Biomedical subjects

Martin Kaltenhäuser

Publications and source records attributed to Martin Kaltenhäuser.

8 recordsLinked to original sources

PubMed2007

Spatial relationship of source localizations in patients with focal epilepsy: Comparison of MEG and EEG with a three spherical shells and a boundary element volume conductor model.

Epilepsy surgery is an option for patients with pharmacoresistant focal epilepsies, but it requires a precise focus localization procedure. Magnetoencephalography (MEG) and electroencephalography (EEG) can be used for analysis of interictal activity. The aim of this prospective study was to compare clusters of source localization results with MEG and EEG using a three spherical shells (3SS) and a boundary element method (BEM) volume conductor model. The study was closed when 100 patients met the inclusion criteria. Simultaneous MEG and EEG were recorded during presurgical evaluation. Epileptiform signals were analyzed using an equivalent current dipole model. Centroids of source localizations from MEG, EEG, 3SS, and BEM in their respective combinations were compared. In a 3SS model, MEG source localizations were 5.6 mm inferior to those obtained by EEG, while in a BEM model MEG source localizations were 6.3 mm anterior and 4.8 mm superior. The mean scattering of source localizations between both volume conductor models was 19.5 mm for EEG and 9.6 mm for MEG. For MEG no systematic difference between BEM and 3SS source localizations was found. For EEG, source localizations with BEM were 5.9 mm posterior and 11.7 mm inferior to those determined using 3SS. No differences were found between the 46 temporal and the 54 extratemporal lobe epilepsy patients. The observed systematic differences of source localizations of epileptic spikes due to the applied source signal modality and volume conductor model should be considered in presurgical evaluation when only one source signal and volume conductor model is available.

Adult↗

PubMed2006

Spontaneous magnetoencephalographic activity in patients with obsessive-compulsive disorder.

Non-invasive functional imaging techniques have begun to delineate the underlying neurophysiological basis of obsessive-compulsive disorder (OCD). In the present study, we investigated slow (2-6 Hz) and fast (12.5-30 Hz) spontaneous magnetoencephalographic (MEG) activity in ten patients with obsessive-compulsive disorders compared to ten healthy control subjects. Fast MEG activity was significantly elevated in OCD patients. The corresponding dipole density maxima were concentrated on the left superior temporal gyrus. Although no differences were detected in the absolute dipole numbers between controls and OCD patients regarding slow MEG activity, only the latter showed a clustering of slow MEG activity over their left dorsolateral prefrontal cortex. We conclude that alterations of spontaneous MEG activity in prefrontal and temporal cortices may be linked to the pathogenesis of OCD. Therefore, we provide further functional neuroimaging evidence that the complex features of OCD have neural correlates, which may help in a future understanding of this disease.

Adult↗

PubMed2005

Persistent idiopathic facial pain exists independent of somatosensory input from the painful region: findings from quantitative sensory functions and somatotopy of the primary somatosensory cortex.

In 14 patients with unilateral persistent idiopathic facial pain (PIFP), classified according to the criteria of the International Headache Society, and 16 age-matched control subjects sensory functions were examined on the face by quantitative sensory testing (QST). Additionally, the somatotopy of the primary somatosensory cortex (SI) to tactile input from the pain area was evaluated by means of magnetoencephalography. Previously reported abnormalities in PIFP as a dishabituation of the R2 component of the blink reflex and psychiatric disturbances were co-evaluated. Psychiatric evaluation included a Structured Clinical Interview for axis-I DSM IV disorders (SCID-I) and employment of the SCL-90-R and a depression scale (ADS). Thresholds to touch, pin prick, warm, cold, heat and pressure pain as well as the pain ratings to single and repetitive (perceptual wind up) painful pin prick stimuli did not indicate a significant sensory deficit or hyperactivity in the pain area when compared with the asymptomatic side nor when compared with the values of healthy control subjects. QST results were not significantly altered in patients (n=4) that showed an abnormal dishabituation of the R2 component of the blink reflex. The interhemispheric difference in distance between the cortical representation of the lip and the index finger did not differ between patients and control subjects. Psychiatric evaluation did not disclose significant abnormalities at a group level. It is concluded that PIFP is maintained by mechanisms which do not involve somatosensory processing of stimuli from the pain area.

