Telencephalic connections of the trigeminal system in the pigeon (Columba livia): a trigeminal sensorimotor circuit

The vocal control pathways in budgerigars differ from those in songbirds

Previous studies concluded that parrots and oscine songbirds, two taxa that have independently evolved the ability to learn vocalizations, possess similar neural circuits for vocal control. These investigations suggested, however, that the vocal control systems of parrots and songbirds may also differ in several respects. Most importantly, auditory inputs to the vocal control system derive from Field L in songbirds, but this area does not appear to project to the vocal control system in parrots. The principal aims in the present study were, therefore, to determine 1) exactly how similar the vocal control system in budgerigars is to that in songbirds and 2) whether the vocal control system in budgerigars receives auditory inputs from areas other than Field L. Biotinylated and fluorescently labeled dextrans were injected into five telencephalic nuclei of the vocal control system in budgerigars and into the physiologically identified auditory portions of the frontal neostriatum and nucleus basalis. The results indicate that the forebrain vocal control system in budgerigars is only superficially similar to that in songbirds. Many of the vocal control nuclei differ between the two taxa in both cytoarchitecture and connections. The nuclei in budgerigars that are comparable to those of the accessory loop of the vocal control system in songbirds, for example, do not form an accessory loop in budgerigars. The vocal control systems in the two taxa differ most significantly in the source of their auditory inputs. In songbirds, auditory information is conveyed to the vocal control system via Field L, whereas, in budgerigars, the auditory inputs to the vocal control system derive from nucleus basalis and the frontal neostriatum. A phylogenetic analysis suggests that the midbrain and medullary vocal control pathways are homologous across all birds, but that most of the vocal control circuits in the forebrain have probably evolved independently in parrots and songbirds.

Connections of the basal telencephalic areas c and d in the turtle brain

Tracer substances were injected into the basal telencephalic areas c and d of the turtle brain. These areas (Acd) have recently been shown to be connected reciprocally with the dorsal spino-medullary region, though the particular subregions involved in these projections remained unclear. We demonstrated that the efferent projections of area d terminate predominantly within or immediately adjacent to the trigeminal nuclear complex and in the high cervical spinal gray. The dendritic domain of the vagus-solitarius complex and the dorsal column nuclear complex might also receive some basal telencephalic efferents. The afferent projections to Acd, on the other hand, arise predominantly in the dorsal column nuclei as defined according to cytoarchitectural and hodological criteria. A few retrogradely labeled cells were found in the vagus-solitarius complex, the principal trigeminal nucleus and the high cervical spinal cord. Numerous labeled cells were found in the dorsolateral isthmo-rhombencephalic tegmentum, especially the n. visceralis secundarius, the n. vestibularis superior and parts of the lateral lemniscal complex. Aminergic cell populations projecting to Acd were the n. raphes inferior and superior, the locus coeruleus, the substantia nigra, pars compacta and the ventral tegmental area. Other meso-diencephalic cell groups were the griseum centrale (including the n. laminaris of the torus semicircularis), the n. interpeduncularis dorsalis, the nucleus of the fasciculus longitudinalis medialis, the nucleus and the nucleus interstitialis of flm, the n. interstitialis commissuralis posterior and then n. caudalis. Several hypothalamic regions, the reuniens complex and the perirotundal region of the thalamus also appeared to project heavily to Acd. Telencephalic areas retrogradely labeled after injection of tracer into Acd and its immediate surroundings were the rostral part of the lateral (olfactory) cortex, adjacent regions of the basal dorsal ventricular ridge and the n. centralis amygdalae, the n. tractus olfactorius lateralis as well as the areas g and h. The data suggest that areas c and d may correlate best with the 'extended' amygdala in mammals; further correlation with structures similar to the ventral striopallidum, however, cannot be excluded. Homostrategies are discussed with regard to the processing of higher-order somatovisceral information in turtles, birds and mammals.

