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Biomedical subjects

A Schnitzler

Publications and source records attributed to A Schnitzler.

At least 37 records · Page 2Linked to original sources
PubMed2001

Differential coding of pain intensity in the human primary and secondary somatosensory cortex.

The primary (SI) and secondary (SII) somatosensory cortices have been shown to participate in human pain processing. However, in humans it is unclear how SI and SII contribute to the encoding of nociceptive stimulus intensity. Using magnetoencephalography (MEG) we recorded responses in SI and SII in eight healthy humans to four different intensities of selectively nociceptive laser stimuli delivered to the dorsum of the right hand. Subjects' pain ratings correlated highly with the applied stimulus intensity. Activation of contralateral SI and bilateral SII showed a significant positive correlation with stimulus intensity. However, the type of dependence on stimulus intensity was different for SI and SII. The relation between SI activity and stimulus intensity resembled an exponential function and matched closely the subjects' pain ratings. In contrast, SII activity showed an S-shaped function with a sharp increase in amplitude only at a stimulus intensity well above pain threshold. The activation pattern of SI suggests participation of SI in the discriminative perception of pain intensity. In contrast, the all-or-none-like activation pattern of SII points against a significant contribution of SII to the sensory-discriminative aspects of pain perception. Instead, SII may subserve recognition of the noxious nature and attention toward painful stimuli.

Adult↗
PubMed2000

Cortico-muscular synchronization during isometric muscle contraction in humans as revealed by magnetoencephalography.

Magnetoencephalographic (MEG) and electromyographic (EMG) signals were recorded from six subjects during isometric contraction of four different muscles. Cortical sources were located from the MEG signal which was averaged time-locked to the onset of motor unit potentials. A spatial filtering algorithm was used to estimate the source activity. Sources were found in the primary motor cortex (M1) contralateral to the contracted muscle. Significant coherence between rectified EMG and M1 activity was seen in the 20 Hz frequency range in all subjects. Interactions between the motor cortex and spinal motoneuron pool were investigated by separately studying the non-stationary phase and amplitude dynamics of M1 and EMG signals. Delays between M1 and EMG signals, computed from their phase difference, were found to be in agreement with conduction times from the primary motor cortex to the respective muscle. The time-dependent cortico-muscular phase synchronization was found to be correlated with the time course of both M1 and EMG signals. The findings demonstrate that the coupling between the primary motor cortex and motoneuron pool is at least partly due to phase synchronization of 20 Hz oscillations which varies over time. Furthermore, the consistent phase lag between M1 and EMG signals, compatible with conduction time between M1 and the respective muscle with the M1 activity preceding EMG activity, supports the conjecture that the motor cortex drives the motoneuron pool.

Adult↗
PubMed2000

Enlargement of a chronic aseptic lumbar epidural abscess by intraspinal injections--a rare cause of progressive paraparesis.

The frequent use of invasive procedures at the spinal cord such as epidural injections has led to an increased incidence of iatrogenic abscesses. We report the case of a patient who suffered from low back pain. During epidural lumbar injections of steroids the patient developed severe radicular symptoms, resulting in severe paraparesis. We demonstrate the rare cause of this progressive deterioration, being a combination of a preexisting chronic aseptic epidural abscess and an iatrogenic enlargement by repeated epidural injections. MR-Scans demonstrated a mass lesion at the L4/5 vertebral level, which was surgically removed. Histological evaluation revealed the presence of a chronic aseptic spinal epidural abscess with acute bleedings. Histology and MR-Data disclosed multiple deposits of the applied drug within the abscess and in the surrounding paravertebral soft tissue. The authors prove that the cause of the neurological deterioration was due to epidural injections into a preexisting lumbar chronic aseptic epidural abscess. Harmful and unpleasant complications may occur following epidural injections. Though we present a very rare cause of such complications, a careful monitoring of the neurological status of the patient is necessary as well as the early application of MR imaging in the case of deterioration.

