Distribution of cerebellar terminations and their relation to other afferent terminations in the ventral lateral thalamic region of the monkey

Thalamic astasia: inability to stand after unilateral thalamic lesions

Inability to stand in the absence of motor weakness or marked sensory loss is usually considered to reflect midline cerebellar disease. However, the 15 patients reported here had astasia related to unilateral thalamic lesions, documented by autopsy and computed tomography in 2 patients and by computed tomography in 13. The lesions, including infarction (6), hemorrhage (7), and tumor (2), involved primarily the superoposterolateral portion of the thalamus, but spared the rubral region. Alert, with normal or near-normal strength on isometric muscle testing and a variable degree of sensory loss, the patients could not stand and 7 of them could not sit up unassisted. They fell backwards or toward the side contralateral to the lesion. They appeared to have a deficit of overlearned motor activity of an axial and postural nature. In the vascular cases, the deficit improved in a few days or weeks. However, these patients had a tendency to sustain falls during the rehabilitation period.

Frontal eye field efferents in the macaque monkey: I. Subcortical pathways and topography of striatal and thalamic terminal fields

Anterograde tracers (tritiated leucine, proline, fucose; WGA-HRP) were injected into sites within the frontal eye fields (FEF) of nine macaque monkeys. Low thresholds (less than or equal to 50 microA) for electrically evoking saccadic eye movements were used to locate injection sites in four monkeys. Cases were grouped according to the amplitude of saccades evoked or predicted at the injection site. Dorsomedial prearcuate injection sites where large saccades were elicited were classified as lFEF cases, whereas ventrolateral prearcuate sites where small saccades were evoked were designated sFEF cases. One control case was injected in the medial postarcuate area 6. We found five descending fiber bundles from FEF; fibers to the striatum, which enter the caudate nucleus at or just rostral to the genu of the internal capsule; fibers to the claustrum, which travel in the external capsule; and transthalamic, subthalamic, and pedunculopontine fibers. Our results indicate that transthalamic and subthalamic pathways supply all terminal sites in the thalamus, subthalamus, and tegmentum of the midbrain and pons, whereas pedunculopontine fibers appear to terminate in the pontine and reticularis tegmenti pontis nucleus exclusively. Frontal eye field terminal fields in the striatum were topographically organized: lFEF projections terminated dorsal and rostral to sFEF projections. Thus, lFEF terminal fields were located centrally in the head and body of the caudate nucleus and a small dorsomedial portion of the putamen, whereas sFEF terminal fields were located in ventrolateral parts of the caudate body and ventromedial parts of the putamen. In the claustrum, lFEF projections terminated dorsal and rostral to sFEF projections. Projections from FEF terminated in ventral and caudal parts of the subthalamic nucleus without a clear topography. By comparison, terminal fields from medial postarcuate area 6 were located more caudally and laterally in the striatum and claustrum than projections from FEF, and more centrally in the subthalamic nucleus. In the thalamus, FEF terminal patches in some thalamic nuclei were also topographically organized. Projections from lFEF terminated in dorsal area X, dorsolateral medial dorsal nucleus, pars parvicellularis (MDpc), and the caudal pole of MDpc, whereas projections from sFEF terminated in ventral area X, medial dorsal nucleus, pars multiformis, and caudal medial dorsal nucleus pars densocellularis.(ABSTRACT TRUNCATED AT 400 WORDS)

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.

[Pure spastic hemiplegia of pyramidal origin]

The relationship between the interruption of the human pyramidal tract and its attendant clinical manifestations has been a matter of concern to neurologists and neurosurgeons for over a century. We presently report three cases of unilateral pyramidal tract ischemic lesions within the cerebral hemispheres who presented with a contralateral pure spastic hemiplegia syndrome. In none could we find any disturbance in the somatosensitive evoked potentials of the four limbs. The review of some cases on record since the time of Charcot and Erb has made it clear that the pyramidal syndrome is a valid clinical concept which should be qualified according to the particular animal species one is referring to. In man, it manifests itself by paresis, hyperactive muscular reflexes, spasticity and Babinski sign. Based on this evidence we propose the idea of a "differential control" exerted by the pyramidal tract upon the segmental neuronal pool as its key mode of normal functioning.

Dissociation of the lateral and medial cerebellum in movement timing and movement execution

In a previous study (Ivry and Keele, in press), cerebellar patients were found to be impaired on both a motor and a perceptual task which required accurate timing. This report presents case study analyses of seven patients with focal lesions in the cerebellum. The lesions were predominantly in the lateral, hemispheric regions for four of the patients. For the remaining three patients, the lesions were centered near the medial zone of the cerebellum. The clinical evaluation of the patients also was in agreement with the different lesion foci: lateral lesions primarily impaired fine motor coordination, especially apparent in movements with the distal extremities and medial lesions primarily disturbed balance and gait. All of the patients were found to have increased variability in performing rhythmic tapping when tapping with an effector (finger or foot) ipsilateral to the lesion in comparison to their performance with a contralateral effector. Separable estimates of a central timekeeper component and an implementation component were derived from the total variability scores following a model developed by Wing and Kristofferson (1973). This analysis indicated that the poor performance of patients with lateral lesions can be attributed to a deficit in the central timing process. In contrast, patients with medial lesions are able to accurately determine when to make a response, but are unable to implement the response at the desired time. A similar dissociation between the lateral and medial regions has been observed on a time perception task in patients with cerebellar atrophy. It is concluded that the lateral regions of the cerebellum are critical for the accurate functioning of an internal timing system.

Projection on the motor cortex of thalamic neurons with pallidal input in the monkey

The cortical projection areas of thalamic neurons with basal ganglia and/or cerebellar inputs were studied electrophysiologically in unanesthetized monkeys. Thalamic neurons which receive inhibition from the pallidum were found to project to the motor cortex (area 4) as well as to premotor cortex. The neurons with pallidal input and motor cortical projection were located mainly in VLo. This result indicates that the basal ganglia innervate the motor cortex through the thalamus. Thus the basal ganglia can modify the cortical output for controlling movements directly through this pathway as compared with its influence through the prefrontal and premotor cortices.