Connections of the auditory forebrain in the pigeon (Columba livia)

Ascending auditory efferents in birds terminate mainly within Field L2, a cytoarchitectonically distinct region of the caudomedial telencephalon. The organization of Field L2, and that of its flanking regions, L1 and L3, was investigated with 14C-2-deoxyglucose (14C-2-DG), cytochrome oxidase, and both retrograde and anterograde tracing techniques. Field L2 was found to contain a high concentration of cytochrome oxidase. Following auditory stimulation, 14C-2-DG autoradiography revealed that Field L2 consists of two adjacent but seemingly discontinuous zones, designated Field L2a, which lies ventromedially, and Field L2b, which lies dorsolaterally. Termination of thalamic efferents: The thalamic auditory nuclei ovoidalis (Ov) and semilunaris parovoidalis (SPO) project predominantly upon Field L2, and possibly sparsely upon L1, L3 and the overlying hyperstriatum ventrale (HV). Ov subnuclei project upon L2a and SPO projects predominantly upon L2b. The topography of the projections is inverted along the ventromedial-to-dorsolateral axis of L2, and is in accord with an inverted tonotopic representation of frequencies; high frequencies (< 3.5 kHz) being found in the more ventromedial parts of L2a, and low frequencies and broad band responses in L2b. Intra- and extratelencephalic connections: Field L2a also receives a substantial projection from HV, but the efferent projections of L2a appear confined to adjacent "neostriatal" regions. The subsequent projections of L2b were not identified in this study. L1 and L3 project predominantly to the dorsal neostriatum (Nd) caudolateral to Field L, and have fewer projections to the caudomedial paleostriatum and anterior hyperstriatum accessorium. Nd projects massively upon the ventromedial nucleus of the intermediate archistriatum (Aivm), which has bilateral projections upon the caudomedial telencephalon and is the origin of a major descending pathway having dense terminations surrounding the ovoidalis complex (Ov and SPO), MLd, the lateral lemniscal nuclei, and sparse terminations within SPO itself. It is suggested that within the telencephalon the major components of the auditory pathway consist of cell groups which collectively correspond to the populations of neurons found within the auditory cortex of mammals.

The dopaminergic innervation of the pigeon caudolateral forebrain: immunocytochemical evidence for a 'prefrontal cortex' in birds?

The dopaminergic (DA) innervation of the caudal telencephalon of the pigeon was investigated with an antiserum against glutaraldehyde-conjugated dopamine. It was found that the DA-like fibers were distributed within the Paleostriatum augmentatum and the dorsal Archistriatum in a dense meshwork of fibers, while most of the remaining part of the caudal forebrain was innervated by dopaminergic axons which were coiled up like baskets around unlabelled neurons. Within the basket-type innervated structures, the Neostriatum caudolaterale (Ncl) could be distinguished by the high density of its dopaminergic fibers. Retrograde tracer injections into Ncl revealed afferents from the Area ventralis tegmentalis (AVT) and the n. tegmenti pedunculo-pontinus pars compacta (TPc). Since large numbers of DA-like perikarya could be detected in AVT and TPc, it is supposed that these two structures constitute the main source of the dopaminergic innervation of the Ncl. Previous studies had suggested that the Ncl represents an avian equivalent to the mammalian prefrontal cortex. The present results reveal an organization similar to that of the mesocortico-prefrontal system and would thus strengthen this hypothesis.

Grasping in the pigeon: control through sound and vibration feedback mediated by the nucleus basalis

Pigeons were trained to detect auditory and vibratory stimuli in two separate experiments using an instrumental conditioning procedure. The discriminative stimuli became effective as the subjects grasped a probe with the beak. The pigeons learned to suppress responding upon this grasp-contingent stimulation. Bilateral lesions of the nucleus basalis prosencephali (Bas), known to be involved in the motor control of pecking and to receive short latency input of cochlear and trigeminal origin, eliminated the behavioral stimulus detection. The performance of a control color discrimination was not affected by the Bas lesions, demonstrating that these had a specific effect. The processing of peck-related feedback by the nucleus basalis during the normal food uptake of pigeons is discussed.

