Biomedical subjects

Christoph Braun

Publications and source records attributed to Christoph Braun.

At least 19 recordsLinked to original sources

PubMed2006

BOLD adaptation in vibrotactile stimulation: neuronal networks involved in frequency discrimination.

The present functional magnetic resonance imaging (fMRI) study investigated human brain regions subserving the discrimination of vibrotactile frequency. An event-related adaptation paradigm was used in which blood-oxygen-level-dependent (BOLD) responses are lower to same compared with different pairs of stimuli (BOLD adaptation). This adaptation effect serves as an indicator for feature-specific responding of neuronal subpopulations. Subjects had to discriminate two vibrotactile stimuli sequentially applied with a delay of 600 ms to their left middle fingertip. The stimulus frequency was in the flutter range of 18-26 Hz. In half of the trials, the two stimuli possessed identical frequency (same), whereas in the other half, a frequency difference of +/-2 Hz was used (diff). As a result, BOLD adaptation was observed in the contralateral primary somatosensory cortex (S1), precentral gyrus, superior temporal gyrus (STG); ipsilateral insula as well as bilateral secondary somatosensory cortex and supplementary motor area. When statistically comparing the BOLD time courses between same and diff trials in these cortical areas, it was found that the vibrotactile BOLD adaptation is initiated in the contralateral S1 and STG simultaneously. These findings suggest that the cortical areas responsive to the frequency difference between two serially presented stimuli sequentially process the frequency of a vibrotactile stimulus and constitute a putative neuronal network underlying human vibrotactile frequency discrimination.

Adaptation, Physiological↗

PubMed2006

Cortical activation during word reading and picture naming in dyslexic and non-reading-impaired children.

OBJECTIVE: In a recent study on picture naming and word reading in dyslexics and control children we found a combination of normal picture retrieval times and severe reading impairments in dyslexics. Therefore, we hypothesize that brain response patterns differ between patients and controls during word reading, but are similar in picture naming as a non-letter mediated task. METHODS: Time course of brain activation was investigated by magnetoencephalography during word reading and picture naming in 9 dyslexic children and 13 age-matched controls (aged 9-10 years). RESULTS: We found 5 consecutive activations spreading from occipito-parietal to temporo-frontal sites. Group differences occurred only during reading: a delayed response in temporal superior and angular gyri at 235-285 ms and absence of activation in anterior temporal and inferior frontal regions at 430-530 ms for dyslexics. CONCLUSIONS: Problems in phonological processing are reflected in delay of early activity and absence of late activity in language related brain regions. From the lack of group differences during picture naming, we conclude the presence of two pathways: a phonological/orthographic one for word reading, which is disturbed in dyslexics, and a visual one for picture naming, which can be unaffected in dyslexics. SIGNIFICANCE: Evidence is provided for different pathways for the processing of letter-mediated and visual-eidetic information. This knowledge may be important for dyslexics in the context of coping with everyday demands and for training of relevant skills.

Auditory Perception↗

PubMed2006

Effects of motor activity on the organization of primary somatosensory cortex.

Recent studies have shown that adaptation of representational maps within the primary somatosensory cortex can be induced by task-related motor activity. Here, we explore the relationship between the complexity of the motor task and the extent of task-specific adaptation within the primary somatosensory cortex. We hypothesized that the extent of adaptation increases with the complexity of the motor task. Using neuromagnetic source imaging based on electrical stimulation of the thumb and ring finger, we demonstrate that cortical finger representations are more distant during performance of the pinch finger grip than in a rest condition. Our data suggest that somatosensory cortical maps undergo rapid modulation depending on the task-specific involvement of somatosensory feedback in movements.

Adaptation, Physiological↗

PubMed2006

Periventricular leukomalacia specifically affects cortical MEG response to biological motion.

OBJECTIVE: Periventricular leukomalacia (PVL) underlies most of the neurological morbidity including visual-perceptual deficits in survivors of premature birth. However, it is unknown whether and, if so, how PVL affects functional cortical activity. METHODS: Here, we assessed changes in the magnetoencephalographic (MEG) response to visual displays depicting human locomotion in adolescents who were born premature with magnetic resonance imaging signs of PVL. RESULTS: Dynamics of MEG activity parallel behavioral deficits. Early (140-170 milliseconds) brain activation over the right parietal cortex was weaker in patients compared with term-born controls. INTERPRETATION: This is the first evidence for stimulus-specific modulation of cortical activity by periventricular lesions providing new insights into the functional pathology of PVL.

