Spatial organization of cortical and subcortical afferent projections of the neostriatum in dogs

Injury to the facial nerve in the temporal bone presents a challenge to the recovery of nerve function, in that the fallopian canal in which it lies is poorly vascularized. This study was designed to determine if wrapping an intratemporal facial nerve defect repaired with a cable graft with a well-vascularized temporoparietal fascial (TPF) flap would improve facial nerve regeneration. To evaluate this question, a defect was created in the intratemporal left facial nerve of 10 rabbits. All nerves were repaired using cable grafts. In 5 animals, the nerve graft was wrapped with temporoparietal fascia, whereas in the other 5 rabbits it was not. Three additional animals underwent exposure only. The contralateral nerve served as a control in all animals. Quantitative analysis of the nerve graft 12 weeks after repair revealed greater recovery of original fiber diameter and myelin sheath thickness in TPF flap-wrapped repairs. Histological evidence of improved neural regeneration and functional nerve recovery was also seen in the repairs where the TPF flap was utilized. Nerve conduction and electromyographic studies of the cable-grafted nerve at 6 and 12 weeks were equivocal, however.     

The laminar organization of the afferent connections of the cortical column in field 17 in the cat

The laminar structure of the cortical column connections in area 17 of the cat was studied using the microiontophoretic injection of the horseradish peroxidase. Following the enzyme injection in one column at different depths below the cortical surface the identification of morphological types of labelled neurons and the estimation of their localization were performed. When enzyme has been delivered in the whole depth of the column pyramidal neurons labelled were found in upper (I/III) and lower (V/VI) layers (ratio II;I). When the depth of enzyme injection exceeded the cortex width the cells in layer IV were labelled as well. The ratio between the quantity of cells labelled in upper and lower layers was preserved. (II; I). After the enzyme injection in the upper part of the column labelled cells were found mainly in the upper layers. It is concluded that the neurons of the column of have extensive (up to 5 mm), predominantly horizontal afferent connections with the cells in upper and lower layers while the connections with neurons in layer IV are local and do not extend beyond 0.5 mm.     

The organization of corticothalamic projections: reciprocity versus parity

All neocortical areas receive inputs from and project back to the thalamus. It is often said that the corticothalamic projections are organized in a way that reciprocates the spatial distribution of thalamocortical pathways. The present review examines to what extent this rule of reciprocity is actually supported by the most recent neuroanatomical data, particularly those relating to the central organization of the vibrissal sensory system in the rat. A critical survey of previous studies is made and new results are presented concerning the fine-grained organization of corticothalamic projections in this sensory system. Together, prior results and the present set of new data confirm the existence of both, reciprocal and nonreciprocal patterns of corticothalamic connectivity. This conclusion leads us to propose that the spatial organization of corticothalamic connections complies with a more fundamental rule, the rule of parity, from which reciprocity follows as a general, but not obligatory consequence. The rule of parity states that the distribution of corticothalamic projections across and within the thalamic nuclei is determined by the branching patterns of the different classes of prethalamic afferents. The anatomical, developmental and physiological consequences of this rule are discussed. The rule of parity suggests that, according to the behavioral context, both prethalamic and corticothalamic pathways may function in a feedback mode.     

Random motor generation in a finger tapping task: influence of spatial contingency and of cortical and subcortical hemispheric brain lesions

OBJECTIVE: To test the hypothesis that, during random motor generation, the spatial contingencies inherent to the task would induce additional preferences in normal subjects, shifting their performances farther from randomness. By contrast, perceptual or executive dysfunction could alter these task related biases in patients with brain damage. METHODS: Two groups of patients, with right and left focal brain lesions, as well as 25 right handed subjects matched for age and handedness were asked to execute a random choice motor task--namely, to generate a random series of 180 button presses from a set of 10 keys placed vertically in front of them. RESULTS: In the control group, as in the left brain lesion group, motor generation was subject to deviations from theoretical expected randomness, similar to those when numbers are generated mentally, as immediate repetitions (successive presses on the same key) are avoided. However, the distribution of button presses was also contingent on the topographic disposition of the keys: the central keys were chosen more often than those placed at extreme positions. Small distances were favoured, particularly with the left hand. These patterns were influenced by implicit strategies and task related contingencies. By contrast, right brain lesion patients with frontal involvement tended to show a more square distribution of key presses--that is, the number of key presses tended to be more equally distributed. The strategies were also altered by brain lesions: the number of immediate repetitions was more frequent when the lesion involved the right frontal areas yielding a random generation nearer to expected theoretical randomness. The frequency of adjacent key presses was increased by right anterior and left posterior cortical as well as by right subcortical lesions, but decreased by left subcortical lesions. CONCLUSIONS: Depending on the side of the lesion and the degree of cortical-subcortical involvement, the deficits take on a different aspect and direct repetions and adjacent key presses have different patterns of alterations. Motor random generation is therefore a complex task which seems to necessitate the participation of numerous cerebral structures, among which those situated in the right frontal, left posterior, and subcortical regions have a predominant role.     

