Biomedical subjects

A Schnitzler

Publications and source records attributed to A Schnitzler.

At least 55 records · Page 3Linked to original sources

PubMed1999

Parallel activation of primary and secondary somatosensory cortices in human pain processing.

Cerebral processing of pain has been shown to involve primary (SI) and secondary (SII) somatosensory cortices. However, the temporal activation pattern of these cortices in nociceptive processing has not been demonstrated so far. We therefore used whole-head magnetoencephalography to record cortical responses to cutaneous laser stimuli in six healthy human subjects. By using selective nociceptive stimuli our results confirm involvement of contralateral SI and bilateral SII in human pain processing. Beyond they show for the first time simultaneous activation onset of contralateral SI and SII after approximately 130 ms, indicating parallel thalamocortical distribution of nociceptive information. This contrasts to the serial cortical organization of tactile processing in higher primates and instead corresponds to the parallel cortical organization in lower primates and nonprimates. Thus our finding suggests preservation of the basic mammalian parallel organizational scheme in human pain processing, whereas in the tactile modality parallel organization appears to be abandoned in favor of a serial processing scheme. Functionally, preservation of direct access to SII underscores the relevance of this area in human pain processing, probably reflecting an important role of SII in nociceptive learning and memory.

Adult↗

PubMed1998

Interaction of finger representation in the human first somatosensory cortex: a neuromagnetic study.

Neuromagnetic responses to separate tactile stimulation of digits I, II and V and simultaneous stimulation of digit pairs II and I, and II and V, were recorded in six healthy adult subjects using a 122-channel whole-head neuromagnetometer in order to investigate functional overlap of finger representations in primary somatosensory cortex (SI). Evoked responses to single digit stimulation were explained by time-varying equivalent current dipoles (ECDs) located in SI. These ECDs were then used to explain responses to stimulation of digit pairs. A cortical interaction ratio (IR) was defined as the vector sum of peak source amplitudes to separate stimulations of two fingers divided by the vector sum of source amplitudes to simultaneous stimulation of the two digits. Mean IR was significantly higher (P<0.05; Wilcoxon test) for digit pair II + I (1.69+/- 0.15) compared to digit pair II + V (1.14+/- 0.12). These results indicate that there is an overlap of finger representations in human SI which differs between anatomically adjacent and non-adjacent digit pairs.

Adult↗

PubMed1998

Functional organization of the auditory cortex is different in stutterers and fluent speakers.

Impaired auditory feedback has been suggested to cause stuttering, and subtle irregularities of audition have been reported in behavioural studies. To characterize processing at the auditory cortical level, we recorded neuromagnetic responses to monaural tones in nine stutterers and 10 fluent speakers while the subjects were reading silently, with mouth movements only, aloud, and in chorus with another person. The basic functional organization of the auditory cortices was found to be different in stutterers and controls. The altered interhemispheric balance in stutterers was affected by speech production, due to changes in the left auditory cortical representation, and more severely by self-paced than accompanied speech. This may lead to transient non-optimal interpretation of the auditory input and affect speech fluency.

Adult↗

PubMed1998

Early-onset multisystem degeneration with central motor, autonomic and optic nerve disturbances: unusual Riley-Day syndrome or new clinical entity?

We report a 21-year-old woman presenting with a slowly progressive tetraparesis, optic nerve atrophy on both sides, and autonomic disturbances since early childhood. The patient has been carefully followed up for 5 years with clinical and ancillary investigations. The results and the time course strongly suggest an underlying degenerative syndrome affecting parts of three major systems: autonomic, motor and visual. Some symptoms resemble familial dysautonomia (FD, Riley-Day syndrome), however, hallmarks of FD, such as absence of fungiform papillae of the tongue, abnormal reaction on intradermal histamine injection, absent tendon reflexes, are missing, and central motor disturbances have not been described in FD. We consider this syndrome a slowly progressive multisystemic degeneration with two unusual hitherto unreported features: the combination of affected systems (autonomic and motor systems, optic nerves), and the early onset.

Adult↗

PubMed1998

Somatic and limbic cortex activation in esophageal distention: a functional magnetic resonance imaging study.

