Biomedical subjects

Volker Hömberg

Publications and source records attributed to Volker Hömberg.

6 recordsLinked to original sources

PubMed2006

Motor recovery as assessed with isometric finger movements and perfusion magnetic resonance imaging after acute ischemic stroke.

OBJECTIVE: Recovery from hemiparetic stroke is variable. An important goal for clinicians and clinical researchers is to identify predictors of recovery. The initial phase after acute ischemic stroke is considered to be of major importance for neurological outcome. The authors sought to determine in patients with acute ischemic stroke whether early motor recovery, as measured by repetitive isometric index-thumb oppositions, is correlated with ischemic lesion volume. METHODS: Thirty-six acute hemiparetic stroke patients with residual hand function were investigated. The European Stroke Scale (ESS) score was determined on admission and at discharge. Performance of repetitive index finger-thumb pinch movements was measured daily during the 1st 8 days after stroke onset. Brain ischemia volume was determined digitally in time-to-peak magnetic resonance images of per-fusion. RESULTS: The recovery of patients with (P = 0.002) and without (P < 0.001) thrombolysis as assessed with the ESS was paralleled by an increase in isometric grip force and movement rate (P < 0.05). Recovery was predicted by the area of moderately impaired perfusion indicated by the per-fusion mismatch volume (r = 0.578, P < 0.001). CONCLUSIONS: In acute stroke, recovery of hand function is predicted by the volume of salvageable ischemic tissue, as determined by the perfusion mismatch.

Aged↗

PubMed2004

Effects of single pulse TMS on spatio-temporal integration in sequential isochronus movements.

This study was designed to investigate the effect of single pulse transcranial magnetic stimulation (TMS) on the isochronic performance of sequential movements which were recorded using a digitising pad. Magnetic stimulation was applied through an 8-shaped magnetic coil over primary motor and premotor cortex at a specific time point while executing the first of a three movement sequence. TMS applied to the premotor cortex showed an alteration effect on the first movement while stimulation of the primary motor cortex influenced the second movement in the sequence. Results suggest that the premotor cortex is involved in online monitoring and controlling of spatio-temporal features of trajectories while the motor cortex contributes to the execution of movements. Isochrony is maintained to a high degree under TMS which has been found in other studies to delay reaction times. The results show that although TMS has a significant influence on motor performance, isochrony is a robust component of motor programs, not readily to be disturbed.

Adult↗

PubMed2004

Reorganisation of cerebral circuits in human ischemic brain disease.

Animal experiments suggest that reorganisation of cerebral representations is the neurobiological basis of post-lesional recovery. In human ischemic brain disease recovery is a dynamic and sustained process beginning after stroke manifestation. The mechanisms underlying recovery can be investigated non-invasively in the human brain using functional neuroimaging and transcranial magnetic stimulation (TMS). In the acute stage, the mismatch area of the perfusion deficit and the impaired water diffusion as assessed by magnetic resonance imaging (MRI) shows the brain tissue that potentially can be rescued by thrombolysis or emergency carotid endarterectomy. Since spontaneous motor recovery is a function of the corticospinal tract integrity, early reperfusion of ischemic tissue is critical. In the subacute and chronic stage after stroke, recovery of motor function was shown to take place irrespective of a concomitant affection of the somatosensory system. Functional MRI with simultaneous recordings of the electromyogram provides evidence that the abnormal activation of motor and premotor cortical areas in both hemispheres related to finger movements has a large interindividual variability. As evident from TMS, recovery results from regression of perilesional inhibition and from remote intracortical disinhibition. Repetitive training, constraint induced training and motor imagery can augment recovery promoting a re-emerging activation in the affected hemisphere. Evolution of altered local perilesional and large-scale bihemispheric circuits appears to allow for post-lesional deficit compensation.

Brain Ischemia↗

PubMed2003

Remote changes in cortical excitability after stroke.