Blinking↗

PubMed2004

Hyperexcitability of the primary somatosensory cortex in migraine--a magnetoencephalographic study.

The excitability of the cerebral cortex in the interictal state of migraine appears to be fundamental in the brain's susceptibility to migraine attacks. Subpopulations of cortical neurons are reported to have different physiological response properties to different interstimulus intervals (ISIs) and, hence, may be differentially altered or modulated in migraine. The aim of this study therefore was to evaluate response characteristics of temporally and spatially defined neuronal subpopulations in the cortex of migraineurs. To this end, we measured, by means of magnetoencephalography (37-channel neuromagnetometer), the response properties of the early components of the somatosensory evoked magnetic fields following electrical stimulation of the median nerve, the N20m and P35m, at ISIs ranging between 0.3 and 6 s. As a measure of the number of excited neurons underlying the N20m and P35m, we evaluated the root mean square (r.m.s.) of the deflections across all 37 channels at the corresponding latencies and the corresponding dipole moment of the equivalent current dipole (ECD strength). Twenty consecutive women with at least three migraine attacks/month (range 3-8/month) fulfilling the International Headache Society criteria and 20 age-matched healthy women were included in the study. In migraineurs, the r.m.s. and ECD strength of N20m was increased at all ISIs (r.m.s., P < 0.05; ECD strength, P < 0.01) and positively related to the mean attack frequency (r.m.s., R(s) = 0.6, P < 0.01; ECD strength, R(s) = 0.5, P < 0.05). In contrast, the r.m.s. and ECD strength of P35m did not differ significantly between migraineurs and control subjects and did not correlate significantly with the frequency of migraine attacks. Responses to different ISIs did not differ significantly between migraineurs and control subjects. The r.m.s. of N20m was stable for ISIs between 0.5 and 6 s and decreased significantly at an ISI of 0.3 s. In contrast, the r.m.s. of P35m decreased continuously as the ISI was decreased below 6 s and this reached significance for an ISI of < or =1 s. Habituation of N20m or P35m, i.e. a decrease in response magnitude following repetitive stimulation over time, was not found in either the control subjects or in the migraineurs. It is concluded that the population of neurons in the primary somatosensory cortex underlying the N20m are hyperexcitable and that this hyperexcitability is linked to the frequency of migraine attacks. This hyperexcitability appears not to be related to habituation since habituation was not found in the control subjects. In contrast, the magnitude of P35m is not pathophysiologically linked to the interictal state of migraine. Furthermore, the cellular mechanisms causing ISI-dependent depression of N20m and P35m are not altered in migraine.

Adult↗

PubMed2004

Cortical activity associated with auditory hallucinations.

Auditory hallucinations are one the most enigmatic and hampering symptoms associated with schizophrenia. Non-invasive functional imaging techniques have begun to delineate the underlying neuronal basis. We investigated the spontaneous magnetoencephalographic activity in a 33-year-old male schizophrenic patient and compared the results to those obtained from 13 healthy controls. Despite current neuroleptic medication (clozapine) the patient was still suffering from auditory hallucinations. Using the dipole density method, we were able to demonstrate an increase of fast MEG activity (12.5-30 Hz) in the left auditory cortex associated with hallucinations. This activity was absent in healthy controls. We conclude that an increase in fast MEG activity in the auditory cortex is a neurophysiologic correlate for auditory hallucinations in schizophrenia.

Adult↗

PubMed2002

Post-apoplectic reorganization of cortical areas processing passive movement and tactile stimulation--a neuromagnetic case study.

Magnetoencephalography (MEG) was used in a patient with right centro-parietal stroke to investigate the cortical processing of tactile pneumatic stimulation and passive movement of the impaired left and unaffected right-hand index finger. Source localization of somatosensory evoked magnetic fields (SEF) recorded 2 weeks after infarction demonstrated a spatial displacement of the contralateral SI generators in the affected hemisphere. The distance between SI sources activated by either stimulation technique was noticeably enlarged in comparison to the left hemisphere and to previous data from 12 healthy subjects. Follow-up MEG after 6 months revealed a closer spatial arrangement of the two modality-specific SEF generators and a diminution of the interhemispheric asymmetry of proprioception-related SI sources. The topographical alterations were accompanied by clear clinical improvement of both joint position sense and tactile sensation. The occurrence of ipsilateral SI activity following passive movement of only the impaired index finger might suggest a disinhibition of subthreshold, transcallosal excitatory pathways.

