other animals by many elements of advanced cognition and behaviour, including language, judgement and reasoning. What is special about the human brain that gives rise to these abilities? Could the foremost part of the prefrontal cortex (the frontopolar cortex), which has become considerably enlarged in humans during evolution compared with other animals, be important in this regard, especially as, in primates, it contains a unique cytoarchitectural field, area 10? The first studies of the function of the frontopolar cortex in monkeys have now provided critical new insights about its precise role in monitoring the significance of current and alternative goals. In human evolution, the frontopolar cortex may have acquired a further role in enabling the monitoring of the significance of multiple goals in parallel, as well as switching between them. Here, we argue that many other forms of uniquely human behaviour may benefit from this cognitive ability mediated by the frontopolar cortex.