Reorganization of the projection from the sensory cortex to the motor cortex following elimination of the thalamic projection to the motor cortex in cats; Golgi, electron microscope and degeneration study

Changes of terminal connections of projection fibers from area 2 of the sensory cortex to the motor cortex following chronic lesion in the thalamus were examined using the electron microscope. The lesioned areas included nucleus ventralis anterior, n. ventralis lateralis and rostral part of n. ventralis posterolateralis. The synaptic sites were identified using the Golgi impregnation method to identify postsynaptic neurons in the motor cortex and the axonal degeneration method to identify presynaptic terminals of fibers originating from area 2. The following results were obtained. (1) The number of degenerating terminals per unit area in the motor cortex was increased to nearly twice that in normal animals. (2) The number of degenerating terminals synapsing with stellate cells was not increased but stayed more or less the same as in normal animals. (3) The number of degenerating terminals contacting pyramidal cells increased substantially, to more than twice that in normal animals. (4) These newly formed synapses were found on proximal dendritic shafts of the pyramidal cells in both layers III and V, suggesting that these synapses occupied the spaces where the thalamocortical terminals were located. (5) The functional significance of these newly formed synapses was discussed in relation to the recovery of motor function following thalamic lesion.

Selective proprioceptive loss from a thalamic lacunar stroke

In an elderly woman a small thalamic infarct, documented by computed tomography and nuclear magnetic resonance imaging, caused proprioceptive loss contralaterally without impairment of other sensory modalities. This patient, the first so reported, demonstrates the anatomic separation of spinothalamic and dorsal column/medial lemniscus sensory modalities in the human thalamus.

Sagittal cytoarchitectonic maps of the Macaca mulatta thalamus with a revised nomenclature of the motor-related nuclei validated by observations on their connectivity

Cytoarchitectonic atlas plates of the Macaca mulatta thalamus are presented in the sagittal plane of section with a revised nomenclature of the motor thalamic region. The proposed changes in nomenclature are based on the analysis of topographical relationships between nigral, pallidal, and cerebellar projections to the thalamus studied in 13 rhesus monkeys with the use of autoradiography technique. Mapping of the projection zones of these motor-related systems in serial sagittal sections revealed that they are completely segregated with each honoring cytoarchitectonic boundaries of specific nuclear subdivisions. The available data on thalamic connectivity together with the results of the present study allowed us to divide the primate "motor" thalamus into two major territories: (1) the ventral anterior region (VA) and (2) the ventral lateral region (VL). Although the designation of these two areas of the motor thalamus is the same as the classic one, the nuclear subdivisions that compose them differ significantly from those described in previous classifications. As is delineated in the maps, VA represents the basal ganglia territory of the motor thalamus where nigral projections coincide with its magnocellular part (VAmc), and pallidal projections occupy densicellular (VAdc) and parvicellular (VApc) subdivisions. VAdc corresponds closely to VLo of Olszewski; however, we prefer the new term in order to avoid possible conceptual confusions with the ventral lateral region (VL), which does not receive basal ganglia projections. The VL region is characterized as a distinct cytoarchitectonic entity of the motor thalamus that receives cerebellar projections and includes area X, VPLo, VLc, and VLps of Olszewski. The ventral medial region (VM in the present study or VLm in Olszewski terminology) is usually considered together with the basal ganglia territory on a common connectional basis. However, we did not obtain convincing data to support this view, since evidence of terminal labeling was observed only in (or around) fiber bundles passing through the nucleus with other areas free of label. Rather, in this study VM was treated as an intermediate zone between the subthalamus and motor thalamus where fiber bundles from basal ganglia and cerebellum are organized in a topographical manner before reaching their destinations in the VA and VL regions, respectively. Other major thalamic regions represented in the maps were delineated purely on cytoarchitectonic grounds and their traditional nomenclature was maintained.(ABSTRACT TRUNCATED AT 400 WORDS)

A quantitative study of the distribution of neurons projecting to the precentral motor cortex in the monkey (M. fascicularis)

The relative numbers and locations of neurons projecting to the "forelimb" region of the precentral motor cortex were studied in three monkeys by using the retrograde transport of horseradish peroxidase. Within the forelimb area of the motor cortex itself, there are extensive and profuse interconnections. However, regions within this area receive afferents from very few neurons in other parts of the motor cortex representing hindlimb or head movements. Most of the motor cortical representation of the forelimb in the anterior bank of the central sulcus is devoid of callosal connections. In both the ipsilateral and contralateral hemispheres, the premotor (lateral area 6) and supplementary motor (medial area 6) areas dominate quantitatively the inputs to the motor cortical representation of the forelimb. The afferents from the premotor area are restricted and come from a region immediately behind the arcuate spur and adjacent parts of the superior and inferior limbs of the arcuate sulcus in the floor, caudal bank, and caudal lip of that sulcus. From the supplementary motor area (SMA), afferents originate from its whole rostrocaudal extent. Thalamic nuclear regions projecting to a restricted zone in the anterior bank of the central sulcus are recipients of cerebellar and somatosensory outputs. Involvement of more anterior parts of the motor cortex by the tracer labels thalamocortical cells, which are targets of pallidal output also. Within the first somatosensory cortex, cytoarchitectonic areas 1, 2, and 3a project to area 4. The projection from area 3a may provide one pathway by which short-latency peripheral inputs, especially from muscles, reach the motor cortex.