Brain Ischemia↗

PubMed2002

Somatotopic organization of the ventral and dorsal finger surface representations in human primary sensory cortex evaluated by magnetoencephalography.

Cortical reorganization of the subtly differentiated hand map after peripheral nerve injury might be better understood if there was a topographic conception of the homuncular representation of the dorsal finger surfaces in humans, in addition to the well-established sequential rostrocaudal array of the ventral finger aspects in cortical area 3b. In the present magnetoencephalographic study, tactile pneumatic stimulation was delivered to the fingertip and to the ventral and dorsal proximal phalanx of each digit of the dominant hand in 20 right-handed volunteers. Source localization of equivalent current dipoles underlying the recorded somatosensory evoked magnetic field was performed using a Cartesian coordinate system established by the anatomical landmarks nasion and preauricular points. Of the first major peak of each somatosensory evoked field, the region with the maximum field power (root-mean-square across channels) was selected for source reconstruction. Analysis of variance for repeated measures yielded significant results with respect to the arrangement of digits along the vertical coordinate axis, demonstrating a sequential array from the most inferiorly located D1 to the most superiorly located D5 for all different stimulus positions. This is the first study providing evidence for a sequential topographical arrangement of not only the ventral but also the dorsal surface representations of the individual digits in the human somatosensory cortex. The study contributes to a better understanding of the somatosensory hand representation in human primary cortex and provides useful information with regard to cortical plasticity studies in patients with peripheral nerve injuries at the upper extremity.

Adult↗

PubMed2002

Temporo-spatial analysis of cortical activation by phasic innocuous and noxious cold stimuli--a magnetoencephalographic study.

Clinical findings and recent non-invasive functional imaging studies pinpoint the insular cortex as the crucial brain area involved in cold sensation. By contrast, the role of primary (SI) and secondary (SII) somatosensory cortices in central processing of cold is controversial. So far, temporal activation patterns of cortical areas involved in cold processing have not been examined. Using magnetoencephalography, we studied, in seven healthy subjects, the temporo-spatial dynamics of brain processes evoked by innocuous and noxious cold stimulation as compared to tactile stimuli. For this purpose, a newly designed and magnetically silent cold-stimulator was employed. In separate runs, cold and painful cold stimuli were delivered to the dorsum of the right hand. Tactile afferents were stimulated by pneumatic tactile stimulation.Following innocuous cold stimulation (DeltaT=5+/-0.3 degrees C in 50+/-2ms), magnetic source imaging revealed an exclusive activation of the contra- and ipsilateral posterior insular cortex. The mean peak latencies were 194.3+/-38.1 and 241.0+/-31.7ms for the response in the ipsi- and contralateral insular cortex, respectively. Based on the measurement of onset latencies, the estimated conduction velocity of peripheral nerve fibres mediating cold fell in the range of Adelta-fibres (7.4+/-0.8 m/s). Noxious cold stimulation (DeltaT=35+/-5 degrees C in 70+/-12ms) initially activated the contra- and ipsilateral insular cortices in the same latency ranges as innocuous cold stimuli. Additionally, we found an activation of the contra- and ipsilateral SII areas (peak latencies 304+/-22.7 and 310.1+/-19.4ms, respectively) and a variable activation of the cingulate cortex. Notably, neither cold- nor painful cold stimulation produced an activation of SI. By contrast, the evoked cortical responses following tactile stimulation could be located to the contralateral SI cortex and bilateral SII. In conclusion, this study strongly corroborates the posterior insular cortex as the primary somatosensory area for cortical processing of cold sensation. Furthermore, it supports the role of SII and the cingulate cortex in mediating freeze-pain. Therefore, these results suggest different processing of cold, freeze-pain and touch in the human brain.

Adult↗