Adolescent↗

PubMed2006

Coherent corticomuscular oscillations originate from primary motor cortex: evidence from patients with early brain lesions.

Coherent oscillations of neurons in the primary motor cortex (M1) have been shown to be involved in the corticospinal control of muscle activity. This interaction between M1 and muscle can be measured by the analysis of corticomuscular coherence in the beta-frequency range (beta-CMCoh; 14-30 Hz). Largely based on magnetoencephalographic (MEG) source-modeling data, it is widely assumed that beta-CMCoh reflects direct coupling between M1 and muscle. Deafferentation is capable of modulating beta-CMCoh, however, and therefore the influence of reafferent somatosensory signaling and corresponding neuronal activity in the somatosensory cortex (S1) has been unclear. We present transcranial magnetic stimulation (TMS) and MEG data from three adult patients suffering from congenital hemiparesis due to pre- and perinatally acquired lesions of the pyramidal tract. In these patients, interhemispheric reorganization had resulted in relocation of M1 to the contralesional hemisphere, ipsilateral to the paretic hand, whereas S1 had remained in the lesioned hemisphere. This topographic dichotomy allowed for an unequivocal topographic differentiation of M1 and S1 with MEG (which is not possible if M1 and S1 are directly adjacent within one hemisphere). In all patients, beta-CMCoh originated from the contralesional M1, in accordance with the TMS-evoked motor responses, and in contrast to the somatosensory evoked fields (SEFs) for which the sources (N20m) were localized in S1 of the lesioned hemisphere. These data provide direct evidence for the concept that beta-CMCoh reflects the motorcortical efferent drive from M1 to the spinal motoneuron pool and muscle. No evidence was found for a relevant contribution of neuronal activity in S1 to beta-CMCoh.

Adult↗

PubMed2006

Abnormal reactivity of the primary somatosensory cortex during the experience of pain in complex regional pain syndrome: a magnetoencephalograhic case study.

A 49-year-old male worker developed persistent pain in his left wrist after work strain injuries. Clinical symptoms met with criteria for Complex Regional Pain Syndrome (CRPS) type I. In the present study, the effect of the experience of pain on the somatotopy of the primary cortical hand representation was investigated. Somatosensory evoked magnetic fields (SEF) elicited by non-painful tactile stimulation at the index finger of the affected and the unaffected hand were recorded when experiencing pain elicited by a moderate physical load condition (holding a 1.6 kg object in the hand). It was shown that MEG and subjective responses to innocuous tactile stimuli were reduced when simultaneous nociceptive stimulation was applied. These findings suggest a gating effect in the central nervous system elicited by concurrent simultaneous information from two different somatosensory modalities (pain and tactile). The results revealed the existence of nociceptive-induced plastic changes in the central nervous system associated with CRPS type I.

Brain Mapping↗

PubMed2006

Modulation of visual stimulus discrimination by sustained focal attention: an MEG study.

PURPOSE: Visual attention, normally focused on the center of the visual field, can be shifted to a location in the periphery. This process facilitates the recognition of objects in the attended region. The present experiment was designed to investigate the time course of sustained attention that is known to augment stimulus perception in normal subjects. METHODS: Cortical activity of the human brain related to shifts of the attentional focus was examined with magnetoencephalography. Subjects had to identify a stimulus presented on a screen at one of two locations in the periphery of their visual fields. Sustained attention was either deployed toward the target by a preceding cue or not. RESULTS: Results confirmed a reaction time advantage on recognizing objects in the part of the visual field where attention had been deployed. A stronger magnetic brain response was detected for noncued targets at a latency of 260 to 380 ms after target onset. Source localization revealed a neuronal generator of the attention-related component in the parietal cortex. CONCLUSIONS: Sustained attention facilitates target detection. The component that is localized in the parieto-occipital cortex in the noncued condition is thought to reflect a transient shift of attention toward the target location.

Adult↗

PubMed2005

Do cortical maps depend on the timing of sensory input? Experimental evidence and computational model.

