Evaluation of thalamocortical impulse propagation in the akinetic Rigd type of Parkinson's disease using high-frequency (600 Hz) SEP oscillations.

Unlabelled: Human median nerve somatosensory evoked potentials exhibit low-amplitude, high-frequency (600 Hz) oscillations (HFOs) superimposed onto the primary cortical response 'N20.' Previous EEG-studies indicated the HFOs to reflect in part activity generated at the thalamus and within the thalamocortical radiation. Expecting impairment of thalamocortical impulse propagation in Parkinson's disease (PD) the present study aimed to explore the performance of the HFOs in a cohort of PD patients in comparison to an exactly age- and sex-matched group of controls.

The impact of stimulus properties on low- and high-frequency median nerve somatosensory evoked potentials.

Questioning whether stimulation properties in median nerve somatosensory evoked potentials show interactions multichannel recordings were performed in a three-factorial repeated measures design with the parameters (i) eyes opened versus eyes closed, (ii) stimulation intensity above motor threshold versus intensity sub motor threshold, (iii) stimulation rate 0.5 Hz versus 9 Hz resulting in somatosensory evoked potentials recorded during eight different conditions. Varying the stimulation intensity revealed an impact on the amplitude and the latency of the N20 source activity and on the amplitude, the duration and the number of peaks of the high frequency oscillatory (HFOs) sources.

The temporal pattern of motion in depth perception derived from ERPs in humans.

Former studies have demonstrated the cortical regions being involved in visual motion processing. The strength of neuronal activation was found to depend on the direction of motion. In particular the detection of optic flow towards the observer seems of particular importance due to its obvious biological relevance.

Temporal activation patterns of lateralized cognitive and task control processes in the human brain.

In a recent fMRI study with identical word stimuli we demonstrated task-dependent lateralization of brain activity during visual processing, with left-hemispheric activations for letter decisions and right-hemispheric activations for visuospatial decisions (Stephan, K.E., Marshall, J.

Timing of visuo-spatial information processing: electrical source imaging related to line bisection judgements.

This study deconvolves the temporal dynamics of the neural processes underlying line bisection judgements (i.e., the landmark task).

Loudness dependence of evoked dipole source activity during acute serotonin challenge in females.

Objectives: Direct challenge of cortical serotonergic (5-hydroxytryptamine, 5-HT) availability by tryptophan depletion test (TDT) was used to assess the hypothesized inverse relationship between central 5-HT function and loudness dependence of auditory evoked potentials (LDAEPs). Gender must be taken into particular account here, since there are gender differences in 5-HT brain synthesis, with women reacting more strongly to TDT.

Methods: In a double-blind, controlled cross-over study, 16 healthy females were ingested two highly concentrated amino acid mixtures with (+TRP) or without TRP (-TRP).

Cerebral processing of spontaneous reversals of the rotating Necker cube.

The cerebral processing of spontaneous perceptive reversals of the rotating Necker cube was studied in humans by combined functional MRI and electroencephalography. These reversals prefer certain positions of the Necker cube and can be studied without external reference of the perception. Functional MRI revealed six bilaterally active regions in the visual, parietal, and premotor cortex.

Short-term cortical reorganization by deafferentation of the contralateral sensory cortex.

The topographic arrangement of the human primary somatosensory cortex following deafferentation of the contralateral cortex has been investigated by means of dipole source analysis. Somatosensory-evoked potentials were obtained by electrical stimulation of digit 1 and digit 5 of the left hand before and after anesthesia of digits 2-4 of the right hand during different terms of attention. Anesthesia induced an expansion of the three-dimensional distance between digits 1 and 5.

Comparative source localization of electrically and pressure-stimulated multichannel somatosensory evoked potentials.

The purpose of the study was to determine if there is a difference in the determination of the cortical hand area by dipole source estimation after artificial and natural stimuli. In principle, there are advantages of both methods: pressure stimulation is less invasive and compatible to fMRI, whereas electrical stimulation can be applied with higher stimulus rates and elicits sharper waveforms. Electrical and pressure stimulation was performed simultaneously on the thumb and fifth finger on eight healthy volunteers.

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

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 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.

Transcranial direct current stimulation applied over the somatosensory cortex - differential effect on low and high frequency SEPs.

Objective: Transcranial direct current stimulation (tDCS) has an influence on the excitability of the human motor cortex measured by motor evoked potentials (MEPs) after transcranial magnetic stimulation. Low and high frequency (HFOs) components of somatosensory evoked potentials (SEPs) were studied questioning whether a comparable effect can be observed after applying tDCS to the human somatosensory cortex.

Methods: Multichannel median nerve SEPs were recorded before and after applying tDCS of 1mA over a period of 9min with the cathode placed over the somatosensory cortex and the anode over the contralateral forehead and vice versa in a second session.

Temporal pattern of source activities evoked by different types of motion onset stimuli.

The aim of this study was to compare the time course of motion-related source activities evoked by the onset of different kinds of visual motion stimuli in human subjects. Event-related potentials (ERP) were recorded from 64 scalp electrodes in ten healthy subjects while they were viewing four different types of motion stimuli (translation, rotation, expansion and contraction). Following a new approach combining a current density reconstruction with clustering algorithms, source maxima in the time range from 50 to 400 ms after the onset of the visual stimulus were localized and the time courses of activation were elaborated.

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

Various 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.

High-frequency somatosensory thalamocortical oscillations and psychopathology in schizophrenia.

Human cortical somatosensory evoked potentials (SEPs), which are presumably generated in afferent thalamocortical and early cortical fibers, reveal a burst of superimposed early (N20) high-frequency oscillations (HFOs), around 600 Hz. There is increasing evidence of an imbalance of thalamocortical systems in schizophrenic patients. In order to assess correlations between somatosensory evoked oscillations and symptoms of schizophrenia, we investigated median nerve SEPs in 20 inpatients and their age-matched and gender-matched healthy controls using a multichannel EEG.

Patterns of disturbed impulse propagation in multiple sclerosis identified by low and high frequency somatosensory evoked potential components.

In human median nerve somatosensory evoked potentials (SSEPs), high frequency (600 Hz) oscillations (HFOs) are superimposed onto the low frequency SSEP component N20. High frequency oscillations are generated both in deep axon segments of thalamo-cortical projection neurons and at the primary somatosensory cortex. The present study aimed to test the hypothesis that HFOs might be more sensitive to temporal dispersion caused by demyelinating lesions in multiple sclerosis (MS) than the N20.

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

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.

Enhanced intensity dependence as a marker of low serotonergic neurotransmission in borderline personality disorder.

Dysfunction of central serotonergic activity has been assumed in patients with borderline personality disorder (BPD) characterized by a prominent impulsive behavioral style. Following the high serotonergic innervation of the primary auditory cortex, there is increasing evidence of the intensity dependence of auditory evoked potentials (AEP), especially the N1/P2 component, indicating serotonergic neurotransmission in animals and humans. 15 females who met the IPDE-criteria for BPD and a group of comparative healthy females (controls) completed extensive personality questionnaires which gave special regard to impulsiveness.

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

'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.

Spatial direction of attention enhances right hemispheric event-related gamma-band synchronization in humans.

Gamma-band oscillations are related to sensory information processing and attention. To further illuminate the relationship of gamma-band activity and selective somatic attention, we have studied the effects of direction of attention on the stimuli of somatosensory evoked potentials. Responses during focused attention to stimulation of the right median nerve and ignored stimulation at the right tibial nerve were compared with responses of ignored stimulation of the right median nerve but focused attention to stimulation at the right tibial nerve.

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

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 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).