Fabian Klostermann

Publications of Fabian Klostermann

• Abnormal distracter processing in adults with attention-deficit-hyperactivity disorder.

  Authors: Frank Marzinzik, Michael Wahl, Doris Krüger, Laura Gentschow, Michael Colla, Fabian Klostermann

  PloS one. 01/2012; 7(3):e33691.

  Subjects with Attention-Deficit Hyperactivity Disorder (ADHD) are overdistractible by stimuli out of the intended focus of attention. This control deficit could be due to primarily reducedSubjects with Attention-Deficit Hyperactivity Disorder (ADHD) are overdistractible by stimuli out of the intended focus of attention. This control deficit could be due to primarily reduced attentional capacities or, e. g., to overshooting orienting to unexpected events. Here, we aimed at identifying disease-related abnormalities of novelty processing and, therefore, studied event-related potentials (ERP) to respective stimuli in adult ADHD patients compared to healthy subjects. Fifteen unmedicated subjects with ADHD and fifteen matched controls engaged in a visual oddball task (OT) under simultaneous EEG recordings. A target stimulus, upon which a motor response was required, and non-target stimuli, which did not demand a specific reaction, were presented in random order. Target and most non-target stimuli were presented repeatedly, but some non-target stimuli occurred only once ('novels'). These unique stimuli were either 'relative novels' with which a meaning could be associated, or 'complete novels', if no association was available. In frontal recordings, a positive component with a peak latency of some 400 ms became maximal after novels. In healthy subjects, this novelty-P3 (or 'orienting response') was of higher magnitude after complete than after relative novels, in contrast to the patients with an undifferentially high frontal responsivity. Instead, ADHD patients tended to smaller centro-parietal P3 responses after target signals and, on a behavioural level, responded slower than controls. The results demonstrate abnormal novelty processing in adult subjects with ADHD. In controls, the ERP pattern indicates that allocation of meaning modulates the processing of new stimuli. However, in ADHD such a modulation was not prevalent. Instead, also familiar, only context-wise new stimuli were treated as complete novels. We propose that disturbed semantic processing of new stimuli resembles a mechanism for excessive orienting to commonly negligible stimuli in ADHD.

• Malnutritional neuropathy under intestinal levodopa infusion.

  Authors: Fabian Klostermann, Constanze Jugel, Thomas Müller, Frank Marzinzik

  Journal of neural transmission (Vienna, Austria : 1996). 07/2011; 119(3):369-72.

  Levodopa/Carbidopa intestinal gel infusion (LCIG) for Parkinson's disease is under debate to provoke polyneuropathy (PNP). In our cohort of 20 thus treated patients, two developed debilitating axonalLevodopa/Carbidopa intestinal gel infusion (LCIG) for Parkinson's disease is under debate to provoke polyneuropathy (PNP). In our cohort of 20 thus treated patients, two developed debilitating axonal PNP with deficient pyridoxin and folate levels, and marginal cobalamin. Homocysteine was highly elevated. The neuropathies responded to vitamin replacement. We assume that LCIG can provoke PNP most likely of malnutritional origin. To avoid this side effect, the assessment of predisposing factors before treatment as well as neurophysiological and laboratory screenings appear necessary.

• Jejunal levodopa infusion in long-term DBS patients with Parkinson's disease.

  Authors: Fabian Klostermann, Constanze Jugel, Frank Marzinzik

  Movement disorders : official journal of the Movement Disorder Society. 06/2011; 26(12):2298-9.

• Elevation of total homocysteine levels in patients with Parkinson's disease treated with duodenal levodopa/carbidopa gel.

  Authors: Thomas Müller, Constanze Jugel, Reinhard Ehret, Georg Ebersbach, Gunar Bengel, Siegfried Muhlack, Fabian Klostermann

  Journal of neural transmission (Vienna, Austria : 1996). 02/2011; 118(9):1329-33.