Parallel evolution in mammalian and avian brains: comparative cytoarchitectonic and cytochemical analysis

Comparative morphology, which is based on the selection theory of evolution, analyses the impact of function upon structure and, therefore, emphasizes the adaptive events and biological advantage during the evolution of organs. A comparison based on analogies is described here as an adequate method. The hypothesis is proposed that the evolution of the brain follows the same trends in birds as in mammals. This hypothesis is proved by (1) allometric studies of brain weight and brain structure volume in relation to body weight in mammals and birds; (2) architectonic studies using image analysis on cell and fibre stains as well as on histochemical preparations and receptor autoradiography; and (3) hodological studies with injections of [3H]leucin, HRP and WGA-HRP. The results reveal a vast amount of structural and functional similarities in avian and mammalian brain organization, especially an expansion of structures that permit multimodal integration capacity in the telencephalon. Thus, a parallel evolution occurred in these two groups of vertebrates. It is argued that this may be a general phenomenon in evolution. A cladistic approach, which is based on the concept of homologies (plesio-, apomorphies), pushes aside the existence of analogies. For this reason, cladism does not seem to be a method to answer questions of evolutionary morphology adequately.

Visuomotor feeding perturbations after lateral telencephalic lesions in pigeons

Pigeons with lesions of the lateral part of the telencephalon, visual Wulst, and fronto-archistriatal tract were compared with sham-operated controls in 2 procedures. In one of them the time it took the pigeons to grasp and eat a certain number of grains was recorded. In the other experiment the number of grains was counted that the pigeons consumed out of a mixture of grains and pebbles within a fixed time interval. Only the pigeons with lateral telencephalic lesions were impaired. While in the first experiment the lateral ablated birds improved with time there was no recovery of performance in the second experiment.

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.

Peripheral and central terminations of hypoglossal afferents innervating lingual tactile mechanoreceptor complexes in Fringillidae

Injections of cholera toxin B subunit conjugated to horseradish peroxidase (CTB-HRP) were made into the lingual branch of the hypoglossal nerve in four species of finch in order to identify the innervation of the mechanoreceptors of the dermal papillae of the tongue, and simultaneously to determine the pattern of central projections of lingual hypoglossal afferents. The results showed that hypoglossal fibers innervate all the Herbst corpuscles and terminal cell receptors of the elaborately organized papillae of the dorsum of the tongue, of the shorter papillae in the ventral tongue, and the loose collection of Herbst corpuscles in the subpapillary region. Labelled fibers were also observed in the intralingual glands, in the intrinsic tongue muscles, and in the posterodorsal epithelium where they formed budlike structures. Retrogradely labelled cell bodies were located in the jugular ganglion and their central processes ascended and descended throughout the brainstem within the descending trigeminal tract (TTD). Terminal fields were observed within the dorsolateral part of the nucleus caudalis of TTD, predominantly ipsilaterally, and within the medial part of the dorsal horn of the first 4-6 cervical segments bilaterally. There were dense patches of termination over a dorsolateral subnucleus of the interpolated nucleus of TTD, and within two regions of the principal sensory trigeminal nucleus: a large one laterally and a small one medially. Terminal fields were also observed within the nucleus ventralis lateralis anterior of the rostral solitary complex, and within adjacent nuclei, which are probably equivalent to the dorsal sensory nuclei of the facial and glossopharyngeal nerves of other avian species. The results are interpreted in the light of the role of the tongue in species-specific patterns of feeding in finches, and the possible requirement for the central integration of touch and taste.

Trigeminal deafferentation and prehension in the pigeon

During the grasping and manipulation phases of the pigeon's ingestive pecking behavior, jaw opening movements are scaled to the size of the target (food) object. To assess the contribution of beak mechanoreceptor afferents to the control of scaling we examined the effects of bilateral trigeminal deafferentation upon the kinematics of jaw opening trajectories. Deafferented subjects exhibited both a transient reduction in the accuracy of peck localization and a more persistent deficit in the effectiveness of their ingestive pecking response. However, they continued to exhibit the same classes of jaw movement described for the normal pigeon. The functional relation between target size and gape remained unchanged after deafferentation as did the relationships among kinematic variables controlling jaw opening. However, deafferentation produced small but significant increase in the absolute values of peak gape for both grasping and mandibulation which reflects an increase in peak opening velocity. The results are discussed in relation to the problem of sensory control of rapid targeted movements.

