Somatosensory areas in the telencephalon of the pigeon. I. Response characteristics

Does a Vertebrate Morphotype of Pallial Subdivisions Really Exist?

BACKGROUND

Comparative neuroanatomists have long sought to determine which part of the pallium in nonmammals is homologous to the mammalian neocortex. A number of similar connectivity patterns across species have led to the idea that the basic organization of the vertebrate brain is relatively conserved; thus, efforts of the last decades have been focused on determining a vertebrate "morphotype" - a model comprising the characteristics believed to have been present in the last common ancestor of all vertebrates.

SUMMARY

The endeavor to determine the vertebrate morphotype has been riddled with controversies due to the extensive morphological diversity of the pallium among vertebrate taxa. Nonetheless, most proposed scenarios of pallial homology are variants of a common theme where the vertebrate pallium is subdivided into subdivisions homologous to the hippocampus, neocortex, piriform cortex, and amygdala, in a one-to-one manner. We review the rationales of major propositions of pallial homology and identify the source of the discrepancies behind different hypotheses. We consider that a source of discrepancies is the prevailing assumption that there is a single "morphotype of the pallial subdivisions" throughout vertebrates. Instead, pallial subdivisions present in different taxa probably evolved independently in each lineage.

KEY MESSAGES

We encounter discrepancies when we search for a single morphotype of subdivisions across vertebrates. These discrepancies can be resolved by considering that several subdivisions within the pallium were established after the divergence of the different lineages. The differences of pallial organization are especially remarkable between actinopterygians (including teleost fishes) and other vertebrates. Thus, the prevailing notion of a simple one-to-one homology between the mammalian and teleost pallia needs to be reconsidered.

Variations in touch representation in the hummingbird and zebra finch forebrain

Somatosensation is essential for animals to perceive the external world through touch, allowing them to detect physical contact, temperature, pain, and body position. Studies on rodent vibrissae have highlighted the organization and processing in mammalian somatosensory pathways.1,2 Comparative research across vertebrates is vital for understanding evolutionary influences and ecological specialization on somatosensory systems. Birds, with their diverse morphologies, sensory abilities, and behaviors, serve as ideal models for investigating the evolution of somatosensation. Prior studies have uncovered tactile-responsive areas within the avian telencephalon, particularly in pigeons,3,4,5,6 parrots,7 and finches,8 but variations in somatosensory maps and responses across avian species are not fully understood. This study aims to explore somatotopic organization and neural coding in the telencephalon of Anna's hummingbirds (Calypte anna) and zebra finches (Taeniopygia guttata) by using in vivo extracellular electrophysiology to record activity in response to controlled tactile stimuli on various body regions. These findings reveal unique representations of body regions across distinct forebrain somatosensory nuclei, indicating significant differences in the extent of areas dedicated to certain body surfaces, which may correlate with their behavioral importance.

The expression of tyrosine hydroxylase and DARPP-32 in the house crow (Corvus splendens) brain

Birds of the family Corvidae which includes diverse species such as crows, rooks, ravens, magpies, jays, and jackdaws are known for their amazing abilities at problem-solving. Since the catecholaminergic system, especially the neurotransmitter dopamine, plays a role in cognition, we decided to study the distribution of tyrosine hydroxylase (TH), the rate-limiting enzyme in the synthesis of catecholamines in the brain of house crows (Corvus splendens). We also studied the expression of DARPP-32 (dopamine and cAMP-regulated phosphoprotein), which is expressed in dopaminoceptive neurons. Our results demonstrated that as in other avian species, the expression of both TH and DARPP-32 was highest in the house crow striatum. The caudolateral nidopallium (NCL, the avian analogue of the mammalian prefrontal cortex) could be differentiated from the surrounding pallial regions based on a larger number of TH-positive "baskets" of fibers around neurons in this region and greater intensity of DARPP-32 staining in the neuropil in this region. House crows also possessed distinct nuclei in their brains which corresponded to song control regions in other songbirds. Whereas immunoreactivity for TH was higher in the vocal control region Area X compared to the surrounding MSt (medial striatum) in house crows, staining in RA and HVC was not as prominent. Furthermore, the arcopallial song control regions RA (nucleus robustus arcopallialis) and AId (intermediate arcopallium) were strikingly negative for DARPP-32 staining, in contrast to the surrounding arcopallium. Patterns of immunoreactivity for TH and DARPP-32 in "limbic" areas such as the hippocampus, septum, and extended amygdala have also been described.

Body Topography Parcellates Human Sensory and Motor Cortex

The cytoarchitectonic map as proposed by Brodmann currently dominates models of human sensorimotor cortical structure, function, and plasticity. According to this model, primary motor cortex, area 4, and primary somatosensory cortex, area 3b, are homogenous areas, with the major division lying between the two. Accumulating empirical and theoretical evidence, however, has begun to question the validity of the Brodmann map for various cortical areas. Here, we combined in vivo cortical myelin mapping with functional connectivity analyses and topographic mapping techniques to reassess the validity of the Brodmann map in human primary sensorimotor cortex. We provide empirical evidence that area 4 and area 3b are not homogenous, but are subdivided into distinct cortical fields, each representing a major body part (the hand and the face). Myelin reductions at the hand-face borders are cortical layer-specific, and coincide with intrinsic functional connectivity borders as defined using large-scale resting state analyses. Our data extend the Brodmann model in human sensorimotor cortex and suggest that body parts are an important organizing principle, similar to the distinction between sensory and motor processing.

The anatomy of the bill tip of kiwi and associated somatosensory regions of the brain: comparisons with shorebirds

