Ventralis Posterior Lateralis Research Articles

The terminations of the spinothalamic tract in the cat

The termination sites of the spinothalamic tract (STT) in the cat have been examined using the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Cats which received an injection of WGA-HRP at the spinal cervical level (C7–C8) displayed anterograde labelling in the ventral posterior lateral (VPL), ventrolateral, lateral posterior, limitans, suprageniculate, medial geniculate pars magnocellularis, central lateral, paracentral, centrum medianum, submedius, central medial, reuniens, rhomboid and periventricular thalamic nuclei. Lumbar injection (L2–L3) produced a similar although less intense pattern of labelling, with only the VPL displaying an obvious topological organization. Although the STT terminations in the cat appear to be less dense than those observed in the rat or monkey the present results demonstrate that in the cat a widely variety of thalamic nuclei receive a direct STT projection and that the cat VPL, like rat, monkey and man receives a direct STT input.

On the Question of the Ventral Intermediate Nucleus in Primate Thalamus

Cytoarchitectural and hodological evidence is given which supports the contention that the large-celled, intermediate zone between ventral posterior lateral (VPL) and ventral lateral (VL) nuclei is an independent thalamic nucleus, designated as the ventral intermediate nucleus (Vim), in the thalamic ventral tier of <i>Galago senegalensis. </i>Observation of Nissl-stained sections indicates that Vim contains cells which are larger than those in VL and more scattered in appearance than those in VPL. Fink and Heimer stained brains show that after cord hemisection the spinothalamic degeneration in Vim is sparse in amount and scattered in organization as opposed to the 'bursts' of dense degeneration in VPL. Following cortical injection of horseradish peroxidase, thalamocortical relay cells in Vim are distinct from those in VPL in both size and organization. Consequently, this study corroborates previous results on another primate and suggests that a distinct VPL-VL transitional nucleus, Vim, is present in the ventral tier of the prosimian primate <i>Galago senegalensis. </i>The functional significance of Vim and its possible role in the evolution of primate locomotor behavior are discussed.

On the Question of the Ventral Intermediate Nucleus in Primate Thalamus (Part 2 of 2)

Cytoarchitectural and hodological evidence is given which supports the contention that the large-celled, intermediate zone between ventral posterior lateral (VPL) and ventral lateral (VL) nuclei is an independent thalamic nucleus, designated as the ventral intermediate nucleus (Vim), in the thalamic ventral tier of <i>Galago senegalensis. </i>Observation of Nissl-stained sections indicates that Vim contains cells which are larger than those in VL and more scattered in appearance than those in VPL. Fink and Heimer stained brains show that after cord hemisection the spinothalamic degeneration in Vim is sparse in amount and scattered in organization as opposed to the 'bursts' of dense degeneration in VPL. Following cortical injection of horseradish peroxidase, thalamocortical relay cells in Vim are distinct from those in VPL in both size and organization. Consequently, this study corroborates previous results on another primate and suggests that a distinct VPL-VL transitional nucleus, Vim, is present in the ventral tier of the prosimian primate <i>Galago senegalensis. </i>The functional significance of Vim and its possible role in the evolution of primate locomotor behavior are discussed.

Spinal cord evaluation by cortical evoked responses.

In ten monkeys, selective segmental lesions of the dorsal columns at the upper thoracic and middle cervical levels resulted in almost total attenuation of the cortical evoked potential responses to peripheral nerve stimulation. Conversely isolated segmental dorsal column preservation showed intact transmission of the evoked responses at rostral spinal cord, nucleus ventralis posterior lateralis, and cortical levels. Responses recorded from the intralaminar thalamic nuclei in the region of nucleus centrum medianum were unaffected by dorsal column ablation, but were markedly attenuated following bilateral ventral column ablation.

