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Biomedical subjects

Christian W Hess

Publications and source records attributed to Christian W Hess.

At least 19 recordsLinked to original sources
PubMed2006

Repetitive TMS over the human oculomotor cortex: comparison of 1-Hz and theta burst stimulation.

The aim of the study was to compare the effect duration of two different protocols of repetitive transcranial magnetic stimulation (rTMS) on saccade triggering. In four experiments, two regions (right frontal eye field (FEF) and vertex) were stimulated using a 1-Hz and a theta burst protocol (three 30Hz pulses repeated at intervals of 100ms). The same number of TMS pulses (600 pulses) was applied with stimulation strength of 80% of the resting motor threshold for hand muscles. Following stimulation the subjects repeatedly performed an oculomotor task using a modified overlap paradigm, and saccade latencies were measured over a period of 60min. The results show that both 1-Hz and theta burst stimulation had inhibitory effects on saccade triggering when applied over the FEF, but not over the vertex. One-hertz rTMS significantly increased saccade latencies over a period of about 8min. After theta burst rTMS, this effect lasted up to 30min. Furthermore, the decay of rTMS effects was protocol-specific: After 1-Hz stimulation, saccade latencies returned to a baseline level much faster than after theta burst stimulation. We speculate that these time course differences represent distinct physiological mechanisms of how TMS interacts with brain function.

Adult↗
PubMed2006

To look or not to look at threat? Scanpath differences within a group of spider phobics.

Predicting the behavior of phobic patients in a confrontational situation is challenging. While avoidance as a major clinical component of phobias suggests that patients orient away from threat, findings based on cognitive paradigms indicate an attentional bias towards threat. Here we present eye movement data from 21 spider phobics and 21 control subjects, based on 3 basic oculomotor tasks and a visual exploration task that included close-up views of spiders. Relative to the control group, patients showed accelerated reflexive saccades in one of the basic oculomotor tasks, while the fear-relevant exploration task evoked a general slowing in their scanning behavior and pronounced oculomotor avoidance. However, this avoidance strongly varied within the patient group and was not associated with the scores from spider avoidance-sensitive questionnaire scales. We suggest that variation of oculomotor avoidance between phobics reflects different strategies of how they cope with threat in confrontational situations.

Adult↗
PubMed2006

Epilepsy and obstructive sleep apnea.

A few publications documented the coexistence of epilepsy and obstructive sleep apnea (OSA). The extent, nature, and clinical relevance of this association remain poorly understood. We retrospectively reviewed the database of our sleep center to identify patients with both sleep apnea and epilepsy. Characteristics of epilepsy, sleep history, presence of excessive daytime sleepiness [Epworth Sleepiness Scale (ESS)] and polysomnographic data were assessed. The effect of continuous positive airway pressure (CPAP) on seizure reduction was prospectively analyzed after a median interval of 26 months (range: 2-116 months) from the diagnosis of OSA. OSA was found in 29 epilepsy patients (25 men and 4 women) with a median age of 56 years (range: 37-79). The median apnea hypopnea index was 33 (range: 10-85), the oxygen desaturation index was 12 (range 0-92), and 52% of the patients had an ESS score >10. In 27 patients, epilepsy appeared 1 month to 44 years prior to the diagnosis of OSA. In 21 patients, the appearance of OSA symptoms coincided with a clear increase in seizure frequency or the first appearance of a status epilepticus. Treatment with CPAP was continued with good compliance in 12 patients and led to a significant reduction of both ESS scores and seizure frequency in 4 patients. Our data suggest the importance of considering diagnosis and treatment of OSA in epilepsy patients with poor seizure control and/or reappearance of seizures after a seizure-free interval.

Adult↗
PubMed2006

One-Hertz transcranial magnetic stimulation over the frontal eye field induces lasting inhibition of saccade triggering.

The aim of the study was to examine the effect of low-frequency repetitive transcranial magnetic stimulation on saccade triggering. In five participants, a train of 600 pulses with a frequency of 1 Hz was applied over the right frontal eye field and--as control condition--over the vertex. After repetitive transcranial magnetic stimulation application, oculomotor performance was evaluated with an overlap paradigm. The results show that the repetitive transcranial magnetic stimulation effect was specific for frontal eye field stimulation. Saccade latencies were found to be increased bilaterally for several minutes after the stimulation, and the time course of recovery was different for the ipsilateral and contralateral sides. The results are discussed in the light of possible local and remote repetitive transcranial magnetic stimulation effects on the oculomotor network.