Three families of probe-foraging birds, Scolopacidae (sandpipers and snipes), Apterygidae (kiwi), and Threskiornithidae (ibises, including spoonbills) have independently evolved long, narrow bills containing clusters of vibration-sensitive mechanoreceptors (Herbst corpuscles) within pits in the bill-tip. These 'bill-tip organs' allow birds to detect buried or submerged prey via substrate-borne vibrations and/or interstitial pressure gradients. Shorebirds, kiwi and ibises are only distantly related, with the phylogenetic divide between kiwi and the other two taxa being particularly deep. We compared the bill-tip structure and associated somatosensory regions in the brains of kiwi and shorebirds to understand the degree of convergence of these systems between the two taxa. For comparison, we also included data from other taxa including waterfowl (Anatidae) and parrots (Psittaculidae and Cacatuidae), non-apterygid ratites, and other probe-foraging and non probe-foraging birds including non-scolopacid shorebirds (Charadriidae, Haematopodidae, Recurvirostridae and Sternidae). We show that the bill-tip organ structure was broadly similar between the Apterygidae and Scolopacidae, however some inter-specific variation was found in the number, shape and orientation of sensory pits between the two groups. Kiwi, scolopacid shorebirds, waterfowl and parrots all shared hypertrophy or near-hypertrophy of the principal sensory trigeminal nucleus. Hypertrophy of the nucleus basorostralis, however, occurred only in waterfowl, kiwi, three of the scolopacid species examined and a species of oystercatcher (Charadriiformes: Haematopodidae). Hypertrophy of the principal sensory trigeminal nucleus in kiwi, Scolopacidae, and other tactile specialists appears to have co-evolved alongside bill-tip specializations, whereas hypertrophy of nucleus basorostralis may be influenced to a greater extent by other sensory inputs. We suggest that similarities between kiwi and scolopacid bill-tip organs and associated somatosensory brain regions are likely a result of similar ecological selective pressures, with inter-specific variations reflecting finer-scale niche differentiation.

Aromatase expression in the brain of the ruffed grouse (Bonasa umbellus) and comparisons with other galliform birds (Aves, Galliformes)

The enzyme aromatase is important for regulating sexual and aggressive behaviors during the reproductive season, including many aspects of courtship. In birds, aromatase is expressed at high levels in a number of different brain regions. Although this expression does vary among species, the extent to which the distribution of aromatase positive cells reflects species differences in courtship and other behaviors is not well established. Here, we examine the distribution of aromatase immunoreactive (ARO) neurons in the brain of a species with a unique courtship display, the ruffed grouse (Bonasa umbellus). Unlike most other galliforms, male ruffed grouse do not vocalize as part of their courtship and instead use their wings to create a non-vocal auditory signal to attract females. Because aromatase is involved in courtship behaviors in several bird species, including other galliforms, we hypothesized that aromatase distribution in the ruffed grouse would differ from that of other galliforms. We used an antibody raised against quail aromatase to examine aromatase immunoreactivity in the ruffed grouse, the closely related spruce grouse (Falcipennis canadensis) and the Japanese quail (Coturnix japonica). In all three species, ARO neurons were identified in the medial preoptic nucleus, the bed nucleus of the stria terminalis and the nucleus ventromedialis hypothalami. Both grouse species had ARO neurons in two regions of the telencephalon, the hyperpallium, and entopallium, and the ruffed grouse also in field L. ARO neurons were only found in one region in the telencephalon of the Japanese quail, the septum. In general, breeding male ruffed grouse had significantly more ARO neurons and those neurons were larger than that of both the non-breeding male and female ruffed grouse. Aromatase expression in the telencephalon of the ruffed grouse suggests that steroid hormones might modulate responses to visual and acoustic stimuli, but how this relates to species differences in courtship displays and co-expression with estrogenic receptors is yet to be determined.

Morphometric analysis of telencephalic structure in a variety of neognath and paleognath bird species reveals regional differences associated with specific behavioral traits

Birds exhibit a huge array of behavior, ecology and physiology, and occupy nearly every environment on earth, ranging from the desert outback of Australia to the tropical rain forests of Panama. Some birds have adopted a fully nocturnal lifestyle, such as the barn owl and kiwi, while others, such as the albatross, spend nearly their entire life flying over the ocean. Each species has evolved unique adaptations over millions of years to function in their respective niche. In order to increase processing power or network efficiency, many of these adaptations require enlargements and/or specializations of the brain as a whole or of specific brain regions. In this study, we examine the relative size and morphology of 9 telencephalic regions in a number of Paleognath and Neognath birds and relate the findings to differences in behavior and sensory ecology. We pay particular attention to those species that have undergone a relative enlargement of the telencephalon to determine whether this relative increase in telencephalic size is homogeneous across different brain regions or whether particular regions have become differentially enlarged. The analysis indicates that changes in the relative size of telencephalic regions are not homogeneous, with every species showing hypertrophy or hypotrophy of at least one of them. The three-dimensional structure of these regions in different species was also variable, in particular that of the mesopallium in kiwi. The findings from this study provide further evidence that the changes in relative brain size in birds reflect a process of mosaic evolution.

Interactions between environmental changes and brain plasticity in birds

Neurogenesis and neuronal recruitment occur in many vertebrates, including humans. Most of the new neurons die before reaching their destination. Those which survive migrate to various brain regions, replace older ones and connect to existing circuits. Evidence suggests that this replacement is related to acquisition of new information. Therefore, neuronal replacement can be seen as a form of brain plasticity that enables organisms to adjust to environmental changes. However, direct evidence of a causal link between replacement and learning remains elusive. Our hypothesis is that increased neuronal recruitment is associated with increase in memory load. Moreover, since neuronal recruitment is part of a turnover process, we assume that the same conditions that favor survival of some neurons induce the death of others. I present studies that investigated the effect of various behaviors and environmental conditions (food-hoarding, social change, reproductive cycle) on neuronal recruitment and survival in adult avian brains, and discuss how these phenomena relate to the life of animals. I offer a frame and rationale for comparing neuronal replacement in the adult brain, in order to uncover the pressures, rules, and mechanisms that govern its constant rejuvenation. The review emphasizes the importance of using various approaches (behavioral, anatomical, cellular and hormonal) in neuroethological research, and the need to study natural populations, in order to fully understand how neurogenesis and neuronal replacement contribute to life of animals. Finally, the review indicates to future directions and ends with the hope that a better understanding of adult neuronal replacement will lead to medical applications.

Localization of CB1 cannabinoid receptor mRNA in the brain of the chick (Gallus domesticus)

The cannabinoid receptor one (CB1) is prevalent in the brains of many species. Receptor binding, in situ hybridization and immunohistochemical surveys have described the distribution of this receptor in a limited number of species. The current study used in situ hybridization to examine the expression of CB1 mRNA in the chick brain, a non-mammalian vertebrate. The results were compared to the observed patterns of expression for CB1 mRNA, protein, and agonist binding that have been reported for other avian species and mammals. Importantly, since CB1 receptors are typically located on neuronal terminals, comparison of the somatic mRNA expression with previously reported descriptions of the location of functional receptors, allows speculation about the circuits that make use of these receptors. The expression pattern for CB1 mRNA appears to be highly conserved across species in key areas such as the cerebellum and portions of the forebrain. For example, high levels of expression were observed in the avian amygdala and hippocampus, areas which express high levels of CB1 in mammals. The avian substantia nigra and ventral tegmental area, however, showed specific labeling. This finding is in stark contrast to the high levels of receptor binding or CB1 protein, but not CB1 mRNA in these areas of the mammalian brain. Moderate labeling was also seen throughout the hyperpallium and mesopallium. Throughout the brain, a number of regions that are known to be involved in visual processing displayed high levels of expression. For example, the tectum also had strong mRNA expression within layers 9-11 of the stratum griseum et fibrosum superficale and stratum album centrale.

