The insula of Reil revisited: multiarchitectonic organization in macaque monkeys.

The insula of Reil represents a large cortical territory buried in the depth of the lateral sulcus and subdivided into 3 major cytoarchitectonic domains: agranular, dysgranular, and granular. The present study aimed at reinvestigating the architectonic organization of the monkey's insula using multiple immunohistochemical stainings (parvalbumin, PV; nonphosphorylated neurofilament protein, with SMI-32; acetylcholinesterase, AChE) in addition to Nissl and myelin. According to changes in density and laminar distributions of the neurochemical markers, several zones were defined and related to 8 cytoarchitectonic subdivisions (Ia1-Ia2/Id1-Id3/Ig1-Ig2/G). Comparison of the different patterns of staining on unfolded maps of the insula revealed: 1) parallel ventral to dorsal gradients of increasing myelin, PV- and AChE-containing fibers in middle layers, and of SMI-32 pyramidal neurons in supragranular layers, with merging of dorsal and ventral high-density bands in posterior insula, 2) definition of an insula "proper" restricted to two-thirds of the "morphological" insula (as bounded by the limiting sulcus) and characterized most notably by lower PV, and 3) the insula proper is bordered along its dorsal, posterodorsal, and posteroventral margin by a strip of cortex extending beyond the limits of the morphological insula and continuous architectonically with frontoparietal and temporal opercular areas related to gustatory, somatosensory, and auditory modalities.

Does greater low frequency EEG activity in normal immaturity and in children with epilepsy arise in the same neuronal network?

Greater low frequency power (<8 Hz) in the electroencephalogram (EEG) at rest is normal in the immature developing brain of children when compared to adults. Children with epilepsy also have greater low frequency interictal resting EEG activity. Whether these power elevations reflect brain immaturity due to a developmental lag or the underlying epileptic pathophysiology is unclear. The present study addresses this question by analyzing spectral EEG topographies and sources for normally developing children and children with epilepsy. We first compared the resting EEG of healthy children to that of healthy adults to isolate effects related to normal brain immaturity. Next, we compared the EEG from 10 children with generalized cryptogenic epilepsy to the EEG of 24 healthy children to isolate effects related to epilepsy. Spectral analysis revealed that global low (delta: 1-3 Hz, theta: 4-7 Hz), medium (alpha: 8-12 Hz) and high (beta: 13-25 Hz) frequency EEG activity was greater in children without epilepsy compared to adults, and even further elevated for children with epilepsy. Topographical and tomographic EEG analyses showed that normal immaturity corresponded to greater delta and theta activity at fronto-central scalp and brain regions, respectively. In contrast, the epilepsy-related activity elevations were predominantly in the alpha band at parieto-occipital electrodes and brain regions, respectively. We conclude that lower frequency activity can be a sign of normal brain immaturity or brain pathology depending on the specific topography and frequency of the oscillating neuronal network.

Cross-modal plasticity in the human thalamus: evidence from intraoperative macrostimulations.

During stereotactic functional neurosurgery, stimulation procedure to control for proper target localization provides a unique opportunity to investigate pathophysiological phenomena that cannot be addressed in experimental setups. Here we report on the distribution of response modalities to 487 intraoperative thalamic stimulations performed in 24 neurogenic pain (NP), 17 parkinsonian (PD) and 10 neuropsychiatric (Npsy) patients. Threshold responses were subdivided into somatosensory, motor and affective, and compared between medial (central lateral nucleus) and lateral (ventral anterior, ventral lateral and ventral medial) thalamic nuclei and between patients groups. Major findings were as follows: in the medial thalamus, evoked responses were for a large majority (95%) somatosensory in NP patients, 47% were motor in PD patients, and 54% affective in Npsy patients. In the lateral thalamus, a much higher proportion of somatosensory (83%) than motor responses (5%) was evoked in NP patients, while the proportion was reversed in PD patients (69% motor vs. 21% somatosensory). These results provide the first evidence for functional cross-modal changes in lateral and medial thalamic nuclei in response to intraoperative stimulations in different functional disorders. This extensive functional reorganization sheds new light on wide-range plasticity in the adult human thalamocortical system.

Thalamocortical theta coherence in neurological patients at rest and during a working memory task.

