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Biomedical subjects

H Hielscher

Publications and source records attributed to H Hielscher.

At least 19 recordsLinked to original sources
PubMed2006

Effects of stimulus-response compatibility in Parkinson's disease: a psychophysiological analysis.

The present study investigated the mechanisms underlying stimulus-response compatibility effects in Parkinson's disease patients and matched controls. Since basal ganglia are involved in the selection and inhibition of competing responses we examined whether basal ganglia dysfunction in Parkinson's disease leads to greater interference effects compared to the control subjects. Reaction times and lateralized movement-related cortical potentials (lateralized readiness potential: LRP) were recorded in two modified Eriksen flanker tasks. Both groups were influenced by compatibility conditions; interference was seen as enhanced reaction time and error rate, as well as incorrect early LRP and delayed late LRP in incongruent trials. Altogether, behavioral and electrophysiological measures showed the interference to be rather smaller for the patients than for the controls. In contrast, facilitation did not differ among groups. Hence the claim that Parkinson's disease patients are more influenced than controls by interfering directional stimuli appears not always valid.

Electroencephalography↗
PubMed2001

Action monitoring, error detection, and the basal ganglia: an ERP study.

The error negativity (Ne or ERN) is an event-related brain potential component, which is assumed to reflect error detection. Recently it has been hypothesized that the basal ganglia are assumed to play a crucial role in error detection. In the present study we ask whether the Ne is altered in patients with Parkinson's disease (PD), who have an impaired function of the basal ganglia. We recorded the Ne in patients and in matched controls, while they performed different tasks that require a relatively high cognitive control, which is supposed to pose particular problems on PD. The Ne was in fact smaller in the patients than in the controls in all tasks. Our results suggest an impairment of error detection in PD for different types of demanding tasks. This supports the hypothesis that the basal ganglia do play an important role for error detection in action monitoring.

Aged↗
PubMed2001

Multichannel derived median nerve SEP compared to EEG in patients with vascular cerebral lesions.

In order to compare the sensitivity of multichannel derived median nerve SEP with EEG in vascular cerebral lesions we examined 22 normals and 23 patients. SEP components within the first 50 ms could be divided into main waveform patterns: (1) a W-shaped parietal pattern consisting of N20, P25, N35 and P45 in most cases. (2) a frontal pattern with P20 and N30 as well as possibly detectible N24, P28, P33, N40 and P50. (3) a central P22. Two younger normals showed a V-shaped parietal pattern with N20 and P35, a frontal pattern with P20 and N36, and central P22 with a remarkably long latency. All components could be analysed sufficiently by means of three representative electrode positions (stimulation right/left): P3/P4, C3/C4, and F3/F4, which reduces the expense of recording and analysing considerably. 21 patients (91.3%) showed abnormal results in SEP, whereas 14 patients (60.9%) in EEG. A three channel electrode array can increase the usefulness of SEP and detect cerebral dysfunctions in cerebral lesions in spite of normal EEG under routine examination conditions. Analysis of multichannel derived SEPs during treatment and recovery after stroke and search for the prognostic value in the acute stage of the disease should be done in future.

Adult↗
PubMed1992

The importance of MRI (magnetic resonance imaging) for the diagnosis of brainstem infarction.

As experience with it accumulates, high resolution MRI seems more capable of representing morphological alterations of the central nervous system than cranial computer tomography (CCT). The question thus arises whether the detection of brainstem infarctions with MRI might not be easier than with CCT and how the topography of brainstem lesions demonstrated with MRI correlate with clinical symptoms and signs. 16 patients with definite clinical symptoms of brainstem infarction were examined by MRI. The examination took place between the 10th and 14th day after the occurrence of the infarction. Using MRI, we found pathological results in only 8 of these cases. In only 5 of these cases a clear relationship between the neurological picture and the topography of the lesion could be shown. These findings demonstrate that despite the high quality of the MRI images, the clinical examination for symptoms and signs is more important than imaging in the brainstem infarction.

Arteries↗
PubMed1990

Effects of ipsapirone on spatial and temporal changes in somatosensory evoked potentials after middle cerebral artery occlusion in the rat.