Fast adaptations in the functional organization of primary sensory cortex are generally assumed to result from changes of network connectivity. However, the effects of intrinsic neuronal excitability alterations due to the activation of neighboring cortical representational zones, which might as well account for the changes of cortical representative maps, have been paid little attention to. In a recent experiment (Braun et al. 2000b) we showed by neuromagnetic source imaging that random or fixed sequence stimulation of three digits of both hands led to stimulation-timing-induced changes in primary somatosensory (SI) cortical maps. The distance between the cortical representation of thumb and middle finger became significantly shorter during the fixed sequence stimulation. The analysis on the time course of the cortical map changes revealed that these reorganizations occurred within minutes and were fully reversible. The previously reported results were interpreted as the involvement of a superordinate center responsible for detecting and activating the appropriate maps. Here we present an alternative parsimonious explanation that is supported by a computational model. Based on the experimental evidence, we developed a simple model that took intrinsic neuronal excitability together with subthreshold activation into account and assumed partial cortical overlap of the representational zones of neighboring digits. Furthermore, in the model the neuronal excitability decayed slowly with respect to the stimulation frequency. The observed cortical map changes in the experiment could be reproduced by the two-layer feed-forward computational network. Our model thus suggests that the dynamic shifts of cortical maps can be explained by the state and time course of intrinsic neuronal excitability and subthreshold activation, without involving changes in network connectivity.

Adult↗

PubMed2005

Coordinate processing during the left-to-right hand transfer investigated by EEG.

Information about visuomotor tasks is coded in extrinsic, object-centered and intrinsic, body-related coordinates. For the reproduction of a trained task in mirror orientation with the opposite untrained hand, acquired extrinsic coordinates must be transformed. In contrast, intrinsic coordinates have to be modified during the execution of the originally oriented task. As shown recently, processes of coordinate transformations during the right-to-left hand transfer are associated with movement preparation and occur preferentially in the left hemisphere. Here, movement-related potentials, EEG power, and EEG coherence were recorded during the repetition of a drawing task previously trained by the nondominant left hand (Learned-task) and its execution in original and mirror orientation by the right hand (Normal- and Mirror-task). To identify EEG correlates of coordinate processing during intermanual transfer rather than effects due to the use of the right versus left hand, only those EEG data were analyzed which differed between the Normal- and Mirror-tasks. Whereas the Normal-task did not differ from the Learned-task in any of these predefined EEG parameters, beta coherence increased in the Mirror-task in the period ranging from 1 to 2 s after movement onset. These increases were especially prominent between hemispheres but were also observed symmetrically in the parieto-frontal electrode pairs of both hemispheres. Behavioral data revealed that the performance in the Learned- and both transfer tasks improved after left-hand training. Results of the present study indicate that coordinate transformation during the left-to-right hand transfer occurs in the phase of movement execution and affects predominantly extrinsic coordinates. Intrinsic coordinates are presumably mainly used in their original form. The modification of extrinsic coordinates is accompanied by increased information flow between both hemispheres; thereby inter-hemispheric connections--as mediated via the corpus callosum--seem to play a central role.

Adult↗

PubMed2005

Brain processes associated with target finding.

The response execution stage of cognitive skill consists of several substages, including finding the proper response location among available alternatives and moving the effector to the target location. In order to unravel the brain dynamics associated with the finding process, the present experiments used two experimental conditions. In the number condition, which requires both finding and moving, subjects are presented on each trial with a digit, 0-9, are required to find that digit on a circular clock face, and then to move a cursor to that target's location. In the arrow condition, an arrow pointing to the location of the target on the clock face circumference appears simultaneously with the target digit; no target finding is required because subjects need only to move the cursor along the path marked by the arrow. A pilot and the main experiment revealed that response initiation times but not movement times were affected by these experimental manipulations. Analysis of magnetoencephalographic (MEG) activity revealed an early occipital activity which was not affected by experimental manipulations. Later activity with central-parietal and parieto-temporal loci presumably reflected changes in the dorsal and ventral pathways, respectively, and these were affected by experimental conditions. Finally, finding processes seem to be associated with a second late activation of the ventral pathway presumably reflecting ongoing recognition processes.

Adolescent↗

PubMed2005

The dynamics of visual pattern masking in natural scene processing: a magnetoencephalography study.

We investigated the dynamics of natural scene processing and mechanisms of pattern masking in a scene-recognition task. Psychophysical recognition performance and the magnetoencephalogram (MEG) were recorded simultaneously. Photographs of natural scenes were briefly displayed and in the masked condition immediately followed by a pattern mask. Viewing the scenes without masking elicited a transient occipital activation that started approximately 70 ms after the pattern onset, peaked at 110 ms, and ended after 170 ms. When a mask followed the target an additional transient could be reliably identified in the MEG traces. We assessed psychophysical performance levels at different latencies of this transient. Recognition rates were reduced only when the additional activation produced by the pattern mask overlapped with the initial 170 ms of occipital activation from the target. Our results are commensurate with an early cortical locus of pattern masking and indicate that 90 ms of undistorted cortical processing is necessary to reliably recognize a scene. Our data also indicate that as little as 20 ms of undistorted processing is sufficient for above-chance discrimination of a scene from a distracter.