  Levodopa/carbidopa (LD/CD) application elevates total plasma homocysteine (thcys). We determined thcys-, LD- and 3-O-methyldopa (3-OMD) concentrations in 28 patients with Parkinson's disease (PD) onLevodopa/carbidopa (LD/CD) application elevates total plasma homocysteine (thcys). We determined thcys-, LD- and 3-O-methyldopa (3-OMD) concentrations in 28 patients with Parkinson's disease (PD) on a LD/CD duodenal gel treatment. We found a distinct thcys increase (29.52 ± 28.98 μmol/l [median ± SD]) above the 15 μmol/l threshold and a significant (R = 0.7) correlation between LD and 3-OMD. thcys ascent was observed in relation with the onset of atherosclerosis, non-motor symptoms and polyneuropathy in PD patients in the long term.

• Benefit from jejunal levodopa in a patient with apomorphine pump.

  Authors: Fabian Klostermann, Constanze Jugel, Frank Marzinzik

  Journal of neurology. 02/2011; 258(2):311-2.

• Modulation of habit formation by levodopa in Parkinson's disease.

  Authors: Frank Marzinzik, Johann Wotka, Michael Wahl, Lea K Krugel, Catarina Kordsachia, Fabian Klostermann

  PloS one. 01/2011; 6(11):e27695.

  Dopamine promotes the execution of positively reinforced actions, but its role for the formation of behaviour when feedback is unavailable remains open. To study this issue, the performance ofDopamine promotes the execution of positively reinforced actions, but its role for the formation of behaviour when feedback is unavailable remains open. To study this issue, the performance of treated/untreated patients with Parkinson's disease and controls was analysed in an implicit learning task, hypothesising dopamine-dependent adherence to hidden task rules. Sixteen patients on/off levodopa and fourteen healthy subjects engaged in a Go/NoGo paradigm comprising four equiprobable stimuli. One of the stimuli was defined as target which was first consistently preceded by one of the three non-target stimuli (conditioning), whereas this coupling was dissolved thereafter (deconditioning). Two task versions were presented: in a 'Go version', only the target cue required the execution of a button press, whereas non-target stimuli were not instructive of a response; in a 'NoGo version', only the target cue demanded the inhibition of the button press which was demanded upon any non-target stimulus. Levodopa influenced in which task version errors grew from conditioning to deconditioning: in unmedicated patients just as controls errors only rose in the NoGo version with an increase of incorrect responses to target cues. Contrarily, in medicated patients errors went up only in the Go version with an increase of response omissions to target cues. The error increases during deconditioning can be understood as a perpetuation of reaction tendencies acquired during conditioning. The levodopa-mediated modulation of this carry-over effect suggests that dopamine supports habit conditioning under the task demand of response execution, but dampens it when inhibition is required. However, other than in reinforcement learning, supporting dopaminergic actions referred to the most frequent, i. e., non-target behaviour. Since this is passive whenever selective actions are executed against an inactive background, dopaminergic treatment could in according scenarios contribute to passive behaviour in patients with Parkinson's disease.

• Speed effects of deep brain stimulation for Parkinson's disease.

  Authors: Fabian Klostermann, Michael Wahl, Frank Marzinzik, Jan Vesper, Werner Sommer, Gabriel Curio

  Movement disorders : official journal of the Movement Disorder Society. 10/2010; 25(16):2762-8.

  Deep brain stimulation (DBS) of the subthalamic nucleus (STN) accelerates reaction time (RT) in patients with Parkinson's disease (PD), particularly in tasks in which decisions on the response sideDeep brain stimulation (DBS) of the subthalamic nucleus (STN) accelerates reaction time (RT) in patients with Parkinson's disease (PD), particularly in tasks in which decisions on the response side have to be made. This might indicate that DBS speeds up both motor and nonmotor operations. Therefore, we studied the extent to which modifications of different processing streams could explain changes of RT under subthalamic DBS. Ten PD patients on-DBS and off-DBS and 10 healthy subjects performed a choice-response task (CRT), requiring either right or left finger button presses. At the same time, EEG recordings were performed, so that RTs could be assessed together with lateralized readiness potentials (LRP), indicative of movement preparation. Additionally, an oddball task (OT) was run, in which right finger responses to target stimuli were recorded along with cognitive P300 responses. Generally, PD patients off-DBS had longer RTs than controls. Subthalamic DBS accelerated RT only in CRT. This could largely be explained by analog shortenings of LRP. No DBS-dependent changes were identified in OT, neither on the level of RT nor on the level of P300 latencies. It follows that RT accelerations under DBS of the STN are predominantly due to effects on the timing of motor instead of nonmotor processes. This starting point explains why DBS gains of response speed are low in tasks in which reactions are initiated from an advanced level of movement preparation (as in OT), and high whenever motor responses have to be raised from scratch (as in CRT).

