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PubMed2000

The role of the human thalamus in language and memory: evidence from electrophysiological studies.

The data reviewed here indicate that electrical stimulation of the dominant ventrolateral thalamus can produce deficits in language processing that are not seen after similar stimulation of the nondominant ventrolateral thalamus. The nature of the language deficit produced varies, depending upon the rostrocaudal location of the stimulation site. Stimulation of the anterior left ventrolateral thalamus in right-handed patients resulted in production of a repeated erroneous word, stimulation of the medial ventrolateral thalamus evoked perseveration, and stimulation of the posterior ventrolateral thalamus and anterior pulvinar resulted in misnaming and omissions. Additional studies have examined the effect of electrical thalamic stimulation on verbal and nonverbal short-term memory. Left (but not right) ventrolateral thalamic stimulation during verbal memory input greatly decreased subsequent recall errors, while stimulation during verbal memory retrieval increased recall errors. This finding contrasted with those obtained from studies on nonverbal memory, in which right ventrolateral stimulation during memory input decreased recall errors, while left thalamic stimulation at the same stage increased recall errors. Left pulvinar stimulation disrupted verbal memory processing, while right pulvinar stimulation disrupted nonverbal memory processing. Limited evidence suggests that the effects of thalamic electrical stimulation on verbal memory may persist for several days after the stimulation has ended. The lateralization of thalamic functions also affects the motoric aspects of speech production. Left (but not right) ventrolateral thalamic stimulation disrupted speech articulation and increased the expiratory phase of respiration. The fact that these motor effects were evoked from the same general area of the thalamus that produced the language deficits discussed above raises the possibility that the thalamus is involved in coordinating the cognitive and motoric aspects of language production. A model of thalamic function is discussed in which defined regions of the thalamus operate as a "specific alerting response," increasing the input to memory of category-specific material while simultaneously inhibiting retrieval from memory.

Electrophysiology↗

PubMed1988

Distribution of nicotinic receptors in human thalamus as visualized by 3H-nicotine and 3H-acetylcholine receptor autoradiography.

Nicotinic cholinergic receptors in human thalamus were measured using (-)3H-nicotine (20 nM) and 3H-acetylcholine (3H-ACh) (20 nM) as radioligands. The specific binding for 3H-nicotine to homogenates of thalamus was 51.6 +/- 8.3 pmol/g protein and for 3H-ACh 18.6 +/- 1.9 pmol/g protein. Receptor autoradiography indicated a high labelling of both 3H-Nicotine and 3H-ACh in the antero-ventral nucleus of thalamus and dorso-medial nucleus of thalamus, while the labelling was lower in the postero-lateral nucleus of thalamus and in the postero-lateral ventral nucleus of thalamus. Quantitative measurement of the 3H-nicotine autoradiograms showed highest labelling in the anteroventral nucleus of thalamus (17.34 +/- 0.76 pmol/g tissue). This study indicates a heterogeneous distribution of high-affinity nicotinic receptors in the human thalamus.

Acetylcholine↗

PubMed2001

Jun, Fos and Krox in the thalamus after C-fiber stimulation: coincident-input-dependent expression, expression across somatotopic boundaries, and nucleolar translocation.