A pathway for predation in the brain of the barn owl (Tyto alba): projections of the gracile nucleus to the "claw area" of the rostral wulst via the dorsal thalamus

The Wulst of birds, which is generally considered homologous with the isocortex of mammals, is an elevation on the dorsum of the telencephalon that is particularly prominent in predatory species, especially those with large, frontally placed eyes, such as owls. The Wulst, therefore, is largely visual, but a relatively small rostral portion is somatosensory in nature. In barn owls, this rostral somatosensory part of the Wulst forms a unique physical protuberance dedicated to the representation of the contralateral claw. Here we investigate whether the input to this "claw area" arises from dorsal thalamic neurons that, in turn, receive their somatosensory input from the gracile nucleus. After injections of biotinylated dextran amine into the gracile nucleus and cholera toxin B chain into the claw area, terminations from the former and retrogradely labeled neurons from the latter overlapped substantially in the thalamic nucleus dorsalis intermedius ventralis anterior. These results indicate the existence in this species of a "classical" trisynaptic somatosensory pathway from the body periphery to the telencephalic Wulst, via the dorsal thalamus, one that is likely involved in the barn owl's predatory behavior. The results are discussed in the context of somatosensory projections, primarily in this and other avian species.

The evolution of stereopsis and the Wulst in caprimulgiform birds: a comparative analysis

Owls possess stereopsis (i.e., the ability to perceive depth from retinal disparity cues), but its distribution amongst other birds has remained largely unexplored. Here, we present data on species variation in brain and telencephalon size and features of the Wulst, the neuroanatomical substrate that subserves stereopsis, in a putative sister-group to owls, the order Caprimulgiformes. The caprimulgiforms we examined included nightjars (Caprimulgidae), owlet-nightjars (Aegothelidae), potoos (Nyctibiidae), frogmouths (Podargidae) and the Oilbird (Steatornithidae). The owlet-nightjars and frogmouths shared almost identical relative brain, telencephalic and Wulst volumes as well as overall brain morphology and Wulst morphology with owls. Specifically, the owls, frogmouths and owlet-nightjars possess relatively large brains and telencephalic and Wulst volumes, had a characteristic brain shape and displayed prominent laminae in the Wulst. In contrast, potoos and nightjars both had relatively small brains and telencephala, and Wulst volumes that are typical for similarly sized birds from other orders. The Oilbird had a large brain, telencephalon and Wulst, although these measures were not quite as large as those of the owls. This gradation of owl-like versus nightjar-like brains within caprimulgiforms has significant implications for understanding the evolution of stereopsis and the Wulst both within the order and birds in general.

Telencephalic projections to the nucleus of the basal optic root and pretectal nucleus lentiformis mesencephali in pigeons

In birds, the nucleus of the basal optic root (nBOR) of the accessory optic system (AOS) and the pretectal nucleus lentiformis mesencephali (LM) are involved in the analysis of optic flow and the generation of the optokinetic response. In several species, it has been shown that the AOS and pretectum receive input from visual areas of the telencephalon. Previous studies in pigeons using anterograde tracers have shown that both nBOR and LM receive input from the visual Wulst, the putative homolog of mammalian primary visual cortex. In the present study, we used retrograde and anterograde tracing techniques to further characterize these projections in pigeons. After injections of the retrograde tracer cholera toxin subunit B (CTB) into either LM or nBOR, retrograde labeling in the telencephalon was restricted to the hyperpallium apicale (HA) of the Wulst. From the LM injections, retrograde labeling appeared as a discrete band of cells restricted to the lateral edge of HA. From the nBOR injections, the retrograde labeling was more distributed in HA, generally dorsal and dorso-medial to the LM-projecting neurons. In the anterograde experiments, biotinylated dextran amine (BDA) was injected into HA and individual axons were reconstructed to terminal fields in the LM and nBOR. Those fibers projecting to the nBOR also innervated the adjacent ventral tegmental area. However, tracing of BDA-labeled axons revealed no evidence that individual neurons project to both LM and nBOR. In summary, our results suggest that the nBOR and LM receive input from different areas of the Wulst. We discuss how these projections may transmit visual and/or somatosensory information to the nBOR and LM.

The avian song system in comparative perspective

The song system of oscine birds has become a versatile model system that is used to study diverse problems in neurobiology. Because the song system is often studied with the intention of applying the results to mammalian systems, it is important to place song system brain nuclei in a broader context and to understand the relationships between these avian structures and regions of the mammalian brain. This task has been impeded by the distinctiveness of the song system and the vast apparent differences between the forebrains of birds and mammals. Fortunately, accumulating data on the development, histochemistry, and anatomical organization of avian and mammalian brains has begun to shed light on this issue. We now know that the forebrains of birds and mammals are more alike than they first appeared, even though many questions remain unanswered. Furthermore, the song system is not as singular as it seemed-it has much in common with other neural systems in birds and mammals. These data provide a firmer foundation for extrapolating knowledge of the song system to mammalian systems and suggest how the song system might have evolved.