• Potentials of telemedicine for green health care.

  Authors: Heinrich J Audebert, Thomas Meyer, Fabian Klostermann

  Frontiers in neurology. 01/2010; 1:10.

  Neurological facilities are traditionally centered in academic hospitals and often far away from the patients' living area. Both, the transfer of patients to remote hospitals and inpatient treatmentNeurological facilities are traditionally centered in academic hospitals and often far away from the patients' living area. Both, the transfer of patients to remote hospitals and inpatient treatment are associated with high energy consumption. Numbers of patients with neurological diseases are expected to increase along with the demographical changes and the environmental impact of neurological treatment should become a target for health policy, therefore. Positive effects have been demonstrated for the use of telemedicine by improving inpatient treatment in local community hospitals or avoiding hospital admissions via monitoring of complex diseases in outpatient settings. We discuss the potentials of telemedicine in the field of in- and outpatient neurological care as well as the need for more scientific evaluation on environmental impacts.

• Differential influence of levodopa on reward-based learning in Parkinson's disease.

  Authors: Susanne Graef, Guido Biele, Lea K Krugel, Frank Marzinzik, Michael Wahl, Johann Wotka, Fabian Klostermann, Hauke R Heekeren

  Frontiers in human neuroscience. 01/2010; 4:169.

  The mesocorticolimbic dopamine (DA) system linking the dopaminergic midbrain to the prefrontal cortex and subcortical striatum has been shown to be sensitive to reinforcement in animals and humans.The mesocorticolimbic dopamine (DA) system linking the dopaminergic midbrain to the prefrontal cortex and subcortical striatum has been shown to be sensitive to reinforcement in animals and humans. Within this system, coexistent segregated striato-frontal circuits have been linked to different functions. In the present study, we tested patients with Parkinson's disease (PD), a neurodegenerative disorder characterized by dopaminergic cell loss, on two reward-based learning tasks assumed to differentially involve dorsal and ventral striato-frontal circuits. 15 non-depressed and non-demented PD patients on levodopa monotherapy were tested both on and off medication. Levodopa had beneficial effects on the performance on an instrumental learning task with constant stimulus-reward associations, hypothesized to rely on dorsal striato-frontal circuits. In contrast, performance on a reversal learning task with changing reward contingencies, relying on ventral striato-frontal structures, was better in the unmedicated state. These results are in line with the "overdose hypothesis" which assumes detrimental effects of dopaminergic medication on functions relying upon less affected regions in PD. This study demonstrates, in a within-subject design, a double dissociation of dopaminergic medication and performance on two reward-based learning tasks differing in regard to whether reward contingencies are constant or dynamic. There was no evidence for a dose effect of levodopa on reward-based behavior with the patients' actual levodopa dose being uncorrelated to their performance on the reward-based learning tasks.

• Thalamo-cortical processing of near-threshold somatosensory stimuli in humans.

  Authors: Fabian Klostermann, Michael Wahl, Jesko Schomann, Andreas Kupsch, Gabriel Curio, Frank Marzinzik

  The European journal of neuroscience. 10/2009;