We simultaneously recorded the local field potential (LFP) in the thalamus and the electroencephalogram (EEG) on the scalp of 5 patients suffering from neurogenic pain, epilepsy and movement disorders. In an earlier study [], we have investigated the slowing of EEG and the high thalamocortical coherence in the framework of thalamocortical dysrhythmia, the common underlying pathophysiology. The current study focuses on the effects of different cognitive conditions. When patients rested with eyes closed, a theta peak dominated the EEG spectra. The peak height was reduced upon opening the eyes, reminiscent of the classical alpha blocking. This peak reduction also appeared in the thalamic LFP recording. When patients activated their working memory by counting backwards, the theta peak increased in scalp EEG or in the LFP recorded in thalamic nuclei VA/VL. The coherence estimates between EEG and LFP ranged between 21% and 76% for different patients and cognitive conditions (mean: 50%). The involvement of both cortex and thalamus in working memory and the high thalamocortical coherence underline, in addition to cortico-cortical interactions, the importance of thalamocortical modules in the generation of higher cognitive functions.

[Toward a unified theory of positive symptoms]. / Vers une théorie unifiée des symptômes positifs.

Defined more than one century ago, the concept of positive symptoms has become obsolete, except in the psychiatric domain. However, its relevance remains intact today when considering such pathophysiologies as neuropathic (phantom) pain, movement disorders, tinnitus, epilepsy, and psychiatric disorders. Beside their very different clinical characteristics, all these symptoms arise from a lesion in the nervous system. Furthermore, they are paradoxical in the sense that they correspond to a spontaneous hyperactivity of the injured functional system, concomitant to the usual deficits resulting from the lesion. Could these similarities reflect the existence of some common pathophysiological process? A peculiar electrophysiological property of thalamic cells is likely to be compatible with this hypothesis. A thalamic cell produces action potentials when depolarised by excitatory inputs. Conversely, its ability to produce action potentials is decreased or even completely suppressed when the same cell is hyperpolarized by inhibitory influences. However, depending on its level of hyperpolarization, this cell can also produce rhythmic paradoxical bursts of activity at low frequency (3-4 Hz). In this context, a lesion involving, for example, the somatosensory excitatory fibres gives rise to hyperpolarization of the corresponding thalamic cells, which may produce such rhythmic bursting activity. This causes an increase of low frequency thalamo-cortical activity, which, through reduction of collateral cortico-cortical inhibition, induces high frequency activity in neighbouring thalamo-cortical loops ("edge effect"). This leads to the appearance of the clinical symptoms, in this case, pain. Electrophysiological recordings performed in patients suffering from sensory or motor positive symptoms have shown the presence of such deleterious sequence of events. Furthermore, the efficiency of neurosurgical treatments that are used against some positive symptoms can be explained on the basis of such a dynamic process. Both considerations support the validity of the proposed hypothesis and open avenues for the control of other positive symptoms.

Neuropsychiatric thalamocortical dysrhythmia: surgical implications.

Clearly, more clinical experience must be amassed to define in detail the possibilities of this surgical approach in disabling neuropsychiatric disorders. We propose, however, that the evidence for benign and efficient surgical intervention against the neuropsychiatric TCD syndrome is already compelling. The potential appearance of strong postoperative reactive manifestations requires a close association between surgery and psychotherapy, with the latter providing support for the integration of the new situation as well as the resolution of old unresolved issues.

Brain sources of EEG gamma frequency during volitionally meditation-induced, altered states of consciousness, and experience of the self.

Multichannel EEG of an advanced meditator was recorded during four different, repeated meditations. Locations of intracerebral source gravity centers as well as Low Resolution Electromagnetic Tomography (LORETA) functional images of the EEG 'gamma' (35-44 Hz) frequency band activity differed significantly between meditations. Thus, during volitionally self-initiated, altered states of consciousness that were associated with different subjective meditation states, different brain neuronal populations were active. The brain areas predominantly involved during the self-induced meditation states aiming at visualization (right posterior) and verbalization (left central) agreed with known brain functional neuroanatomy. The brain areas involved in the self-induced, meditational dissolution and reconstitution of the experience of the self (right fronto-temporal) are discussed in the context of neural substrates implicated in normal self-representation and reality testing, as well as in depersonalization disorders and detachment from self after brain lesions.