Avian somatosensory system: II. Ascending projections of the dorsal column and external cuneate nuclei in the pigeon

The ascending projections of the dorsal column and external cuneate nuclei (DCN/CuE) in the pigeon were investigated in anterograde tracing experiments by using autoradiography or wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). The results show that the majority of ascending projections decussate via internal arcuate fibers to form a contralateral medial lemniscus which ascends in a ventral position. In the brainstem, terminal fields were observed in the ventral lamella of the inferior olive (OI), the parabrachial nuclei (PB) of the dorsolateral pons, the intercollicular nucleus (ICo) of the midbrain, and the nucleus pretectalis diffusus (PD). In the diencephalon there were terminal fields in the strata cellulare externum and internum (SCE and SCI) of the caudal hypothalamus; in the intercalated (ICT), ventrolateral (VLT), and reticular nuclei of the ventral thalamus; in the nuclei principalis precommissuralis (PPC), spiriform medialis (SpM), and dorsolateralis posterior, pars caudalis (cDLP) of the caudal thalamus; and in the nuclei dorsalis intermedius ventralis anterior (DIVA), dorsolateralis posterior, pars rostralis (rDLP), dorsolateralis anterior (DLA), and dorsolateralis anterior, pars medialis (DLM) of the rostrodorsal thalamus. The origins of these projections within the DCN/CuE complex were verified in retrograde tracing experiments with WGA-HRP and were found to be partly differentiable with respect to their targets. The projections to DIVA, rDLP, DLA, DLM, cDLP, and SpM arise from all rostrocaudal levels of the DCN/CuE complex; those to ICo arise from caudomedial nuclear regions, while those to the hypothalamus and ventral thalamus arise from rostrolateral nuclear regions. Projections to PB arise from lamina I neurons of the dorsal horn of upper cervical spinal cord segments and from CuE. No evidence was found of a projection to the cerebellum. The distribution of the cells of origin of the medial lemniscus (ML) within the DCN/CuE complex was found to be largely coextensive with the areas of termination of primary spinal (Wild: J. Comp. Neurol. 240:377-395, '85) and some trigeminal (Dubbledam and Karten: J. Comp. Neurol. 180:661-678, '78) afferents. Furthermore, the areas of termination of the ML within the rostrodorsal and caudal thalamus are also either coextensive or closely associated with nuclei which provide a somatosensory projection to separate regions of the telencephalon (Wild: Brain Res. 412:205-223, '87). There are thus clear similarities in the overall pattern of somatosensory projections in the pigeon and in many mammalian species.

Neuroanatomical substrates involved in the control of food intake

Five neural pathways were reviewed regarding their specific role in the control of food intake in birds. The five pathways included the trigeminal sensorimotor system, the visual system/basal ganglia pathway, the gustatory system, the olfactory pathway, and the autonomic nervous system/parasympathetic pathway. The trigeminal system is the pathway best understood among the five systems associated with feeding. It begins with sensory nerves innervating the upper and lower mandibles and buccal cavity and ends with nerves projecting to jaw muscles. The function of the pathway is to control the grasping and mandibulation of pellets or seeds. The visual system includes both the tectofugal and thalamofugal pathways. Both visual pathways interact with the avian paleostriatal complex. The latter is equivalent to the mammalian basal ganglia. The second pathway is important in food recognition as well as in orienting the body with respect to its position in three-dimensional space. The third neural circuit involves the sense of taste. Approximately 300 taste buds have been identified within the buccal cavity of the chicken, suggesting that the gustatory system is better developed than once thought. The fourth pathway involves the olfactory system; as in the visual system, more than one pathway has been identified. The dominant pathway appears to project to the piriform cortex, a structure that may play a role in monitoring essential amino acid contents of the brain. The fifth pathway involves an interaction of the hypothalamus and the dorsal motor nucleus of the vagus. This pathway is important in activating the parasympathetic nervous system and in preparing an organism to feed. All five pathways play different roles in controlling food intake in birds.

Cerebellar connections of the trigeminal system in the pigeon (Columba livia)

Wheat germ-agglutinin conjugated horseradish peroxidase (WGA-HRP) was used to delineate trigeminocerebellar connections in the pigeon. Subnucleus oralis of the nucleus of the descending trigeminal tract (nTTD) is the exclusive origin of trigeminal mossy fibers, which terminate in lobules VIII and IXa. The trigemino-olivary projection originates from subnucleus interpolaris of nTTD, but the existence of an additional pathway relaying in the adjacent lateral reticular formation (i.e. the plexus of Horsley) cannot be excluded. Structures linking the trigeminal cerebellar projections to jaw motoneurons were identified within the cerebellar cortex, the deep cerebellar nuclei and the lateral medullary reticular formation, completing a trigeminocerebellar sensorimotor circuit for the jaw.