Anterograde transsynaptic degeneration in the deep cerebellar nuclei of Purkinje cell degeneration (pcd) mutant mice

The genetically-determined loss of Purkinje cells (PCs) in 'Purkinje cell degeneration' (pcd) mutant mice results in the loss of presynaptic afferents to the deep cerebellar nuclei (DCN). This deafferentation takes place between postnatal day (P)17 and P45, i.e. after the maturation of cerebellar circuitry. We examined the DCN of normal and pcd mutant mice by quantitative light microscopic methods to determine whether neuronal atrophy or loss in the DCN take place during and after the loss of their input from the PCs. Neuronal diameters in control mice were 16.4 +/- 0.72 microns (mean +/- S.D.) at P23 and 15.6 +/- 0.64 microns at P300. The respective values in pcd mutant mice were 15.7 +/- 0.58 microns and 13.5 +/- 0.24 microns. Diameters in 300-day-old mutants were significantly smaller than those in both age-matched controls and 23-day-old mutants (P less than 0.001). Neuronal populations in the DCN of control mice were 10,167 +/- 949 at P23 and 10,429 +/- 728 at P300. The respective values in mutants were 9,436 +/- 1,366 and 7,424 +/- 1,324. There was a significant difference of 29% [95% confidence limits: 9-45%] between 300-day-old mutants and age-matched controls (P less than 0.01), and a significant loss of 21% [95% confidence limits: 4-36%] in 300-day-old mutants with respect to 23-day-old mutants (P less than 0.05). The total volume of the DCN was 22% less in 300-day-old mutants in relation to 23-day-old mutants (P less than 0.05). These findings support the idea that the stability of DCN neurons in the mature cerebellum depends in part on the synaptic input from PCs.

Cerebellar hemispheric agenesis

A case report is reported of bilateral cerebellar hemispheric agenesis which was associated with secondary degeneration of cerebellofugal and cerebellopetal tracts. Somatotopic correlations between the cerebellar and the medullary olive lesions were obvious: preserved dorsal accessory olives pattern correlated with the spared vermis and normal medial accessory olives with the spared flocculi. Cerebellopetal degeneration was more difficult to analyse. The relation of cerebellar agenesis with basal ganglia abnormalities and microcephaly is discussed.

Thalamic connectivity of the second somatosensory area and neighboring somatosensory fields of the lateral sulcus of the macaque

The thalamocortical relations of the somatic fields in and around the lateral sulcus of the macaque were studied following cortical injections of tritated amino acids and horseradish peroxidase (HRP). Special attention was paid to the second somatosensory area (S2), the connections of which were also studied by means of thalamic isotope injections and retrograde degeneration. S2 was shown to receive its major thalamic input from the ventroposterior inferior thalamic nucleus (VPI) and not, as previously reported, from the caudal division of the ventroposterior lateral nucleus (VPLc). Following small injections of isotope or HRP into the hand representation of S2, only VPI was labeled. Larger injections, which included the representations of more body parts, led to heavy label in VPI, with scattered label in VPLc, the central lateral nucleus (CL), and the posterior nucleus (Po). In addition, small isotope injections into VPLc did not result in label in S2 unless VPI was also involved in the injection site, and ablations of S2 led to cell loss in VPI. Comparison of injections involving different body parts in S2 suggested a somatotopic arrangement within VPI such that the trunk and lower limb representations are located posterolaterally and the hand and arm representations anteromedially. The location of the thalamic representations of the head, face, and intraoral structures that project to S2 may be in the ventroposterior medial nucleus (VPM). The granular (Ig) and dysgranular (Id) fields of the insula and the retroinsular field (Ri) each receive inputs from a variety of nuclei located at the posteroventral border of the thalamus. Ig receives its heaviest input from the suprageniculate-limitans complex (SG-Li), with additional inputs from Po, the magnocellular division of the medial geniculate n. (MGmc), VPI, and the medial pulvinar (Pulm). Id receives its heaviest input from the basal ventromedial n. (VMb), with additional inputs from VPI, Po, SG-Li, MGmc, and Pulm. Ri receives its heaviest input from Po, with additional input from SG-Li, MGmc, Pulm, and perhaps VPI. Area 7b receives its input from Pulm, the oral division of the pulvinar, the lateral posterior n., the medial dorsal n., and the caudal division of the ventrolateral n. These results indicate that the somatic cortical fields, except for those comprising the first somatosensory area, each receive inputs from an array of thalamic nuclei, rather than just one, and that individual thalamic somatosensory relay nuclei each project to more than one cortical field.

Neural correlates of isometric force in the "motor" thalamus

The relationship between single cell activity in the "motor" thalamus and the generation of isometric force between the fingers has been investigated in 2 monkeys. Neurons related to the task were found in the thalamic motor regions VLo, VPLo, and VA where microstimulation occasionally elicited motor reactions in hand and fingers. 58% of these 55 neurons, designated "typical", showed modulation of their discharge patterns with force similar to neurons in precentral cortex and could be assigned to one of 5 discharge patterns described for the motor cortex. Only a small percentage of the thalamic neurons were found to have phasic activity. The other "atypical" neurons (42%) had discharge patterns with complex sequences of phasic and tonic activation with respect to force. For 18 typical and atypical neurons with tonic and phasic-tonic modulation of their firing rate with force significant regression coefficients between firing rate and static force were observed. The mean index of force sensitivity (rate-force slope) was 54.5 Hz/N for the neurons increasing their discharge rate with force, i.e. approximately that of precentral cells. Neurons tested for their sensory properties had receptive fields located on hand and/or fingers and were activated mainly by stimulation of muscle and joint receptors. The characteristics of these thalamic neurons are compared to those of precentral cells recorded under identical experimental conditions and are discussed in relation to the known input-output relationships of the motor thalamic nuclei. The data strongly support the hypothesis that parameters of movement, in particular force are represented by the activity of neurons in the "motor" thalamus.