Expression of the inducible transcription factors Jun, Fos and Krox is commonly used to map neurons in the brain that are activated by sensory inputs. However, some neurons known to be electrically excited by such inputs do not always express these factors. In particular, stimulation of hindlimb sensory nerve C-fibers induces expression of c-Fos in the medial thalamus (the mediodorsal, intermediodorsal, centrolateral and centromedial), but not in the lateral thalamus (the ventroposterolateral, ventroposteromedial and posterior group). We hypothesized that c-Fos expression might only occur in these lateral areas after more complex stimulation patterns, or that only other transcription factors can be induced in these areas by such stimuli. Thus we examined the effects of single, repeated and coincident C-fiber inputs on expression of six inducible transcription factors in the medial, lateral and reticular thalamus of the rat. A weak C-fiber input caused by noxious mechanical stimulation of the skin of one hindpaw did not induce expression of c-Fos, FosB, Krox-20 or Krox-24; but it did reduce the basal expressions of c-Jun and JunD in both the medial and lateral areas. An intense input produced by electrical stimulation of all the C-fibers in one sciatic nerve also failed to induce expression of c-Fos, FosB, Krox-20 or Krox-24 in the medial or lateral areas. However, in the medial thalamus it increased c-Jun and reduced the basal expression of JunD, whereas in the lateral thalamus it had no effect on c-Jun but again reduced the basal expression of JunD. With repeated stimulation, i.e. when the noxious stimulus was applied to the contralateral hindpaw 6 h after the sciatic stimulation, there was again no induction of c-Fos, FosB or Krox-20 in the medial thalamus; but there was an increase in c-Jun and Krox-24, and a decrease in JunD levels. In the lateral thalamus the repeated stimulation again failed to induce c-Fos, but the expressions of FosB, c-Jun and Krox-24 were increased, and that of JunD was again reduced. With coincident stimulation, i.e. when a stimulus was applied to each hindpaw simultaneously, c-Fos and Krox-24 remained absent; but there was a marked induction of FosB and Krox-20, a strong repression of c-Jun, and no effect or a reduction of the basal levels of JunD. This coincident stimulation also caused FosB to appear in the nucleolus of many thalamic neurons. MK-801, but not L-NAME, blocked all these changes. In summary, noxious stimulation affects the expression of all transcription factors in the medial, lateral and reticular thalamus in a complex manner depending upon the inducible transcription factor considered, the thalamic nucleus, and the stimulation paradigm. The expression of some transcription factors uniquely after simultaneous inputs suggests they act as coincidence detectors at the gene level.

Afferent Pathways↗

PubMed2000

Functional plasticity in primate somatosensory thalamus following chronic lesion of the ventral lateral spinal cord.

The long-term consequences of thoracic spinothalamic tract lesion on the physiological properties of neurons in the ventral posterior lateral nucleus of the thalamus in monkeys were assessed. Neurons responding to both compressive and phasic brush stimuli (multireceptive neurons), but not brush-specific (low-threshold) neurons, in the partially deafferented thalamus showed increased spontaneous activity, increased responses evoked by cutaneous stimuli and larger mean receptive field size than the same types of cells in the thalamus with intact innervation. The spike train properties of both the spontaneous and evoked discharges of cells were also altered so that there was an increased incidence of spike-bursts in cells of deafferented thalamus. These changes were widespread in the thalamus, and included cells in both the fully innervated forelimb representation and the partially denervated hindlimb representation ipsilateral to the lesion. The spontaneous and evoked spike trains in the ipsilateral thalamus also show increased frequency of both spike-burst and non-burst events compared to the intact thalamus. These results indicate that chronic spinothalamic tract lesion produces widespread changes in the physiological properties of a discrete cell population of the thalamus.The findings in this study indicate that the thalamic processing of somatosensory information conveyed by the lemniscal system is altered by transection of the spinothalamic tract. This change in sensory processing in the thalamus would result in altered cortical processing of innocuous somatosensory inputs following deafferentation and so possibly contribute to the generation of the central pain syndrome.

Action Potentials↗

PubMed1997

Electrical stimulation of the substantia nigra reticulata: detection of neuronal extracellular GABA in the ventromedial thalamus and its regulatory mechanism using microdialysis in awake rats.