Adult↗
PubMed2006

Cortical reorganization after brain damage: the oculomotor model.

Recovery from eye movement deficits after cortical lesions is amazingly rapid and almost complete, which is in sharp contrast to most other neurological deficits of cerebral lesions. The underlying mechanisms of this successful recovery remain uncertain. We had the rare opportunity to examine two patients with recovery from saccade deficits after a lesion restricted to the frontal eye field (FEF) by means of transcranial magnetic stimulation (TMS). The results provide direct evidence that recovery depended on the integrity of the oculomotor regions of the nonlesioned contralesional hemisphere, and that the compensatory network is task-specific.

Animals↗
PubMed2006

Extending lifetime of plastic changes in the human brain.

The ability of the brain to adjust to changing environments and to recover from damage rests on its remarkable capacity to adapt through plastic changes of underlying neural networks. We show here with an eye movement paradigm that a lifetime of plastic changes can be extended to several hours by repeated applications of theta burst transcranial magnetic stimulation to the frontal eye field of the human cortex. The results suggest that repeated application of the same stimulation protocol consolidates short-lived plasticity into long-lasting changes.

Adult↗
PubMed2005

Oculomotor behaviour in simultanagnosia: a longitudinal case study.

The aim of the present single case study was to investigate oculomotor recovery in a patient with simultanagnosia due to biparietal hypoxic lesions. Applying visual exploration as well as basic oculomotor tasks in three consecutive test sessions--i.e. 8 weeks, 14 weeks, and 37 weeks after brain damage had occurred--differential recovery was observed. While visual exploration remarkably improved, an impaired disengagement of attention persisted. The improvement of exploration behaviour is interpreted within an oculomotor network theory and implications for a deficit-specific recovery from simultanagnosia are discussed.

Agnosia↗
PubMed2005

Uncrossed cortico-muscular projections in humans are abundant to facial muscles of the upper and lower face, but may differ between sexes.

It is a popular concept in clinical neurology that muscles of the lower face receive predominantly crossed cortico-bulbar motor input, whereas muscles of the upper face receive additional ipsilateral, uncrossed input. To test this notion, we used focal transcranial magnetic brain stimulation to quantify crossed and uncrossed cortico-muscular projections to 6 different facial muscles (right and left Mm. frontalis, nasalis, and orbicularis oris) in 36 healthy right-handed volunteers (15 men, 21 women, mean age 25 years). Uncrossed input was present in 78% to 92% of the 6 examined muscles. The mean uncrossed: crossed response amplitude ratios were 0.74/0.65 in right/left frontalis, 0.73/0.59 in nasalis, and 0.54/0.71 in orbicularis oris; ANOVA p>0.05). Judged by the sizes of motor evoked potentials, the cortical representation of the 3 muscles was similar. The amount of uncrossed projections was different between men and women, since men had stronger left-to-left projections and women stronger right-to-right projections. We conclude that the amount of uncrossed pyramidal projections is not different for muscles of the upper from those of the lower face. The clinical observation that frontal muscles are often spared in central facial palsies must, therefore, be explained differently. Moreover, gender specific lateralization phenomena may not only be present for higher level behavioural functions, but may also affect simple systems on a lower level of motor hierarchy.

Adult↗
PubMed2005

Allocentric and egocentric spatial impairments in a case of topographical disorientation.

We describe a patient with a topographical disorientation after a stroke of the right mediotemporooccipital lobe including the parahippocampal cortex (PHC). Clinical observations and neuropsychological testing reveal an impairment of allocentric spatial representations as well as impairments of visuospatial learning and memory. These findings are in accordance with the well-known function of the PHC in topographical disorientation. As a new finding, results from oculomotor tasks show additional impairments of the egocentric spatial coordinate frame suggesting that in topographical disorientation due to a lesion of the right mediotemporooccipital lobe not only allocentric but also egocentric visuospatial functions are disturbed.