Disease Progression↗
PubMed2000

Single word reading in developmental stutterers and fluent speakers.

Ten fluent speakers and nine developmental stutterers read isolated nouns aloud in a delayed reading paradigm. Cortical activation sequences were mapped with a whole-head magnetoencephalography system. The stutterers were mostly fluent in this task. Although the overt performance was essentially identical in the two groups, the cortical activation patterns showed clear differences, both in the evoked responses, time-locked to word presentation and mouth movement onset, and in task-related suppression of 20-Hz oscillations. Within the first 400 ms after seeing the word, processing in fluent speakers advanced from the left inferior frontal cortex (articulatory programming) to the left lateral central sulcus and dorsal premotor cortex (motor preparation). This sequence was reversed in the stutterers, who showed an early left motor cortex activation followed by a delayed left inferior frontal signal. Stutterers thus appeared to initiate motor programmes before preparation of the articulatory code. During speech production, the right motor/premotor cortex generated consistent evoked activation in fluent speakers but was silent in stutterers. On the other hand, suppression of motor cortical 20-Hz rhythm, reflecting task-related neuronal processing, occurred bilaterally in both groups. Moreover, the suppression was right-hemisphere dominant in stutterers, as opposed to left-hemisphere dominant in fluent speakers. Accordingly, the right frontal cortex of stutterers was highly active during speech production but did not generate synchronous time-locked responses. The speech-related 20-Hz suppression concentrated in the mouth area in fluent speakers, but was evident in both the hand and mouth areas in stutterers. These findings may reflect imprecise functional connectivity within the right frontal cortex and incomplete segregation between the adjacent hand and mouth motor representations in stutterers during speech production. A network including the left inferior frontal cortex and the right motor/premotor cortex, likely to be relevant in merging linguistic and affective prosody with articulation during fluent speech, thus appears to be partly dysfunctional in developmental stutterers.

Adult↗
PubMed2000

Neurophysiology and functional neuroanatomy of pain perception.

The traditional view that the cerebral cortex is not involved in pain processing has been abandoned during the past decades based on anatomic and physiologic investigations in animals, and lesion, functional neuroimaging, and neurophysiologic studies in humans. These studies have revealed an extensive central network associated with nociception that consistently includes the thalamus, the primary (SI) and secondary (SII) somatosensory cortices, the insula, and the anterior cingulate cortex (ACC). Anatomic and electrophysiologic data show that these cortical regions receive direct nociceptive thalamic input. From the results of human studies there is growing evidence that these different cortical structures contribute to different dimensions of pain experience. The SI cortex appears to be mainly involved in sensory-discriminative aspects of pain. The SII cortex seems to have an important role in recognition, learning, and memory of painful events. The insula has been proposed to be involved in autonomic reactions to noxious stimuli and in affective aspects of pain-related learning and memory. The ACC is closely related to pain unpleasantness and may subserve the integration of general affect, cognition, and response selection. The authors review the evidence on which the proposed relationship between cortical areas, pain-related neural activations, and components of pain perception is based.

Animals↗
PubMed2000

Functional neuroimaging of visceral sensation.

The use of functional brain imaging techniques has led to considerable advances in our understanding of brain processing of human visceral sensation. The use of complementary techniques such as functional MRI, positron emission tomography, magnetoencephalography, and EEG has led to the identification of a network of brain areas that process visceral sensation. These studies suggest that unlike somatic sensation, which has an intense homuncular representation in the primary somatosensory cortex (SI), visceral sensation is primarily represented in the secondary somatosensory cortex, whereas representation in SI is vague. This difference could account for the poor localization of visceral sensation in comparison with somatic sensation. However, in a manner similar to that of somatic sensation, visceral sensation is represented in the paralimbic and limbic structures such as the insular, anterior cingulate, and prefrontal cortices. These areas are likely to mediate the affective and cognitive components of visceral sensation. Recent studies suggest that negative emotional factors such as fear, and cognitive factors such as attention can modulate the brain processing of visceral sensation in the insular and anterior cingulate cortices. In addition, alterations in the pattern of cortical processing of visceral sensation have been described in patients with functional gastrointestinal pain. It is likely that future research into the factors that modulate the brain processing of visceral sensation in health and disease are likely to improve further our understanding of the pathophysiology of functional visceral pain disorders.