The cerebral control of the somatosensory and auditory afferent projections to the cerebral cortex in man and animals

The main purpose of the present paper was consisted in studying of topology (spreading) of the somatosensory and auditory projections in cortex of both brain hemispheres in humans under different functional states conditions: during quiet walking state and during realization of the meditative programme. At the same time for the purpose of verification these steering mechanisms a number of experiments were realized in animals with neurosurgical cutting of brainstem ascending projections, which control the transfer of somatosensory and auditory sensibility. Experimental study was realized with two groups of subjects--8 subjects (age from 25 to 35 years old) and 25 (age from 25 to 40 years old) subjects practicing technique of Transcendental Meditation (TM). In addition to the mentioned above group some groups of animals were used in the experiments. Among them there were used the groups of monkeys (8 macaque rhesus and macaque nemestrina) and cats (10 animals) in conditions of acute experiment, under tiopenthal anesthesia. Two experimental methods were used in the study: electrophysiological for subjects and neurosurgical, additionally for animals. For evaluation of the brain reactivity in subjects registration of the somatosensory, to median nerve stimulation, and auditory, to bilateral application of auditory clicks, evoked potentials (EPs) in the symmetrical cortical structures of the brain was used. Registration of the somatosensory and auditory evoked potentials in animals was realized not only from the cortex, but from the brainstem somatosensory and auditory structures. SSEP in subjects-meditators were registered before and during meditation programme. In animals SSEP and AEP registration on the corresponding stimuli realized before and after neurosurgical operation--section of the midbrain tegmentum. Specific alterations of the early (up to 80 ms) and late components SSEP and AEP complexes in forms of topology spreading and diminution of registration areas of these components were obtained during the meditation. Origins of these functional reorganization are discussed from the positions of internal 'feed-back' inhibition.     

The generalized cone in human spatial organization

The generalized cone is one of the newer concepts useful for describing spatial structures, and it has become popular as a volumetric primitive in models of object recognition. Apart from this use of the concept (or perhaps underlying it), the generalized cone can be considered a species of spatial regularity. In the general definition of symmetry as invariance across transformation, the generalized cone is a combination of translation and dilation symmetry. In such symmetry, there is homogeneity both of the slants of edges and surfaces of an object about an axis and the radial positions of these features about the axis. The results of two research projects are reviewed suggesting that the generalized cone is useful in human spatial organization. In the first instance, each of the three simpler regular polyhedra, the Platonic Solids, are easiest to perceive and imaging when they are organized as generalized cones. In the second instance, people imagine simple rotations best when the symmetric space that would be traced by the motion is aligned with salient spatial reference systems.     

The organization of the cortical projection system of the putamen in dogs

Organization of cortical projections in dorsal and ventral segments of putamen rostral and caudal regions was studied in dogs using retrograde axonal transport of horse radish peroxidase. Dorsal region was shown to receive projections from neo- and mesocortex, while ventral is linked with all cortical units: neo-, meso- and allocortex. Dorsal part of putamen is to greater extent connected with cortical fields, relating to motor aspects of behavior (motor, premotor and somatosensory). Ventral region basically receives projections from the so called limbic cortical fields (cingular, insulary, orbital, periamygdalary and perirhinal). However, results of the present study do not allow to conclude on absolute division of projections of functionally different systems and only indicate the prevalence of one of them in certain topographic zone of the structure studied, i.e. elements of distinctive topography. consisting in presence of dorsal motor and ventral limbic morpho-functional regions are characteristic for dog putamen. No diversities in distribution of cortical projectional fibres along rostrocaudal axis of the structure were revealed. Initial neurons, projecting in putamen are of multilaminary localisation in the cortex.     

The role of temporal cortical areas in perceptual organization

The visual areas of the temporal lobe of the primate are thought to be essential for the representation of visual objects. To examine the role of these areas in the visual awareness of a stimulus, we recorded the activity of single neurons in monkeys trained to report their percepts when viewing ambiguous stimuli. Visual ambiguity was induced by presenting incongruent images to the two eyes, a stimulation condition known to instigate binocular rivalry, during which one image is seen at a given time while the other is perceptually suppressed. Previous recordings in areas V1, V2, V4, and MT of monkeys experiencing binocular rivalry showed that only a small proportion of striate and early extrastriate neurons discharge exclusively when the driving stimulus is seen. In contrast, the activity of almost all neurons in the inferior temporal cortex and the visual areas of the cortex of superior temporal sulcus was found to be contingent upon the perceptual dominance of an effective visual stimulus. These areas thus appear to represent a stage of processing beyond the resolution of ambiguities--and thus beyond the processes of perceptual grouping and image segmentation--where neural activity reflects the brain's internal view of objects, rather than the effects of the retinal stimulus on cells encoding simple visual features or shape primitives.     

