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PubMed2004

Very fast oscillations evoked by median nerve stimulation in the human thalamus and subthalamic nucleus.

Very fast oscillations (VFOs; 500-1,500 Hz) are associated with sensory-evoked potentials (SEPs), but their origin is unknown. To characterize the origins of VFOs, we studied 35 patients with deep brain stimulation (DBS) electrodes [15 with thalamic and 20 with the subthalamic nucleus (STN) electrodes]. We recorded median nerve stimulation-evoked SEPs from the thalamus and STN with microelectrodes during stereotactic surgery and from the contacts of the DBS electrodes postoperatively. We also examined the firing of individual neurons in thalamus in relation to the VFOs. In the thalamus, VFOs with frequencies around 1,000 Hz were superimposed on slow potentials. Both slow and fast SEP components showed phase reversals in the somatosensory thalamus [ventralis caudalis (Vc)]. Median nerve poststimulus time histograms showed that single thalamic neurons fired at preferred times at intervals between 0.8 to 1.2 ms that were synchronous with the VFOs, although the neurons fired only once or a few times per trial. In the STN, low-amplitude SEPs with VFOs were observed at a latency similar to the thalamic SEPs. The VFOs from STN probably represent volume conduction, possibly from the medial lemniscus. We conclude that the thalamic VFOs are generated within Vc and that they induce time-locked firing in a network of neurons.

Adult↗
PubMed2002

Neuromodulatory role of serotonin in the ferret thalamus.

Serotonergic fibers broadly innervate the thalamus and may influence the sleep wake cycle, attention, and other processes through modulation of neurons in this structure. However, the actions of serotonin in the dorsal thalamus have been investigated in detail only in the dorsal lateral geniculate nucleus. In the present study, we examined the action of serotonin in several different regions of the ferret dorsal thalamus, including the associative nuclei, using the in vitro slice preparation and intracellular recording techniques. In nearly all nuclei examined, the predominant action of serotonin was one of hyperpolarization and inhibition of the tonic firing mode. The magnitude of the hyperpolarizing response decreased with age and varied greatly across and somewhat within nuclei maintaining the following relationship (in descending order of magnitude): lateral posterior, lateral dorsal, pulvinar, mediodorsal, center median, anteroventral, central lateral, ventral basal, and medial geniculate. This hyperpolarization is elicited through two mechanisms: one direct and the other via local interneurons. The direct action occurs through an increase in potassium conductance mediated through the 5-HT(1A) receptor. This conclusion is supported by the findings that it persists in the presence of tetrodotoxin and block of GABAergic synaptic transmission, the reversal potential shifts in a Nernstian fashion with changes in extracellular potassium concentration, and the response is antagonized by the 5-HT(1A) antagonist WAY100635 and mimicked by the application of the 5-HT(1A)-selective agonist 8-OH DPAT. The second mechanism by which 5-HT evoked a hyperpolarization was through the activation of local interneurons. In slices in which GABA receptors were not blocked, 5-HT application increased the frequency and amplitude of spontaneous inhibitory postsynaptic potentials (IPSPs) occurring in thalamocortical neurons. Application of 5-HT to physiologically or morphologically identified interneurons evoked a prolonged suprathreshold depolarization. Our results suggest that serotonergic inputs act differentially across the thalamus in a complex manner involving direct and indirect mechanisms. It appears that 5-HT has a greater direct postsynaptic inhibitory influence in the posterior, medial, and intralaminar nuclei than in the primary sensory nuclei.

Animals↗
PubMed1991

Activity of neurons in cerebellar-receiving and pallidal-receiving areas of the thalamus of the behaving monkey.