Microelectrode recording and macrostimulation in thalamic and subthalamic MRI guided stereotactic surgery.

Stereotactic neurosurgery aims at placing therapeutic lesions or chronic stimulating electrodes at very precise locations within the brain. Microelectrode recording and macrostimulation are used in addition to anatomoradiological techniques to optimize targeting. Recently, the usefulness of electrophysiological procedures has been questioned. Based on more than 500 therapeutic stereotactic lesions in the last 10 years at the thalamic and subthalamic levels, we evaluate here retrospectively the utility of the two electrophysiological procedures. In two of the three stereotactic targets considered in this study, intraoperative electrophysiological confirmation is mandatory because of the target size with respect to interindividual anatomical variations and of the more or less close vicinity of eloquent structures.

The Morel stereotactic atlas of the human thalamus: atlas-to-MR registration of internally consistent canonical model.

In 1997, Morel, Magnin, and Jeanmonod presented a microscopic stereotactic atlas of the human thalamus. Parcellations of thalamic nuclei did not only use cyto- and myeloarchitectonic criteria, but were additionally corroborated by staining for calcium-binding proteins, which bears functional significance. The atlas complies with the Anglosaxon nomenclature elaborated by Jones and the data were sampled in three orthogonal planes in the AC-PC reference space. We report on the generation of three-dimensional digital models of the thalamus based on the three sets of sections (sagittal, horizontal, and frontal). Spatial differences between the three anatomical specimens were evaluated using the centers of gravity of 13 selected nuclei as landmarks. Subsequent linear regression analysis yielded equations, which were used to normalize the frontal and horizontal digital models to the sagittal one. The outcome is an internally consistent Canonical Model of Morel's atlas, which minimizes the linear component of the variability between the three sectioned anatomical specimens. In addition, we demonstrate the feasibility of the atlas-to-MRI registration in conjunction with on-line visualization of the trajectory in the digital models.

Effects of medial thalamotomy and pallido-thalamic tractotomy on sleep and waking EEG in pain and Parkinsonian patients.

OBJECTIVES: Investigation of sleep and sleep EEG before and after stereotactic neurosurgery. METHODS: All-night polysomnographic recordings were obtained in 3 neurogenic pain patients and 3 parkinsonian patients. One subject of each group was recorded in addition 3 months after surgery. Stereotactic operations were performed in the medial thalamus and on the pallido-thalamic tract to relieve neurogenic pain and parkinsonian symptoms, respectively. RESULTS: Sleep efficiency was little affected by the surgical intervention in neurogenic pain patients and a dramatic reduction in REM sleep occurred, which had recovered in the subject recorded after 3 months. After the surgery parkinsonian patients showed an increase in total sleep time and in sleep efficiency, and a decrease in REM sleep latency. Sleep efficiency remained elevated in the 3 months follow-up. Medial thalamotomy abolished spindle frequency activity (SFA) in the power and coherence spectra in non-REM sleep stage 2 systematically. Pallido-thalamic tractotomy attenuated SFA only to varying degrees. After 3 months SFA had reemerged. The alpha peak of the waking EEG was shifted to lower frequencies after surgery in 5 of 6 patients and had reverted to the original frequency 3 months later. CONCLUSIONS: Medial thalamotomy or pallido-thalamic tractotomy had acute and reversible effects on the EEG and long-term deleterious side effects of stereotactic surgery on sleep and sleep EEG are improbable. The results provide further evidence for the involvement of the human thalamus in the generation of sleep spindles.

Single-unit analysis of the pallidum, thalamus and subthalamic nucleus in parkinsonian patients.