Early somatosensory evoked potentials

the early somatosensory evoked potential secondary to median nerve stimulation in the human had an onset latency of 9–12 msec when recorded from scalp electrodes at vertex-to-mastoid, vertex-to-inion or at the base of the skull. Similar latencies were observed from responses recorded over the cervical dorsal columns during neurologic surgery. A latency difference of 1.5 msec was observed between the early response and the responses recorded from the junction of medial lemniscus and nucleus ventralis posterior lateralis of the thalamus during human stereotaxic surgery. Cervical cord transections and transection at the mid-pontine levels of the monkey showed that the evoked potential was due to generators between these levels. Depth recording of the monkey indicate that the early evoked potential originates in the region of dorsal column nuclei, while the later components are secondary to generators in cerebral cortex.

An autoradiographic analysis of the efferent connections from premotor and adjacent prefrontal regions (areas 6 and 9) in macaca fascicularis.

The efferent connections from area 6 and adjacent regions of area 9 were investigated in 9 adult monkeys (Macaca fascicularis) using the autoradiographic technique. Injection fields throughout these regions projected ipsilaterally to area 7 in the parietal lobe, n. caudatus, claustrum, n. ventralis anterior, n. parafascicularis, n. medialis dorsalis, n. reticularis thalami, colliculus superior, griseum centralis, griseum pontis and n. reticularis tegmenti pontis. The dorsolateral and medial aspects of areas 6 and 9 projected to the caudal cingulate gyrus, n. ventralis lateralis pars caudalis and n. interstitialis of Cajal. Axons originating in the ventrolateral cortex of areas 6 and 9 terminated in the orbital cortex. Projections arising from area 6 were traced to area 4, into the ventral bank of the rostral cingulate sulcus, to putamen, n. centralis superior lateralis, area X and its caudal continuation within n. ventralis posterior lateralis pars oralis, to n. ruber pars parvocellularis as well as the bulbar reticular formation. Adjacent prefrontal areas projected to the medial aspect of area 24, to areas 19, 20, 21 and 49/27 and to parts of the lateral thalamic nuclear group. This prefrontal projection pattern was in many respects also seen in cases injected into the dorsolateral portion of area 6, while its medial and ventrolateral subdivisions showed additional projections to n. ventralis medialis, the medial parts of centrum medianum as well as spinal and prorhinal projections, respectively.Furthermore, extensive bilateral connections were found within the frontal lobe, to basal ganglia, n. parafascicularis, n. centralis thalami, n. ruber, griseum pontis, n. reticularis tegmenti pontis, bulbar reticular formation and, more selectively, to colliculus superior and n. medialis dorsalis. Evidence was also presented for direct prefrontal connections to amygdala and corticonigral projections arising from areas 6 and 9. The results are discussed with respect to the intermediate position of area 6 between primary motor and prefrontal cortex as well as to differences of projection patterns within area 6 itself and, in particular, the supplementary motor area.

Effect of dihydroergotoxine on thalamic- and pyramidal-evoked responses in the cat under transient ischemia.

Iterative transient cerebral ischemic aggressions were produced by interrupting the blood flow in both common carotid arteries for 2 min in unanesthetized cats whose basilar artery has been permanently ligated. The influence of ischemia upon cerebral cortex was assessed by recording electrocortical activity (ECoG), indirect pyramidal tract response (I) and thalamic (nucleus ventralis posterior lateralis) evoked potentials induced by electrical stimulation of the contralateral forelimb. In control animals, the repetition of ischemic episodes delayed the recovery of the indirect pyramidal tract response, demonstrating an impairment of cortical excitability. Otherwise, cerebral ischemia induced an increase of thalamic-evoked responses. This phenomenon appears to result from the suppression of inhibitory corticofugal influence. The effects of dihydroergotoxine mesylate (DHET) upon these responses have been evaluated after intravenous administration (0.05, 0.3 and 0.6 mg/kg). DHET did not significantly modify the disappearance times of the ECoG and of the I cortico-pyramidal response or the recovery delay of the ECoG, but it improved the recovery time of I and inhibited the ischemic increase of the thalamic-evoked potential (0.3 and 0.6 mg/kg). These results suggest that DHET exerts a protective effect on the ischemic cerebral cortex in the experimental conditions used.