Little is known about the cerebral representations of visceral sensations in humans. Using functional magnetic resonance imaging (fMRI), we mapped the cortical areas of the human brain that were activated by mechanical stimulation of the esophagus in 5 healthy volunteers. Stimulation probes were placed into the distal part of the esophagus and inflated to produce a local distention. The cerebral activation pattern was related to the strength and quality of the stimulus. The weakest stimulus accompanied by a well-localized albeit weak retrosternal sensation activated only the parietal opercular cortices, probably including the secondary somatosensory cortex (SII). Additional activation of the primary sensorimotor cortex (SI) at the level of the face and mouth representation as well as of the right premotor cortex was found during repetitive distention of the esophagus at 0.5 Hz. Repetitive stimulation at 1 Hz additionally activated the insula bilaterally. The strongest distention stimulus, which caused a painful retrosternal sensation, resulted in an activation of the anterior cingulate cortex. Our findings demonstrate that SII is the primary cortical target of visceral afferents originating in the esophagus. Limbic structures become engaged when the visceral sensation is unpleasant or painful.

Adult↗

PubMed1998

Handedness and asymmetry of hand representation in human motor cortex.

The cortical representation of five simple hand and finger movements in the human motor cortex was determined in left- and right-handed people with whole-head magnetoencephalography. Different movements were found to be represented by spatially segregated dipolar sources in primary motor cortex. The spatial arrangement of neuronal sources for digit and wrist movements was nonsomatotopic and varied greatly between subjects. As an estimator of hand area size in primary motor cortex, we determined the smallest cuboid volume enclosing the five dipole sources within the left and right hemisphere of each subject. Interhemispheric comparison revealed a significant increase of this volume in primary motor cortex opposite to the preferred hand. This asymmetry was due to a greater spatial segregation of neuronal dipole generators subserving different hand and finger actions in the dominant hemisphere. Mean Euclidean distances between dipole sources for different movements were 10.7 +/- 3.5 mm in the dominant and 9.4 +/- 3.5 mm in the nondominant hemisphere (mean +/- SD; P = 0. 01, two-tailed t-test). The expansion of hand representation in primary motor cortex could not simply be attributed to a greater number of pyramidal cells devoted to each particular movement as inferred from current source amplitudes. The degree of hemispheric asymmetry of hand area size in the primary motor cortex was correlated highly with the asymmetry of hand performance in a standardized handedness test (r = -0.76, P < 0.01). These results demonstrate for the first time a biological correlate of handedness in human motor cortex. The expansion of hand motor cortex in the dominant hemisphere may provide extra space for the cortical encoding of a greater motor skill repertoire of the preferred hand.

Adult↗

PubMed1997

Cooperative functions of the reaper and head involution defective genes in the programmed cell death of Drosophila central nervous system midline cells.

In Drosophila, the chromosomal region 75C1-2 contains at least three genes, reaper (rpr), head involution defective (hid), and grim, that have important functions in the activation of programmed cell death. To better understand how cells are killed by these genes, we have utilized a well defined set of embryonic central nervous system midline cells that normally exhibit a specific pattern of glial cell death. In this study we show that both rpr and hid are expressed in dying midline cells and that the normal pattern of midline cell death requires the function of multiple genes in the 75C1-2 interval. We also utilized the P[UAS]/P[Gal4] system to target expression of rpr and hid to midline cells. Targeted expression of rpr or hid alone was not sufficient to induce ectopic midline cell death. However, expression of both rpr and hid together rapidly induced ectopic midline cell death that resulted in axon scaffold defects characteristic of mutants with abnormal midline cell development. Midline-targeted expression of the baculovirus p35 protein, a caspase inhibitor, blocked both normal and ectopic rpr- and hid-induced cell death. Taken together, our results suggest that rpr and hid are expressed together and cooperate to induce programmed cell death during development of the central nervous system midline.

Animals↗

PubMed1997

Modulation of human cortical rolandic rhythms during natural sensorimotor tasks.

We studied modulation of cortical neuromagnetic rhythms in association with left and right median nerve stimulation, during rest, finger movements, and passive tactile hand stimulation, in seven healthy, right-handed adults. In the rest condition, the amplitude of the rhythmic sensorimotor activity decreased immediately after the median nerve stimuli and increased above the prestimulus level within 0.4 s afterward, especially in the 7- to 25-Hz band. The rebound occurred 100-300 ms earlier for 20 (7-15)-than for 10 (15-25)-Hz activity. Suppressions and rebounds were strongest in the contralateral sensorimotor hand area for the 20-Hz, but not for the 10-Hz, activity. The maximum rebound was on average 22-34% stronger in the left than in the right hemisphere. Active exploration of objects abolished rebounds of both 10- and 20-Hz signals in the contralateral hemisphere and markedly diminished them ipsilaterally. Finger movements without touching an object and passive tactile stimulation produced a weaker effect. The sensorimotor rhythms thus show a characteristic suppression and subsequent rebound after electrical median nerve stimulation. The rebound is left-hemisphere dominant in right-handed subjects and its suppression reveals bilateral cortical activation during both motor tasks and passive tactile stimulation, especially for explorative finger movements.