1. Thalamic neurons that receive synaptic input from the globus pallidus or the cerebellar nuclei were identified in awake monkeys trained to perform an arm-reaching task. The location of electrophysiologically identified cerebellar-receiving (CR) and pallidal-receiving (PR) neurons was used to identify a total of 264 thalamic neurons in cerebellar (CB) or pallidal (GP) regions of the thalamus. 2. Stimulation in the brachium conjunctivum or white matter adjacent to the cerebellar nuclei excited 85 neurons in the thalamus at short latencies. These CR neurons were located in the oral portion of the ventral posterolateral nucleus (VPLo), in caudal portions of the ventral lateral nucleus (VLc), and in area X. 3. Stimulation in the internal globus pallidus (GPi) inhibited 10 thalamic neurons at short latency. These PR neurons were located in rostral portions of VLc, in the oral part of the ventral lateral nucleus (VLo), and in the parvicellular part of the ventral anterior nucleus (VApc). 4. There was no clear single somatotopic organization of neurons in CB and GP regions of the thalamus, as defined by "free-form" responses to passive manipulation and observation of eye movements. There was, in fact, a tendency for two representations, each, of the head/eye/mouth cells and cells with modifications of activity in response to manipulation of the arm. 5. During the hold period before illumination of a visual target, the mean firing rates and variability of discharge of arm-related CR and PR neurons did not differ significantly. This was also true for the total sample of arm-related neurons in the CB versus GP regions. 6. The activity of many neurons in both the CB and GP regions began to change before the reaching movement and, for some, before the earliest recorded changes in electromyographic (EMG) activity. The initial change was an increase in discharge for greater than 75% of the cells studied in both the CB and GP regions. 7. During the reaching task, there also was no significant difference in the time of the initial change in discharge of neurons in the CB versus GP regions of the thalamus. 8. These data are consistent with the hypothesis that the initial task-related change in discharge of PR thalamic neurons is dominated by input from the cerebral cortex and that pallidal input modulates later phases of their movement-related changes in activity.

Animals↗
PubMed1996

Contrasting locations of pallidal-receiving neurons and microexcitable zones in primate thalamus.

1. In two awake, juvenile male Macaca fascicularis monkeys, microstimulation was applied in ventralis anterior (VA), ventralis lateralis (VL), or ventralis posterior lateralis (VPL) of the thalamus. Thalamic recording was used to identify the region that contained pallidal-receiving (PR) thalamic neurons, cells that responded orthodromically to stimulation in the internal pallidal segment (GPi). Thalamic stimulation was used to elicit motor responses. Penetrations in the thalamus and the pallidum focused on areas with activity related to contralateral arm movement. Fifty-one PR cells were identified electrophysiologically in VL oralis (VLo), VL caudalis (VLc) and VA pars parvocellularis (VApc). 2. With a subject at rest, trains of stimuli were applied through the thalamic microelectrode. Palpable or visible muscle twitches or joint movements were evoked by short trains (12 pulses) of stimuli applied in VLc and VPL oralis (VPLo); thresholds there ranged from 5 to 75 microA. In VA and VLo, areas where PR neurons were located, even longer trains (24 pulses) of stimuli with currents up to 200 microA usually failed to evoke movement. In the caudal portions of VLo, near VPLo, there were some microexcitable sites found near PR cells where stimuli at approximately 50 microA elicited movement. 3. From microstimulation studies combined with histological reconstruction, Ashe and co-workers hypothesized that microexcitable zones were cerebellar receiving areas (CR) and nonexcitable zones were PR areas. Our data support theirs and add electrophysiological identification of PR areas. Further, we injected wheat germ agglutinin-horseradish peroxidase (WGA-HRP) into the thalamus at one of the more rostral microexcitable sites, just caudal and lateral to identified PR cells. The tetra-methyl benzidine-reacted HRP label was found in the contralateral deep cerebellar nuclei (DCN) but not in ipsilateral GPi, showing that even this rostral microexcitable zone was a CR area. 4. Together with evidence from the literature, the data are consistent with the hypothesis that PR cells have relatively weak access to spinal-destined motor outputs, whereas thalamocortical neurons from VPLo and VLc have more secure access. In addition to characteristics of cell discharge and responses to somatosensory stimulation, microexcitability may be a further aid in tentative electro-physiological identification of PR versus CR areas of the motor thalamus without necessarily recording thalamic neuronal responses to stimulation in GPi or the DCN.

Animals↗
PubMed1996

Low-frequency rhythms in the thalamus of intact-cortex and decorticated cats.