Fastigial nucleus projections in the midbrain and thalamus in dogs

Efferent connections to midbrain and thalamus from portions of the cerebellar fastigial nucleus were investigated using autoradiographic techniques. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area which produced maximal increases in blood pressure and heart rate was localized in each dog. A mixture of [3H]leucine and [3H]proline (4:1) was injected into that area and autoradiograms were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. The rostral-caudal extent of injection sites were mapped in the horizontal plane from sequential coronal, thionin-stained sections and "primary" and "secondary" injection zones were defined according to specific criteria. Labeled axons reached the mesencephalon via the contralateral uncinate fasiculus. Ascending fibers assembled in a diffuse contingent at the prerubral level adjacent to the ventrolateral periaqueductal gray. The heaviest projections were contralateral to the injection site, but ipsilateral terminals were observed as well. In the midbrain, axons entered the contralateral and ipsilateral superior colliculus to branch repeatedly and terminate in the deep and intermediate layers. Additional terminals were observed bilaterally in the nuclei of the posterior commissure and pretectal areas at the midbrain-diencephalic junction. In the thalamus, labeled axons formed into three groups which terminated in: the contralateral paraventricular complex and medial dorsal nucleus; the contralateral central medial, paracentral, parafasicular and central lateral nuclei, and the contralateral ventral medial and ventral lateral nuclei. There was a sparse projection to the ipsilateral ventral lateral nucleus. The contralateral projection to the ventral medial and ventral lateral nuclei was marked by dense clusters of label ventral to the internal medullary lamina extending, in the dorsal ventral lateral nucleus, to its rostral pole. Projections to specific somesthetic thalamus or the hypothalamus were not observed. These ascending projections in the canine brain generally conform to those described in other nonprimate mammals. The fastigial nucleus presumably provides information concerning equilibrium and body proprioception to the superior colliculus and to thalamic nuclei including both specific motor relay and "nonspecific" midline and intralaminar nuclei, much the same as reported in the cat. The projection to the ventral medial and ventral lateral thalamic nuclei terminate in areas known to participate in the control of axial and proximal limb muscle activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Volitional movement is not preceded by cortical slow negativity in cerebellar dentate lesion in man

Slow negative potential preceding voluntary self-paced middle finger extension, as recorded from scalp electrodes by backward averaging technique, was absent in two patients with dyssynergia cerebellaris myoclonica (Ramsay Hunt syndrome); but present in two patients with cerebellar cortical degeneration. As the main pathological lesion in Ramsay Hunt syndrome is in the dentate nucleus and its efferent pathway, the present results are in conformity with the experimental finding that the premotor and motor cortices receive strong inputs from the cerebellar efferent system.

Do thalamic regions which project to rostral primate motor cortex receive spinothalamic input?

The purpose of this study was to examine whether spinal pathways terminate in regions of the primate thalamus which project directly to the motor cortex. In order to examine this issue we employed a 'double labeling' procedure which utilized transport of both anterograde and retrograde tracers in the same macaque. One tracer substance was injected into the cervical spinal cord and the other was injected into the rostral zone of primary motor cortex. We observed no overlap of spinothalamic terminations and thalamic regions which project to the motor cortex. Thus, our results provide no anatomical support for a direct thalamic relay of peripheral afferent input to the motor cortex of primates.

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 thalamic relations of the caudal inferior parietal lobule and the lateral prefrontal cortex in monkeys: divergent cortical projections from cell clusters in the medial pulvinar nucleus

The thalamic relations of the caudal inferior parietal lobule and the dorsolateral prefrontal cortex in monkeys have been investigated with both anterograde and retrograde neuroanatomical tracing techniques. The results of these experiments indicate that the medial pulvinar nucleus (Pul.m.) is the principal thalamic relay to the gyral surface of the caudal inferior parietal lobule (area 7a). Within the Pul.m. there are two or three disklike aggregates of neurons which project to area 7a; these disklike neuronal aggregates are oriented from dorsomedial to ventrolateral and extend over most of the rostrocaudal extent of the nucleus. Within these disks there are rodlike clusters of neurons which are elongated in the rostrocaudal dimension of the thalamus, and which project in a topographically ordered manner to area 7a. Thus, the more rostrally located neurons within the Pul.m. disks project to more rostral parts of area 7a and, conversely, the more caudally located neurons project to the caudal part of this cortical field. Similarly, the medial part of each disk projects to the lateral part of area 7a while the laterally placed neurons project to the medial part of the cortical field. In addition to its input from the Pul.m., area 7a is also reciprocally connected with the magnocellular division of the nucleus ventralis anterior, with the nuclei which abut upon the medullary capsule of the laterodorsal nucleus, and with the suprageniculate nucleus and the nucleus limitans. The cortex on the lateral bank of the intraparietal sulcus (the so-called lateral intraparietal area, LIP) projects principally to the lateral pulvinar nucleus (Pul.l) of the thalamus rather than to Pul.m. Area LIP has been found to project to the pregeniculate nucleus, the zona incerta, the anterior pretectal nucleus, and the superior colliculus. Area 7a projects to none of these structures, but it does project to the posterior pretectal nucleus. The thalamic relations of the neighboring cortical regions, such as the prelunate gyrus and area 7b, are also distinct from those of area 7a. It thus seems that the prelunate gyrus is primarily interconnected with the Pul.l., and area 7b with the oral pulvinar nucleus. Taken together these different subcortical relationships provide further evidence for the view that the caudal inferior parietal lobule is not a homogeneous cortical area, but is composed of a number of subsidiary fields. The projection from the Pul.m. to the lateral prefrontal cortex arises from disklike aggregates of neurons, similar in their orientation to the neuronal disks that project to area 7a.(ABSTRACT TRUNCATED AT 400 WORDS)

Responses of precentral cells during cooling of post-central cortex in conscious monkeys

A cooling plate was implanted over the forelimb representation in area 2 of the post-central region of cerebral cortex in two monkeys. Recordings were made of the discharges of thirty-seven movement-related neurones (thirty-four precentral and three post-central) in the forelimb motor representation of the cerebral cortex during active and passively imposed limb movements before, during and after cooling area 2 and local surrounding regions. Perfusion of the cooling plate with ice-cooled water for 3-5 min caused marked clumsiness of the conscious animal's forelimb movement and anaesthesia of the contralateral hand. Cooling of area 2 did not reduce the responses of area 4 cells to passive joint movements, nor did it alter the over-all pattern of activity of these cells during self-initiated lever pulling while that could still be performed. Cooling of area 2 did cause a significant increase in background cellular discharge in area 4 while the animal was at rest. Afferent impulses which are generated by passive joint movement and which have been shown to influence cells in area 4 of the conscious monkey at short latencies are probably not transmitted through cortico-cortical connexions from area 2.