Aged↗
PubMed2005

The role of the human posterior parietal cortex in memory-guided saccade execution: a double-pulse transcranial magnetic stimulation study.

The present study investigated the role of the right posterior parietal cortex (PPC) in the triggering of memory-guided saccades by means of double-pulse transcranial magnetic stimulation (dTMS). Shortly before saccade onset, dTMS with different interstimulus intervals (ISI; 35, 50, 65 or 80 ms) was applied. For contralateral saccades, dTMS significantly decreased saccadic latency with an ISI of 80 ms and increased saccadic gain with an ISI of 65 and 80 ms. Together with the findings of a previous study during frontal eye field (FEF) stimulation the present results demonstrate similarities and differences between both regions in the execution of memory-guided saccades. Firstly, dTMS facilitates saccade triggering in both regions, but the timing is different. Secondly, dTMS over the PPC provokes a hypermetria of contralateral memory-guided saccades that was not observed during FEF stimulation. The results are discussed within the context of recent neurophysiological findings in monkeys.

Adult↗
PubMed2004

Repetitive transcranial magnetic stimulation: a putative add-on treatment for major depression in elderly patients.

Repetitive transcranial magnetic stimulation (rTMS) is a recent putative treatment for affective disorders. Several studies have demonstrated antidepressant effects of rTMS in younger patients; we aimed to assess its effect in older outpatients with treatment-resistant major depression. Twenty-four outpatients (mean age=62 years, S.D.=12) with major depression were randomized for sham or real stimulation and received 10 daily rTMS sessions (20 Hz, 2-s trains, 28-s intertrain intervals, 100% of motor threshold) in addition to the antidepressant medication. For sham stimulation, the coil was tilted 90 degrees. Depression severity was assessed using the Hamilton Depression Rating Scale, the Beck Depression Inventory, items from the NIMH self-rated symptom scale, and a visual analog depression scale. Mini-Mental Status Examination performance, memory, and executive and attentional functions were measured to control for cognitive side effects. Depression ratings revealed significant antidepressant effects within 2 weeks in both sham and real stimulation groups; however, there were no between-group differences. Treatment with rTMS was safe; adverse events were rare and not more prevalent in either group, and cognitive assessment did not show any deterioration. We were unable to demonstrate any additional antidepressant effects of real stimulation in elderly patients with treatment-resistant major depression. Therapeutic effects of rTMS in this clinically challenging patient group remain to be demonstrated.

Aged↗
PubMed2004

Significance of coil orientation for motor evoked potentials from nasalis muscle elicited by transcranial magnetic stimulation.

OBJECTIVE: In transcranial magnetic stimulation (TMS) of the motor cortex, the optimal orientation of the coil on the scalp is dependent on the muscle under investigation, but not yet known for facial muscles. METHODS: Using a figure-of-eight coil, we compared TMS induced motor evoked potentials (MEPs) from eight different coil orientations when recording from ipsi- and contralateral nasalis muscle. RESULTS: The MEPs from nasalis muscle revealed three components: The major ipsi- and contra-lateral middle latency responses of approximately 10 ms onset latency proved entirely dependent on voluntary pre-innervation. They were most easily obtained from a coil orientation with posterior inducing current direction, and in this respect resembled the intrinsic hand rather than the masseter muscles. Early short duration responses of around 6 ms onset latency were best elicited with an antero-lateral current direction and not pre-innervation dependent, and therefore most probably due to stimulation of the nerve roots. Late responses (>18 ms) could inconsistently be elicited with posterior coil orientations in pre-innervated condition. CONCLUSIONS: By using the appropriate coil orientation and both conditions relaxed and pre-innervated, cortically evoked MEP responses from nasalis muscle can reliably be separated from peripheral and reflex components and also from cross talk of masseter muscle activation.

Adult↗
PubMed2004

Residual oculomotor and exploratory deficits in patients with recovered hemineglect.