Animals↗
PubMed2000

Differential organization of touch and pain in human primary somatosensory cortex.

Processing of tactile stimuli within somatosensory cortices has been shown to be complex and hierarchically organized. However, the precise organization of nociceptive processing within these cortices has remained largely unknown. We used whole-head magnetoencephalography to directly compare cortical responses to stimulation of tactile and nociceptive afferents of the dorsum of the hand in humans. Within the primary somatosensory cortex (SI), nociceptive stimuli activated a single source whereas tactile stimuli activated two sequentially peaking sources. Along the postcentral gyrus, the nociceptive SI source was located 10 mm more medially than the early tactile SI response arising from cytoarchitectonical area 3b and corresponded spatially to the later tactile SI response. Considering a mediolateral location difference between the hand representations of cytoarchitectonical areas 3b and 1, the present results suggest generation of the single nociceptive response in area 1, whereas tactile stimuli activate sequentially peaking sources in areas 3b and 1. Thus nociceptive processing apparently does not share the complex and hierarchical organization of tactile processing subserving elaborated sensory capacities. This difference in the organization of both modalities may reflect that pain perception rather requires reactions to and avoidance of harmful stimuli than sophisticated sensory capacities.

Adult↗
PubMed2000

Neuromagnetic correlates of sensorimotor synchronization.

Sensorimotor synchronization tasks, in which subjects have to tap their finger in synchrony with an isochronous auditory click, typically reveal a synchronization error with the tap preceding the click by about 20 to 50 msec. Although extensive behavioral studies and a number of different explanatory accounts have located the cause of this so-called "negative asynchrony" on different levels of processing, the underlying mechanisms are still not completely understood. Almost nothing is known about the central processes, in particular, which sensory or motor events are synchronized by subjects. The present study examined central-level processing in synchronization tasks with magnetoencephalography (MEG). Eight subjects synchronized taps with their right index finger to an isochronous binaural pacing signal presented at an interstimulus interval of 800 msec. To gain information on central temporal coupling between "tap" and "click," evoked responses were averaged time-locked to the auditory signal and the tap onset. Tap-related responses could be explained with a three dipole model: One source, peaking at approximately 77 msec before tap onset, was localized in contralateral primary motor cortex (MI); the two other sources, peaking approximately at tap onset and 75 msec after tap onset, in contralateral primary somatosensory cortex (SI). Temporal coupling of these sources was compared in relation to different trigger points. The second SI source was equally well time-locked to the tap and to the auditory click. Furthermore, analysis of the time locking of this source activity as a function of the temporal order of tap and click showed that the second event - irrespective whether tap or click - was decisive in triggering the second SI source. This suggests that subjects use mainly sensory feedback in judging and evaluating whether they are "keeping time."

Acoustic Stimulation↗
PubMed2000

Synchronised oscillations of the human sensorimotor cortex.

Oscillations are a prominent feature of macroscopic human sensorimotor cortical activity as recorded non-invasively with electroencephalography (EEG) and magnetoencephalography (MEG). The advent of whole-scalp MEG systems allowing rapid non-invasive recording from the entire cortex and accurate localisation of neural sources, and the development of refined signal analysis methods are important factors that led to an increasing interest in studies of sensorimotor oscillations during the last 10 years. Investigations on healthy subjects revealed frequency-specific localisation and modality-specific reactivity of 10 Hz and 20 Hz sensorimotor oscillations. Task-specific coherence between motor cortical and electromyographic oscillations, reflecting cortico-motoneuronal coupling, point towards a functional role of precentral oscillations in the cortical control of voluntary movements. Furthermore, abnormal cortico-motoneuronal coupling may underlie clinical symptoms of motor disorders, such as tremor. Thus, investigation of oscillatory sensorimotor activity proceeds from phenomenology to function and provides an interesting approach to address questions in human motor physiology and pathophysiology.