Revised nomenclature for avian telencephalon and some related brainstem nuclei

The standard nomenclature that has been used for many telencephalic and related brainstem structures in birds is based on flawed assumptions of homology to mammals. In particular, the outdated terminology implies that most of the avian telencephalon is a hypertrophied basal ganglia, when it is now clear that most of the avian telencephalon is neurochemically, hodologically, and functionally comparable to the mammalian neocortex, claustrum, and pallial amygdala (all of which derive from the pallial sector of the developing telencephalon). Recognizing that this promotes misunderstanding of the functional organization of avian brains and their evolutionary relationship to mammalian brains, avian brain specialists began discussions to rectify this problem, culminating in the Avian Brain Nomenclature Forum held at Duke University in July 2002, which approved a new terminology for avian telencephalon and some allied brainstem cell groups. Details of this new terminology are presented here, as is a rationale for each name change and evidence for any homologies implied by the new names. Revisions for the brainstem focused on vocal control, catecholaminergic, cholinergic, and basal ganglia-related nuclei. For example, the Forum recognized that the hypoglossal nucleus had been incorrectly identified as the nucleus intermedius in the Karten and Hodos (1967) pigeon brain atlas, and what was identified as the hypoglossal nucleus in that atlas should instead be called the supraspinal nucleus. The locus ceruleus of this and other avian atlases was noted to consist of a caudal noradrenergic part homologous to the mammalian locus coeruleus and a rostral region corresponding to the mammalian A8 dopaminergic cell group. The midbrain dopaminergic cell group in birds known as the nucleus tegmenti pedunculopontinus pars compacta was recognized as homologous to the mammalian substantia nigra pars compacta and was renamed accordingly; a group of gamma-aminobutyric acid (GABA)ergic neurons at the lateral edge of this region was identified as homologous to the mammalian substantia nigra pars reticulata and was also renamed accordingly. A field of cholinergic neurons in the rostral avian hindbrain was named the nucleus pedunculopontinus tegmenti, whereas the anterior nucleus of the ansa lenticularis in the avian diencephalon was renamed the subthalamic nucleus, both for their evident mammalian homologues. For the basal (i.e., subpallial) telencephalon, the actual parts of the basal ganglia were given names reflecting their now evident homologues. For example, the lobus parolfactorius and paleostriatum augmentatum were acknowledged to make up the dorsal subdivision of the striatal part of the basal ganglia and were renamed as the medial and lateral striatum. The paleostriatum primitivum was recognized as homologous to the mammalian globus pallidus and renamed as such. Additionally, the rostroventral part of what was called the lobus parolfactorius was acknowledged as comparable to the mammalian nucleus accumbens, which, together with the olfactory tubercle, was noted to be part of the ventral striatum in birds. A ventral pallidum, a basal cholinergic cell group, and medial and lateral bed nuclei of the stria terminalis were also recognized. The dorsal (i.e., pallial) telencephalic regions that had been erroneously named to reflect presumed homology to striatal parts of mammalian basal ganglia were renamed as part of the pallium, using prefixes that retain most established abbreviations, to maintain continuity with the outdated nomenclature. We concluded, however, that one-to-one (i.e., discrete) homologies with mammals are still uncertain for most of the telencephalic pallium in birds and thus the new pallial terminology is largely devoid of assumptions of one-to-one homologies with mammals. The sectors of the hyperstriatum composing the Wulst (i.e., the hyperstriatum accessorium intermedium, and dorsale), the hyperstriatum ventrale, the neostriatum, and the archistriatum have been renamed (respectively) the hyperpallium (hypertrophied pallium), the mesopallium (middle pallium), the nidopallium (nest pallium), and the arcopallium (arched pallium). The posterior part of the archistriatum has been renamed the posterior pallial amygdala, the nucleus taeniae recognized as part of the avian amygdala, and a region inferior to the posterior paleostriatum primitivum included as a subpallial part of the avian amygdala. The names of some of the laminae and fiber tracts were also changed to reflect current understanding of the location of pallial and subpallial sectors of the avian telencephalon. Notably, the lamina medularis dorsalis has been renamed the pallial-subpallial lamina. We urge all to use this new terminology, because we believe it will promote better communication among neuroscientists. Further information is available at http://avianbrain.org

c-fos is induced in the hippocampus during consolidation of sexual imprinting in the zebra finch (Taeniopygia guttata)

c-fos was used to mark regions of enhanced neuronal activity during sexual imprinting, an early learning process by which information about the prospective sexual partner is acquired and consolidated. In the present study, we demonstrate that the hippocampus, already known for its specialized spatial memory capacities in navigating pigeons and in food-storing birds, depicts a selective differential c-fos induction in a situation shown to lead to sexual imprinting, that is, exposing previously isolated male birds to a female for 1 h. c-fos induction is lateralized, the left hippocampus showing more c-fos activity than the right. Our results would indicate a role for the hippocampus in the consolidation process of imprinting, probably in the transfer of information to the other telencephalic areas that show alterations in synaptic connectivity as a result of consolidation of sexual imprinting.

A direct cerebrocerebellar projection in adult birds and rats

The rostral Wulst of birds, like the somatosensory cortex of mammals, receives somatosensory information from the thalamus and projects to the brainstem and spinal cord via a pyramidal-like tract. Using anterograde and retrograde tract-tracers, we show here, in adult zebra finches, that the rostral Wulst also projects directly to the cerebellar cortex and deep nuclei. In the cortex, the cerebrocerebellar fibers resemble neither mossy nor climbing fibers, but more closely resemble the multilayer fibers shown to originate from the hypothalamus in mammals. We also show that a sparse projection to the cerebellum from the mammalian neocortex, originally thought to be lost during early development, is present in the adult rat. Although the functional implications of these results are obscure, they suggest a revision of the concept of the "cerebrocerebellar system", which is generally considered to involve a pontine relay.

Do birds possess homologues of mammalian primary visual, somatosensory and motor cortices?

Recent data on the expression of several homeobox genes in the embryonic telencephalon of mammals, birds and reptiles support the homology of a part of the avian pallium, named the Wulst, and at least the more-medial and superior parts of mammalian neocortex. This conclusion is also supported by previous embryological, topological and hodological data. Furthermore, new evidence on the connections and electrophysiological properties of specific subfields within the avian Wulst, and on the thalamic territories that project to these fields, supports the more-specific conclusion that a primary visual area and a primary somatosensory-somatomotor area are present in the avian Wulst; these areas are likely to be homologous to their counterparts in mammals. In spite of this, developmental, morphological and comparative evidence indicate that some structural and physiological traits that appear to be similar in the Wulst and neocortex (such as the lamination or binocularity) evolved independently in birds and mammals.

Rostral wulst of passerine birds: II. Intratelencephalic projections to nuclei associated with the auditory and song systems

We have previously shown that the hyperstriatum accessorium (HA) of the rostral wulst in zebra finches and green finches is the origin of a pyramidal-like tract with substantial projections to the brainstem and cervical spinal cord. Here, we show that the HA also is the origin of a set of intratelencephalic projections with terminal fields in the lateral part of the frontal neostriatum, the shell surrounding the lateral magnocellular nucleus of the anterior neostriatum, the lobus parolfactorius surrounding area X, the nucleus interface, auditory fields L1 and L3, the shelf underlying the high vocal center, the dorsolateral caudal neostriatum, the dorsocaudal part of the nucleus robustus archistriatalis, and the ventral archistriatum. The cells of origin of these projections are located predominantly laterally in the HA, close to and sometimes within the intercalated HA, which receives somatosensory projections from the dorsal thalamus. The specific implications of these findings for auditory and vocal function are unclear, but the apparent overlap of auditory and somatosensory inputs in several of these regions suggests the possibility of mechanisms for stimulus enhancement or depression, depending on the congruence of stimuli within a cell's "in-register" multiple receptive fields.