Prehension in the pigeon. I. Descriptive analysis

Eating in the pigeon involves a series of jaw movements some of which serve a prehensile function; i.e., they are utilized in the grasping and manipulation of objects. These prehensile behaviors are extremely brief (30-80 ms), produce an adjustment of jaw opening amplitude to the size of the food object, are mediated by an effector system involving a relatively small number of muscles and are amenable to both "reflexive" and "voluntary" control. This combination of structural simplicity and functional complexity suggests that the pigeon's jaw movements may provide a useful "model system" for the study of motor control mechanisms in targeted movements. The present report provides a classification of jaw opening movements occurring during eating and a preliminary determination of the extent to which each movement class is scaled to the size of the food object. Jaw movements were monitored during responses to spherical food pellets of six different sizes (3.2-11.1 mm in diameter) using a transducing system which produces a continuous record of gape (i.e., interbeak distance). Assignment to movement classes was then carried out using a computer-assisted scoring program. Functions relating jaw opening amplitude to target size were determined for each movement class. Four jaw movement classes were identified: Prepecks (just prior to pecking), Grasps (opening movements made during pecking but prior to contact with the target), Mandibulations (movements serving to position and transport the object within the buccal cavity) and Swallows. For two of these movement classes (Grasps, Mandibulations) jaw opening amplitude is scaled to pellet size but the scaling functions differ in ways that reflect the functional requirements of the two behaviors.(ABSTRACT TRUNCATED AT 250 WORDS)

Nucleus basalis prosencephali, a substrate of apomorphine-induced pecking in pigeons

Microinjections of the dopamine agonist apomorphine into the nucleus basalis prosencephali of pigeons elicit stereotyped pecking behaviour. Injections of 6-hydroxydopamine, a toxic dopamine antagonist, into the same nucleus impair stereotyped pecking induced by systemic apomorphine administration, but do not interfere with pecking in the normal feeding context.

Vestibular projections to the thalamus of the pigeon: an anatomical study

In a series of retrograde tracing studies involving the injection of WGA-HRP into the thalamus of the pigeon, labeled neurons were consistently observed in anterior regions of the vestibular nuclei. Following small dorsal thalamic injections, labeled neurons were located predominantly in rostroventrolateral regions of the superior vestibular nucleus, less numerously within the ventral part of the lateral vestibular nucleus, and least numerously within the medial vestibular nucleus. Following large dorsal thalamic injections, many more vestibular neurons were labeled, and these were distributed more extensively throughout anterior parts of the superior, lateral, and medial nuclei. No labeled neurons were found in the descending nucleus. Injections of tritiated amino acids into vestibular nuclei revealed a terminal field within the dorsal thalamic nucleus: dorsolateralis posterior, pars rostralis. The location of this field between auditory, somatosensory, and paleostriatally and neostriatally projecting nuclei suggests a general similarity to the organization of vestibulothalamic projections in mammals.

The avian somatosensory system: connections of regions of body representation in the forebrain of the pigeon

In order to establish the basic connectivity of physiologically identified somatosensory regions of the thalamus and telencephalon in the pigeon, injections of wheatgerm agglutinin-horseradish peroxidase were made under electrophysiological control and the projections were charted following conventional neurohistochemistry. The physiological recordings generally confirmed the findings of Delius and Bennetto (Brain Research, 37 (1972) 205-221) of somatosensory sites within the dorsal thalamus, anterior hyperstriatum and caudomedial neostriatum, and the anatomical results show that the thalamic cells of origin of the projections to the two telencephalic regions are largely separate: a rostral cell group comprising nucleus dorsalis intermedius ventralis anterior projects to the anterior hyperstriatum accessorium (HA), whilst a caudal cell group comprising caudal regions of nucleus dorsolateralis posterior (DLP) projects to the medial neostriatum intermedium and caudale (NI/NC). Caudal DLP is also the origin of a visual projection to NI/NC, and its terminal field also approximates that of the thalamic auditory nucleus ovoidalis. Since the anterior HA and NI/NC were here shown to be reciprocally connected, there is a possibility of multimodal input to both telencephalic regions. HA was also further defined as the origin of the basal branch of the septomesencephalic tract, and hence potentially provides an outlet for both telencephalic somatosensory regions. The results are discussed within a comparative context.