How do the basal ganglia and cerebellum gain access to the cortical motor areas?

We have used retrograde transport of wheat germ agglutinin conjugated to horseradish peroxidase to examine the origin of the thalamic input to the two premotor areas with the densest projections to the motor cortex. These are: arcuate premotor area (APA) and the supplementary motor area (SMA). Retrograde transport demonstrated that the two premotor areas and the motor cortex each receive thalamic input from separate, cytoarchitectonically well-defined subdivisions of the ventrolateral thalamus. According to the nomenclature of Olszewski (1952), input to the APA originates largely from area X; input to the SMA originates largely from the pars oralis subdivision of the nucleus ventralis lateralis (VLo); and that to the motor cortex is largely from the pars oralis subdivision of the nucleus ventralis posterior lateralis (VPLo). These observations, when combined with prior studies on the termination of various subcortical efferents in the thalamus, lead to the following scheme of projections: rostral portions of the deep cerebellar nuclei project to motor cortex via VPLo, caudal portions of the deep cerebellar nuclei project to the APA via area X; and the globus pallidus projects to the SMA via VLo. Thus each thalamocortical pathway is associated with a distinct subcortical input.

Connections of area 2 of somatosensory cortex with the anterior pulvinar and subdivisions of the ventroposterior complex in macaque monkeys

The principal goal of the present study was to determine the thalamic connections of area 2 of postcentral somatosensory cortex of monkeys. The placement of injections of anatomical tracers (horseradish peroxidase, wheat germ agglutinin, or 3H-proline) was guided by extensive microelectrode maps of cortex in the region of the injection site. These maps identified the body parts represented in the cortex included in the injection site, and provided information about the physiological boundaries of area 2, which was related later to the cortical architecture. Most injections were placed in the representation of the hand in area 2, which was highly responsive to cutaneous stimuli and could be mapped in detail. Injections were also placed in other parts of area 2, area 1, or area 5, and some injections involved more than one area. As other investigators have determined, regions of retrograde and anterograde thalamic label overlapped, demonstrating that connections with cortex are reciprocal. Injections completely confined to area 2 consistently produced label in two locations: the anterior pulvinar (Pa) and a dorsal capping zone of the ventroposterior complex that we term the ventroposterior superior nucleus (VPS). Single restricted injection sites resulted in one region of label in VPS, and multiple foci of label in Pa. In some cases where the injection was confined to the representation of the hand in area 2, label was also found more ventrally in the ventroposterior complex in ventroposterior nucleus proper (VP). Thus, area 2 receives input from Pa, VPS, and, at least in some locations and individuals, VP. Injections of tracers into area 1 confirmed previous findings that area 1 is densely interconnected with VP. In addition, there appear to be sparse connections with VPS. There was no evidence of connections with Pa. Evidence from injection sites that extended from area 2 into areas 5 and 7, and from injection sites in area 5, indicates that the lateral posterior nucleus (LP) projects to rostral areas 5 and 7. The results support the conclusion that area 2 is a functionally distinct subdivision of somatosensory cortex, and indicate that area 2 has thalamic connections that are characteristic of both "sensory" (VP and VPS) and "association" (Pa) cortical fields.

The frontal agranular cortex and the organization of purposeful movements

A critical review of the traditional concepts of cortical association and motor areas is followed by a description of the functional organization and intrinsic and extrinsic cortical connectivity of the arcuate premotor area (APA). It is concluded that the frontal cortical organization of externally triggered purposeful movements is made possible by the associative character of Brodmann's area 6 and by its peculiar pattern of intra-areal connectivity.

Organization of the nigrothalamocortical system in the rhesus monkey

The nigrothalamocortical connections and their topography were analyzed by autoradiography and double or triple retrograde labeling with the fluorescent dyes Fast Blue, Diamidino Yellow, and Propidium Iodide. Injections of tritiated leucine into different parts of the substantia nigra (SN) revealed that the medial SN projects to the medial magnocellular subdivisions of the ventral anterior (VAmc) and mediodorsal (MDmc) nuclei of the thalamus while the lateral SN projects to the more lateral and more posterior part of the VAmc, and the paralaminar, parvicellular, and densocellular subdivisions of the mediodorsal nucleus (MDmf, MDpc, and MDdc). With the exception of the MDmf, terminal areas observed in the mediodorsal nucleus were in the form of scattered clusters of grains. Analysis of the thalamus in cases with fluorescent dye injections into the lateral orbital gyrus (Walker's area 11), principal sulcus (area 46), anterior bank of the arcuate gyrus (areas 8 and 45), supplementary motor area (area 6), and motor cortex (area 4) revealed topographic organization of the nigrothalamocortical projection system. The parts of the VAmc and MDmc which receive afferents from the medial part of the SN in turn project to the most anterior regions of the frontal lobe including principal sulcus and orbital cortex. The lateral posterior VAmc, MDmf, MDpc, and MDdc, all of which receive afferents from the lateral part of the SN; project to more posterior regions of the frontal lobe including, in addition to the principal sulcus, the frontal eye field and also areas of the premotor cortex. These findings indicate that the SN has preferential targets in the thalamus and cerebral cortex which are segregated from those of the globus pallidus and cerebellum. Whereas the motor cortex is the primary target of cerebellar output (Asanuma et al., '83b), and the premotor cortex is the target of pallidal output (Schell and Strick, '84), the SN output appears to be directed more anteriorally--to the prefrontal cortex.