Prefrontal cortical projections to the hypothalamus in macaque monkeys

The organization of projections from the macaque orbital and medial prefrontal cortex (OMPFC) to the hypothalamus and related regions of the diencephalon and midbrain was studied with retrograde and anterograde tracing techniques. Almost all of the prefrontal cortical projections to the hypothalamus arise from areas within the "medial prefrontal network," as defined previously by Carmichael and Price ([1996] J. Comp. Neurol. 371:179-207). Outside of the OMPFC, only a few neurons in the temporal pole, anterior cingulate and insular cortex project to the hypothalamus. Axons from the OMPFC also innervate the basal forebrain, zona incerta, and ventral midbrain. Within the medial prefrontal network, different regions project to distinct parts of the hypothalamus. The medial wall areas 25 and 32 send the heaviest projections to the hypothalamus; axons from these areas are especially concentrated in the anterior hypothalamic area and the ventromedial hypothalamic nucleus. Orbital areas 13a, 12o, and Iai, which are related to the medial prefrontal network, selectively innervate the lateral hypothalamic area, especially its posterior part. The cellular regions of the paraventricular, supraoptic, suprachiasmatic, arcuate, and mammillary nuclei are conspicuously devoid of cortical axons, but many axons abut the borders of these nuclei and may contact dendrites that extend from them. Areas within the orbital prefrontal network on the posterior orbital surface and agranular insula send only weak projections to the posterior lateral hypothalamic area. The rostral orbital surface does not contribute to the cortico-hypothalamic projection.     

The spatial organization of the EEG and individual psychological characteristics

The influence of cognitive styles (analytic versus synthetic style, rigid versus flexible cognitive control, impulsivity versus reflexivity, field-dependence versus independence) on the information brain processes was estimated by means of analysis of spatial organization of cortical electrical activity (48 derivations) in 40 right-handed subjects (aged from 18 to 40) during their realization of verbal and non-verbal tasks using successive and simultaneous processing modes. Modulation of the "cognitive axis" (activity of the left anterior and right posterior cortical areas) was revealed connected with the factor of task subjective difficulty, especially in case of simultaneous processing mode. The combination of the synthetic cognitive style and flexibility of the cognitive control may be thought of as being the most favourable for the activation of the "cognitive axis" and utilization of the left- and right-hemispheric information processing, especially in non-standard situations.     

Constraints on cortical and thalamic projections: the no-strong-loops hypothesis

The many distinct cortical areas of the macaque monkey visual system can be arranged hierarchically, but not in a unique way. We suggest that the connections between these cortical areas never form strong, directed loops. For connections between the visual cortex and particular thalamic nuclei, we predict that certain types of connections will not be found. If strong, directed loops were to exist, we suggest that the cortex would go into uncontrolled oscillations.     

Individual differences in spatial organization of cortical electrical activity during formation of a set to visual stimuli

Vascular affections of the brain remain a formidable psychiatric challenge nowadays. According to WHO reports cerebrovascular disorders constitute one of the three chief causes of mortality in the population of the economically developed countries of the world. The most important cause of vascular psychoses is considered to be atherosclerosis and hypertensive disease. Today vascular psychoses have become a most common type of abnormal mental states in young adults (greater then 30-40 years old). The studies made have yielded evidence in support of the psychoses morbidity to be dependent upon particular season of year as well as on the climatic features of the locality. Natural factors have been found out to affect the prevalence of vascular psychoses in Chernivtsi Province. The findings obtained suggest to us a substantial prevalence of atherosclerotic and hypertensive psychoses in the plains-men living under conditions of a mild climate.     

Synaptology of the nigrostriatal projection in relation to the compartmental organization of the neostriatum in the rat