Microelectrode-guided stereotactic operations performed in 29 parkinsonian patients allowed the recording of 86 cells located in the globus pallidus and 563 in thalamic nuclei. In the globus pallidus, the average firing rate was significantly higher in the internal (91+/-52 Hz) than in the external (60+/-21 Hz) subdivision. This difference was further accentuated when the average firing rate in the external subdivision was compared with that of the internal part of the internal subdivision (114+/-30 Hz). A rhythmic modulation in globus pallidus activities was observed in 19.7% of the cells, and this only during rest tremor episodes. In these cases, modulation frequency of unit activities was not statistically different from the rest tremor frequency (average: 4.6+/-0.5 vs 4. 4+/-0.4 Hz, respectively). In the medial thalamus, four types of unit activities could be defined. A sporadic type was mainly found in the parvocellular division of the mediodorsal nucleus (96.8% of the cells recorded) and in the centre median-parafascicular complex (74.2%). Two other types of activities characterized by random or rhythmic bursts fulfilling the extracellular criteria of low-threshold calcium spike bursts were concentrated in the central lateral nucleus (62.3%) and the paralamellar division of the mediodorsal nucleus (34.1%). These activities could be recorded independently of the presence of a rest tremor. When a tremor episode occurred, the rhythmic low-threshold calcium spike bursts had an interburst frequency similar to rest tremor frequency, although they were not synchronized with it. The fourth type, the so-called tremor locked, was also characterized by rhythmic bursts which, however, did not display low-threshold calcium spike burst properties. These bursts occurred only when a rest tremor was present and was in-phase with the electromyographic bursts. All tremor-locked cells were located in the centre median-parafascicular complex. In the lateral thalamus, cells exhibiting random or rhythmic low-threshold calcium spike bursts were found preponderantly in the ventral anterior nucleus (53.4%) and in the ventral lateral anterior nucleus (52.7%). Tremor-locked units were confined to the ventral division of the ventral lateral posterior nucleus (35.4%). None of the random or rhythmic low-threshold calcium spike bursting units responded to somatosensory stimuli or voluntary movements, either in the medial or in the lateral thalamus. The presence of low-threshold calcium spike bursts at the thalamic level, together with the paucity (8%) of responses to voluntary movements compared to what is found in normal non-human primates, demonstrate a pathological state of inhibition due to the overactivity of the internal subdivision of the globus pallidus units. Activities of the thalamic cells producing low-threshold calcium spike bursts are not synchronized with each other or with the tremor. However, this does not exclude a causal role of these activities in the generation of tremor. Indeed, it has been demonstrated that even random electrical stimulations of the rolandic cortex in parkinsonian patients induce tremor episodes, probably due to the triggering of rhythmic, low-threshold calcium spike-dependent, thalamocortical activities. Similarly, low-threshold calcium spike bursts could be at the origin of rigidity and dystonia through an activation of the supplementary motor area and of akinesia when reaching the pre-supplementary motor area. We conclude that the intrinsic oscillatory properties of individual neurons, combined with the dynamic properties of the thalamocortical circuitry, are responsible for the three cardinal parkinsonian symptoms.

Thalamocortical dysrhythmia: A neurological and neuropsychiatric syndrome characterized by magnetoencephalography.

Spontaneous magnetoencephalographic activity was recorded in awake, healthy human controls and in patients suffering from neurogenic pain, tinnitus, Parkinson's disease, or depression. Compared with controls, patients showed increased low-frequency theta rhythmicity, in conjunction with a widespread and marked increase of coherence among high- and low-frequency oscillations. These data indicate the presence of a thalamocortical dysrhythmia, which we propose is responsible for all the above mentioned conditions. This coherent theta activity, the result of a resonant interaction between thalamus and cortex, is due to the generation of low-threshold calcium spike bursts by thalamic cells. The presence of these bursts is directly related to thalamic cell hyperpolarization, brought about by either excess inhibition or disfacilitation. The emergence of positive clinical symptoms is viewed as resulting from ectopic gamma-band activation, which we refer to as the "edge effect." This effect is observable as increased coherence between low- and high-frequency oscillations, probably resulting from inhibitory asymmetry between high- and low-frequency thalamocortical modules at the cortical level.

Accuracy of MRI-guided stereotactic thalamic functional neurosurgery.