Cortical Synchronization↗
PubMed1999

Magnetic stimulation of the dorsal premotor cortex modulates the Simon effect.

In choice reaction tasks, subjects typically respond faster when the relative spatial positions of stimulus and response match than when they do not match. A prominent explanation attributes this 'Simon effect' to automatic response activation elicited by spatial correspondence, which facilitates or competes with the controlled selection of the response demanded by the stimulus. To test this account, we applied repetitive transcranial magnetic stimulation (rTMS) on the dorsal premotor cortex (PMd), as this area may subserve the inhibitory control of automatic response activation. Temporary interference with PMd was predicted to release the automatic activation from inhibition and thereby enhance the Simon effect. The results confirmed a modulation for trials following an incompatible trial, providing new evidence for competition between automatic and controlled response activation as a mechanism underlying the Simon effect.

Adult↗
PubMed1999

Native language, gender, and functional organization of the auditory cortex.

Whole-head magnetoencephalography was employed in 40 normal subjects to investigate whether the basic functional organization of the auditory cortex varies with linguistic environment. Robust activations of the bilateral supratemporal auditory cortices to 1-kHz pure tones, maximum at about 100 ms after stimulus onset, were studied in Finnish and German female and male subject groups with monolingual background. Activations elicited by the tones were mutually indistinguishable in German and Finnish women. In contrast, German men showed significantly stronger auditory responses to pure tones in the left, language-dominant hemisphere than Finnish men. We discuss the possibility that the prominent left-hemisphere activation in German males reflects higher frequency resolution required for distinguishing between German than Finnish vowels and that the clear effect of native language in male but not in female auditory cortex derives from more pronounced functional lateralization in men. The present data suggest that the influence of native language can extend to auditory cortical processing of pure-tone stimuli with no linguistic content and that this effect is conspicuous in the male brain.

Acoustic Stimulation↗
PubMed1999

Magneto-encephalographic correlates of the lateralized readiness potential.

To determine the onset of movement-related EEG activity accompanying stimulus-induced movements, it is commonly isolated from overlapping stimulus-related activity by a subtraction procedure, yielding the lateralized readiness potential (LRP). In order to elucidate the generation of the LRP and to explore whether magnetoencephalographic (MEG) measures have advantages over the LRP as a measure of response selection, MEG activity was recorded in four healthy adults during self-paced and stimulus-induced hand movements. Self-paced movements were preceded by readiness fields in all subjects, explained by sources in contralateral and (for 2/8 response sides) also ipsilateral hemispheres. Movement-related activity preceding stimulus-induced movements could only be modeled adequately when stimulus-related activity was removed by subtracting MEG signals for left and right hand movements. Thus identified source locations showed no systematic deviation from the sources for readiness fields, supporting a generation of the movement-related activity in primary motor cortex. The corresponding source waveforms allowed latency determinations of motor cortex activity as markers for response-choice timing. MEG thus provides information on the time course of hand-specific motor cortex activation for each hemisphere separately, where the electro-encephalographic LRP provides a composite measure for both hemispheres.

Adult↗
PubMed1999

Pain affect without pain sensation in a patient with a postcentral lesion.

We report findings from clinical examination and cutaneous laser stimulation in a 57-year-old male, who suffered from a right-sided postcentral stroke. In this patient, we were able to demonstrate (i) a dissociation of discriminative and affective components of pain perception and, for the first time in humans, (ii) the dependence of sensory-discriminative pain component and first pain sensation on the integrity of the lateral pain system.

Affect↗
PubMed1999

Cortical activation during oesophageal stimulation: a neuromagnetic study.