  Abstract Somatosensory stimuli elicit complex cortical responses that are discernible as somatosensory evoked potentials (SEPs) in scalp electroencephalographic recordings. Whereas earlier SEPAbstract Somatosensory stimuli elicit complex cortical responses that are discernible as somatosensory evoked potentials (SEPs) in scalp electroencephalographic recordings. Whereas earlier SEP components, occurring up to 100 ms after stimulus delivery, have been labeled 'preconscious', later responses have been associated with stimulus awareness. To date, how far these processes are primarily cortical or comprise additional subcortical operations remains open. Therefore, we recorded thalamic and scalp SEPs evoked by perceived as well as unperceived median nerve stimulation in neurosurgical patients with electrodes implanted into the ventral intermediate nucleus of the thalamus for deep brain stimulation. At stimulation intensities below perceptual threshold, only thalamic SEP components appeared consistently during the first 75 ms after stimulus delivery. Stimulation that was perceived by the patients elicited cortical as well as thalamic SEPs that lasted longer than 75 ms. These results indicate that the thalamus remains active after the primary propagation of a sensory signal to the cortex, and suggest that the transition from elementary to higher-order somatosensory processing is based on thalamo-cortical interactions.

• The human thalamus processes syntactic and semantic language violations.

  Authors: Michael Wahl, Frank Marzinzik, Angela D. Friederici, Anja Hahne, Andreas Kupsch, Gerd-Helge Schneider, Douglas Saddy, Gabriel Curio, Fabian Klostermann

  Neuron. 10/2008; 59(5):695-707.

  Numerous linguistic operations have been assigned to cortical brain areas, but the contributions of subcortical structures to human language processing are still being discussed. Using simultaneousNumerous linguistic operations have been assigned to cortical brain areas, but the contributions of subcortical structures to human language processing are still being discussed. Using simultaneous EEG recordings directly from deep brain structures and the scalp, we show that the human thalamus systematically reacts to syntactic and semantic parameters of auditorily presented language in a temporally interleaved manner in coordination with cortical regions. In contrast, two key structures of the basal ganglia, the globus pallidus internus and the subthalamic nucleus, were not found to be engaged in these processes. We therefore propose that syntactic and semantic language analysis is primarily realized within cortico-thalamic networks, whereas a cohesive basal ganglia network is not involved in these essential operations of language analysis.

• The Human Thalamus is Crucially Involved in Executive Control Operations.

  Authors: Frank Marzinzik, Michael Wahl, Gerd-Helge Schneider, Andreas Kupsch, Gabriel Curio, Fabian Klostermann

  Journal of cognitive neuroscience. 04/2008;

  Abstract The processing of executive control is thought to involve cortical as well as thalamic brain areas. However, in which way thalamic structures contribute to the control of behavior and howAbstract The processing of executive control is thought to involve cortical as well as thalamic brain areas. However, in which way thalamic structures contribute to the control of behavior and how cortical versus thalamic processing is coordinated remain to be settled. We therefore aimed at specifying respective activations during the performance of a go/no-go task. To this end, electroencephalogram was recorded simultaneously from scalp and thalamic electrodes in seven patients undergoing deep brain stimulation. Meanwhile, left- or right-directed precues were presented indicating with which index finger a button press should be putatively executed. Thereafter, 2 sec elapsed until a go or no-go stimulus determined if the prepared movement had to be performed or withheld. In fronto-central scalp as well as in thalamic recordings, event-related potentials upon go versus no-go instructions were expressed differentially. This task effect was unrelated to motor processes and emerged significantly prior at thalamic than at scalp level. Amplitude fluctuations of depth and scalp responses showed site- and task-dependent correlations, particularly between thalamic and no-go-related activities at frontal recording sites. We conclude that an early classification of go and no-go instructions is performed already thalamically. It further appears that this information is subsequently utilized by cortical areas engaged in the definite inhibition of the prepared action.

• Human high frequency somatosensory evoked potential components are refractory to circadian modulations of tonic alertness.

  Authors: René Gobbelé, Till D Waberski, Dinah Thyerlei, Melanie Thissen, Bruno Fimm, Fabian Klostermann, Gabriel Curio, Helmut Buchner

  Journal of clinical neurophysiology : official publication of the American Electroencephalographic Society. 03/2007; 24(1):27-30.