Our goal was to evaluate the accuracy of stereotactic technique using MRI in thalamic functional neurosurgery. A phantom study was designed to estimate errors due to MRI distortion. Stereotactic mechanical accuracy was assessed with the Suetens-Gybels-Vandermeulen (SGV) angiographic localiser. Three-dimensional MRI reconstructions of 86 therapeutic lesions were performed. Their co-ordinates were corrected from adjustments based on peroperative electrophysiological data and compared to those planned. MR image distortion (maximum: 1 mm) and chemical shift of petroleum oil-filled localiser rods (2.2 mm) induced an anterior target displacement of 2.6 mm (at a field strength of 1.5 T, frequency encoding bandwidth of 187.7 kHz, on T1-weighted images). The average absolute error of the stereotactic material was 0.7 mm for anteroposterior (AP), 0.5 mm for mediolateral (ML) and 0.8 mm for dorsoventral (DV) co-ordinates (maximal absolute errors: 1.6 mm, 2.2 mm and 1.7 mm, respectively; mean euclidean error: 1 mm). Three-dimensional MRI reconstructions showed an average absolute error of 0.8 mm, 0.9 mm and 1.9 mm in AP, ML and DV co-ordinates, respectively (maximal absolute errors: 2.4 mm, 2.7 mm and 5.7 mm, respectively; mean euclidean error: 2.3 mm). MRI distortion and chemical-shift errors must be determined by a phantom study and then compensated for. The most likely explanation for an average absolute error of 1.9 mm in the DV plane is displacement of the brain under the pressure of the penetrating electrode. When this displacement is corrected for by microelectrode recordings and stimulation data, MRI offers a high degree of accuracy and reliability for thalamic stereotaxy.

Microanatomic and vascular aspects of the temporomesial region.

OBJECTIVE: The aim of this work was to provide a detailed description of the arterial vascularization of the temporomesial region (TMR), correlated with the definitions of the macroscopic and cytoarchitectonic subdivisions of this area. METHODS: Selective colored arterial injections were performed in 16 hemispheres to study their blood supply. Four hemispheres were used to illustrate the macroscopic aspect of the TMR and were then cut into thin sections and stained with Nissl's stain to study the cytoarchitectonic areas. RESULTS: The surface of the TMR is subdivided into several areas: anteriorly, the lateral olfactory gyrus is covered by prepiriform cortex; dorsomedially, the semilunar gyrus and uncus hippocampi consist, respectively, of cortical amygdaloid nucleus and hippocampal cytoarchitectonic fields; and ventrolaterally, the anterior part of the parahippocampal gyrus is covered by periamygdaloid cortex, entorhinal, and transentorhinal areas and its posterior part is covered by Fields TH and TF per Von Economo and subicular complex. Six cortical arterial groups were defined: Group I, anterosuperior parahippocampal arteries (mean, 3.9 arteries) vascularize the ambiens, semilunar, and lateral olfactory gyri (origins: middle cerebral artery, anterior choroidal artery [AChA], posterior cerebral artery [PCA], and internal carotid artery); Group II, anteroinferior parahippocampal arteries (mean, 2.8 arteries) irrigate the anterior ventrolateral region of the parahippocampal gyrus (origins: middle cerebral artery, PCA, and AChA); Group III, medial uncal arteries (mean, 1.9 arteries) supply the medial part of uncus hippocampi (origins: AChA and PCA); Group IV, lateral uncal arteries (mean, 2.9 arteries) vascularize the lateral part of the uncus hippocampi (origins: AChA and PCA); Group V, several small posterior parahippocampal arteries irrigate Fields TF and TH per Von Economo (origins: PCA and AChA); and Group VI, posterior hippocampal arteries (mean, 3.2 arteries) irrigate the posterior part of hippocampal formation (origin: PCA). Many anastomoses are found among these arteries, particularly in the ventrolateral part of the TMR. Three groups of amygdaloid arteries were defined: Group I, the anterolateral group (mean, 5.7 arteries) (origin: middle cerebral artery); Group II, the medial group (mean, 6.4 arteries) (origins: AChA, internal carotid artery, and PCA); and Group III, the posterolateral group (mean, 5 arteries) (origins: AChA and internal carotid artery). CONCLUSION: We hope that this work will be useful for any microneurosurgical procedures on the TMR. We have clarified the macroscopic and histological definitions of the cortical and nuclear areas of the TMR and the arterial groups closely related to them. The systematic analysis of the variability of the arterial vascularization of this area was our second goal; such a goal, however, requires more observations to be exhaustive. The numerous interterritorial anastomoses found inside the TMR imply that a selective presurgical injection of short-acting barbiturates to evaluate its functions (Wada test) may well result in its diffusion to other areas of the TMR.