A combination of electrical stimulation and microdialysis was used to study the nigrothalamic gamma aminobutyric acid (GABA)ergic system and its regulatory mechanisms in awake rats. Extracellular GABA levels in the ventromedial nucleus of the thalamus were detected in 3-min fractions collected before, during and after a 10-min stimulation period of the substantia nigra reticulata. Electrical stimulation of the substantia nigra reticulata increased the GABA levels to 155% of basal values in the ventromedial thalamus only during the first 3-min interval upon stimulation. The increase in GABA levels was tetrodotoxin-dependent, implicating an exocytotic origin. The basal levels of extracellular GABA in the ventromedial thalamus were of nonexocytotic origin. To study the mechanism underlying the fast compensatory response in neuronal GABA release after nigral stimulation, local infusions into the ventromedial thalamus of reuptake inhibitors and GABA antagonists were performed and the effect of nigral stimulation was examined under the various applications. Local infusion of the reuptake inhibitors nipecotic acid (500 microM) and SKF 89976-A (20 and 50 microM) increased extracellular GABA levels to 350%, 180% and 600%, respectively, of basal values in the ventromedial thalamus tetrodotoxin-independently. Under these conditions, the increase in extracellular GABA was absent (nipecotic acid) or suppressed (20% of basal values; SKF 89976-A for both doses), leaving it unsolved whether or not the uptake system was responsible for the fast compensation in neuronal GABA after stimulation. The GABA-A antagonist bicucilline (50 microM) was ineffective when infused locally in the ventromedial thalamus, but prolonged the increase in neuronal GABA release after nigral stimulation; the GABA levels were increased during two 3-min samples to approximately 165%, indicating a functional role for GABA-A receptors in regulating the release of GABA from nigrothalamic GABAergic neurons. The GABA-B receptor antagonist CGP 35348 (50 microM) did not affect GABA levels when infused locally in the ventromedial thalamus and neither affected the response in neuronal GABA after stimulation. This finding does not support a role for GABA-B receptors in controlling the release from the nigrothalamic neurons.

Animals↗

PubMed1987

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)

Animals↗

PubMed2002

Functional anatomy of thalamus and basal ganglia.

THALAMUS: The human thalamus is a nuclear complex located in the diencephalon and comprising of four parts (the hypothalamus, the epythalamus, the ventral thalamus, and the dorsal thalamus). The thalamus is a relay centre subserving both sensory and motor mechanisms. Thalamic nuclei (50-60 nuclei) project to one or a few well-defined cortical areas. Multiple cortical areas receive afferents from a single thalamic nucleus and send back information to different thalamic nuclei. The corticofugal projection provides positive feedback to the "correct" input, while at the same time suppressing irrelevant information. Topographical organisation of the thalamic afferents and efferents is contralateral, and the lateralisation of the thalamic functions affects both sensory and motoric aspects. Symptoms of lesions located in the thalamus are closely related to the function of the areas involved. An infarction or haemorrhage thalamic lesion can develop somatosensory disturbances and/or central pain in the opposite hemibody, analgesic or purely algesic thalamic syndrome characterised by contralateral anaesthesia (or hypaesthesia), contralateral weakness, ataxia and, often, persistent spontaneous pain. BASAL GANGLIA: Basal ganglia form a major centre in the complex extrapyramidal motor system, as opposed to the pyramidal motor system (corticobulbar and corticospinal pathways). Basal ganglia are involved in many neuronal pathways having emotional, motivational, associative and cognitive functions as well. The striatum (caudate nucleus, putamen and nucleus accumbens) receive inputs from all cortical areas and, throughout the thalamus, project principally to frontal lobe areas (prefrontal, premotor and supplementary motor areas) which are concerned with motor planning. These circuits: (i) have an important regulatory influence on cortex, providing information for both automatic and voluntary motor responses to the pyramidal system; (ii) play a role in predicting future events, reinforcing wanted behaviour and suppressing unwanted behaviour, and (iii) are involved in shifting attentional sets and in both high-order processes of movement initiation and spatial working memory. Basal ganglia-thalamo-cortical circuits maintain somatotopic organisation of movement-related neurons throughout the circuit. These circuits reveal functional subdivisions of the oculomotor, prefrontal and cingulate circuits, which play an important role in attention, learning and potentiating behaviour-guiding rules. Involvement of the basal ganglia is related to involuntary and stereotyped movements or paucity of movements without involvement of voluntary motor functions, as in Parkinson's disease, Wilson's disease, progressive supranuclear palsy or Huntington's disease. The symptoms differ with the location of the lesion. The commonest disturbances in basal ganglia lesions are abulia (apathy with loss of initiative and of spontaneous thought and emotional responses) and dystonia, which become manifest as behavioural and motor disturbances, respectively.