Projections from the primary somatosensory cortex to basal ganglia and thalamus in the monkey

Radioactive amino acids were injected into the postcentral cortex (areas 3, 1 and 2) in 6 monkeys (Macaca fascicularis). Fibers were traced to the ipsilateral putamen, to Olszewski's n. ventralis posterior lateralis pars caudalis, n. ventralis posterior medialis and inferior, to n. pulvinaris oralis, n. suprageniculatus and corpus geniculatum mediale pars magnocellularis. Furthermore, there were faint postcentral projections to claustrum, n. caudatus, n. centralis lateralis, n. centrum medianum, zona incerta and with respect to the postcentral face region to n. medialis dorsalis pars multiformis. Discrepancies with earlier findings were discussed and comparison was made between pre- and postcentral target regions.

Neural pathway mediating somatic evoked responses in the caudate nucleus of cats

The course of somatic afferents to caudate nucleus (CN) was investigated. In curarized cats discrete lesions in intralaminar nuclei, n. centralis medialis (NCM) affect evoked responses (ER) in CN to radial nerve stimulation. NCM lesions totally abolish these somatic responses, while after subthalamic lesions ER appear only when a high stimulus intensity is used. Lesions in the specific relay nuclei, ventralis posterior lateralis (VPL) have no effect on somatic ER in CN. Barbiturates (10 mg/kg) abolish somatic ER in CN. Stimulation of the ponto-mesencephalic reticular formation (RF) in a region where visual and somatic responses are recorded shows lowest threshold values for eliciting evoked responses in NCM and CN. The potentials in CN to RF stimulation are restricted to this nucleus and disappear in the internal capsule.

Anatomical analysis of ventrolateral thalamic input to primate motor cortex.

1. The origin and topographical organization of input to the arm area of the primate motor cortex from the ventrolateral thalamus were examined using the method of retrograde transport of horseradish peroxidase (HRP). 2. A thin, continuous slab of labeled neurons was found in the ventrolateral thalamus followingmultiple injections of HRP into the arm area of the motor cortex. The slab of labeled neurons was flanked, medially and laterally, by groups of unlabeled neurons. 3. The origin of ventrolateral thalamic input was more extensive than previously thought. Labeled neurons were found from A10.0 to A6.0 and occurred in three ventolateral thalamic subdivisions: ventralis lateralis pars oralis (VLo), ventralis lateralis pars caudalis (VLc), and ventralis posterior lateralis pars oralis (VPLo). For simplicity this region containing labeled neurons has been termed the ventrolateral thalamic (VL) arm area. 4. Injections of HRP into the somatic sensory cortex indicated that the thalamic regions which project to the somatic sensory cortex are separate from the VL arm area. 5. The distribution of labeled neurons following single injections of HRP into different regions of the motor cortex arm area indicated that the VL arm area is topographically organized, particularly its caudal part. Ventral regions of the VL arm area were labeled following HRP injections into motor cortex regions adjacent to the central sulcus where the representation of largely distal musculature is localized. Dorsal regions of the VL arm area were labeled following HRP injections into motor cortex regions more rostral to the central sulcus where the representation of more proximal musculature is localized. 6. A larger region of the VL arm area was labeled following HRP injections adjacent to the central sulcus than following the more rostral motor cortex injections. This suggests that, like the arm area of the motor cortex, more of the VL arm area is allotted to the representation of distal than proximal musculature. 7. Following very small cortical HRP injections, isolated labeled thalamic neurons were diffusely scattered throughout a 3-mm rostrocaudal extent of the VL arm area. In addition, a small focal cluster of labeled thalamic neurons was also seen. The labeled cluster was limited to 0.5 mm rostrocaudally and 300 mum in width. The focal distribution of labeled thalamic neurons suggests that aspects of a point to point organization may exist in the connection between VL and the motor cortex arm area.