Does sacral posterior rhizotomy suppress autonomic hyper-reflexia in patients with spinal cord injury?

OBJECTIVE: To study the occurrence of autonomic hyper-reflexia (AHR) after intradural sacral posterior rhizotomy combined with intradural sacral anterior root stimulation, performed to manage the neurogenic hyper-reflexic bladder and to determine the pathophysiological basis of the uncontrolled hypertensive crisis after sacral de-afferentation. PATIENTS AND METHODS: Ten patients with spinal cord injury operated using Brindley's method between September 1990 and February 1994 were reviewed. Systematic continuous non-invasive recordings of cardiovascular variables (using a photoplethysmograph) were made during urodynamic recordings and the pre- and post-operative vesico-urethral and cardiovascular data compared. RESULTS: Nine of the 10 patients were examined using a new prototype measurement system; one woman refused the last urodynamic assessment. Eight of the nine patients who presented with AHR before operation still had the condition afterward. There was a marked elevation in systolic and diastolic blood pressure during the urodynamic examination in all eight patients, despite complete intra-operative de-afferentation of the bladder in five. The elevation of blood pressure started during the stimulation-induced bladder contractions and increased during voiding in all cases. Five patients showed a decrease in heart rate during the increase in blood pressure. However, in three patients the heart rate did not change or even sometimes slightly increased as the arterial blood pressure exceeded 160 mmHg, when the blood pressure and heart rate then increased together. CONCLUSIONS: These results confirm that even after complete sacral de-afferentation. AHR persisted in patients with spinal cord injury and always occurred during the stimulation-induced voiding phase. In cases of incomplete de-afferentation, small uninhibited bladder contractions without voiding occurred during the filling phase. The blood pressure then increased but never reached the value recorded during stimulation-induced micturition. Stimulation of afferents that enter the spinal cord by the thoracic and lumbar roots and that are not influenced by sacral rhizotomy could explain why AHR increases during urine flow. The distinct threshold of decreased heart rate by increasing blood pressure to > 160 mmHg focuses attention on the chronotropic influences of the sympathetic nerves in the heart by an exhausted baroreceptor reflex.

Multiarchitectonic and stereotactic atlas of the human thalamus.

To improve anatomical definition and stereotactic precision of thalamic targets in neurosurgical treatments of chronic functional disorders, a new atlas of the human thalamus has been developed. This atlas is based on multiarchitectonic parcellation in sections parallel or perpendicular to the standard intercommissural reference plane. The calcium-binding proteins parvalbumin (PV), calbindin D-28K (CB), and calretinin (CR) were used as neurochemical markers to further characterize thalamic nuclei and delimit subterritories of functional significance for stereotactic explorations. Their overall distribution reveals a subcompartmentalization of thalamic nuclei into several groups. Predominant PV immunostaining characterizes primary somatosensory, visual and auditory nuclei, the ventral lateral posterior nucleus, reticular nucleus (R), and to a lesser degree also, lateral part of the centre median nucleus, and anterior, lateral, and inferior divisions of the pulvinar complex. In contrast, CB immunoreactivity is prevalent in medial thalamic nuclei (intralaminar and midline), the posterior complex, ventral posterior inferior nucleus, the ventral lateral anterior nucleus, ventral anterior, and ventral medial nuclei. The complementary distributions of PV and CB appear to correlate with distinct lemniscal and spinothalamic somatosensory pathways and to cerebellar and pallidal motor territories, respectively. Calretinin, while overlapping with CB in medial thalamic territories, is also expressed in R and limbic associated anterior group nuclei that contain little or no CB. Preliminary analysis indicates that interindividual nuclear variations cannot easily be taken into account by standardization procedures. Nevertheless, some corrections in antero-posterior coordinates in relation to different intercommissural distances are proposed.

Posterior sacral rhizotomy and intradural anterior sacral root stimulation for treatment of the spastic bladder in spinal cord injured patients.