Basal Ganglia↗

PubMed1999

Nitric oxide synthase-containing projections to the ventrobasal thalamus in the rat.

Microiontophoretic studies of thalamic neurons suggests that nitric oxide (NO) plays an important role in mediating somatosensory transmission. The thalamus contains few nitric oxide synthase (NOS)-immunoreactive neurons; thus, the major source of thalamic NO is presumably from NOS-positive axons of extrathalamic origin. The cells of origin of these putative NOS-containing pathways to the ventrobasal thalamus were investigated in rats by combining retrograde tracing with immunocytochemistry for NOS. The location and morphology of double-labeled neurons was compared with that of single-labeled neurons. The most significant sources of NOS-containing afferents to the thalamus were found to be the pedunculopontine (PPN) and laterodorsal tegmental (LDT) nuclei. NOS-immunoreactive neurons in these cholinergic nuclei project bilaterally to the thalamus, most strongly ipsilaterally. The thalamus appears to be a major target of PPN, since even selective thalamic injections result in retrograde labeling of at least one third of its NOS-immunoreactive neurons. A significant number of NOS-negative neurons in both the PPN and LDT also project to the thalamus. Minor sources of NOS-containing thalamic afferents include the lateral hypothalamus, the dorsal, median and pontine raphe nuclei, the parabrachial nuclei, and the pontomedullary reticular formation. In all these structures, NOS-negative thalamopetal neurons greatly outnumber the NOS-positive ones. Ascending sensory pathways to the thalamus, including those from the sensory trigeminal nuclei, the dorsal column nuclei, and the spinal cord, as well as the auditory and vestibular centers, arise exclusively from NOS-negative neurons. The major NOS-positive projections are implicated in affective and alerting systems, supporting that NO may act to modulate attentiveness in thalamic relay nuclei.

Afferent Pathways↗

PubMed1993

Brainstem peptidergic neurons projecting to the medial and lateral thalamus and zona incerta in the rat.

The presence of neuropeptides in brainstem neurons that project to the medial and lateral thalamus and zona incerta has been studied in the rat. Brainstem neurons were retrogradely labeled from the medial and lateral thalamus and the zona incerta by colloidal gold-WGA-HRP and, after silver intensification of the retrograde label, their content of immunoreactivity for nine different neuropeptides was determined after colchicine administration. The medial thalamus and zona incerta both received a large peptidergic input and the lateral thalamus a smaller input from neurons in several brainstem nuclei. These were principally from the locus coeruleus, parabrachial nucleus, the dorsal raphe and the dorsal tegmentum. The principal input to the medial thalamus arose from neurotensin, neuropeptide Y and galanin neurons in the locus coeruleus, neurotensin neurons in the dorsal tegmentum, dynorphin neurons in the parabrachial nucleus and dorsal tegmentum, galanin neurons in the dorsal raphe, substance P neurons in the lateral and dorsal periaqueductal grey and calcitonin gene-related peptide neurons in the nucleus paragigantocellularis. The principal peptidergic input to the zona incerta was from dynorphin neurons in the nucleus of the solitary tract, bombesin neurons in the lateral reticular nucleus, calcitonin gene-related peptide and cholecystokinin neurons in the dorsal tegmentum, substance P, bombesin and galanin neurons in the locus coeruleus, dynorphin and substance P neurons in the lateral periaqueductal grey and cholecystokinin neurons in the substantia nigra, ventral tegmental nucleus and raphe linearis. The principal peptidergic input to the lateral thalamus came from calcitonin gene-related peptide and cholecystokinin neurons in the dorsal tegmentum, calcitonin gene-related peptide and galanin neurons in the locus coeruleus; substance P, neuropeptide Y, galanin and calcitonin gene-related peptide neurons in the dorsal raphe, substance P neurons in the lateral periaqueductal gray, galanin neurons in the nucleus interpedunculus and cholecystokinin neurons in the raphe linearis. In all these cases, from 25% to virtually all of the projection neurons in the brainstem nucleus could contain immunoreactivity to the neuropeptide. A lesser, but significant peptidergic input to the thalamus and zona incerta also arose from the trigeminal nucleus, the substantia nigra, the nucleus of the solitary tract, the lateral reticular nucleus, the interpeduncular nucleus, the raphe linearis, the paragigantocellularis, the inferior olive and ventral tegmental area. Overall, the neuropeptides most frequently present in the projection neurons were substance P, calcitonin gene-related peptide, galanin and cholecystokinin. Bombesin, neuropeptide Y, neurotensin and dynorphin were less common; and enkephalin was present in only a small percentage of projection neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1999