Representation of vestibular afferents in somatosensory thalamic nuclei of the squirrel monkey (Saimiri sciureus).

1. In awake squirrel monkeys the thalamus was investigated for neuronal responses to vestibular, auditory, visual, proprioceptive, and exteroceptive somatosensory stimulation. The vestibular representation in the thalamus was focused.2. Units responding to electrical vestibular stimulation were found to be scattered within thalamic nuclei receiving somatosensory afferents.3. Ventrobasal neurons have previously been considered place and modality specific. The present data suggest exceptions to this belief. Vestibular input converges with somatotopically organized proprioceptive afferents on neurons in the nucleus ventralis posterior lateralis, pars oralis (identical to nucleus ventralis intermedius), as well as in the posterior portion of the caudal part of the same nucleus. Convergence of both modalities was also found in other nuclei, mainly belonging to the posterior nuclear group, where auditory convergence was also demonstrated.4. Of the vestibular cells in the nucleus ventralis posterior lateralis, 23% projected to the sensorimotor cortex, some with collaterals to both pre- and postcentral gyri.

Thalamic projections from the precentral motor cortex in Macaca fascicularis

Radioactive amino acids were injected into area 4 in 7 monkeys ( Macaca fascicularis). Ipsilateral corticothalamic projections were traced to Olszewski's nucleus ventralis lateralis pars oralis and pars medialis, the nucleus ventralis posterior lateralis pars oralis, the nucleus ventralis posterior medialis and inferior and to the nucleus reticularis. Some fibers appeared to terminate in the ipsilateral nucleus ventralis lateralis pars caudalis, the nucleus lateralis posterior and the nucleus subthalamicus. A bilateral representation was found in the nucleus centrum medianum, possibly in the paracentralis-centralis lateralis complex and in the paralamellar portion of the nucleus medialis dorsalis. The contralateral labeling was due to fibers crossing via the massa intermedia and was most intense in the cases following injections into the motor face region. A somatotopic arrangement was clearly present in the nucleus ventralis lateralis pars oralis, the nucleus ventralis posterior lateralis pars oralis and the nucleus ventralis posterior medialis. The origin of the projections to the nucleus ventralis posterior medialis needs further clarification.

The dorsal column nuclear projections to the nucleus ventralis posterior lateralis thalami and the inferior olive in the cat: an autoradiographic study.

This autoradiographic study demonstrates a topical projection of the dorsal column nuclei to the contralateral nucleus ventralis posterior lateralis thalami and the accessory part of the inferior olive. In contrast to earlier anatomical studies the projections of the gracile nucleus and the internal cuneate nucleus proved to be independent and entirely contralateral. Fibers from the gracile nucleus terminate only in the lateral part of the nucleus ventralis posterior lateralis (VPL1) and from the internal cuneate nucleus only in the medial part of this nucleus (VPLm). Projections of the gracile nucleus to the contralateral inferior olive are restricted to the caudal one-third of the medial accessory olive and the ventrolateral part of the dorsal accessory olive. The internal cuneate nucleus is only connected with the dorsomedial part of the rostral two-thrids of the dorsal accessory olive. Our material does not allow conclusions about projections from the dorsal column nuclei to other thalamic nuclei and about rostrocaudal point to point relationships between the dorsal column nuclei and the thalamus or the inferior olive.