  The impact of vigilance states, such as sleep or arousal changes, on the high-frequency (600 Hz) components (HFOs) of somatosensory evoked potentials (SEPs) is known. The present study sought toThe impact of vigilance states, such as sleep or arousal changes, on the high-frequency (600 Hz) components (HFOs) of somatosensory evoked potentials (SEPs) is known. The present study sought to characterize the effects of circadian fluctuations of tonic alertness on HFOs in awake humans. Median nerve SEPs were recorded at four times during a 24-hour waking period. In parallel to the SEP recordings, a reaction-time (RT) task was performed to assess tonic alertness. Additionally, the spontaneous EEG was monitored. The low-frequency SEP component N20 and the early and late HFO parts did not change across the measurement sessions. In contrast, RTs were clearly prolonged at night and on the second morning. EEG also showed increased delta power at night. HFOs are sensitive to pronounced vigilance changes, such as sleep, but are refractory to fluctuations of tonic alertness. Tonic alertness is regarded to be the top-down cognitive control mechanism of wakefulness, whereas sleep is mediated by overwhelming bottom-up regulation, which seems apparently more relevant for, at least in part, subcortically triggered high-frequency burst generation in the ascending somatosensory system.

• Task-related differential dynamics of EEG alpha- and beta-band synchronization in cortico-basal motor structures.

  Authors: Fabian Klostermann, Vadim V Nikulin, Andrea Annette Kühn, Frank Marzinzik, Michael Wahl, Alek Pogosyan, Andreas Kupsch, Gerd-Helge Schneider, Peter Brown, Gabriel Curio

  The European journal of neuroscience. 03/2007; 25(5):1604-15.

  Movement-related processing results in the modulation of neuronal synchronization over several electroencephalography (EEG) frequency ranges, including alpha- (8-12 Hz) and beta-band (14-30 Hz).Movement-related processing results in the modulation of neuronal synchronization over several electroencephalography (EEG) frequency ranges, including alpha- (8-12 Hz) and beta-band (14-30 Hz). Whether modulation patterns differ across sites within the motor system remains unclear, but could denote how information is conveyed across the cortico-basal network. We therefore compared the event-related synchronization/desynchronization (ERS/ERD) in recordings from the scalp, basal ganglia and thalamic structures during a motor task. Simultaneous depth and scalp EEG were recorded in 13 patients, undergoing deep brain stimulation of the thalamic ventral intermediate nucleus (VIM) or the subthalamic nucleus (STN). They performed a choice-reaction task with pre-cued Go-signals, instructive for either left- or right-sided button presses. In the beta-band, pre-cues and Go-signals were followed by ERD starting well before and peaking at task execution, uniformly in all cortical and subcortical recordings. In contrast, a comparable alpha-band ERD was only seen at the scalp, whereas mirror-like ERS were observed in the motor-inhibitory STN. In VIM, which receives strong somatosensory afferences, a major alpha-ERD upon the Go-signal did not start until the motor response. These dissociations of task-related Alpha- and Beta-band dynamics tag a functional diversity in cortico-basal networks, which are simultaneously active in motor processing. Whereas the uniform downregulation of Beta-activity points to an anti-kinetic operation mode throughout the motor system, site-dependent courses of Alpha-synchronization rather reflect the coordination of activity levels in functionally divergent motor structures during the preparation and execution of movements.

• Mental chronometry of target detection: human thalamus leads cortex.

  Authors: Fabian Klostermann, Michael Wahl, Frank Marzinzik, Gerd-Helge Schneider, Andreas Kupsch, Gabriel Curio

  Brain : a journal of neurology. 05/2006; 129(Pt 4):923-31.

  Attentive monitoring of environmental stimuli is most fundamental for rapid target detection. The aim of this study was to assess the timing of thalamic versus cortical processes involved in thisAttentive monitoring of environmental stimuli is most fundamental for rapid target detection. The aim of this study was to assess the timing of thalamic versus cortical processes involved in this cognitive operation. To this end, simultaneous depth and scalp EEG was recorded in eight patients with essential tremor, undergoing thalamic deep brain stimulation (DBS), when the DBS electrodes could be accessed via their temporarily externalized leads. The patients performed an oddball task consisting of 300 presentations of one frequent and two rare visual cues, appearing in randomized order. One of the rare cues was defined as a target, the occurrences of which had to be indicated by a button press (motor condition) or silently counted (non-motor condition). At the scalp and the thalamus, event-related potentials (ERP) were largest upon target presentation, with peak latencies in the time domain of classical P300 responses. Remarkably, target-specific thalamic ERP emerged significantly prior to scalp P300. Furthermore, whereas scalp ERP had a higher amplitude upon rare than upon frequent non-target signals, thalamic ERP were independent of stimulus probability. This pattern was identified during motor and non-motor task execution. We conclude that the human thalamus specifically supports the early recognition of target events and can widely distribute this label through its divergent cortical projections.