Characterization of the extent of pontomesencephalic cholinergic neurons' projections to the thalamus: comparison with projections to midbrain dopaminergic groups.

We sought to determine whether pontomesencephalic cholinergic neurons which we have been shown previously to project to the substantia nigra and ventral tegmental area also contribute to the thalamic activation projection from the pedunculopontine and laterodorsal tegmental nuclei. Retrograde tracing, immunohistochemical localization of choline acetyltransferase and statistical methods were used to determine the full extent of the cholinergic projection from the pedunculopontine and laterodorsal tegmental nuclei to the thalamus. Progressively larger Fluoro-Gold injections in to the thalamus proportionally labeled increasing numbers of pontomesencephalic cholinergic cells both ipsi- and contralaterally in the pedunculopontine and laterodorsal tegmental nuclei. Multiple large thalamic injections left only a small fraction of the ipsilateral pontomesencephalic cholinergic group unlabeled. This small remainder did not correspond to the populations which project to the substantia nigra and ventral tegmental area, thereby indicating that substantia nigra- and ventral tegmental area-projecting cholinergic neurons must also project to the thalamus. We examined whether there existed any set of cholinergic neurons in the pedunculopontine and laterodorsal tegmental nuclei which did not innervate a thalamic target. The distribution of descending projections of the pedunculopontine and laterodorsal tegmental nuclei demonstrated that the unlabeled remainder cannot correspond to a purely descending group. We also show that substance P-positive cholinergic cells in the laterodorsal tegmental nucleus project to the thalamus. Further studies demonstrated that the small population of cholinergic cells left unlabeled from the thalamus were the smallest sized cholinergic cells, and included two groups of small, light-staining cholinergic cells located in the parabrachial area and central gray, adjacent to the main pedunculopontine and laterodorsal tegmental nuclei cholinergic groups. These small cells, in contrast to thalamic-projecting cholinergic cells, did not stain positively for reduced nicotinamide adenine dinucleotide phosphate-diaphorase. Taken together, these results indicated that all of the reduced nicotinamide adenine dinucleotide phosphate diaphorase-positive/choline acetyltransferase-positive neurons of the pedunculopontine/laterodorsal tegmental nuclei ascend to innervate some portion of the thalamus, in addition to the other targets they innervate. These findings indicate that the diverse physiological and behavioral effects attributed to the activity of pontomesencephalic cholinergic neurons should not be dissociated from their activating effects in the thalamus.

Animals↗

PubMed2004

Thalamus and penile erection.

Penile erection is a complex neurovascular event. The neuronal system involved is often divided into a spinal (generator) and supraspinal (controller) network. Little is known about the supraspinal control. The recent finding of changes in penile erection following deep brain stimulation of the thalamus in two patients has raised the question as to what extent the thalamus is involved in erectile function. The thalamus has generally been regarded as a group of relay nuclei that served as a 'gate' for sexual information from the spinal cord towards higher centres. Recent evidence, however, suggests a more integrated regulatory function. Our review of the literature from 1960 until 2003 revealed 13 reports describing original data (preclinical and clinical). Various thalamic regions, varying from the midline thalamus to the posterior thalamus, have been reported to be activated during erection. The majority of the reports, however, showed that mainly the mediodorsal (MD) nucleus and the centromedian-parafascicular nucleus (Cm-Pf complex) are involved in penile erection. MD is the second largest nuclear aggregation located within the medial part of the thalamus. Anatomically, the MD is closely related to the Cm-Pf complex. The Cm-Pf complex is one of the most important relay stations in which the anterolateral spinothalamic pathway is further processed. This pathway is thought to transmit peripheral sexual sensations. On the whole, the present data on the role of the thalamus in erection are far from complete and future experiments are required to delineate its involvement.