Cerebello-cortical linkage in the monkey as revealed by transcellular labeling with the lectin wheat germ agglutinin conjugated to the marker horseradish peroxidase

The possibility of a cerebellar linkage, via the thalamus with medial area 6 of the cerebral cortex was further explored in the present experiments (cf. preceding companion paper). It was found that HRP conjugated to the lectin wheat germ agglutinin injected into motor cortical areas was transported beyond the thalamus to the contralateral intracerebellar nuclei when the survival time was 4-7 days. It is suggested that the labeling in the deep cerebellar nuclei occurred via the thalamic relay where cerebellofugal fibre terminals had taken up the marker substance released by corticothalamic fibre terminals or by the retrogradely labeled thalamic perikarya. In general, transcellular labeling of perikarya was weaker than retrograde labeling in the thalamic cells. Some of the nuclear zones in the cerebellum showed relatively dense granulations of the reaction product; in other zones only cells with few granules were seen, and large parts of the nuclei were not labeled at all. The topography of secondary labeling in the cerebellar nuclei depended on the cortical injection sites. In all cases, most labeling was found in the contralateral dentate nucleus. The interposed nucleus received a fair amount of heavy labeling only in the precentral arm and face cases. Very little labeling was seen in the fastigial nucleus and in the cerebellar nuclei ipsilateral to the cortical injections. A somatotopic organization of secondary labeling was noted in the precentral cases with the face being represented caudally, the hindlimb rostrally and the arm between the face and the hindlimb representation. This is in agreement with previous anatomical and electrophysiological investigations. These observations thus lend support to the conclusion that the SMA receives a transthalamic input not only from the basal ganglia but also from the cerebellum, especially from its lateral, neo-cerebellar portion.

The thalamic connections with medial area 6 (supplementary motor cortex) in the monkey (macaca fascicularis)

The interrelationship of medial area 6 (supplementary motor area) with the thalamus was investigated by means of anterograde and retrograde tracing methods. Nine monkeys were prepared for autoradiography or histochemistry with the marker HRP conjugated to the lectin wheat germ agglutinin. Three of the monkeys received injections into the precentral cortex for comparison. Previous observations were confirmed that the thalamic relays to the motor areas are organized as crescent-shaped lamellae which transgress cytoarchitectonic boundaries. The thalamic VA-VL complex receiving fibres from areas 4 and medial area 6 also sends fibres to these same areas. The thalamic relay to medial area 6 comprised the following subdivisions: VLo, VLc, area X of Olszewski, VLm and, to a smaller extent VA. Labeling (mostly anterograde only) was also prominent in some thalamic compartments outside the 'motor' thalamus: R, CL, CM-Pf, MD, LP, PULo. It was noted that rostral and caudal injections into the medial area 6 resulted in different thalamic labeling: The rostral portion was found to be related mainly with VApc, area X and VLc, the central portion with VLo, and the caudal portion with VLc/VLo. This structural inhomogeneity may reflect also a functional rostro-caudal differentiation of the medial area 6. The thalamic territory projecting to the precentral cortex is separate from the above relay and includes principally VPLo. The present anatomical labeling study is in agreement with the conclusion of Schell and Strick (1984) that the SMA, especially its central portion, is an important target of basal ganglia outflow via the thalamic relay VLo. In addition consistent labeling was also found in thalamic subdivisions (area X, VLc) which had been found to receive cerebellar fibres.

The distribution and topographical organization in the thalamus of anterogradely-transported horseradish peroxidase after spinal injections in cat and raccoon

The distribution of anterogradely-transported horseradish peroxidase (HRP) was examined in the rostral mesencephalon and thalamus of cats and raccoons that had received injections of HRP in the cervical and/or lumbosacral enlargements of the spinal cord. Labeling was consistently observed in a large number of loci. All regions previously identified as targets of spinomesencephalic or spinothalamic fibers were included. Evidence of topographical organization was obtained in several regions. Adjacent fields of labeling were often separable on the basis of the distribution, appearance and topographical organization of the labeling. Subject to the methodological constraints imposed by the possibilities of transneuronal and/or collateral labeling, we conclude that a wide variety of loci in the thalamus receive direct spinal input. The organization of these projections suggests that each terminal region may be associated with different aspects of spinal cord function.

Synaptic organization of the cerebello-thalamo-cerebral pathway in the cat. II. Input-output organization of single thalamocortical neurons in the ventrolateral thalamus

Input-output neural organization of single thalamocortical (T-C) neurons in the ventrolateral nucleus (VL) of the thalamus was investigated using an intracellular recording technique in the anesthetized cat. Stimulation of the dentate (DN) and the interpositus (IN) nuclei produced monosynaptic unitary EPSPs of large amplitude in T-C neurons projecting to the motor cortex or area 6 over the entire mediolateral region of VL. The thalamic projections from DN and IN are very wide and there is a considerable overlap between the dentate and the interpositus projection areas in VL. And in this overlapping area, a considerable number of T-C neurons (50%) receive inputs from both DN and IN. More than 40% of T-C neurons were antidromically activated from widely separated electrodes in the motor cortex, indicating that the cortical arbolization of single T-C neurons is very wide and the number of these neurons with widely divergent projections is considerably large.

Organization of thalamic projections in the nucleus accumbens and the caudate nucleus in cats and its relation with hippocampal and other subcortical afferents

The organization of thalamic projections in the nucleus accumbens (NA) and the caudate nucleus of cats and its relation to other subcortical striatal afferents were studied with a retrograde tracing technique by use of lectin-conjugated horseradish peroxidase. The study showed that the paraventricular and medial parafascicular nuclei (PF) of the thalamus project to the medial NA and the parataenial and medial PF project to the lateral NA. The ventral tegmental area and substantia nigra pars dorsalis (SNpd) project to medial and lateral NA. The midline thalamic nuclei, rostral intralaminar nuclei, ventroanterior nucleus, medial and lateral PF, lateral posterior complex, and nucleus limitans project to medial caudate nucleus. The most medial substantia nigra pars compacta (SNpc) and rostral SNpd project to medial caudate nucleus. The center median, ventrolateral, and the central lateral nuclei of thalamus, SNpc, and SNpd project to lateral caudate nucleus. These results suggest that the thalamic and subcortical nuclei known to connect with the limbic and frontal cortices project to NA and medial caudate nucleus. Those thalamic nuclei connected with the motor system project to lateral caudate nucleus. The hippocampus projects selectively to medial NA. The amygdala, raphe, and other mesencephalic nuclei project only to NA and medial caudate nucleus. The organization of hippocampal, amygdala, and other subcortical afferents suggests that NA and caudate nucleus can be separated into medial "limbic" and lateral nonlimbic "sensory-motor" compartments. A brief review of the distribution pattern of some neurotransmitters, neuropeptides, and their receptors and behavior studies provides additional support to the concept that the striatum can be divided into several subcompartments.