Vestibular, olfactory, and vibratory responses of nucleus basalis prosencephali neurons in pigeons

Evoked multiple unit responses were recorded through chronically implanted electrodes from the nucleus basalis prosencephali of the pigeon (Columba livia) upon vibratory stimulation of the beak-tip and airborne auditory stimulation, thus confirming earlier anatomical and physiological findings. Electrical stimulation of the olfactory nerve led to similar short latency responses. A specific directional sensitivity to rotatory vestibular stimulation was observed. Pitch motions of the head in the downward direction evoked the most pronounced multi-unit responses. These results support the suggestion that the nucleus basalis prosencephali is a sensorimotor coordinator of the pigeon's pecking/feeding behaviour.

The organization of the nucleus basalis-neostriatum complex of the mallard (Anas platyrhynchos L.) and its connections with the archistriatum and the paleostriatum complex

The pattern of connections between the nucleus basalis, neostriatum, hyperstriatum ventrale, paleostriatum complex and archistriatum in the mallard has been analysed using Nissl material and a combination of neuroanatomical tracing procedures (autoradiography, horseradish peroxidase and horseradish peroxidase-wheat germ agglutinin histochemistry, lesion/degeneration technique). The frontal part of the mallard's telencephalon is characterized by its multilayered organization and the predominantly vertical arrangement of the connecting fiber systems. The nucleus basalis, endstation of the ascending sensory trigeminal system, is a large laminar cell area with a dorsal and a ventral layer. The overlying neostriatum frontale can be subdivided into a medial, a dorsal and a ventral intermediate, and a lateral area. The nucleus basalis has distinct connections with the ventral layer and sparse connections with the dorsal layer of the intermediate neostriatum, and abundant reciprocal connections with the ventral layer of the hyperstriatum ventrale. The ventral intermediate neostriatum also has reciprocal connections with the hyperstriatum ventrale; its projections overlap partly with those from the nucleus basalis. The ventral layer of the intermediate neostriatum frontale has a distinct projection upon the paleostriatum augmentatum. The dorsal layer sends fibers to the lateral neostriatum, to the rostral "sensorimotor" part of the archistriatum and to the lateral zone of the lobus parolfactorius. Another source of archistriatal afferents is the paleostriatum ventrale, an area that may also send fibers to the brainstem. Figure 21 summarizes the connections described in this paper. The functional significance of this organization is discussed in relation to its possible role in the guidance of pecking and other feeding behaviors in the mallard. Differences in the organization of the systems in pigeon and mallard are related to the differing degrees of visual and tactile (trigeminal) contributions to feeding in the two birds. It is suggested that the pattern of reciprocal connections between the hyperstriatum ventrale and the nucleus basalis and ventral intermediate neostriatum frontale forms the neuroanatomical substrate for a "comparator-system".

Thalamic projections to the paleostriatum and neostriatum in the pigeon (Columba livia)

Thalamic projections to the paleostriatum and neostriatum in the pigeon have been studied using wheat germ agglutinin-horseradish peroxidase in anterograde and retrograde tracing experiments. Injections centred on different mediolateral regions of the dorsal thalamus produced terminal labelling in correspondingly different mediolateral regions of the striatal complex, comprising paleostriatum augmentation and lobus parolfactorius, within the ventral paleostriatum, and within the neostriatum. Injections into various loci within these regions retrogradely labelled numerous neurons within the dorsal thalamus, the location of which varied systematically with the injection placement; and within various regions of the midbrain and pons. These experiments demonstrate a major thalamic projection to the striatum analogous to that from the midline and intralaminar nuclei to the caudatoputamen in mammals, although the patchy characteristic of mammalian striatal afferent terminations was observed only within ventral regions of the pigeon paleostriatum. In addition the experiments demonstrate that striatal afferents also originate from certain nuclei of the mesencephalic midline which are possibly equivalent to the raphe nuclei.

Anatomical identification of an auditory pathway from a nucleus of the lateral lemniscal system to the frontal telencephalon (nucleus basalis) of the pigeon

Anterograde and retrograde tracing experiments employing WGA-HRP were used to identify an auditory projection area within the frontal telencephalon of the pigeon. The projection originates in a nucleus of the lateral lemniscus, travels with the quintofrontal tract and terminates within nucleus basalis. The location of the projection area and the absence of a thalamic relay in its pathway are consistent with previous reports of short-latency auditory potentials evoked in the vicinity of the nucleus basalis in several avian species.