• 500-1000 Hz responses in the somatosensory system: approaching generators and function.

  Authors: Fabian Klostermann

  Clinical EEG and neuroscience : official journal of the EEG and Clinical Neuroscience Society (ENCS). 11/2005; 36(4):293-305.

  Spontaneous and stimulus-induced oscillatory EEG activities range over a wide scope of frequencies from 1 Hz to 1 kHz. In the ultrafast domain, trains of 5-10 micropotentials are superimposed toSpontaneous and stimulus-induced oscillatory EEG activities range over a wide scope of frequencies from 1 Hz to 1 kHz. In the ultrafast domain, trains of 5-10 micropotentials are superimposed to primary thalamic and cortical components in somtosensory evoked potentials (SEP) as brief bursts of 1000 Hz and 600 Hz, respectively. Over the last years, hypotheses on generators and functions of this frequency-edge of population activity have been elaborated in numerous studies. Here, the relevant findings and ideas were surveyed from the body of literature. Special emphasis was paid to the anatomical and cellular origin of burst SEP, their assumed impact on somatosensory coding and perspectives for scientific as well as clinical applications.

• Electrophysiological evidence for altered early cerebral somatosensory signal processing in schizophrenia.

  Authors: Till D Waberski, Christine Norra, Wolfram Kawohl, Dinah Thyerlei, Dorothee Hock, Fabian Klostermann, Gabriel Curio, Helmut Buchner, Paul Hoff, René Gobbelé

  Psychophysiology. 06/2004; 41(3):361-6.

  Various studies have indicated an impairment of sensory signal processing in schizophrenic patients. Anatomical and functional imaging studies have indicated morphological and metabolic abnormalitiesVarious studies have indicated an impairment of sensory signal processing in schizophrenic patients. Anatomical and functional imaging studies have indicated morphological and metabolic abnormalities in the thalamus in schizophrenia. Other results give evidence for an additional role of cortical dysfunction in sensory processing in schizophrenia. Advanced analysis of human median nerve somatosensory evoked potentials (SEPs) reveals a brief oscillatory burst of low-amplitude and high-frequency activity ( approximately 600 Hz), the so-called high frequency oscillations (HFOs). The present study explores the behavior of HFOs in a cohort of schizophrenic patients in comparison to a group of controls. HFOs in the group of patients appeared with a delayed latency. In the low-frequency part of the SEPs an increase in amplitude was found. These results are interpreted to reflect a lack of somatosensory inhibition in the somatosensory pathway, either at a thalamic or a cortical level.

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• Functional dissociation of a subcortical and cortical component of high-frequency oscillations in human somatosensory evoked potentials by motor interference.

  Authors: René Gobbelé, Till Dino Waberski, Dinah Thyerlei, Melanie Thissen, Felix Darvas, Fabian Klostermann, Gabriel Curio, Helmut Buchner

  Neuroscience letters. 11/2003; 350(2):97-100.

  To identify the possibly divergent impact on early and late high-frequency oscillations (HFOs) in human somatosensory evoked potentials (SEPs), we have studied motor interference effects on the HFOs,To identify the possibly divergent impact on early and late high-frequency oscillations (HFOs) in human somatosensory evoked potentials (SEPs), we have studied motor interference effects on the HFOs, and the relevance of such effects for the controversy concerning their origins. While the late HFO is thought to be generated in the somatosensory cortex, there is an ongoing discussion whether the early burst is of cortical or subcortical origin. Movements of the index finger were performed in parallel with median nerve SEP recordings. The intracortically generated N20-SEP and the late HFO were attenuated by the motor task, while the brainstem low-frequency P14-SEP and the early HFO remained unaffected. These differing effects are consistent with a generation of the early HFOs by cortical presynaptic activity in terminals of the thalamocortical projection, and confirm a postsynaptic intracortical origin of the late burst subcomponent.