Cortical and brain stem afferents to the ventral thalamic nuclei of the cat demonstrated by retrograde axonal transport of horseradish peroxidase

After horseradish peroxidase (HRP) injections into various parts of the ventral thalamic nuclear group and its adjacent areas, the distribution of labeled neurons was compared in the cerebral cortex, basal ganglia, and the brain stem. The major differences in distribution patterns were as follows: Injections of HRP into the lateral or ventrolateral portions of the ventroanterior and ventrolateral nuclear complex of the thalamus (VA-VL) produced retrogradely labeled neurons consistently in area 4 gamma (lateral part of the anterior and posterior sigmoid gyri, lateral sigmoid gyrus and the lateral fundus of the cruciate sulcus), the medial division of posterior thalamic group (POm), suprageniculate nucleus (SG) and anterior pretectal nucleus ipsilaterally, and in the nucleus Z of the vestibular nuclear complex bilaterally. Injections into the medial or dorsomedial portion of the VA-VL resulted in labeled neurons within the areas 6a beta (medial part of the anterior sigmoid gyrus), 6a delta (anterior part of ventral bank of buried cruciate sulcus), 6 if. fu (posterior part of the bank), fundus of the presylvian sulcus (area 6a beta), medial part of the nucleus lateralis posterior of thalamus and nucleus centralis dorsalis ipsilaterally, and in the entopeduncular nucleus (EPN) and medial pretectal nucleus bilaterally. Only a few neurons were present in the contralateral area 6a delta. After HRP injections into the ventral medial nucleus (VM), major labeled neurons were observed in the gyrus proreus, area 6a beta (mainly in the medial bank of the presylvian sulcus), and EPN ipsilaterally, and in the medial pretectal nucleus and substantia nigra bilaterally. Following HRP injections into the centre médian nucleus (CM), major labeled neurons were found in the areas 4 gamma, 6a beta, and the orbital gyrus ipsilaterally, and in the EPN, rostral and rostrolateral parts of the thalamic reticular nucleus, locus ceruleus, nucleus reticularis pontis oralis et caudalis and nucleus prepositus hypoglossi bilaterally. The contralateral intercalatus nucleus also possessed labeled neurons. With HRP injections into the paracentral and centrolateral nuclei, labeled neurons were observed in the gyrus proreus and the cortical areas between the caudal presylvian sulcus and anterior rhinal sulcus ipsilaterally, and in the nuclei interstitialis and Darkschewitsch bilaterally. Minor differences in the distribution pattern were observed in the superior colliculus, periaqueductal gray, mesencephalic and medullary reticular formations, and vestibular nuclei in all cases of injections.

An HRP study of hypothalamo-cerebellar and cerebello-hypothalamic connections in squirrel monkey (Saimiri sciureus)

This study describes the distribution of labeled hypothalamic neurons in squirrel monkey following pressure injections of horseradish peroxidase (HRP) into cerebellar cortex and the pattern of labeling in the cerebellar nuclei subsequent to iontophoretic injections localized in the hypothalamus. Two types of HRP (HRP and a wheat germ agglutinin conjugate, HRP-WGA) were used as tracers; tetramethylbenzidine was the chromogen. Retrogradely filled neurons were found in lateral (LHAr) and posterior (PHAr) hypothalamic areas, and in the lateral mammillary (LMNu) and supramammillary (SMNu) nuclei following injections into ansiform and paramedian lobules and into the paraflocculus. Labeled cells were occasionally seen in the medial mammillary nucleus (parafloccular cases) and among fascicles of the mammillothalamic tract (all posterior lobe cases) immediately above the medial nucleus. After injections into the anterior lobe, labelling was again found in the LHAr, PHAr, LMNu, and SMNu. In addition, retrogradely filled cells were present in ventromedial, dorsomedial, and dorsal hypothalamic nuclei and in the dorsal hypothalamic area. Labeled cells were occasionally found among fascicles of the fornix along its intrahypothalamic course. In general, labeling extends into slightly more rostral hypothalamic levels in anterior lobe cases when compared to posterior lobe experiments. We interpret these data as indicating that some hypothalamic neurons project directly to the cerebellar cortex (i.e., hypothalamo-cerebellar fibers); this projection is bilateral with an ipsilateral preponderance. In experiments with injections of HRP-WGA into the cerebellar nuclei, anterogradely filled axons were traced into the contralateral PHAr and LHAr; this was suggestive of a direct cerebello-hypothalamic projection. Following iontophoretic injections localized in the LHAr and the medial mammillary nucleus, labeling was seen in the medial (NM), posterior interposed (NIP), and lateral (NL) cerebellar nuclei; this is essentially a contralateral projection. Retrogradely labeled cells were found in the rostral and ventral NM, the ventral and dorsocaudal NL, and diffusely throughout the NIP. On the basis of the known distribution of cerebello-thalamic fibers and other criteria, these labeled cells are representative of a true cerebello-hypothalamic projection. It is suggested that the cerebellum, through these pathways, may have a relatively direct influence on visceral centers in the brainstem and spinal cord.

Levodopa-induced dyskinesia and thalamotomy

Levodopa-induced dyskinesia of the limbs in thirteen cases of Parkinsonism, which was choreic, ballistic or dystonic in type, was alleviated almost completely by stereotaxic surgery using a microelectrode technique for the ventralis oralis anterior and posterior nuclei of the thalamus, but much less by the ventralis intermedius nucleus. Control of levodopa-induced dyskinesias by thalamic lesions in the course of routine treatment of Parkinsonism is discussed.