Functional organization of forebrain pathways for song production and perception

This article reviews the organization of the forebrain nuclei of the avian song system. Particular emphasis is placed on recent physiologic recordings from awake behaving adult birds while they sing, call, and listen to broadcasts of acoustic stimuli. The neurons in the descending motor pathway (HVc and RA) are organized in a hierarchical arrangement of temporal units of song production, with HVc neurons representing syllables and RA neurons representing notes. The nuclei Uva and NIf, which are afferent to HVc, may help organize syllables into larger units of vocalization. HVc and RA are also active during production of all calls. The patterns of activity associated with calls differ between learned calls and those that are innately specified, and give insight into the interactions between the forebrain and midbrain during calling, as well as into the evolutionary origins of the song system. Neurons in Area X, the first part of the anterior forebrain pathway leading from HVc to RA, are also active during singing. Many HVc neurons are also auditory, exhibiting selectivity for learned acoustic parameters of the individual bird's own song (BOS). Similar auditory responses are also observed in RA and Area X in anesthetized birds. In contrast to HVc, however, auditory responses in RA are very weak or absent in awake birds under our experimental paradigm, but are uncovered when birds are anesthetized. Thus, the roles of both pathways beyond HVc in adult birds is under review. In particular, theories hypothesizing a role for the descending motor pathway (RA and below) in adult song perception do not appear to obtain. The data also suggest that the anterior forebrain pathway has a greater motor role than previously considered. We suggest that a major role of the anterior forebrain pathway is to resolve the timing mismatch between motor program readout and sensory feedback, thereby facilitating motor programming during birdsong learning. Pathways afferent to HVc may participate more in sensory acquisition and sensorimotor learning during song development than is commonly assumed.

The avian somatosensory system: the pathway from wing to Wulst in a passerine (Chloris chloris)

The organization of the wing component of the dorsal column-medial lemniscal pathway, and somatosensory projections from the thalamus to the Wulst, are described for an oscine member of the major group of birds, the Passeriformes. Wing primary afferents terminate throughout the cervical spinal cord, but between the brachial enlargement and the spino-medullary junction, they are confined to medial lamina V. Within the medulla, terminations extend rostrally and laterally to occupy the cuneate (Cu) and external cuneate nuclei (CuE). Ascending projections from Cu and CuE form the contralateral medial lemniscus, which has extensive projections to the midbrain and to the thalamus. In the midbrain the projections surround the central auditory nucleus densely, and terminate more sparsely within it. In the thalamus, specific terminations were observed in nucleus uvaeformis and in the nucleus dorsalis intermedius ventralis anterior (DIVA). DIVA projects to the ipsilateral rostral Wulst where it terminates in the intercalated hyperstriatum accessorium, in a distinct, regular patchy fashion. The somatosensory projections to the telencephalon in green finch are similar to those in pigeon, but dissimilar to those in budgerigar.

A non-thalamic pathway contributes to a whole body map in the brain of the budgerigar

Nucleus basalis (Bas) of the budgerigar contains an ordered, but distorted, somatotopic representation of the whole body, as does the primary somatosensory cortex (SI) of mammals. Unlike SI, however, the beak and body regions of Bas receive their sensory input via disynaptic pathways relaying in the pons. That to the body parts originates in a previously undescribed nucleus that receives its inputs from primary afferents via a novel, ipsilateral somatosensory pathway.

Organization of the dopaminergic innervation of forebrain areas relevant to learning: a combined immunohistochemical/retrograde tracing study in the domestic chick

The mediorostral neostriatum/hyperstriatum ventrale (MNH) and neostriatum dorsocaudale (Ndc) of the domestic chick are crucially involved in auditory filial imprinting, whereas the lobus parolfactorius (LPO) seems to be involved in the emotional modulation of behavior. Because there is evidence that MNH and Ndc are akin to higher association areas in mammals, the present study evaluates the dopaminergic and thalamic input to these areas, as well as to the avian caudate/putamen homologue LPO, by using retrograde pathway tracing, together with dopamine (DA) and tyrosine hydroxylase (TH) immunohistochemistry. By combining DA immunohistochemistry with retrograde fluorescent tracing, we demonstrated that dopaminergic afferents to the MNH and Ndc arise mainly from the area ventralis, whereas the main dopaminergic input to the LPO arises from the substantia nigra. The main thalamic input to the MNH and LPO arises from the dorsal thalamic nuclei, n. dorsomedialis anterior and n. dorsolateralis anterior, whereas the thalamic input to the Ndc arises from the n. dorsolateralis posterior and n. subrotundus. Furthermore, there are reciprocal intratelencephalic connections between distinct parts of the neostriatum caudale and the mediorostral neostriatum. DA-immunoreactive (ir) fibers are present at moderate densities in the MNH and Ndc and at high densities in the LPO. At the ultrastructural level, DA- and TH-ir axon terminals in the MNH and Ndc form predominantly symmetric synaptic contacts with dendritic shafts, which are often situated in close vicinity to unstained terminals. These results indicate that the general organization of dopaminergic afferents to the chick telecephalon is similar to that of the mesotelencephalic dopaminergic subsystems in mammals such as the mesostriatal and mesolimbocortical DA system.