The patch-matrix organization of the striatal complex, which is fundamental to the structural and functional organization of the basal ganglia, is characterized on the basis of both connections and neurochemistry. In order to determine whether differences in the connections and neurochemistry are reflected in differences in synaptic organization, we examined the synaptology of the dopaminergic nigrostriatal projection in the patch-matrix complex of the rat. Three approaches were used. First, deposits of the anterograde tracer, biotinylated dextran amine, were placed in the substantia nigra. Sections of perfuse-fixed neostriatum were then processed to reveal anterogradely-labelled nigrostriatal axons and calbindin-D28k immunoreactivity, a marker for the patch-matrix complex. Secondly, sections of perfuse-fixed neostriatum were immunolabelled to reveal both tyrosine hydroxylase, a marker for dopaminergic structures and calbindin-D28k. Labelled axons in the patches and the matrix were examined at both the light and the electron microscopic levels. Finally, in order to test for the presence of fixed GABA in sub-type of anterogradely-labelled terminals in the neostriatum, ultrathin sections were immunolabelled by the post-embedding immunogold method. Based on morphological analysis, anterogradely-labelled nigrostriatal axons were divided into two types (Type I and Type II). The density of tyrosine hydroxylase labelling in the neostriatum prevented the classification of immunolabelled nigrostriatal axons. The Type I anterogradely-labelled axons and tyrosine hydroxylase-positive axons were found both in the patches and in the matrix. They both formed symmetrical synapses with spines, dendrites and occasionally somata. The morphology, dimensions, type of synaptic specialization and the distribution of postsynaptic targets of axons labelled by both methods were similar in the patches and the matrix. The Type I anterogradely-labelled axons were immunonegative for GABA. The Type II anterogradely-labelled axons were GABA-immunopositive, were found only in the matrix and were only present in those animals in which retrograde labelling was observed in the globus pallidus, they are thus not part of the dopaminergic nigrostriatal projection. It is concluded that although the patch-directed and matrix-directed dopaminergic projections from the ventral mesencephalon arise from different populations of dopaminergic neurons, their innervation of neurons in the patches and matrix is similar. The anatomical substrate, and therefore probably also the mechanism, for dopaminergic modulation of the flow of cortical information through the striatal complex in essentially the same in the patch and in the matrix sub-divisions of the striatal complex.     

Temporal cortical projections to the olfactory tubercle in the rhesus monkey

Chickens that had been vaccinated with a lentogenic strain 2 to 9 weeks before challenge with a virulent virus remained clinically normal following challenge and circulated virus within leukocytes for as long as ten days. The virulent virus was detected by inoculating embryonating eggs with leukocytes separated from blood shortly after drawing. Freezing the leukocytes before inoculating the eggs reduced isolation 64.8%. Virus was demonstrated most readily in chickens challenged when antibody was decreasing, about 9 weeks after vaccination. The observation that virus in blood may be contained within a cellular component and be readily demonstrable only if the cells are separated and washed is significant both to an understanding of the immunological responsiveness of vaccinated chickens exposed to field challenge and to an understanding of epizootiological events.     

Topographical organization of subicular neurons projecting to subcortical regions

Direct projections from the subiculum to the septum, thalamus, and hypothalamus were studied in the rat by the fluorescent retrograde double-labeling technique with Fast blue and Diamidino yellow. The results confirm and extend the previously reported findings. The dorsal subiculum projects primarily to the lateral septum, anterior and midline thalamus, and mammillary complex. The distribution areas of cell bodies of these projection neurons are substantially segregated, depending on their target region, and few single neurons project to two of the target regions by way of axon collaterals. The ventral subiculum projects mainly to the lateral septum, midline thalamus, and ventromedial hypothalamic area. The distribution areas of cell bodies of these projection neurons are considerably overlapped with one another, and a number of single neurons send axon collaterals to two of the lateral septum, midline thalamus, and ventromedial hypothalamic area. It is, thus, indicated that the populations of subicular neurons projecting to each of the subcortical structures examined are more distinctly segregated in the dorsal subiculum than in the ventral subiculum.     

Spatial organization and plasticity of the primary and secondary olfactory projections in goldfish

Crystals of the lipophilic tracer DiI were applied to discrete regions of the olfactory epithelium of goldfish to trace the primary sensory projection to the olfactory bulb. Receptors from the anterior half of the sensory sheet project primarily to glomeruli in the medial half of the bulb and receptors in the posterior half terminate mainly within the lateral half of the bulb. This pattern disappeared following ablation of selected, discrete epithelial regions. In order to investigate reorganization of secondary olfactory projections, unoperated control and unilaterally bulbectomized animals received injections of [3H]proline into the right olfactory bulb. Densities of silver grains per unit area were determined within six different forebrain nuclei in both the right and left hemispheres of each animal. Of the six areas examined, three demonstrated a significantly greater density of afferent innervation from the ipsilateral versus contralateral bulb; a difference which disappeared in two of these three regions after bulbectomy. Thus, for at least two forebrain nuclei, bulb removal caused a change in the afferent input from the spared olfactory bulb to those regions. We conclude that both primary and secondary olfactory projections in goldfish are capable of some degree of reorganization following insult.     

Brain stem and primary afferent projections to the ventromedial group of propriospinal neurones in the cat

The preparation of charcoal-gelatin disks and their use for removing free steroid in radioimmunoassays are described. Plasma concentrations of several steroids were determined using charcoal-gelatin disks or charcoal suspension and the results are compared. The advantages of using charcoal-gelatin disks are discussed.