• Dissociation of human thalamic and cortical SEP gating as revealed by intrathalamic recordings under muscle relaxation.

  Authors: Fabian Klostermann, René Gobbele, Helmut Buchner, Gabriel Curio

  Brain research. 01/2003; 958(1):146-51.

  'Gating' refers to a reduction of cortical somatosensory evoked potentials (SEP) under multiple simultaneous afferent inputs. This study used the opportunity for intrathalamic recordings in patients'Gating' refers to a reduction of cortical somatosensory evoked potentials (SEP) under multiple simultaneous afferent inputs. This study used the opportunity for intrathalamic recordings in patients with movement disorders to clarify to what extent cortical SEP gating is preceded by thalamic gating. Recordings were performed in 10 patients, narcotised by intravenous propofol when receiving implantation of a therapeutic deep brain stimulator system. SEP were elicited by an 8.1-Hz median nerve stimulation at twice motor threshold and were recorded simultaneously from both intrathalamic and scalp electrodes before and after the application of the depolarising muscle blocker succinylcholine which eliminated both the background muscular tone and the repetitive muscle twitches caused by the median nerve stimulation. Peripheral compound action potentials recorded at the upper arm remained unchanged after complete muscle relaxation, proving a continuously effective nerve stimulation. In contrast, the primary cortical SEP component (N20) was significantly increased under succinylcholine (+17%). This cortical release from gating was not paralleled, however, by an increased thalamic response; rather, the primary thalamic response (P16) showed a slight (-9%) but highly significant amplitude reduction. As the recordings were performed in narcotised patients, any potentially variable attentional bias on part of the subjects can be excluded as confounding factor when comparing the two experimental conditions with vs. without reafferent somatosensory inflow. Thus, given the high signal-to-noise ratio of intrathalamically recorded SEP, the present study shows a distinct thalamo-cortical dissociation with the primary somatosensory cortex representing the predominant level exhibiting SEP gating.

• Intrathalamic non-propagating generators of high-frequency (1000 Hz) somatosensory evoked potential (SEP) bursts recorded subcortically in man.

  Authors: Fabian Klostermann, René Gobbele, Helmut Buchner, Gabriel Curio

  Clinical neurophysiology : official journal of the International Federation of Clinical Neurophysiology. 08/2002; 113(7):1001-5.

  OBJECTIVES: Recently, bursts of high-frequency (1000 Hz) median nerve somatosensory evoked potential (SEP) wavelets were recorded subcortically near and inside the thalamus from deep brain electrodesOBJECTIVES: Recently, bursts of high-frequency (1000 Hz) median nerve somatosensory evoked potential (SEP) wavelets were recorded subcortically near and inside the thalamus from deep brain electrodes implanted for tremor therapy. This study aimed to clarify whether these subcortical SEP bursts reflect evoked axonal volleys running in the thalamocortical radiation or a locally restricted intrathalamic response.METHODS: During deep brain electrode implantation, median nerve SEP were recorded in 7 patients sequentially along the subcortical stereotactic trajectory at sites +20 and +10 mm above the respective target nucleus (ventral intermediate thalamus or nucleus subthalamicus). Low- and high-frequency SEP components (corner frequency 430 Hz) were analyzed separately with respect to peak latency and amplitude as they changed along the recording trajectory.RESULTS: Individual wavelets of the subcortical 1000 Hz SEP burst showed fixed peak latencies independent from the depth of the electrode penetration; they increased markedly in amplitude with decreasing distance to the thalamus. In contrast, the amplitude gradient between the two recording sites was shallower for the low-frequency SEP component, which peaked earlier at the lower recording site.CONCLUSIONS: Subcortically recorded 1000 Hz SEP wavelet bursts predominantly reflect locally restricted near-field activity, presumably generated in the somatosensory relay nucleus. In contrast, the variable peak latency of the subcortical low-frequency component could reflect postsynaptic potentials sequentially evoked during passage of the lemniscal afferences curving through the thalamus and contributions from the thalamocortical radiation.