Animals↗

PubMed2001

Radial migration in the cerebral cortex is enhanced by signals from thalamus.

The six layered cerebral cortex derives from cells that divide in the ventricular zone and migrate to their final destination in the cortical plate (future cortex). In the mouse, cortical layer III and IV neurons undergo their final mitotic division at around E16, at which time thalamic axons are beginning to enter the cortex. We used bromodeoxyuridine-birth dating of cells in cortical slice cultures to show that the thalamus enhances the migration out of the ventricular zone of future layer III/IV cells. When cortical slices were cultured alone, less than 35% of cells born in vitro on E16 were present in the pial half of the slice after 48 h in culture. In contrast, when cortical slices were cocultured with thalamus, 69% of these cells were found in the pial half of the slice. Explants of other developing tissues did not mimic the effect of the thalamus. The thalamus had no obvious effect on cortical radial glial cells, cortical cell viability or maintenance of cortical slice structure. We found that most precursors born at a similar age but in vivo, shortly before cortical slices were isolated, migrated to the pial half of the cultured slices in the absence of a cocultured thalamic explant. Thus, E16 cortical slices cultured without thalamus permit migration of cells born in vivo and therefore already exposed to the thalamus. Our results indicate that the thalamus provides factors to E16-born cortical precursors that enhance their directed migration out of the ventricular zone to the cortical plate.

Animals↗

PubMed2002

Spectrotemporal receptive fields in the lemniscal auditory thalamus and cortex.

Receptive fields have been characterized independently in the lemniscal auditory thalamus and cortex, usually with spectrotemporally simple sounds tailored to a specific task. No studies have employed naturalistic stimuli to investigate the thalamocortical transformation in temporal, spectral, and aural domains simultaneously and under identical conditions. We recorded simultaneously in the ventral division of the medial geniculate body (MGBv) and in primary auditory cortex (AI) of the ketamine-anesthetized cat. Spectrotemporal receptive fields (STRFs) of single units (n = 387) were derived by reverse-correlation with a broadband and dynamically varying stimulus, the dynamic ripple. Spectral integration, as measured by excitatory bandwidth and spectral modulation preference, was similar across both stations (mean Q(1/e) thalamus = 5.8, cortex = 5.4; upper cutoff of spectral modulation transfer function, thalamus = 1.30 cycles/octave, cortex = 1.37 cycles/octave). Temporal modulation rates slowed by a factor of two from thalamus to cortex (mean preferred rate, thalamus = 32.4 Hz, cortex = 16.6 Hz; upper cutoff of temporal modulation transfer function, thalamus = 62.9 Hz, cortex = 37.4 Hz). We found no correlation between spectral and temporal integration properties, suggesting that the excitatory-inhibitory interactions underlying preference in each domain are largely independent. A small number of neurons in each station had highly asymmetric STRFs, evidence of frequency sweep selectivity, but the population showed no directional bias. Binaural preferences differed in their relative proportions, most notably an increased prevalence of excitatory contralateral-only cells in cortex (40%) versus thalamus (23%), indicating a reorganization of this parameter. By comparing simultaneously along multiple stimulus dimensions in both stations, these observations establish the global characteristics of the thalamocortical receptive field transformation.

Acoustic Stimulation↗

PubMed2000

A role for Pax6 in the normal development of dorsal thalamus and its cortical connections.