Several studies on hemineglect have reported that patients recover remarkably well when assessed with neuropsychological screening tests, however, they show deficits on novel or complex tasks. We investigated whether such deficits can be revealed with eye movement analysis, applying two basic oculomotor tasks as well as two exploratory tasks. Eye movements were recorded in eight hemineglect patients at least eleven months after right-hemisphere brain damage had occurred. Sixteen healthy volunteers participated in the control group. Regarding the basic oculomotor tasks, only the overlap task revealed residual deficits in patients, suggesting that a directional deficit in disengaging attention persisted during recovery. Further residual deficits were evident in the exploratory tasks. When everyday scenes were explored, patients showed a bias in early orienting towards the ipsilateral hemispace. In a search task, they demonstrated the same orienting bias as well as a non-directional deficit concerning search times. Moreover, patients preferentially fixated in the contralateral hemispace, but did not benefit from this asymmetry in terms of search times, i.e. they did not detect contralateral targets faster than ipsilateral ones. This suggests a dissociation between oculomotor processes and attentional ones. In conclusion, we have identified behavioural aspects that seem to recover slower than others. A disengagement deficit and biases in early orienting have been the most pronounced residual oculomotor deficits.

Adult↗
PubMed2004

Single-pulse transcranial magnetic stimulation over the frontal eye field can facilitate and inhibit saccade triggering.

The aim of this study was to investigate the effect of single-pulse transcranial magnetic stimulation on the triggering of saccades. The right frontal eye field was stimulated during modified gap and overlap paradigms with flashed presentation of the lateral visual target of 80 ms. In order to examine possible facilitating or inhibitory effects on saccade triggering, three different time intervals of stimulation were chosen, i.e. simultaneously with onset of the target, during the presentation and after target end. Stimulation applied simultaneously with target onset significantly decreased the latency of contralateral saccades in the gap but not in the overlap paradigm. Stimulation after target end significantly increased saccade latency for both sides in the gap paradigm and for the contralateral side in the overlap paradigm. Stimulation during presentation had no effect in either paradigm. The results show that, depending on the time interval and the paradigm tested, a facilitation or inhibition of saccade triggering can be achieved. The results are discussed in a context of two probable transcranial magnetic stimulation effects, a direct interference with the frontal eye field on the one hand and a remote interference with the superior colliculus on the other hand.

Adult↗
PubMed2003

Information processing in long delay memory-guided saccades: further insights from TMS.

The performance of memory-guided saccades with two different delays (3 s and 30 s of memorisation) was studied in eight subjects. Single pulse transcranial magnetic stimulation (TMS) was applied simultaneously over the left and right dorsolateral prefrontal cortex (DLPFC) 1 s after target presentation. In both delays, stimulation significantly increased the percentage of error in amplitude of memory-guided saccades. Furthermore, the interfering effect of TMS was significantly higher in the short delay compared to that of the long delay paradigm. The results are discussed in the context of a mixed model of spatial working memory control including two components: First, serial information processing with a predominant role of the DLPFC during the early period of memorisation and, second, parallel information processing, which is independent from the DLPFC, operating during longer delays.

Adult↗
PubMed2002

Acute disseminated encephalomyelitis in adults: a reappraisal of clinical, CSF, EEG, and MRI findings.

OBJECTIVES: To establish an adequate definition of acute disseminated encephalomyelitis (ADEM) in adults, based on our clinical observations of a case-series. METHODS: Over a period of three years 10 adult patients with a para- or postinfectious disseminated (diffuse or multifocal) syndrome of the CNS fulfilling predefined strict criteria for the diagnosis of ADEM were encountered and systematically followed. RESULTS: The age ranged from 21 to 62 years, two were men. MRI was normal in 5 patients and only mildly abnormal in the remaining patients. CSF was normal in 5 patients and mildly abnormal in the remainder, EEG was abnormal in 7/8 patients. All patients survived and were followed over a period of 30 months (range: 8 to 48 months). Nine patients were left with some residual defects, consisting most often of a mild cognitive impairment. CONCLUSIONS: The EEG as an investigation of brain function can be crucial in establishing the organic nature of disease. MRI is important to exclude other diffuse or multifocal encephalopathies. However, in contrast to previous reports in the literature abnormal MRI should not be considered mandatory in adult ADEM. Difficulties in the diagnosis of ADEM are discussed and the importance of clinical and paraclinical findings for establishing the diagnosis is outlined.

Adult↗