The somatotopic organization of the ventroposterior thalamus of the squirrel monkey, Saimiri sciureus

Multiunit microelectrode mapping techniques were used to investigate the organization of the somatosensory thalamus in squirrel monkeys. Receptive fields and response characteristics were determined for closely spaced recording sites along arrays of electrode penetrations that passed through the ventral thalamus dorsoventrally, rostrocaudally, or lateromedially. The results were related to thalamic architecture and led to the following conclusions: (1) A large, single, systematic representation of the body surface occupied most or all of the ventroposterior nucleus, VP. The nucleus was further defined by a distinct cytoarchitectonic appearance, produced by densely packed, deeply stained neurons. (2) Recording sequences in VP were characterized by (a) abrupt shifts in receptive field locations over short recording distances indicating that the electrode had crossed discontinuities or folds in the representation, (b) long sequences of overlapping receptive fields indicating regions of continuous representation and the maintenance of adjacency in the map, and (c) similar receptive field locations for sites along the trajectory of a penetration indicating regions of isorepresentation. Major somatotopic discontinuities were associated with crossing narrow cell-poor laminae that partially divided VP into subnuclei related to the hand, foot, trunk, and tail in lateral VP and the face in medial VP. Somatotopic discontinuities occurred for electrode penetrations in all three planes, but discontinuities were greater and more frequent for lateromedial electrode penetrations. Lines of isorepresentation and gradual change were most extensive in the rostrocaudal and dorsoventral planes. We hypothesize that the disruptions, regions of isorepresentation, and regions of gradual change result from the thickening, splitting, and folding of a two-dimensional representation of the skin surface to occupy a three-dimensional volume. (3) The magnifications of various skin surfaces in VP were variable so that some skin surfaces, especially the tips of the digits, occupied relatively large portions of the nucleus, while other skin surfaces such as the trunk activated little tissue. It appeared that regions of isorepresentation varied in extent according to magnification factor and position in the map. (4) Within VP, neurons could be classified as slowly adapting or rapidly adapting to maintained skin indentation. Each type of neuron formed small groups or clusters in the nucleus so that several successive recording sites typically encountered one type before a sequence of the other type was observed.(ABSTRACT TRUNCATED AT 400 WORDS)

Anatomical evidence for segregated focal groupings of efferent cells and their terminal ramifications in the cerebellothalamic pathway of the monkey

Patterns of termination of the cerebellothalamic pathway were investigated using anterograde tracing techniques. The thalamic projections from each of the deep cerebellar nuclei are topographically organized in two and possibly in three dimensions. First, the caudo-rostral cerebellar nuclear dimension is mapped onto the mediolateral dimension within the cell-sparse ventral lateral thalamic region (VPLo, VLc, VLps, and nucleus X). By correlating this topographic ordering with the previously established lamellar organization of the cell-sparse thalamic region a somatotopy is inferred within the deep cerebellar nuclei, with caudal body parts represented anteriorly and rostral body parts represented posteriorly in each nucleus. A second topography consists of the mapping of the mediolateral dimension of the dentate and interpositus nuclei onto the ventrodorsal dimension of the lamellae in the thalamus. Since the thalamic connections with motor cortex predict a somatotopic organization with distal body parts ventral and axial parts dorsal in thalamus, each cerebellar nucleus should, therefore, represent axial body parts laterally and distal parts medially. A third mapping dimension is shown for the dentatothalamic projection: dorsal parts of the dentate nucleus project posteriorly within the cell-sparse thalamic region, and ventral parts project anteriorly. The significance of this as regards representation of the body is not known. Subsidiary foci of terminations within the cell-sparse thalamic region are visible following tritiated amino acid injections into each of the deep cerebellar nuclei. Following dentate injections these foci appear as anteroposteriorly elongated, rod-like aggregations of terminations which are similar to the rod-like aggregations of thalamocortical relay cells which have been demonstrated following focal injections of horseradish peroxidase into the motor cortex. The interpositothalamic and the fastigiothalamic terminations are elongated and appear as focal clusters in all planes of section. The interpositothalamic clusters are distributed within posterodorsally curving planar sheets. An anterograde double labeling technique, using a combination of the autoradiographic technique with the axonal degeneration technique, was used to investigate the interrelations of the terminations from different nuclei and from different parts of the same nucleus. Rods from different parts of the dentate nucleus terminate independently of one another. Dentatothalamic rods and interpositothalamic clusters, though interdigitating within the same thalamic region, do not overlap. This topographic and modular organization of the cerebellothalamic pathway suggests that the cerebellar input may reflect both the somatotopic and the columnar organization of the motor cortex.

Cytoarchitectonic delineation of the ventral lateral thalamic region in the monkey

The cytoarchitecture of the ventral lateral region of the primate thalamus has been appraised in the frontal, parasagittal and horizontal planes. A morphologically distinct region, possessing a sparse and diffuse distribution of large and small neurons is identified. The region includes several nuclei previously separately named by Olszewski. These are nuclei VPLo, VLc, X, VLps, and some cellular extensions into the VLo nucleus. The whole zone is continuous, and it is shown that no clear separation exists between any of the previously identified subnuclei. Connectional grounds are given for suggesting that this region should be considered as a common cerebellar relay nucleus to motor cortex. Morphological criteria for distinguishing the cell-sparse nucleus from adjacent nuclei are given. These cytological criteria provide a basis for the experimental analysis of cortical and subcortical connectivity of the ventral lateral thalamic region. Close attention was paid to the border between the VPLo nucleus and the VPLc nucleus. VPLc is separated from VPLo by a clear border, and no transitional zone can be detected in the parasagittal or horizontal planes. Previous ambiguities in the delineation of the VPLo-VPLc border probably stem from analysis in the frontal plane, in which the border is not clear.