1. The patterns and synchronization of low-frequency, sleeplike rhythms (slow, spindle and delta oscillations) were compared in the intact-cortex and decorticated hemispheres of cats under ketamine-xylazine anesthesia. Intracellular recordings were performed in intact and decorticated hemispheres from 58 rostrolateral thalamic reticular (RE) neurons and from 164 thalamocortical (TC) neurons in the ventrolateral (VL) nucleus. In the decorticated hemisphere, dual intracellular recordings were performed from five RE-VL cell couples and from 12 TC cell couples within the VL nucleus. In addition, field potentials were simultaneously recorded from the neocortex (electroencephalogram) and ipsilateral thalamus [electrothalamogram (EThG)] of the intact (right) hemisphere, while EThG was recorded from the VL nucleus of the decorticated (left) hemisphere. 2. The slow oscillation (< 1 Hz) was absent in all 72 VL cells and in 23 of 25 RE cells from the decorticated hemisphere, as well as in the EThG recorded from the VL nucleus in the decorticated hemisphere, whereas it was simultaneously present in the cortex and thalamus of the intact hemisphere. The remaining two RE neurons (8%) in the decorticated hemisphere oscillated in close time relation with the slow oscillation in the cortex and thalamus of the opposite hemisphere; averaged activities showed that the onset of depolarization in RE cell followed 12 ms after the sharp depth-negative (depolarizing) component in the contralateral cortex. We view this result as the electrophysiological correlate of a disynaptic excitatory pathway consisting of crossed cortical projections, first relayed in contralateral dorsal thalamic nuclei. 3. The patterns of thalamic spindles (7-14 Hz) differed between the two hemispheres. Whereas the decorticated hemisphere displayed prolonged, waxing and waning spindles, the spindles in the intact-cortex hemisphere were short and exclusively waning and followed the depth-negative component of cortical slow oscillation. This result indicates that the synchronized corticothalamic drive associated with the slow oscillation fully entrains thalamic circuits from the onset of spindles, thus preventing further waxing. Similar differences between waxing and waning and waning spindles were obtained by stimulating with different intensities the thalamus in the decorticated hemisphere. 4. Simultaneous intracellular recordings from two VL cells or from RE and VL cells showed nearly simultaneous spindle sequences in the decorticated hemisphere. 5. The hyperpolarization-activated intrinsic delta oscillation (1-4 Hz) of TC cells was asynchronous in the decorticated hemisphere. 6. These results strengthen the idea that the slow oscillation is cortical in origin; demonstrate a full, short-range, intrathalamic synchrony of spindles in the absence of cortex; and indicate that the pattern of spindles, a sleep rhythm that is conventionally regarded as purely thalamic, is shaped by the corticothalamic feedback.

Animals↗
PubMed1997

Spinal strychnine alters response properties of nociceptive-specific neurons in rat medial thalamus.

Experiments in both conscious and anesthetized animals indicate that intrathecal (i.t.) strychnine (STR; glycine receptor antagonist) produces acute, reversible allodynia, as evidenced by inappropriate behavioral and autonomic responses to cutaneous tactile stimuli. Although STR is known to produce disinhibition of afferent input to the spinal cord, changes in spinal reflexes cannot fully explain the complex behaviors observed following i.t. STR. Which supraspinal sites are involved in STR-dependent allodynia and how this abnormal somatosensory message is relayed to these sites remain to be determined. The medial thalamus contains many nociceptive-specific (NS) neurons and is believed to be involved in mediating the affective-motivational aspects of pain. It is thus important to determine whether spinally administered STR elicits changes in the responses of medial thalamic NS neurons. Extracellular single-unit recordings were conducted in urethan-anesthetized rats (290-490 g). A detailed characterization of 20 thalamic NS units (1 per rat; 2 in 1 case) was conducted before and immediately after i.t. STR (40 microg). Initially, all of the units in this study were classified as NS, because they were excited by noxious pinch but not by innocuous tactile stimuli. After i.t. STR, all (formerly NS) units exhibited significant responses to innocuous tactile stimuli (brush and/or air jet) applied to lumbar or sacral dermatomes. This effect of STR on thalamic NS neurons was acute and reversible. The majority of units (11 of 20) also exhibited an increase in spontaneous firing rate. Although the complete pinch receptive field (RF) could not be determined for all units, the available data indicate that the RFs for brush stimulation after i.t. STR were substantially different from the pre-STR pinch RFs for all but three units. The same i.t. STR injection that caused the observed changes in medial thalamus also produced allodynia, in the form of brush-evoked cardiovascular or motor responses, in 18 of the 19 rats. The ability of NS cells in medial thalamus to respond to tactile input after i.t. STR suggests that the STR lowers the threshold of nociceptive neurons that project directly and/or indirectly to medial thalamus. These observations suggest that ascending nociceptive pathways and medial thalamic structures contribute to the expression of STR-dependent allodynia.