Intratelencephalic projections of the visual wulst in pigeons (Columba livia)

The visual wulst is the telencephalic target of the thalamofugal visual pathway of birds, and thus the avian equivalent of the striate cortex of mammals. The anterograde tracer Phaseolus vulgaris leucoagglutinin was used to follow the intratelencephalic connections of the major constituents of the visual wulst in pigeons. In particular, efferent pathways from the granular layer (Intercalated nucleus of the hyperstriatum accessorium, IHA), supragranular layer (hyperstriatum accessorium, HA), and infragranular layers (hyperstriatum intercalatus superior and/or hyperstriatum dorsale, HIS/HD) were investigated. These efferent projections were confirmed by injections of the retrograde tracer cholera toxin subunit B into their terminal fields. When a deposit of the anterograde tracer was centered in IHA, which receives the visual thalamic input, efferent fibers were seen mainly dorsomedially to IHA. When a deposit of the anterograde tracer was centered in HA, efferent fibers were seen to extend mainly in three directions: 1) medially to the tractus septomesencephalicus, which sends projections to extratelencephalic visual nuclei: 2) ventrolaterally to the lateral portion of the neostriatum frontale, where there were also labeled cells after the retrograde tracer was injected in HA; and 3) ventromedially to the paleostriatal complex, which is the avian equivalent of the mammalian caudale, 5) neostriatum intermedium, 6) archistriatum intermedium, and 7) hyperstriatum laterale. Finally, HIS/HD have projections predominantly to HA and the dorsocaudal telencephalon (area corticoidea dorsolateralis and area parahippocampalis), as well as relatively minor projections to the areas which also receive projections from HA. No anterogradely labeled fibers were seen in the tractus septomesencephalicus following the tracer injections in HIS/HD. These results indicate that the visual information from the granular layer is distributed via the supragranular layer HA to multiple areas within the telencephalon, such as the neostriatum frontale and paleostriatal complex. In addition, HA is the source of an extratelencephalic projection via the tractus septomesencephalicus. Thus, the avian supragranular layer HA contains neurons which are the source of both intratelencephalic and extratelencephalic projections, whereas neurons of the mammalian cortex are segregated into two distinct layers, supragranular and infragranular layers, based on the targets of their projections. The findings are further discussed and compared to the mammalian striate cortex.

Organization of the avian "corticostriatal" projection system: a retrograde and anterograde pathway tracing study in pigeons

Birds have well-developed basal ganglia within the telencephalon, including a striatum consisting of the medially located lobus parolfactorius (LPO) and the laterally located paleostriatum augmentatum (PA). Relatively little is known, however, about the extent and organization of the telencephalic "cortical" input to the avian basal ganglia (i.e., the avian "corticostriatal" projection system). Using retrograde and anterograde neuroanatomical pathway tracers to address this issue, we found that a large continuous expanse of the outer pallium projects to the striatum of the basal ganglia in pigeons. This expanse includes the Wulst and archistriatum as well as the entire outer rind of the pallium intervening between Wulst and archistriatum, termed by us the pallium externum (PE). In addition, the caudolateral neostriatum (NCL), pyriform cortex, and hippocampal complex also give rise to striatal projections in pigeon. A restricted number of these pallial regions (such as the "limbic" NCL, pyriform cortex, and ventral/caudal parts of the archistriatum) project to such ventral striatal structures as the olfactory tubercle (TO), nucleus accumbens (Ac), and bed nucleus of the stria terminalis (BNST). Such "limbic" pallial areas also project to medialmost LPO and lateralmost PA, while the hyperstriatum accessorium portion of the Wulst, the PE, and the dorsal parts of the archistriatum were found to project primarily to the remainder of LPO (the lateral two-thirds) and PA (the medial four-fifths). The available evidence indicates that the diverse pallial regions projecting to the striatum in birds, as in mammals, are parts of higher order sensory or motor systems. The extensive corticostriatal system in both birds and mammals appears to include two types of pallial neurons: 1) those that project to both striatum and brainstem (i.e., those in the Wulst and the archistriatum) and 2) those that project to striatum but not to brainstem (i.e., those in the PE). The lack of extensive corticostriatal projections from either type of neuron in anamniotes suggests that the anamniote-amniote evolutionary transition was marked by the emergence of the corticostriatal projection system as a prominent source of sensory and motor information for the striatum, possibly facilitating the role of the basal ganglia in movement control.

Visual and somatosensory inputs to the avian song system via nucleus uvaeformis (Uva) and a comparison with the projections of a similar thalamic nucleus in a nonsongbird, Columba livia

Nucleus uvaeformis (Uva), previously identified as a component of song control circuitry in songbirds, and nucleus dorsolateralis posterior thalami, pars caudalis (DLPc) in pigeon, were compared with respect to their relative positions in the dorsolateral part of the posterior thalamus, their cell types, and their afferent and efferent projections. Both nuclei are closely related to the habenulointerpeduncular tract, have similar cell types, and receive a dense projection from deep layers of the optic tectum, predominantly ipsilaterally, and a distinct projection from the dorsal column and external cuneate nuclei, predominantly contralaterally. Recordings of multiple unit activity evoked by visual and somatosensory stimuli were used to guide injections of tracer into either DLPc or Uva, and the projections to the telencephalon were charted. Both nuclei were found to have a major terminal field in the medial part of the ipsilateral neostriatum intermedium (NI), known as nucleus interfacialis (NIf) in songbirds, and a minor terminal field in the roof of the neostriatum caudale (NC). In pigeon, the DLPc terminations in NC were within a region known as neostriatum dorsale (Nd), and, in male songbirds, the Uva terminations were in the high vocal center (HVC). Recordings of visual and somatosensory evoked activity were then used to guide injections of tracer into NI, and the afferent and efferent projections were again compared in pigeon and songbirds. The projections from either DLPc or Uva were confirmed, and terminal fields were observed either in Nd in pigeon, the dorsolateral part of NC in female songbirds, or HVC in male songbirds. Injections of tracer into either Nd or HVC confirmed their sources of afferents in DLPc or Uva, respectively, and in NI, but there was incomplete overlap of the distribution of retrogradely labelled cells in NI and the terminal fields of DLPc or Uva. It is concluded that DLPc and Uva are comparable nuclei having similar afferent and efferent projections relaying visual and somatosensory information to the telencephalon. The possible role of this information in vocal control is discussed.