Brain Mapping↗

PubMed2005

A controlled prospective case control study of a prevention training program in female team handball players: the German experience.

BACKGROUND: Few authors have investigated the effectiveness of preventive intervention in European team handball. PURPOSE: The aim of the present study was to evaluate the effects of a prevention program on the incidence of injuries in female European team handball players. STUDY DESIGN: Prospective controlled study. METHODS: Ten female handball teams (134 players) took part in the prevention program (1. Information about injury mechanism, 2. Balance-board exercises, 3. Jump training) while 10 other teams (142 players) were instructed to train as usual. Over one season all injuries were documented weekly. RESULTS: Ankle sprain was the most frequent diagnosis in both groups with 11 ankle sprains in the control group and 7 ankle sprains in the intervention group (Odds ratio: 0.55, 95% confidence interval: 0.22-1.43). The knee was the second frequent injury site. In the control group 5 of all knee injuries were anterior cruciate ligament (ACL) ruptures (incidence: 0.21 per 1000 h) in comparison with one in the intervention group (incidence: 0.04 per 1000 h). Odds ratio was 0.17 with 95% confidence interval of 0.02-1.5. CONCLUSIONS: This study confirms that proprioceptive and neuromuscular training is appropriate for the prevention of knee and ankle injuries among female European team handball players.

Adult↗

PubMed2005

Objective measurement of tactile mislocalization.

Stimulating the skin with intensities close to the sensory threshold causes erroneous localization of the site of stimulation. Previous studies using manual methods for applying faint tactile stimuli have shown that localization errors obey a somatotopic principle in which tactile stimuli are preferentially mislocalized to sites adjacent to the stimulated skin region. However, manual testing of mislocalization is time consuming and only partially objective because results depend on the skills of the tester. To improve the testing procedure, an automated apparatus was developed. The procedure adjusted stimulus intensity adaptively during testing to remain near the individual subject's sensory threshold, so that mislocalizations occurred often enough to assess somatotopic organization. The new method was applied to 12 healthy subjects. In each subject, the five digits of the right hand were stimulated singly in random order. Localization errors were distributed preferentially to fingers close to the stimulated finger rather than to distant fingers. The profile of mislocalization differed significantly from that expected on the basis of response bias or guessing behavior. The present results replicate previous findings obtained for manual testing with improved sensitivity and indicate that the new technique is a useful tool for the study of somatosensory processing on a perceptual level.

Adult↗

PubMed2004

The right hand knows what the left hand is feeling.

The mislocalization profile, describing incorrect localization of faint tactile stimuli to different regions of the body, has been shown to provide insight into the processing of tactile stimuli. Interhemispheric somatosensory processing was examined in 15 subjects by studying the interference of left-hand stimulation on right-hand perception. In different conditions supra-threshold interference stimuli were applied to the left thumb or little finger either 200 or 500 ms prior to the application of a test stimulus on the right hand. Data show that interference stimuli applied to the left hand massively altered localization responses for stimuli applied to the right side. Stimulating the left thumb yielded an increased number of mislocalizations to the right thumb. Similarly, stimulating the left little finger caused a shift in localization responses towards the right ring finger. Results support the hypothesis that interaction of somatosensory information originating from different sides of the body follows a somatotopic organization.

Adult↗

PubMed2004

Effects of co-activation on cortical organization and discrimination performance.

We used fMRI to investigate the effects of tactile co-activation on the topographic organization of the human primary somatosensory cortex (SI). Behavioral consequences of co-activation were studied in a psychophysical task assessing the mislocalization of tactile stimuli. Co-activation was applied to the index, middle and ring fingers of the right hand either synchronously or asynchronously. Cortical representations for synchronously co-activated fingers moved closer together, whereas cortical representations for asynchronously co-activated fingers became segregated. Behaviorally, this pattern coincided with an increased and reduced number of mislocalizations between synchronously and asynchronously co-activated fingers, respectively. Thus, both synchronous and asynchronous coupling of passive tactile stimulation is able to induce short-term cortical reorganization associated with functionally relevant changes.