The transcription factor Pax6 is widely expressed throughout the developing nervous system, including most alar regions of the newly formed murine diencephalon. Later in embryogenesis its diencephalic expression becomes more restricted. It persists in the developing anterior thalamus (conventionally termed "ventral" thalamus) and pretectum but is downregulated in the body of the posterior (dorsal) thalamus. At the time of this downregulation, the dorsal thalamus forms its major axonal efferent pathway via the ventral telencephalon to the cerebral cortex. This pathway is absent in mice lacking functional Pax6 (small eye homozygotes: Sey/Sey). We tested whether the mechanism underlying this defect includes abnormalities of the dorsal thalamus itself. We exploited a new transgenic mouse ubiquitously expressing green fluorescent protein tagged with tau, in which axonal tracts are clearly visible, and co-cultured dorsal thalamic explants from Pax6(+/+ )or Pax6(Sey/Sey )embryos carrying the transgene with wild-type tissues from other regions of the forebrain. Whereas Pax6(+/+ )thalamic explants produced strong innervation of wild-type ventral telencephalic explants in a pattern that mimicked the thalamocortical tract in vivo, Pax6(Sey)(/Sey) explants did not, indicating a defect in the ability of mutant dorsal thalamic cells to respond to signals normally present in ventral telencephalon. Pax6(Sey)(/Sey) embryos also showed early alterations in the expression of regulatory genes in the region destined to become dorsal thalamus. Whereas in normal mice Nkx2.2 and Lim1/Lhx1 are expressed ventral to this region, in the mutants their expression domains are throughout it, suggesting that a primary action of Pax6 is to generate correct dorsoventral patterning in the diencephalon. Our results suggest that normal thalamocortical development requires the actions of Pax6 within the dorsal thalamus itself.

Alternative Splicing↗

PubMed2000

Functional connectivity in the thalamus and hippocampus studied with functional MR imaging.

BACKGROUND AND PURPOSE: With functional connectivity functional MR imaging, co-variance in signal intensity has been shown in functionally related regions of brain in participants instructed to perform no cognitive task. These changes are thought to represent synchronous fluctuations in blood flow, which imply neuronal connections between the regions. The purpose of this study was to map functional connectivity in subcortical nuclei with functional connectivity functional MR imaging. METHODS: Imaging data were acquired with an echo-planar sequence from six volunteers who performed no specific cognitive task. For functional connectivity functional MR imaging, a "seed" voxel or group of voxels was selected from the resting data set in the thalamus or in the hippocampus. Control voxels in gray matter presumed not to be eloquent cortex were also chosen. The correlation coefficient of the seed voxels and the control voxels with every other voxel in the resting data set was calculated. The voxels with correlation coefficients greater than or equal to 0.5 were mapped onto anatomic images for the functional connectivity functional MR images. The anatomic location of these voxels was determined by conventional parcellation methods. RESULTS: For each participant, functional connectivity functional MR imaging maps based on four seed voxels in the thalamus or hippocampus showed clusters of voxels in the ipsilateral and contralateral thalamus or hippocampus. For control voxels, few voxels in the hippocampus or thalamus showed significant correlation. Significantly more pixels in the ipsilateral hippocampus correlated with the seed voxel than in the contralateral hippocampus. The differences between numbers of functionally connected voxels in ipsilateral thalamus and those in contralateral thalamus were not significant. CONCLUSIONS: The thalamus and hippocampus show functional connectivity, presumably representing synchronous changes in blood flow.

Adult↗

PubMed1992

A comparison of the interaural time sensitivity of neurons in the inferior colliculus and thalamus of the unanesthetized rabbit.