Distributions of GABAA, GABAB, and benzodiazepine receptors in the forebrain and midbrain of pigeons

Autoradiographic and immunohistochemical methods were used to study the distributions of GABAA, GABAB and benzodiazepine (BDZ) receptors in the pigeon fore- and midbrain. GABAA, GABAB and BDZ binding sites were found to be abundant although heterogeneously distributed in the telencephalon. The primary sensory areas of the pallium of the avian telencephalon (Wulst and dorsal ventricular ridge) tended to be low in all three binding sites, while the surrounding second order belt regions of the pallium were typically high in all three. Finally, the outermost rind of the pallium (termed the pallium externum by us), which surrounds the belt regions and projects to the striatum of the basal ganglia, was intermediate in all three GABAergic receptors types. Although both GABAA and benzodiazepine receptors were abundant within the basal ganglia, GABAA binding sites were densest in the striatum and BDZ binding sites were densest in the pallidum. Among the brainstem regions receiving GABAergic basal ganglia input, the anterior and posterior nuclei of the ansa lenticularis showed very low levels of all three receptors, while the lateral spiriform nucleus and the ventral tegmental area/substantia nigra complex contained moderate abundance of the three binding sites. The dorsalmost part of the dorsal thalamus (containing nonspecific nuclei) was rich in all three binding sites, while the more ventral part of the dorsal thalamus (containing specific sensory nuclei), the ventral thalamus and the hypothalamus were poor in all three binding sites. The pretectum was also generally poor in all three, although some nuclei displayed higher levels of one or more binding sites. The optic tectum, inferior colliculus, and central gray were rich in all three sites, while among the isthmic nuclei, the parvicellular isthmic nucleus was conspicuously rich in BDZ sites. The results show a strong correlation of the regional abundance of GABA binding sites with previously described distributions of GABAergic fibers and terminals in the avian forebrain and midbrain. The regional distribution of these binding sites is also remarkably similar to that in mammals, indicating a conservative evolution of forebrain and midbrain GABA systems among amniotes.

The distribution of GABA-containing perikarya, fibers, and terminals in the forebrain and midbrain of pigeons, with particular reference to the basal ganglia and its projection targets

Immunohistochemical techniques were used to study the distributions of glutamic acid decarboxylase (GAD) and gamma-aminobutyric acid (GABA) in pigeon forebrain and midbrain to determine the organization of GABAergic systems in these brain areas in birds. In the basal ganglia, numerous medium-sized neurons throughout the striatum were labeled for GABA, while pallidal neurons, as well as a small population of large, aspiny striatal neurons, labeled for GAD and GABA. GAD+ and GABA+ fibers and terminals were abundant throughout the basal ganglia, and GABAergic fibers were found in all extratelencephalic targets of the basal ganglia. Most of these targets also contained numerous GABAergic neurons. In pallial regions, approximately 10-12% of the neurons were GABAergic. The outer rind of the pallium was more intensely labeled for GABAergic fibers than the core. The olfactory tubercle region, the ventral pallidum, and the hypothalamus were extremely densely labeled for GABAergic fibers, while GABAergic neurons were unevenly distributed in the hypothalamus. GABAergic neurons and fibers were abundant in the dorsalmost part of thalamus and the dorsal geniculate region, while GABAergic neurons and fibers were sparse (or lightly labeled) in the thalamic nuclei rotundus, triangularis, and ovoidalis. Further, GABAergic neurons were abundant in the superficial tectal layers, the magnocellular isthmic nucleus, the inferior colliculus, the intercollicular region, the central gray, and the reticular formation. GABAergic fibers were particularly abundant in the superficial tectal layers, the parvocellular isthmic nucleus, the inferior colliculus, the intercollicular region, the central gray, and the interpeduncular nucleus. These results suggest that GABA plays a role as a neurotransmitter in nearly all fore- and midbrain regions of birds, and in many instances the observed distributions of GABAergic neurons and fibers closely resemble the patterns seen in mammals, as well as in other vertebrates.

Learning selectively increases protein kinase C substrate phosphorylation in specific regions of the chick brain

The effect of imprinting, an early form of exposure learning, on the phosphorylation state of the protein kinase C substrates myristoylated alanine-rich C-kinase substrate (MARCKS) and protein F1/43-kDa growth-associated protein (F1/GAP-43) was studied in two regions of the chick forebrain. One region, the intermediate and medial part of the hyperstriatum ventrale (IMHV), is probably a site of long-term memory; the other, the wulst, contains somatic sensory and visual projection areas. After imprinting, a significant increase in MARCKS protein phosphorylation was observed in the left IMHV but not the right IMHV. No significant alteration in F1/GAP-43 was observed in IMHV. MARCKS was resolved into two acidic components of pI approximately 5.0 and approximately 4.0. Phosphorylation of the pI approximately 5.0 MARCKS but not the pI approximately 4.0 MARCKS was significantly altered by imprinting. The partial correlation between preference score (an index of learning) and phosphorylation, holding constant the effect of approach activity during training, was significant only for the pI approximately 5.0 MARCKS in the left IMHV. A significant negative partial correlation between preference score and F1/GAP-43 phosphorylation in the right wulst was observed. Because the imprinting-induced alteration in MARCKS is selective with respect to phosphoprotein moiety, hemispheric location, and brain region, we propose that these alterations may be central to the learning process.

Overlap of somatic and visual response areas in the Wulst of pigeon

The somatic and visual response areas of the Wulst were investigated electrophysiologically in pigeons. Somatosensory neurons are distributed in the hyperstriatum accessorium (HA), the hyperstriatum intercalatus superior (HIS) and the hyperstraitum dorsal (HD), mainly in HA. The radial nerve response area is relatively larger and overlaps the sciatic nerve area. Visual neurons are located in HA, especially the more superficial part of HA. In the Wulst, the somatic response area overlaps the visual area and there is somatosensory-visual convergence.

An immunocytochemical analysis of the lateral geniculate complex in the pigeon (Columba livia)