Animals↗
PubMed2001

Neurodegeneration in the thalamus following neonatal hypoxia-ischemia is programmed cell death.

We studied neuronal cell body, axonal, and terminal degeneration in brains from 7-day-old rat pups recovered for 0, 1.5, 3, 6, 24, 48, 72 h, and 6 days following hypoxia-ischemia and identified proteins involved in the delayed neurodegeneration in the thalamus. We found that injury is biphasic with initial necrosis in the ipsilateral forebrain by 3 h following hypoxia-ischemia, in contrast to more delayed and apoptotic-like injury in the ventral-basal thalamus, brainstem, and other remote non-forebrain regions. Prior to the appearance of large numbers of apoptotic profiles in the ventral-basal thalamus, expression of Fas death receptor protein, activated forms of caspase 8 and caspase 3, and pro-apoptotic Bcl-2 proteins are increased. This manuscript combines our data on hypoxic-ischemic injury in the developing brain and presents evidence for at least two forms of neurodegeneration, namely, acute necrosis in the forebrain and delayed neurodegeneration in the thalamus, which is death-receptor-mediated programmed cell death.

Animals↗
PubMed1992

Central pain in the absence of functional sensory thalamus.

Since the pioneering publication by Dejerine and Roussy, the thalamus has been commonly implicated in the pathogenesis of central pain. It is well known that cerebral lesions that spare the thalamus as well as both small and large ones within that structure produce similar pain syndromes, but could such pain develop if the thalamus were completely destroyed? CT scans of our patients suggested that it could. Moreover, exhaustive physiological explorations of the thalamus with macro- and microstimulation and microelectrode recordings in 2 more patients in whom CT scans suggested thalamic preservation despite massive suprathalamic infarcts, for the purpose of carrying out deep brain stimulation (DBS), revealed no evidence of ascending or descending diencephalic function. Their sensory examinations were similar to those of patients with congenital hemiatrophy who had undergone hemispherectomy. In 1 case, microstimulation of periaqueductal grey-periventricular grey (PAG-PVG) on the unaffected side of the brain induced the spectrum of responses correctly associated with these areas and during acute stimulation nearly abolished the patient's allodynia and hyperpathia. These observations suggest that processes occurring at a subdiencephalic level (or possibly ipsilaterally) may be involved in the generation of pain. Stroke-induced central pain remains a therapeutic dilemma for the pain surgeon, and the mechanisms underlying this pain state remain a mystery.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebral Arteries↗
PubMed2006

Volumetric analysis and three-dimensional glucose metabolic mapping of the striatum and thalamus in patients with autism spectrum disorders.