Adult↗

PubMed2004

EEG correlates of coordinate processing during intermanual transfer.

Goal-directed movements require mapping of target information to patterns of muscular activation. While visually acquired information about targets is initially encoded in extrinsic, object-centered coordinates, muscular activation patterns are encoded in intrinsic, body-related coordinates. Intermanual transfer of movements previously learned with one hand is accomplished by the recall of unmodified extrinsic coordinates if the task is performed in original orientation. Intrinsic coordinates are retrieved in case of mirror-reversed orientation. In contrast, learned extrinsic coordinates are modified during the mirror movement and intrinsic coordinates during the originally oriented task. To investigate the neural processes of recall and modification, electroencephalogram (EEG) recording was employed during the performance of a figure drawing task previously trained with the right hand in humans. The figure was reproduced with the right hand (Learned-task) and with the left hand in original (Normal-task) and mirror orientations (Mirror-task). Prior to movement onset, beta-power and alpha- and beta-coherence decreased during the Normal-task as compared with the Learned-task. Negative amplitudes over fronto-central sites during the Normal-task exceeded amplitudes manifested during the Learned-task. In comparison to the Learned-task, coherences between fronto-parietal sites increased during the Mirror-task. Results indicate that intrinsic coordinates are processed during the pre-movement period. During the Normal-task, modification of intrinsic coordinates was revealed by cerebral activation. Decreased coherences appeared to reflect suppressed inter-regional information flow associated with utilization of intrinsic coordinates. During the Mirror-task, modification of extrinsic coordinates induced activation of cortical networks.

Adult↗

PubMed2004

Influence of social support and emotional context on pain processing and magnetic brain responses in fibromyalgia.

OBJECTIVE: To examine the effects of social support provided by the presence of patient's significant other on pain ratings, pain thresholds, and brain activity associated with tactile stimulation in 18 fibromyalgia (FM) patients and 18 migraine patients (controls), and to assess the influence of emotional context on thermal pain perception and processing of non-pain-related information. METHODS: Thermal pain thresholds and somatosensory brain magnetic responses elicited by tactile stimulation at the elbow (a painful tender point in the FM group) and at the finger (nonpainful site) were evaluated under 2 experimental conditions of social support: patient alone and patient's significant other present. Brain activity was recorded using a 151-channel whole-head magnetoencephalography system. Additionally, the emotional context during presentation of tactile stimuli was manipulated by presenting aversive, pain-related pictures and neutral pictures and asking the patients to imagine that they were experiencing the situations depicted. RESULTS: Thermal pain thresholds indicated greater sensitivity in FM patients than in migraine patients, as well as enhanced sensitivity at the elbow than at the fingers. Specifically, in FM patients, there were significant reductions in pain sensitivity and subjective pain ratings when patients were stimulated at the painful tender point in the presence of their significant others as compared with the ratings when the patients were alone. Brain activity elicited by elbow stimulation was also significantly reduced in FM patients when a significant other was present as compared with the activity when the patient was alone. These effects were not observed in the migraine patients. CONCLUSION: When the significant other was present, FM patients reported less pain and thermal pain sensitivity and showed diminished brain activity elicited upon tactile stimulation of a tender point compared with these levels when the patients were alone. These findings are consistent with the hypothesis that social support through the presence of a significant other can influence pain processing at the subjective-behavioral level as well as the central nervous system level.

Adult↗

PubMed2004

Neuromagnetic activity in medial parietooccipital cortex reflects the perception of visual motion during eye movements.

We usually perceive a stationary, stable world despite coherent visual motion induced by eye movements. This astonishing example of perceptual invariance results from a comparison of visual information with internal reference signals (nonretinal signals) predicting the visual consequences of an eye movement. The important consequence of this concept is that our subjective percept of visual motion reflects the outcome of this comparison rather than retinal image slip. To localize the cortical networks underlying this comparison, we compared magnetoencephalography (MEG) responses under two conditions of pursuit-induced retinal image motion, which were identical physically but--due to different calibrational states of the nonretinal signal prompted under our experimental conditions--gave rise to different percepts of visual motion. This approach allows us to demonstrate that our perception of self-induced visual motion resides in comparably "late" parts of the cortical hierarchy of motion processing sparing the early stages up to cortical area MT/V5 but including cortex in and around the medial aspect of the parietooccipital cortex as one of its core elements.

Attention↗