The lateral geniculate complex (GL) of pigeons was investigated with respect to its immunohistochemical characteristics, retinal afferents, and the putative transmitters/modulators of its neurons. The distributions of serotonin-, choline acetyltransferase-, glutamic acid decarboxylase-, tyrosine hydroxylase-, neuropeptide Y- (NPY), substance P- (SP), neurotensin- (NT), cholecystokinin- (CCK), and leucine-enkephalin- (L-ENK) like immunoreactive perikarya and fibers were mapped. Retinal projections were studied following injections of Rhodamine-B-isothiocyanate into the vitreous. Transmitter-specific projections onto the visual Wulst and the optic tectum were studied by simultaneous double-labelling of retrograde tracer molecules and immunocytochemical labelling. The GL can be divided into three major subdivisions, the n. geniculatus lateralis, pars dorsalis (GLd; previously designated as the n. opticus principalis thalami, OPT), the n. marginalis tractus optici (nMOT), and the n. geniculatus lateralis, pars ventralis (GLv). All three subdivisions are retinorecipient. The GLd can be further subdivided into at least five components differing in their immunohistochemical characteristics: n. lateralis anterior (LA); n. dorsolateralis anterior thalami, pars lateralis (DLL), n. dorsolateralis anterior thalami, pars magnocellularis (DLAmc); n. lateralis dorsalis nuclei optici principalis thalami (LdOPT); and n. suprarotundus (SpRt). The LdOPT consists of an area of dense CCK-like and NT-like terminals of probable retinal origin. Three subnuclei (DLL, DLAmc, SpRt) were shown to project to the visual Wulst. Cholinergic and cholecystokinergic relay neurons participated in this projection. The nMOT occupies a position between the GLd and GLv and encircles the rostral pole of n. rotundus and the LA. It is characterized mainly by medium sized NPY-like perikarya which were shown to project onto the ipsilateral optic tectum. Bands of NPY-like fibers in the tectal layers 2, 4, and 7 could at least in part be due to this projection of the nMOT. Most of the antisera used revealed transmitter/modulator-specific fiber systems in the GLv which often showed a layer-specific distribution. Perikaryal labelling was only obtained with glutamic acid decarboxylase. On the basis of its chemoarchitectonics, topography, and connectional pattern, the GLd complex of pigeons is most directly equivalent to the mammalian GLd. However, although the different subdivisions of the avian GLd may represent functionally different channels within the thalamofugal pathway similar to the lamina-specific differentiation within the mammalian geniculostriate projection, direct comparison of subnuclei of birds and mammals is not justified at this time. The nMOT appears similar to the intergeniculate leaflet (IGL) and the avian GLv clearly corresponds in many features to the mammalian GLv.

Organization of the anterior dorsal ventricular ridge of the lizard Podarcis hispanica: cytoarchitecture and GABA-immunohistochemistry

The anterior dorsal ventricular ridge (ADVR) of Podarcis hispanica comprises 3 cytoarchitectonic subareas: the rostromedial, caudomedial and lateral ADVR. All 3 subareas showed gamma-aminobutyric (GABA)-like immunoreactivity. GABA-ergic neurons were classified as multipolar (large), stellate (small), bipolar and unipolar cells. Multipolar and stellate GABA-ergic neurons often formed clusters together with GABA-negative cells. Reactive puncta were seen around unreactive somata of the 3 subareas. Like the telencephalic sensory areas of mammals and birds, the ADVR of lizards shows a heterogeneous population of widely distributed GABA-ergic cells that may be the basis for lateral and vertical local inhibition.

Immunohistochemical analysis of the visual wulst of the pigeon (Columba livia)

The avian wulst, a laminated "bulge" in the dorsal telencephalon, contains several distinct regions. The posterolateral portion (visual wulst) has been proposed to be an avian equivalent of the mammalian striate cortex. The present study examines specific neurotransmitters and neuropeptides within the visual wulst by immunohistochemical techniques. Antisera and monoclonal antibodies against choline acetyltransferase (ChAT), nicotinic acetylcholine receptor (nAChR), tyrosine hydroxylase (TH), serotonin (5-HT), glutamic acid decarboxylase (GAD), gamma-aminobutyric acid A receptor (GABAAR), cholecystokinin (CCK), substance P (SP), leucine-enkephalin (L-ENK), neurotensin (NT), neuropeptide Y (NPY), somatostatin (SRIF), corticotropin-releasing factor (CRF), and vasoactive intestinal polypeptide (VIP) were used. Somata and neuropil displaying specific immunoreactivity were generally distributed in accordance with the laminar cytoarchitectonic organization of the wulst. The superficial layer of the wulst, the hyperstriatum accessorium, contained the highest densities of TH-, 5-HT-, SP-, NPY-, SRIF-, CRF-, and VIP-positive neuropil in the wulst, whereas the highest density of CCK- and NT-staining was found in the deepest layer of the wulst, the hyperstriatum dorsale. In addition to the traditionally defined four laminae of the wulst, the immunoreactive staining revealed several subregions within each lamina. The most dorsolateral portion of the wulst contained the highest densities of ChAT- and L-ENK-stained fibers in the wulst, as well as moderately dense staining of neuropil for 5-HT-, TH-, SP-, and CCK-like immunoreactivity. The nAChR-immunoreactivity was faint and distributed rather uniformly throughout the wulst. The results suggest that the wulst consists of multiple regional variations within layers comparable to laminar variations found within different cytoarchitectonic areas of the mammalian neocortex.

Somatosensory areas in the telencephalon of the pigeon. II. Spinal pathways and afferent connections

There are two somatosensory areas in the telencephalon of the pigeon which receive an input from the spinal somatosensory system: one in the rostral Wulst which consists of the three hyperstriatal layers (h. accessorium (HA), h. intercalatus superior (HIS) and h. dorsale (HD] and one in the caudal telencephalon (neostriatum caudale (NC), neostriatum intermedium (NI) and hyperstriatum ventrale (HV]. Recordings of evoked single unit or multi unit activity and of field potentials before and after lesions of spinal pathways at a high cervical level (C4) were made to determine the contribution of these pathways to the transmission of somatosensory signals to these telencephalic areas. The rostral Wulst area receives somatic signals only through dorsal tracts contralateral to the recording site. Inputs from the wing arise mainly through the dorsal columns (DC) and those from the leg largely through the dorsolateral funiculus (DLF). The spinal projection pathway to the caudal neostriatal area includes the dorsal tracts and parts of the lateral funiculi on both sides. There was no difference in response form between the wing and leg responses. Signals transmitted through the lateral pathways were found to elicit the earliest responses (6-13 ms, electrical stimulation) in the caudal forebrain, while signals travelling through the DC arrive later in the caudal area (about 14 ms for wing stimulation) than in the rostral Wulst area (about 9 ms). The afferent thalamic and intratelencephalic connections of the two somatosensory areas in the telencephalon of the pigeon were investigated with retrograde transport of the neuronal tracers horseradish-peroxidase (HRP) or wheatgerm agglutinated HRP (WGA-HRP), Fast Blue (FB) and Rhodamine-isothiocyanat (RITC). Small tracer-injections were made under electrophysiological control at somatosensory responsive locations. These investigations confirm the projection of the caudal part of the nucleus dorsolateralis posterior (DLPc) to the caudal area and of the nucleus dorsalis intermedius ventralis anterior (DIVA) to the rostral area. In addition, it could be shown that the NI/NC projects to the HV thus confirming the electrophysiological results reported in a companion paper (Funke 1989) that the HV is a secondary area. The integrative function of HV is supported by connections to other sensory and motor telencephalic areas. Combined injections of FB and RITC revealed a topographic projection from the DIVA to the anterior Wulst.(ABSTRACT TRUNCATED AT 400 WORDS)