OBJECTIVE: In patients with autism, behavioral deficits as well as neuroimaging studies of the anterior cingulate cortex suggest ventral rather than dorsal striatal and thalamic abnormalities in structure and function. The authors used imaging studies to map volumetric and metabolic differences within the entire dorsoventral extent of the striatum and thalamus. METHOD: Magnetic resonance imaging (MRI) and positron emission tomography (PET) were used to measure volumes and metabolic activity in the thalamus, caudate, and putamen in 17 patients with autism or Asperger's disorder and 17 age- and sex-matched comparison subjects. Subjects performed a serial verbal learning test during the [(18)F]-fluorodeoxyglucose uptake period. The regions of interest were outlined on contiguous axial MRI slices. After PET/MRI coregistration, region-of-interest coordinates were applied to the PET scan for each individual. Between-group differences in metabolism were assessed by three-dimensional statistical probability mapping. RESULTS: The patients with autism spectrum disorders had greater volumes of the right caudate nucleus than comparison subjects as well as a reversal of the expected left-greater-than-right hemispheric asymmetry. Patients also had lower relative glucose metabolic rates bilaterally in the ventral caudate, putamen, and thalamus. Patients with autism had lower metabolic activity in the ventral thalamus than those with Asperger's disorder, but they did not differ from comparison subjects in metabolic activity in the caudate nucleus. CONCLUSIONS: These results are consistent with a deficit in the anterior cingulate-ventral striatum-anterior thalamic pathway in patients with autism spectrum disorders. The results also suggest an important role for the caudate in helping support working-memory demands.

Adolescent↗
PubMed2002

A magnetization transfer analysis of the thalamus in schizophrenia.

The authors investigated the thalamus in schizophrenia by using magnetization transfer ratio (MTR), a novel structural magnetic resonance technique sensitive to subtle neuropathological abnormalities. The dorsomedial nucleus (DMN) and pulvinar were selected because of their connections to limbic, prefrontal, and temporal regions, putatively relevant in schizophrenia. Volume (intracranial; thalamic) and MTR (whole thalamus; DMN; pulvinar) were determined in 25 patients with chronic schizophrenia by DSM-IV criteria and 25 control subjects. There were no significant differences between patients and control subjects in thalamic volume (corrected for intracranial volume) or MTR in whole thalamus, DMN, or pulvinar. No volumetric or MTR abnormalities could be detected in the thalamus of patients with schizophrenia. The findings suggest that abnormalities, if present, are very subtle and beyond the power of resolution of these techniques.

Adult↗
PubMed2006

The motor thalamus in neurosurgery.

The motor thalamus is an important target for the treatment of tremor. It receives afferents from the cerebellum, globus pallidus internus, and substantia nigra and projects mainly to the motor cortex, premotor cortex, and supplementary motor area. Various nomenclatures have been proposed to subdivide the motor thalamus, none of which are universally accepted. Both thalamic lesions and high-frequency stimulation ameliorate tremor in diverse pathological conditions. Modern neurophysiological techniques have allowed the recording of the activity of thalamic neurons in patients with different clinical conditions. This has provided a better understanding of the functions of the motor thalamus in humans. The aim of the present article is to briefly review the major anatomic and physiological aspects of the motor thalamus as well as the electrophysiological findings described in humans undergoing surgical procedures.

Electrophysiology↗
PubMed2005

Involvement of the central thalamus in the control of smooth pursuit eye movements.

During maintenance of smooth pursuit eye movements, the brain must keep track of pursuit velocity to reconstruct target velocity from motion of retinal images. Although a recent study showed that corollary discharge signals through the thalamus to the cortex are used for internal monitoring of saccades, it remains unknown whether signals in the thalamus also contribute to monitoring and on-line regulation of smooth pursuit. The present study sought possible roles of the thalamocortical pathways in pursuit by recording activities of single thalamic neurons and by analyzing the effects of local inactivation. Data showed that many neurons in the ventrolateral thalamus exhibited directional modulation during pursuit. Most neurons discharged before or during initiation of pursuit, and the firing rate was proportional to the speed of target motion in a preferred direction. When the tracking target was extinguished briefly during maintenance of pursuit, these neurons continued firing, indicating that they carried extra-retinal, eye movement signals. The majority of neurons showed no change in activity around the time of small catch-up saccades during pursuit but responded transiently to large (16 degrees) memory-guided saccades in the preferred pursuit direction. Local inactivation of the recording sites did not alter pursuit latency but reduced eye velocity modestly during initiation and maintenance of ipsiversive pursuit. The results suggest that the central thalamus lies within pathways that regulate and monitor smooth pursuit eye movements.

Animals↗
PubMed2005

Spatiotemporal gating of sensory inputs in thalamus during quiescent and activated states.