Adult↗

PubMed1997

Involvement of primary motor cortex in motor imagery: a neuromagnetic study.

Functional brain imaging studies have indicated that several cortical and subcortical areas active during actual motor performance are also active during imagination or mental rehearsal of movements. Recent evidence shows that the primary motor cortex may also be involved in motor imagery. Using whole-scalp magnetoencephalography, we monitored spontaneous and evoked activity of the somatomotor cortex after right median nerve stimuli in seven healthy right-handed subjects while they kinesthetically imagined or actually executed continuous finger movements. Manipulatory finger movements abolished the poststimulus 20-Hz activity of the motor cortex and markedly affected the somatosensory evoked response. Imagination of manipulatory finger movements attenuated the 20-Hz activity by 27% with respect to the rest level but had no effect on the somatosensory response. Slight constant stretching of the fingers suppressed the 20-Hz activity less than motor imagery. The smallest possible, kinesthetically just perceivable finger movements resulted in slightly stronger attenuation of 20-Hz activity than motor imagery did. The effects were observed in both hemispheres but predominantly contralateral to the performing hand. The attempt to execute manipulatory finger movements under experimentally induced ischemia causing paralysis of the hand also strongly suppressed 20-Hz activity but did not affect the somatosensory evoked response. The results indicate that the primary motor cortex is involved in motor imagery. Both imaginative and executive motor tasks appear to utilize the cortical circuitry generating the somatomotor 20-Hz signal.

Adult↗

PubMed1997

The motor syndrome associated with exaggerated inhibition within the primary motor cortex of patients with hemiparetic.

Following transcranial magnetic stimulation (TMS) at stimulation strength of 1.5 times the resting motor threshold, a silent period (SP) of approximately 180 ms duration can be observed in surface EMG-registrations of tonically activated small hand muscles. This SP is believed to be generated cortically and can be prolonged in stroke patients, but it is not known whether a prolongation of the SP has any functional significance. In order to answer the question of whether enhanced cortical inhibition can contribute to pathophysiology of motor dysfunction we studied stroke patients with clearly prolonged SP durations in the first dorsal interosseus muscle (> 2 times that of the intact side), but with normal magnetically evoked motor potentials. Sixteen patients out of a cohort of 174 consecutive patients presenting with acute hemiparetic stroke fulfilled the inclusion criteria. Serial TMS investigations were performed for up to 2 years post-stroke. In all patients, the SP duration decreased in parallel with clinical improvement. In two patients, intermittent clinical deterioration was accompanied by an increase in the SP duration. In four patients, in addition to a markedly prolonged SP duration, the phenomenon of a complete inability to initiate voluntary muscle activity for several seconds, following TMS, could be observed in a number of trials ('motor arrest'). Detailed clinical analysis revealed that, in addition to hemiparesis, distinct motor disturbances in patients with SP prolongation could be observed. These motor disturbances resembled those of motor neglect and were characterized by motivationally dependent under-utilization of the affected arm, impairment of movement initiation, inability to maintain a constant force level and to scale forces, and impairment of individual finger movements. In 12 of the 16 patients at least one additional behavioural manifestation of neglect was present. We suggest that in stroke patients severe motor dysfunction may be caused by hyperactivity of cortical inhibitory interneurons rather than by direct lesions of descending motor tracts. Cortical hyperinhibition may, in turn, result from damage to any of a number of afferent pathways to the motor cortex which modulate local interneuronal activity.

Adult↗

PubMed1997

Modifications of and special operating tricks in the classical technique of surgery against strabismus.