Somatosensory properties of neurons of thalamic nucleus ventralis lateralis

There is an apparent discrepancy between anatomical and neurophysiological observations concerning thalamocortical projections to pericruciate cerebral cortex in the cat. Anatomical studies report that thalamic nucleus ventralis posterior lateralis (VPL) projects to postcruciate cortex and thalamic nucleus ventralis lateralis (VL) to precruciate cortex. Neurons responding to natural and electrical cutaneous stimulation have been recorded previously in VPL and in precruciate and postcruciate cerebral cortex of the chloralose-anesthetized cat. This study reports that only 6% of the recorded VL sample respond to cutaneous stimulation and suggests that the somatosensory neurons of precruciate cortex receive thalamic input from other than thalamic nucleus VL. The VL neurons recorded from in this study are influenced synaptically from precruciate cortex and from cerebellar cortex in various short latency (< 10 msec), long latency (up to 550 msec), or “silent period” patterns of discharge.

Thalamotomy for Alleviation of Intractable Pain

Seventeen patients had thalamotomies for alleviation of pain due to malignancy since January, 1970. In 12 of them, thalamic electrodes were implanted through occipital burr-holes for subsequent radiofrequency thalamotomies. In 4 cases, the lesions were made by the bifrontal approach, and one case was approached from the left occipital and right frontal. The target in 14 cases was the vicinity of the centromedianum; in 3 cases the target was the zona incerta or the nucleus ventralis posterior lateralis. The size of the lesions was 2 × 6 mm in 10 cases, 8.5 × 11.5 mm in 6 cases, and 7 × 10 mm in one case. Three of the 17 cases required no analgesia between thalamotomy and death. In these cases, thalamic lesions were made in the vicinity of the ventrocaudalis parvo-cellularis and centromedianum. Six cases required non-narcotic analgesics; the lesions were located in the vicinity of the centromedianum in all cases. The remaining 8 patients required narcotics. The lesions of all except one were made outside of centromedianum.

Course and termination of fibres from the nucleus Z of the medulla oblongata. An experimental light microscopical study in the cat

Summary The nucleus z of Brodal and Pompeiano, recently shown to be the bulbar relay in the pathway of hind limb group I muscle afferents to the cerebral cortex in the cat, was subjected to experimental lesions in 9 cats. Ensuing degeneration was studied by light microscopy in Fink-Heimer or Nauta impregnated serial transverse sections from the thalamus. In one cat with a restricted lesion of the nucleus z the degenerating fibres were followed from the area of the lesion up to the thalamus. They had a course similar to that of the internal arcuate fibres, penetrated the ipsilateral inferior olivary nucleus at caudal and middle olivary levels, crossed the midline and reached the medial subdivision of the medial lemniscus. Here they could be traced further rostrally to the thalamus. At caudal thalamic levels degenerating fibres traversed the ventral parts of the nucleus ventralis posterior inferior (VPI). Thence most fibres passed in a narrow strip bordering the nucleus ventralis posterior lateralis (VPL) and the lamina medullaris externa (EML) and reached more rostral regions. Some fibres did, however, pass medial and dorsal to the VPL. Terminal fibres were found rostrally in the thalamus in a continuous area extending approximately from the level of the rostral pole of the lateral geniculate body (GLD) to about 1 mm rostral to the rostral pole of the VPL. This area comprised the ventrolateral part of the nucleus ventralis lateralis (VL) and a small portion of the rostrolateral part of the VPL 1 . Some degenerating fibres were observed in the nucleus centrum medianum (CM) and the medial part of the posterior group of nuclei (PO m ). However, it could not be determined whether or not they were terminal. No degenerating fibres were seen in the thalamus ipsilateral to the medullary lesions.

Cortical projections of Nucleus ventralis lateralis in man.

The brains of two patients who died following stereotaxic thalamotomy were prepared using the Marchi technique. In both cases the lesion was limited to the ventro-lateral and ventro-intermedian nuclei. The lesions did not encroach upon the internal capsule. Although some of the fibers were distributed to area 6, the majority could be traced to area 4 and area 3. The similarity of cortical projections from ventralis lateralis and ventralis posterior lateralis suggest a functional unity and support the older idea of the sensory motor cortex.