The localization of low-frequency sounds (less than 3 kHz) along the azimuth involves comparing the ongoing difference in the time of arrival of a sound at the two ears. Information about interaural time differences (ITDs) is derived from an initial comparison performed in the superior olivary complex. However, little is known about which aspects of this information are transformed as it ascends the brainstem. To address this issue, we compared the ITD sensitivity of neurons in the inferior colliculus (IC) and auditory thalamus, successive stations in the auditory pathway. We found ITD sensitivity in the IC and thalamus to be similar in several respects. At both levels, the large majority of neurons responded maximally to ITDs within the range that a rabbit would normally encounter (+/- 300 microseconds) and preferred ipsilateral delays, delays that would be created by sounds in the contralateral sound field. The range of frequencies over which ITD sensitivity was expressed was also similar in the midbrain and thalamus. Several differences were also apparent. In comparison to IC neurons, neurons in the thalamus responded over more restricted ranges of ITD, responded at lower rates, and, in response to monaural stimulation, showed an increased influence of inhibition. Finally, a greater proportion of thalamic units had characteristic delays corresponding to intermediate discharge rates. The preservation of a bias for ipsilateral delays from IC to thalamus suggests that a representation of contralateral azimuths is present at both levels. Similarities between the two levels suggest that information about ITDs is faithfully transmitted from midbrain to thalamus. Differences in ITD sensitivity, such as the sharper tuning for ITDs, suggest that the thalamus is not a simple relay. Enhanced sensitivity to ITDs should translate to better-defined azimuthal receptive fields, and therefore may be a step toward achieving an optimal representation of azimuth within the auditory pathway.

Acoustic Stimulation↗

PubMedDate not supplied

[Neurofunctional aspects of the thalamus].

AIM: To carry out a revision of the principal neurofunctional aspects of the thalamus. DEVELOPMENT: Following the anatomical location of this cerebral structure in the diencephalon, we'll analyze the macroscopic characteristics of the thalamus establishing its anatomical limits. We'll study the main thalamic nuclei, taking into account different criteria: evolution, anatomical and functional, cytoarchitectonic, and connective fibers as well as the principal projections which reach and leave the thalamus, allowing an adequate information processing. The last part of this paper is dedicated to study of the aspects related with the participation of the thalamus in the basic psychofunctional processes and superior processes. CONCLUSIONS: The thalamus, in addition to its implication along with the cerebral cortex in the analysis and integration of sensitive and motor functions, is implied in superior functions like the attention, language, memory and executive function. The pulvinar nucleus, the lateral nuclear group and the anterior nuclear group take part in the language, fundamentally. In the mnesic processes, the scientific studies show that the midline nuclei, mediodorsal thalamic nuclei and intralaminar nuclei of the thalamus are implied in this superior function. Lesions of the thalamus can cause alterations in the executive functions, attention, initiative and temporal organization of the conduct. The mediodorsal nuclei, the intralaminar nuclei and the midline nuclei has been shown to have a critical role in executive function.

Emotions↗

PubMed1996

Specific innervation of the rat thalamus by grafted noradrenergic locus coeruleus neurons.

Growth and distribution of noradrenaline (NA) fibres from the implant into the thalamus of host rats were examined at 5-13 months after the implantation by immunohistochemistry using NA or tyrosine hydroxylase antisera. Cell suspension dissociated from the locus coeruleus (LC) region of 14-day-old rat fetuses was implanted into the center of the unilateral thalamus in adult rats from which the noradrenergic afferents to the thalamus had been eliminated with 6-hydroxydopamine treatment. A dense network of varicose NA-immunoreactive (NA-IR) fibres extended laterally into the posterior thalamic nuclear group and the ventral posterolateral thalamic nucleus from the implant in a pattern similar to that the intrinsic noradrenergic fibres form in the normal thalamus, i.e. laterally rich and medially poor NA fibres. Electron microscopic observations revealed that varicosities of NA-IR fibres formed symmetrical as well as asymmetrical axodendritic synapses and axo-axonic synapses with the host neurons as seen in the normal thalamus. labelled dendrite-like fibres of graft origin penetrated deep into the host brain and received afferents from non-labelled axon terminals. Varicosities of NA-IR fibres in the LC implanted animal formed axo-dendritic synapses at the higher ratio than those in the normal animal did. These results show that implanted fetal noradrenergic neurons innervate target regions of the thalamus specifically as the noradrenergic fibres in the normal thalamus do and maintain the innervation for a long time in the noradrenergically denervated rats.

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