The present study investigates the effects of the 5-hydroxytryptamine1A agonist ipsapirone on electroencephalography and somatosensory evoked potentials after middle cerebral artery occlusion in the rat. We implanted 17 silver ball electrodes symmetrically distributed over the skull in 14 rats and registered electroencephalography activity and somatosensory evoked potentials before, 1 hour, and 1 week after permanent occlusion of the left middle cerebral artery. Before vessel occlusion, a symmetric distribution of electroencephalography power was seen over both hemispheres. Middle cerebral artery occlusion caused a complete abolishment of electroencephalography power in the frontolateral aspects of the affected hemisphere. When electroencephalographic recordings 7 days after the insult were superimposed with three-dimensional-reconstructed pictures of the infarct, a close correspondence of the extention and spatial orientation was noted. Two negative and two positive peaks were consistently recorded before middle cerebral artery occlusion. In both control and ipsapirone-treated (30 mg/kg i.p. 30 minutes after induction of ischemia) animals, the vessel occlusion caused a severe reduction in amplitudes of somatosensory evoked potentials in all areas under record (p less than 0.05). One week after middle cerebral artery occlusion, amplitudes of somatosensory potentials over the lesioned hemisphere were still significantly (p less than 0.05) lower than preischemic values in the control group. When compared with the corresponding values 1 hour after middle cerebral artery occlusion, an albeit insignificant tendency toward increased amplitudes was observed in most areas under record. By contrast, in ipsapirone-treated animals, significant differences compared with preischemic values were no longer present 1 week after the vessel occlusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

[Sural nerve neurography using surface and needle electrodes in polyneuropathies. Comparative study].

It was the objective of our study to find a simple and reliable method for the electroneurographic examination of the sural nerve of patients suffering from polyneuropathy. As a first step, the normal values of persons not affected by this disease were taken by orthodromic technique and surface electrodes. The results were as follows: nerve conduction velocity: 59,44 m/s +/- 5,05; amplitude of the nerve action potential: 6,58 microV +/- 3,05; duration of the amplitude: 2,08 ms +/- 2,7; prolongation of latency after double stimulation: 3,37% +/- 0,77. Then potentials were stimulated by surface- and needle electrodes on the patients affected by polyneuropathy and recorded. Comparing the results gained by the different methods, we found that they correlated in a highly significant way, which means that all the methods are equally applicable. The stimulation and recording by surface electrodes, however, has apart from its reliability the additional advantage of being a simple, quick, and gentle method of examination. There is little objection to applying it repeatedly to the same patient. Further information about polyneuropathy can be obtained by the examination of the relative refractory period.

Action Potentials↗
PubMed1983

[Diplopia as an initial symptom of intracranial tumors].

Among 716 patients with intracranial blastomatous changes 74 showed diplopia as a consequence of involvement of the oculomotorius, trochlearis or (and) the abducens nerve. Diplopia as primary symptom of disease was observed in 20 cases. Patients with isolated initial diplopia were on average 10 years younger than patients where diplopia occurred only in the further course of the tumour. There were no preceding other diseases demonstrable in patients with initial diplopia. Papilloedema did not occur significantly more frequently in them than in patients with diplopia as secondary symptom. In rare cases latency between occurrence of diplopia and further symptoms may be months to two years. For this reason exact neurologic and ophthalmologic follow-up controls, particularly in young patients with isolated persistent diplopia, are required.

Abducens Nerve↗
PubMed1980

Sural nerve conduction velocity and refractory period in diabetics without clinical signs of neuropathy.

Twentysix patients aged 22-76 years with a duration of diabetes of 1 month to 23 years but without signs of symptoms of a peripheral nerve disease were studied. The nerve conduction velocity, the amplitude of the compound action potential and its restitution during the relative refractory period were examined in sural nerves. Nerve conduction velocity of the motor fibers were determined in the median, ulnar, tibial, and peroneal nerves. A reduced conduction velocity in motor nerves of the lower extremities were found in 10%, a reduced sensory nerve conduction velocity in 25%, and pathological changes of the refractory period in 50% of the patients. It is concluded that the determination of the relative refractory period can be used as a sensitive test in the early diagnosis of diabetic neuropathy.

Adult↗
PubMed1980

[Cauda equina neurography. Results from normal persons and patients with lumbosacral root compression syndrome].

The results with the cauda-equina-neurography in more than 150 patients demonstrate a value for differentiation of lumbosacral disorders. The action potentials of normal adults are mostly biphasic, have the same configuration for both sides and their amplitude is between 0,3 and 20 uV. The conduction velocity decreases with age for both nerves. In cases of lumbosacral disorders with isolated nerve root affection by discogenic compressions the potentials are delayed, reduced, polyphasic or absent. Mostly the clinical, electromyographic, myelographic and surgical results correspond with neurographic examination. The examination is possible since technical problems permit a good differentiation and localisation of root lesions.

Adolescent↗