Changes in the cerebral metabolism and the excitability of brain areas remote from an ischaemic brain lesion have been reported in animals and humans and implicated as a mechanism relevant to functional recovery. The aim of the present study was to determine whether changes in the inhibitory and excitatory activity in motor cortex of the non-affected hemisphere are present in stroke patients, and whether these changes are related to the extent of the patients' recovery of function. Transcranial magnetic stimulation (TMS) was used to study the first dorsal interosseus muscle (FDI) of the non-affected hand in 13 patients with good recovery of hand function after stroke, and was compared with left hemispheric stimulation in 13 healthy age-matched volunteers. In the first experiment, paired-pulse TMS with the conditioning stimulus (CS) set at 80% of the subject's motor threshold (MT) and interstimulus intervals (ISIs) of 2, 3, 10 and 15 ms was used. In the second experiment, different intensities of CS were used to study its inhibitory effect on a succeeding suprathreshold test stimulus at an ISI that was kept constant at 2 ms. In a third experiment, the rise in motor evoked potential (MEP) amplitudes with increasing stimulus intensities was measured. In two additional control experiments, the effect of left versus right hemispheric stimulation in normal volunteers and good versus poor recovery of hand function in patients after stroke on the excitability of inhibitory and excitatory activity was studied. MT, mean test MEP and recruitment curves were similar in patients and healthy volunteers. In those patients with good recovery, paired-pulse excitability was increased at ISIs of 2 and 3 ms, similar to healthy volunteers at ISIs of 10 and 15 ms. When tested with different CS intensities at an ISI of 2 ms, inhibitory activity was similar in patients and healthy subjects at small CS intensities, but faded rapidly at higher CS intensities in patients. In contrast, in patients with poor recovery, this increase in cortical excitability at higher CS intensities was not seen. The similarity of MT, mean test MEP and recruitment curves in patients and healthy volunteers indicates that the overall corticomotoneuronal excitability has not changed in patients. The similarity of the inhibitory effect at low CS intensities in the patients with good recovery and healthy subjects, and the steeper increase of conditioned MEP amplitude at higher CS intensities in the recovering patients suggest that in the patients' contralesional motor cortex the balance of excitatory and inhibitory activity was shifted towards an increase of excitatory activity in the neuronal circuits tested at ISIs of 2 and 3 ms. This shares similarities to mechanisms implicated as relevant for reorganizational processes after experimental brain injury and may be relevant for functional recovery after stroke. The absence of changes in cortical excitability in patients with poor recovery supports the relevance of our findings for recovery.

Adult↗

PubMed2002

Hemispheric dissociation of visual-pattern processing and visual rotation.

We aimed at investigating whether on-line and delayed visual pattern processing activated different areas in human prefrontal and parietal cortex. For this purpose we measured the regional cerebral blood flow (rCBF) during simultaneous and successive visual matrix processing in 10 right-handed subjects. Delayed matching to sample activated predominantly left hemispheric ventrolateral prefrontal cortex, Broca's area and parts of the parietal cortex. In contrast, visuospatial matrix rotation showed activation of the right dorsolateral prefrontal cortex and parietal lobe. The present results suggest a hemispheric dissociation of fronto-parietal circuits with a left dominance for visual pattern processing like storage and a right dominance for visuospatial processing.

Adult↗

PubMed2002

Neural correlates of visuospatial imagery.

We studied changes in regional cerebral blood flow (rCBF) in 10 healthy right-handed subjects during a visuospatial imagery task. The subject's task consisted of drawing imagined lines connecting encircled numbers in ascending order and estimating the number of lines crossing. Compared with a control task in which there were no crossed lines, there were significant rCBF increases in the cingulate gyrus, the adjacent superior frontal gyrus and in the left inferior parietal cortex. The rCBF changes of the latter area correlated with task performance time. Since these activation areas are close to those in imagery of movement trajectories, we concluded that they appear to be a subsystem for processing mental visuospatial images.

Adult↗