Even nowadays the idea of most of the operations against strabismus is based on myectomy and reposition of the rectus muscles. At the Department of Ophthalmology of the University Medical School of Debrecen we use mainly these two methods of operation. At our Department we performed 1605 operations against strabismus during the last 10 years. 1269 of our patients had convergent, 336 had divergent strabismus. The majority of the operations were performed on patients less than 6 years of age, under general anesthesia. The outcome of the operation is successful if it results in a situation, in which torque affecting the eyeball stabilizes it in the normal position. The advantage of the combined surgical procedure is that the former muscular balance remains intact, and by relatively small intervention good results can be achieved. In the rectus muscles of squint patients anatomical and histopathological changes could be found, especially if they did not receive pleoptic treatment preoperatively. Depending on the direction of the strabismus one of the muscles is thicker, while the other is thinner, due to hyper- and hypofunction. Our surgical experience of many years showed that by modifying the classical technique of the operations with some fine technical tricks it was possible to increase the success rate. In our film we presented the right way of incising and handling the subconjunctival connective tissue (Tenon capsule) thus making it possible to lay it back to its original place at the end of the operation. This way the chance of postoperative scarring is reduced. We demonstrated how to test the contractility of the muscles by using muscle-hooks, that replaces the forceps test. In case of myectomy we demonstrated the tricks of how to handle the easiest and the finest way. In case of retroposition we can achieve perfect reconstruction and wound healing by using the shown simple technique. We also take much care of suturing the conjunctiva during operations performed on infants that is important because of their undisciplined behavior.

Anesthesia, General↗

PubMed1996

Transcallosally mediated inhibition of interneurons within human primary motor cortex.

The objective of this study was to investigate interhemispheric transcallosal connections between primary motor cortices noninvasively in awake human subjects. For this purpose, focal transcranial magnetic stimulation was performed on eight healthy, right-handed subjects and one patient with congenital collosal agenesis. Using two magnetic stimulators, we investigated the effect of a conditioning magnetic stimulus applied to the motor cortex of one hemisphere on the duration of the silent period (SP) evoked in the first dorsal interosseus (FDI) muscle by a magnetic test stimulus given over the opposite motor cortex. It is well established that SP reflects activation of inhibitory interneurons within primary motor cortex. In all normal subjects, a conditioning stimulus to one hemisphere produced a significant shortening of SP evoked by the test stimulus when the conditioning-test-interval was 10-20 ms. The effect was also observed when an electrical test stimulus was used. The conditioning coil had to be placed over the hand motor area to obtain the maximal effect. The threshold for eliciting this decrease of SP duration was higher than the threshold for eliciting an early excitatory muscle response in the contralateral FDI. Increasing the intensity of the conditioning stimulus led to linear reduction of SP duration. In the patient with callosal agenesis, no such decreasing effect on SP duration was observed. These results suggest that inhibitory interneurons within primary hand motor cortex receive transcallosal inhibitory input from the opposite motor cortex. We propose that modulation of motor cortical interneurons via transcallosal pathways may provide a gain control for the motor cortical output system and subserve interhemispheric coordination in complex, nonsymmetrical bimanual movements.

Adult↗

PubMed1996

Parallel and serial processing of haptic information in man: effects of parietal lesions on sensorimotor hand function.

Recent animal studies have shown that there is an evolutionary shift within the order of primates from parallel to serial processing of haptic information. In an attempt to determine whether there is also evidence of serial processing in humans 10 patients with parietal cortical lesions, three patients with subcortical lesions and one patient after hemispherectomy, were examined. Case-by-case and across subject analysis of lesion type, sensorimotor profile and electrophysiological findings showed that in unihemispheric lesions: (a) there is little impairment of thermesthesia, nociception and vibration sense: (b) two-point discrimination and integrity of the N20 somatosensory component are highly correlated; (c) a loss of the N20 component is accompanied by a severe impairment of stereognosis; (d) conversely, in more posterior lesions astereognosis can occur with an intact N20 component; and (e) if the lesion is in the right hemisphere there is frequently impairment of graphesthesia in both hands. These data are taken to indicate serial processing from SI (as evidenced by an intact N20 component) to posterior parietal cortex allowing progressive spatial and temporal integration. In graphesthesia our data suggest an integrative function of the right parietal cortex for both sides of the body. Other sensory qualities like vibration nociception and thermesthesia are apparently processed in a non-serial, probably parallel way involving both hemispheres. The effects of cerebral lesions in our series suggest parallel as well as serial processing of somesthetic information in man underlying the perception of different haptic features.