PURPOSE: The efficacy of intradural sacral posterior rhizotomy combined with intradural sacral anterior root stimulation in the treatment of the neurogenic hyperreflexic bladder was evaluated. MATERIALS AND METHODS: We reviewed 10 spinal cord injured patients who underwent surgery between September 1990 and February 1994. Bladder function was compared preoperatively and postoperatively. Intraoperative data on electrostimulation of the detrusor and striated muscles were analyzed. RESULTS: Stimulation of the anterior S3 and S4 roots was mostly used to empty the bladder (7 of 10 cases). Preoperative reflex incontinence disappeared in all patients postoperatively. Mean postoperative bladder capacity increases and mean postoperative post-void residual decreases were at least 340 ml. (p < 0.01) and 140 ml. (p < 0.01), respectively. Preoperative vesicorenal reflux disappeared in 2 and improved in 3 cases after sacral deafferentation. Autonomic hyperreflexia, which was present preoperatively in 6 patients, never disappeared but significantly improved after deafferentation. No major complications were noted postoperatively. CONCLUSIONS: Intradural sacral posterior rhizotomy combined with intradural sacral anterior root stimulation is a valuable method to treat the hyperreflexic bladder with incontinence resistant to conservative therapy in spinal cord injured patients. Autonomic hyperreflexia was decreased but not suppressed by posterior sacral rhizotomy.

Low-threshold calcium spike bursts in the human thalamus. Common physiopathology for sensory, motor and limbic positive symptoms.

Positive symptoms arise after lesions of the nervous system. They include neurogenic pain, tinnitus, abnormal movements, epilepsy and certain neuropsychiatric disorders. Stereotactic medial thalamotomies were performed on 104 patients with chronic therapy-resistant positive symptoms. Peroperative recordings of 2012 single units revealed an overwhelming unresponsiveness (99%) to sensory stimuli or motor activation. Among these unresponsive cells, 45.1% presented a rhythmic or random bursting activity. Rhythmic bursting activities had an average interburst interval of 263 +/- 46 ms corresponding to a frequency of 3.8 +/- 0.7 Hz. Frequency variations among the different symptoms were not statistically different. Intraburst characteristics such as the highest frequency encountered in the burst (480 +/- 80 Hz) or the mean frequency of the burst (206 +/- 44 Hz) were also similar in all patients. All bursts, rhythmic or random, fulfilled the extracellular criteria of low-threshold calcium spike (LTS) bursts. After medial thalamotomy and depending on the symptom, 43-67% of the patients reached a 50-100% relief, with sparing of all neurological functions. On the basis of these electrophysiological and clinical results, we propose a unified concept for all positive symptoms centred on a self-perpetuating thalamic cell membrane hyperpolarization, similar to the one seen in slow-wave sleep.

Chronic neurogenic pain and the medial thalamotomy.

69 patients suffering from chronic therapy-resistant neurogenic pain of peripheral and/or central origin underwent a stereotactic medial thalamotomy. Medial thalamic unit recordings were performed peroperatively, allowing the physiological confirmation of the electrode location and the recognition of a specific physiopathology. Thanks to these recordings, a concept was developed, based on the presence of an imbalance between medial (nucleus centralis lateralis mainly) and lateral (nucleus ventroposterior) thalamic nuclei, resulting in an over-inhibition of both by the reticular thalamic nucleus, and then in a paradoxical activation of pain-related cortical areas. The medial thalamotomy, re-actualized by new technical, anatomical and physiological data, offers a 50-100% relief to 67% of all patients with peripheral as well as central neurogenic pain, on all body localizations, without producing neurological deficits and without risk for the development of iatrogenic pain.

Thalamus and neurogenic pain: physiological, anatomical and clinical data.

Microelectrode recordings in the medial thalamus of 45 neurogenic pain patients undergoing medial thalamotomy revealed that most units (316/318) did not respond to somatosensory stimuli, and that half exhibited low-threshold calcium spike bursts. After medial thalamotomy, 67% of the patients reached a 50 to 100% pain relief, without somatosensory deficits. Colocalization of bursting activities and of the most efficient therapeutic lesions in the central lateral nucleus suggests a key role of this structure in neurogenic pain. We propose that neurogenic pain is due to an imbalance between central lateral and ventroposterior nuclei, resulting in an overinhibition of both by the thalamic reticular nucleus.