The main role of the thalamus is to relay sensory inputs to the neocortex according to the regulations dictated by behavioral state. Hence, changes in behavioral state are likely to transform the temporal and spatial properties of thalamocortical receptive fields. We compared the receptive fields of single cells in the ventroposterior medial thalamus (VPM) of urethane-anesthetized rats during quiescent states and during aroused (activated) states. During quiescent states, VPM cells respond to stimulation of a principal whisker (PW) and may respond modestly to one or a few adjacent whiskers (AWs). During either generalized forebrain activation or selective thalamic activation caused by carbachol infusion in the VPM, the responses to AWs enhance so that VPM receptive fields become much larger. Such enlargement is not observed at the level of the principal trigeminal nucleus, indicating that it originates within the thalamus. Interestingly, despite the increase in AW responses during activation, simultaneous deflection of the PW and AWs produced VPM responses that resembled the PW response, as if the AWs were not stimulated. This nonlinear summation of sensory responses was present during both quiescent and activated states. In conclusion, the thalamus suppresses the excitatory surround (AWs) of the receptive field during quiescent states and enlarges this surround during arousal. But, thalamocortical cells represent only the center (PW) of the receptive field when the center (PW) and surround (AWs) are stimulated simultaneously.

Anesthesia↗
PubMed2006

Noradrenergic activation amplifies bottom-up and top-down signal-to-noise ratios in sensory thalamus.

Thalamocortical cells receive sensory signals via primary sensory afferents and cortical signals via corticothalamic afferents. These signals are influenced by a variety of neuromodulators that are released in the thalamus during specific behavioral states. Hence, different neuromodulators may set different thalamic modes of sensory information processing. We found that noradrenergic activation affects sensory and corticothalamic signals in the whisker thalamus differently than cholinergic activation. Whereas cholinergic activation increases the spontaneous firing (noise) and enlarges the receptive fields of ventroposterior medial thalamus (VPM) cells, noradrenergic activation decreases spontaneous firing and focuses receptive fields. Consequently, for sensory signals, noradrenergic activation sets bottom-up thalamic processing to a focused and noise-free excitatory receptive field, which contrasts with the broad and noisy excitatory receptive field characteristic of cholinergic activation. For corticothalamic signals, noradrenergic activation sets top-down processing to a noise-free high-frequency signal detection mode, whereas cholinergic activation produces a noisy broadband signal detection mode. The effects of noradrenergic activation on signal-to-noise ratios of VPM cells were found to be mediated by nucleus reticularis thalamic (nRt) cells. Hence, a major role of nRt cells is to regulate the noise level of thalamocortical cells during sensory processing. In conclusion, different modulators establish distinct modes of bottom-up and top-down information processing in the sensory thalamus.

Action Potentials↗
PubMed1997

Toward an agreement on terminology of nuclear and subnuclear divisions of the motor thalamus.

The nomenclature most commonly applied to the motor-related nuclei of the human thalamus differs substantially from that applied to the thalamus of other primates, from which most knowledge of input-output connections is derived. Knowledge of these connections in the human is a prerequisite for stereotactic neurosurgical approaches designed to alleviate movement disorders by the placement of lesions in specific nuclei. Transfer to humans of connectional information derived from experimental studies in nonhuman primates requires agreement about the equivalence of nuclei in the different species, and dialogue between experimentalists and neurosurgeons would be facilitated by the use of a common nomenclature. In this review, the authors compare the different nomenclatures and review the cyto- and chemoarchitecture of the nuclei in the anterolateral aspect of the ventral nuclear mass in humans and monkeys, suggest which nuclei are equivalent, and propose a common terminology. On this basis, it is possible to identify the nuclei of the human motor thalamus that transfer information from the substantia nigra, globus pallidus, cerebellum, and proprioceptive components of the medial lemniscus to prefrontal, premotor, motor, and somatosensory areas of the cerebral cortex. It also becomes possible to suggest the principal functional systems involved in stereotactically guided thalamotomies and the functional basis of the symptoms observed following ischemic lesions in different parts of the human thalamus.

Afferent Pathways↗
PubMed1997

Toward an agreement on terminology of nuclear and subnuclear divisions of the motor thalamus.