Cortical-subcortical EEG correlates of suppressed motor behavior during sleep and waking in the cat

During suppression of motor behavior in cats, a 12–16 c/sec EEG activity generally localized over the sensorimotor cortex has been described previously and termed the sensorimotor rhythm (SMR). It has recently been shown that SMR conditioning can alter EEG spindle activity of slow wave or quiet sleep. The SMR can also appear in non-phasic portions of rapid eye movements or active sleep. Therefore, the purpose of this study was to examine the SMR and sleep spindle phenomena in detail. Cortical and subcortical EEG data were recorded from the somatosensory, motor and visual systems during sleep and wakefulness. EEG tracings were examined for any EEG rhythms or activity characteristics of any behavioral state or location or both. These results were tabled according to location and state and were quantified. States were defined by using EEG from both the sensorimotor and visual cortex areas, electrooculogram and behavioral observations. The SMR was found primarily within the somatosensory system in nucleus ventralis posterior lateralis (VPL) and its primary cortical projection area, the postcruciate gyrus. It occurred in these structures during the absence of phasic motor activity in both the alert animal and in active sleep. Centrum medianum (CM) also possessed a low voltage SMR correlate in the alert animal. The subcortical correlates of the SMR were not present during quiet sleep. In this state, spindle bursts were located primarily within the motor system in ventralis lateralis (VL) and its cortical projections area, the precruciate gyrus. The cerebral peduncles and CM also displayed sleep spindle activity. The VL-motor cortex spindle bursts showed a marked increase in frequency of occurrence in the 1 min interval preceding active sleep. It was proposed that the generators for the SMR and sleep spindle phenomena are probably located at the thalamic level. Although their thalamocortical projections and correlated behavioral states are relatively discrete, their functional origins both appear to reside in a mechanism concerned with the specific suppression of phasic motor activity.

Corticifugal influences on reticular formation evoked activity in cats

Corticifugal influences descending through the subthalamus have been postulated to be responsible for its role in determining the excitability of the reticular formation (RF) and maintaining the attentive, affective and motor behavior of the animal. Support for this concept comes from acute experiments involving cooling of the secondary somatosensory cortex (SSII) in unanesthetized, immobilized cats. Bilateral cooling of SSII reduced the amplitude of sciatic evoked potentials (EP) along the length of the brain stem RF, though reductions in EP of midbrain RF were more consistent than those in the medullary RF. Sciatic EP in sensory and motor areas at comparable levels of the neuraxis, including ventralis posterior lateralis, showed little or no change. These results suggest that the cortex can exert tonic facilitatory influences on the RF. Cooling of SSII also decreased the amount of inhibitory interaction between paired sciatic EP in the RF which implies an interference with phasic, inhibitory influences. Extirpation of SSII had much the same effect as cooling in reducing sciatic EP in the RF. Unilateral removal of SSII produced a significant decrease in sciatic EP; subsequent removal of contralateral SSII resulted in still more reduction implying that these corticifugal influences originate bilaterally, though the ipsilateral projection may be more pronounced. Persistence of sciatic EP in the RF after bilateral extirpation or pro-longed cooling of SSII suggests that other areas of the cortex are also involved in determining the excitability of the RF to entering sensory input.

Corticothalamic connections of suprasylvian cortex in monkey

Cortical lesions were made along the superior border of the sylvian fissure in 11 squirrel and four macaque monkeys. The course of degenerating fibers in the thalamus was determined by utilizing the Nauta and Fink-Heimer I techniques. The principal projection sites of suprasylvian cortex were found to be the nuclei ventralis posterior medialis, ventralis posterior lateralis, ventralis posterior inferior, pulvinaris oralis, and pulvinaris medialis. Lesser amounts of terminal degeneration occurred in the nuclei reticularis, ventralis lateralis, lateralis posterior, the intralaminar nuclei, and the posterior and pretectal areas of the thalamus. The connections of the suprasylvian cortex that corresponds to somatosensory area II with a phylogenetically new thalamic nucleus, the pulvinaris oralis, suggests a specialization of SII functions in the monkey.