We investigated the neuromagnetic responses to mechanical stimulation of the oesophagus. In six healthy right-handed volunteers (mean age 31.6 years) the proximal and distal oesophagus were stimulated by electronically controlled pump-inflation of a silicone balloon once every 4.5-5.5 sec (dwell time 145 msec). The balloon volume was adjusted to induce different sensation levels (i) just above threshold of perception, (ii) strong sensation and (iii) painful sensation. Evoked magnetic brain responses were recorded time-locked to stimulus onset with a Neuromag-122TM whole-head neuromagnetometer and modelled as equivalent current diploe (ECD) sources. ECDs were superimposed on individual magnetic resonance imaging (MRI) scans. Magnetic brain responses following distal oesophageal stimulation were adequately explained by a time-varying 2-4 dipole model with unilateral or bilateral sources in second somatosensory cortex and later sources in the frontal cortex. With increasing stimulus intensities, latencies of the sources decreased and amplitudes increased. Proximal oesophageal stimulation led to activation of source areas spatially similar to those of distal oesophageal stimulation but with shorter response latencies. Both painful and nonpainful mechanical stimulation of the oesophagus activate the second somatosensory cortex (SII). Evidence for topographic organization of oesophageal afferents in SII is poor.

Adult↗
PubMed1999

Different cortical organization of visceral and somatic sensation in humans.

Sensory stimuli from the visceral domain exhibit perceptual characteristics different from stimuli applied to the body surface. Compared with somatosensation there is not much known about the cortical projection and functional organization of visceral sensation in humans. In this study, we determined the cortical areas activated by non-painful electrical stimulation of visceral afferents in the distal oesophagus, and somatosensory afferents in the median nerve and the lip in seven healthy volunteers using whole-head magnetoencephalography. Stimulation of somatosensory afferents elicited short-latency responses (approximately 20-60 ms) in the primary somatosensory cortex (SI) contralateral (median nerve) or bilateral (lip) to the stimulated side, and long-latency responses (approximately 60-160 ms) bilaterally in the second somatosensory cortex (SII). In contrast, stimulation of visceral oesophageal afferents did not evoke discernible responses in SI but well reproducible bilateral SII responses (approximately 70-190 ms) in close vicinity to long-latency SII responses following median nerve and lip stimuli. Psychophysically, temporal discrimination of successive stimuli became worse with increasing stimulus repetition rates (0.25 Hz, 0.5 Hz, 1 Hz, 2 Hz) only for visceral oesophageal, but not for somatosensory median nerve stimuli. Correspondingly, amplitudes of the first cortical response to oesophageal stimulation emerging in the SII cortex declined with increasing stimulus repetition rates whereas the earliest cortical response elicited by median nerve stimuli (20 ms SI response) remained unaffected by the stimulus frequency. Our results indicate that visceral afferents from the oesophagus primarily project to the SII cortex and, unlike somatosensory afferents, lack a significant SI representation. We propose that this cortical projection pattern forms the neurophysiological basis of the low temporal and spatial resolution of conscious visceral sensation.

Adult↗
PubMed1999

The role of ventral medial wall motor areas in bimanual co-ordination. A combined lesion and activation study.

Two patients with midline tumours and disturbances of bimanual co-ordination as the presenting symptoms were examined. Both reported difficulties whenever the two hands had to act together simultaneously, whereas they had no problems with unimanual dexterity or the use of both hands sequentially. In the first patient the lesion was confined to the cingulate gyrus; in the second it also invaded the corpus callosum and the supplementary motor area. Kinematic analysis of bimanual in-phase and anti-phase movements revealed an impairment of both the temporal adjustment between the hands and the independence of movements between the two hands. A functional imaging study in six volunteers, who performed the same bimanual in-phase and anti-phase tasks, showed strong activations of midline areas including the cingulate and ventral supplementary motor area. The prominent activation of the ventral medial wall motor areas in the volunteers in conjunction with the bimanual co-ordination disorder in the two patients with lesions compromising their function is evidence for their pivotal role in bimanual co-ordination.

Adult↗