The nomenclature most commonly applied to the motor-related nuclei of the human thalamus differs substantially from that applied to the thalamus of other primates, from which most knowledge of input-output connections is derived. Knowledge of these connections in the human is a prerequisite for stereotactic neurosurgical approaches designed to alleviate movement disorders by the placement of lesions in specific nuclei. Transfer to humans of connectional information derived from experimental studies in nonhuman primates requires agreement about the equivalence of nuclei in the different species, and dialogue between experimentalists and neurosurgeons would be facilitated by the use of a common nomenclature. In this review, the authors compare the different nomenclatures and review the cyto- and chemoarchitecture of the nuclei in the anterolateral aspect of the ventral nuclear mass in humans and monkeys, suggest which nuclei are equivalent, and propose a common terminology. On this basis, it is possible to identify the nuclei of the human motor thalamus that transfer information from the substantia nigra, globus pallidus, cerebellum, and proprioceptive components of the medial lemniscus to prefrontal, premotor, motor, and somatosensory areas of the cerebral cortex. It also becomes possible to suggest the principal functional systems involved in stereotactically guided thalamotomies and the functional basis of the symptoms observed following ischemic lesions in different parts of the human thalamus.

Afferent Pathways↗
PubMed2003

Deep arteriovenous malformations of the basal ganglia and thalamus: natural history.

OBJECT: Patients with arteriovenous malformations (AVMs) in a deep location and with deep venous drainage are thought to be at higher risk for hemorrhage than those with AVMs in other locations. Despite this, the natural history of AVMs of the basal ganglia and thalamus has not been well studied. METHODS: The authors retrospectively evaluated a cohort of 96 patients with AVMs in the basal ganglia and thalamus with respect to the tendency of these lesions to hemorrhage between the time of detection and their eventual successful management. The 96 patients studied had a mean age of 22.7 years at diagnosis, and 51% were male. Intracranial hemorrhage (ICH) was the event leading to clinical detection in 69 patients (71.9%), and 85.5% of these patients were left with hemiparesis. After diagnosis, 25 patients bled a total of 49 times. The cumulative clinical follow up after detection but before surgical management was 500.2 patient-years. The risk of hemorrhage after detection of an AVM of the basal ganglia or thalamus was 9.8% per patient-year. CONCLUSIONS: The rate of ICH in patients with AVMs of the basal ganglia or thalamus (9.8%/year) is much higher than the rate in patients with AVMs in other locations (2-4%/year). The risk of incurring a neurological deficit with each hemorrhagic event is high. Treatment of these patients at specialized centers is recommended to prevent neurological injury from a spontaneous ICH.

Adult↗
PubMed2004

Tremor cells in the human thalamus: differences among neurological disorders.

OBJECT: Thalamic neurons firing at frequencies synchronous with tremor are thought to play a critical role in the generation and maintenance of tremor. The authors studied the incidence and locations of neurons with tremor-related activity (TRA) in the thalamus of patients with varied pathological conditions-including Parkinson disease (PD), essential tremor (ET), multiple sclerosis (MS), and cerebellar disorders--to determine whether known differences in the effectiveness of thalamic stereotactic procedures for these tremors could be correlated to differences in the incidence or locations of TRA cells. METHODS: Seventy-five operations were performed in 61 patients during which 686 TRA cells were recorded from 440 microelectrode trajectories in the thalamus. The locations of the TRA cells in relation to electrophysiologically defined thalamic nuclei and the commissural coordinates were compared among patient groups. The authors found that TRA cells are present in patients with each of these disorders and that these cells populate several nuclei in the ventral lateral tier of the thalamus. There were no large differences in the locations of TRA cells among the different diagnostic classes, although there was a difference in the incidence of TRA cells in patients with PD, who had greater than 3.8 times more cells per thalamic trajectory than patients with ET and approximately five times more cells than patients with MS or cerebellar disorders. CONCLUSIONS: There was an increased incidence of TRA in the thalamus of patients with PD. The location of thalamic TRA cells in patients with basal ganglia and other tremor disorders was similar.

Adult↗