Telencephalic bill projections in the Landes goose

Electrical activity of trigeminal central projection areas was recorded in anesthetized and chronic awake geese. Evoked potentials of telencephalic structures were studied after stimulation of the bill, quintofrontal tract (QF), and several telencephalic structures (nucleus basalis [Bas], neostriatum frontale [NF], paleostriatum augmentatum [PA], and neostriatum caudale [NC]). Short-latency evoked potentials were recorded in Bas after stimulation of the bill or QF; this finding is consistent with a direct connection between the main sensory trigeminal nucleus and Bas. Short- and long-latency evoked potentials were recorded in PA and NC after stimulation of the posterior QF. These potentials are concluded to be due to two different pathways: The shorter-latency response is produced by fibers leaving QF posteriorly, while the longer-latency response is derived from fibers traveling along QF, relaying first in Bas and then in NF. From Bas and NF, two pathways convey impulses to NC; only one is relayed in PA.

The cerebellar and vestibular nuclear complexes in the turtle. II. Projections to the prosencephalon

Prosencephalic projections from the cerebellar and vestibular nuclear complexes in the turtle Pseudemys scripta elegans were investigated with anterograde tracing. Following injections of 35S-methionine at various locations within the cerebellar and vestibular nuclear complexes, labeled ascending fibers were found to arise from the lateral cerebellar and the rostral (superior and/or dorsolateral) vestibular nuclei. The great majority of these fibers coursed within the ipsilateral ascending periventricular tract. There were possible terminations in the hypothalamosuprapeduncular region, the ovalis-complex, and the nucleus commissuralis anterior, but scarcely any indication of terminal labeling within the dorsal thalamus. The labeled fibers, however, continued rostralward, entered the lateral forebrain bundle, and terminated in the anterior dorsal ventricular ridge--in all but one case, exclusively ipsilaterally. The terminal area within the lateral division (referred to as area L) of the anterior dorsal ventricular ridge was sharply delimited, being situated ventrolateral to the visually oriented area D of the anterior dorsal ventricular ridge (Balaban and Ulinski, '81), medial to the lateral cortex, and ventral to the pallial thickening (motor pallium of Johnston, '16). The findings are compared with related ones in mammals, particularly those pertaining to telencephalic somatosensorimotor regions and their interactions with the vestibular nuclear complex and the cerebellum.

The avian somatosensory system. I. Primary spinal afferent input to the spinal cord and brainstem in the pigeon (Columba livia)

The process of transganglionic transport was used to determine the pattern of primary afferent projections to the spinal cord and brainstem in the pigeon by (1) applying horseradish peroxidase (HRP) to various peripheral nerves in the leg or wing, (2) by injecting HRP-lectin into feather follicles of the wing or tail, and (3) by injecting HRP-lectin into various muscles of the leg or wing. In the spinal cord major peripheral nerves were represented heavily throughout the dorsal horn laminae but sparsely in more ventral laminae. The representations of these different nerves tended to be located in different mediolateral regions of the dorsal horn. Cutaneous nerves and feather follicles were represented predominantly in laminae I and II, and different sets of follicles were represented in different mediolateral regions of these laminae. Afferent labelling from muscles of the leg and wing was located in the lateral portion of the dorsal horn, predominantly in laminae I, II, and IV. In the caudal medulla the representation of the leg within the gracile nucleus was medial to and separate from that of the wing within the cuneate nucleus (Cu). The wing representation, however, extended laterally throughout the external cuneate nucleus (CuE) and lateral regions of the descending trigeminal tract. There was less evidence of separation of the limb representations at more rostral medullary levels where they both occupied predominantly CuE. Afferent labelling from cutaneous nerves and feather follicles was distributed lightly throughout Cu and CuE, and from muscles of both limbs primarily throughout CuE. There was also a small but specific projection from the limbs to the nucleus of the solitary tract, and from the wing to the principal sensory trigeminal nucleus. These results are discussed within a comparative context with a view to highlighting the similarities and differences in the pattern of primary afferent central projections in different vertebrates.