Adult↗

PubMed1995

Tactile information from the human hand reaches the ipsilateral primary somatosensory cortex.

Neuromagnetic responses to median nerve stimulation were studied in six healthy right-handed subjects. In the rest condition, only the right and left median nerves were alternately stimulated at the wrists. In two other conditions, continuous superficial tactile stimulation was concurrently applied to either the left or right hand. Tactile stimulation of palm and fingers of one hand enhanced, in the ipsilateral primary somatosensory cortex (SI), responses to median nerve stimulation of the other hand. This effect was stronger in the left than the right SI. Our data provide evidence in humans for the access of cutaneous information from the hands to ipsilateral SI, probably via excitatory transcallosal pathways. This interhemispheric information transfer may represent a neurophysiological substrate of somatosensory fusion between the hands.

Adult↗

PubMed1995

Modulation of somatosensory evoked magnetic fields by sensory and motor interferences.

Modulatory influences of skilled exploratory finger movements on somatosensory evoked magnetic fields evoked by median nerve stimulation were investigated in six healthy subjects using a whole head magnetometer (MEG) system. The exploratory finger movements caused major changes in the somatosensory evoked fields. The most prominent effect was a reversal of the dipolar magnetic field around 30 ms after median nerve stimulation. Similar but less pronounced effects were exerted by repetitive finger movements and tactile stimulation of the hand. A dipole analysis and super-imposition of resulting sources on individual MRI scans showed that all somatosensory evoked fields up to 60 ms after stimulation, and the modulation of these responses were located in the primary somatosensory cortex (SI).

Adult↗

PubMed1995

Altered force release control in Parkinson's disease.

Isometric force tracking and force aiming modified by visual feed-back was investigated in Parkinsonian (PD) and control subjects. Production and maintenance of isometric force, production and release of isotonic force, and maximum force were tested. Statistical analysis revealed that the PD patients could perform most force tasks in a similar manner to that of control subjects. However, PD patients had difficulties in sustaining target force over a 30-s period and in performing rapid alternating movements. The major finding in PD patients was an inability to precisely release a target force. Overall these data suggest that the release of a produced force is a sensitive motor control parameter in Parkinson's disease.

Adult↗

PubMed1995

Somatosensory evoked potentials elicited by intraneural microstimulation of afferent nerve fibers.

Cortical somatosensory evoked potentials (SEPs) after intraneural microstimulation (IMS) of cutaneous and afferent muscle nerve fibers in the median nerve were recorded to study the contribution of different afferent fiber groups to the SEP. Thirty-seven cutaneous fiber bundles, 10 afferent muscle nerve fiber bundles, and 45 single mechanoreceptive afferents of FA I- (n = 12), FA II- (n = 8), SA I- (n = 13), and SA II-type (n = 12) were studied in 29 healthy subjects. IMS of cutaneous fiber bundles evoked cortical responses corresponding to the N20 component after median nerve stimulation in 86% of the fascicles studied, whereas IMS of muscle nerve fiber bundles elicited responses only in 20%. After IMS of single mechanoreceptive afferents of FA I-, FA II-, and SA I-type cortical responses were obtained in all groups in approximately 80% of the stimulated units. The latencies of the SEPs evoked by IMS were comparable to that after compound median nerve stimulation (mean difference 0.58 ms). The N20 amplitudes of SEPs after IMS of cutaneous fiber bundles were on average 28% (n = 32) and for single afferents 22% (n = 30) of that after compound nerve stimulation. It is concluded that the median nerve SEPs evoked by compound median nerve stimulation of the resting hand are dominated by cutaneous rather than muscle afferent input. Furthermore, the fact that selective stimulation of only a few cutaneous afferents produces cortical SEPs of rather high amplitude is compatible with the view that sensory information produced by selective afferent stimulation is differentially gated into the somatosensory cortex.

Adult↗

PubMed1995

Neurophysiological techniques in the evaluation of disorders of the spine.

Neurophysiological investigations are indispensable tools in evaluating and quantifying functional impairment of spinal cord structures and adjacent nervous tissue in any disorder of the spine accompanied by neurological symptoms. In this review the relevant neurophysiological techniques will be briefly described and their differential value for diagnosis and prognosis of spinal cord damage discussed. Typical case reports of spine disorders at different spinal levels are presented to illustrate results and interpretations of neurophysiological investigations.

Evoked Potentials↗