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Equivalent dipole generators of electrical brain activity in psychiatric diseases
Society proceedings inflammatory demyelinating polyneuropathy (CIPD) had either a segmental block or pathophysiological dispersion of stimulus conduction. In 8 cases with multifocal motor neuropathy (MMN), proximal degmental block or dispersion was found. In 4 cases, conduction block was the only neuropbysiological correlate of muscle weakness which in part was accompanied by muscle fasciculation. In 3 cases, a conduction block allowed us to differentiate between MMN and spinal muscular atrophy. In two cases of hereditary neuropathy with susceptibility to pressure palsy (HNPP), conduction block was found in regions of entrapment. This was also seen in 3 cases of nerve compression where the conduction block was situated within the lesioned nerve segment. Motor conduction block is the neurophysiological correlate of segmental demyelination. Using the technique of high voltage stimulation, one can also investigate proximal nerve segments. However, conduction block is non-specific and can be found in immunogenic neuropathies, in HNPP and in entrapment syndromes or pressure lesions. For differential diagnosis, clinical and follow-up examinations, which include CSF and immunology, are of importance. 10.
DC-neuromagnetometry of injury currents from human nerve and muscle specimens. - G. Curio a, F. Armbrust a, B.-M. Mackert a, J. Mackert a, M. Burghoff c, L. Trahms c, K.-D. Wolff b, P. Marx a (Depts. of aNeuroiogy and bplastic Surgery, University Klinikum Benjamin Franklin, Berlin; Cphysikalisch-Technische Bundesanstalt, Berlin)
Superconducting Quantum Interference Devices (SQUIDs) allow remote recordings of injury-related neuromagnetic near-DC fields from rat nerve and muscle specimens (Curio et al., EEG 89, 1993:154 160). Here. a recording protocol for potential clinical applications is introduced. Mechanical oscillation of a DC-current source shifts its signal to a higher frequency range containing lower external noise; additionally, narrow band filtering at the modulation frequency can improve the signal-to-noise ratio. A vertical motion was achieved by a nonmagnetically manufactured scissors lift, hydraulically driven via pipelines from outside the magnetically shielded room. Using technical dipoles driven by a DC-current, a system drift of only 60 tT over 15 rain was found. First recordings of human nerve and muscle injury fields generated by specimens freshly resected during tumor operations could easily be performed with sufficient signal-to-noise ratio for at least 90 rain after the resection and showed an approximately exponential decay (time constant: 120 min) which agrees with theoretical predictions and rcsults from anmml studies. Inside a magnetically shielded room in a clinical environment, human nerve and muscle injury currents can be detected. DC-currents due to nerve trauma or after brain ischemia ('peri-inthrct depolarizations') are clinically important perspectives for this DC-neuromagnetometry. 11.
Changes of heart rate variability in the assessment of autonomic dysfunction in Parkinson's disease. - Th. Deiseroth a, W. Greulich a, W. Gehlen b (aKlinik fiir Neurologie, Universit~it Witten/Herdecke, Klinik Ambrock, Hagen; bNeurologische Univcrsitiitsklinik, Ruhr-Universitiit, Knappschaftskrankenhaus, Bochum~
Parkinson's disease is often associated with autonomic dysfunction. The study investigates the frequency of disturbed heart rate variability in Parkinson's disease compared to other neurological dysfunctions and to the dependence of aging. We tested 30 patients with Parkinson's disease aged 39-84 years without any sign of polyneuropathy compared to age-matcbed groups of 30 patients with signs of different kinds of polyneuropathy and 40 healthy persons. The variability of heart rate was observed during the valsalva manouver and deep breathing. A significant correlation to age was found in all groups during valsalva manouver and deep breathing. Also, there were significant differences between the different patients and the patients compared with the healthy persons while deep breathing. The dimensions an the frequency
41P
of autonomoic dysfunction depends on kind and dimension of neurological dysfunction and the progress of aging. Consequently, elderly patients with Parkinson's disease have a double risk in getting autonomic dysfunctions. 12.
Effects from increased doses of carbamazepine on neuropsychological and posturographic parameters of brain function. A. Delcker, S. Neumiiller, H. Wilhelm, H.C. Diener (Department of Neurology, University of Essen, Essen)
Particularly at the beginning of treatment and with increasing doses of carbamazepine, side effects occur. Our aim was to test neurophysiological and neuropsychological side effects of carbamazepine. Twenty-two patients with a trigeminal neuralgia were included for a lollow-up study with a monotherapy of increasing carbamazepine doses (0-600 rag). Patients had a normal neurological examination and a normal cranial computed tomography. The effect of carbamazepine on postural stability was quantified by posturography. Different neuropsychological tests to study cognitive effects of carbamazepine were performed. In sensory analysis the somatosensory ratio was significantly influenced by increased doses (beginning with 400 mg) of carbamazepine during the study. Mean reaction time of tonic alertness and phasic alertness varied significantly with different doses of carbamazepine. An increase in doses of carbamazepine influenced patients' attention during trail-making tests and divided attention tests significantly. Our observations further support that the rate of change of carbamazepine doses is an important determinant of psychomotorical effects. It influences the posture stability in the phase of increasing doses. Somatosensory afferent system is really preferred in reducing use. 13.
Changes in cerebral blood flow velocities following Radermecker complexes in a patient with subacute sclerosing panencephalitis (SSPE): a case report. - B. Diehl a, M. Deppe a, W. Hammacher b, H. Henningsen a, S.R.G. Stodieck a (aDept. of Neurology, University Hospital, AIbert-Schweitzer-Str. 33, 48129 Miinster, Germany; bDept, of Neuropediatrics, Krankenhaus der Stadt Hagen)
The EEG in subacute sclerosing panencephalitis (SSPE) is characterized by generalized periodic high amplitude complexes recurring at intervals of 5-12 s. Little is known about the pathophysiology of this pattern. Most authors favour a brain stem origin.There are no data on the changes in cerebral perfusion following Radermecker complexes. The case of a 15 year old girl who was diagnosed with SSPE 9 months after onset of symptoms with personality changes is presented. Radermecker complexes were first detected on EEG in a late stage (coma) after injection of midazolam and did not ocurr spontaneously until 2 weeks later. In one recording session, 21 Radermecker complexes were monitored simultaneously by scalp EEG and transcranial Doppler sonography (TCD). No motor symptoms were noticed during the recording. Heart cycle integration and baseline correction were applied to minimize spontaneous fluctuations of the TCD signal. Following transformation into percentage units, cerebral blood flow velocities (CBFV) in both middle cerebral arteries (MCA) were averaged time-locked to the occurrence of the complex. Relative to the CBFV before the Radermecker complexes, an increase of max. 4.2% was measured in both MCAs peaking 4.5 s after occurrence of the complex. Then CBFV decreased within the following 5 s, reaching nearly baseline values 10 s after the Radermecker complex. Radermecker complexes, characteristic EEG features of SSPE, were immediately followed by an increase in cerebral perfusion lasting for several seconds. We suggest that this perfusion increase reflects neuronal activation.
14.
Equivalent dipole generators of electrical brain activity in psychiatric diseases. - T. Dierks, K. Maurer (Dept. of Psychiatry I, Univ. of Frankfurt/Main)
42P
Society proceedings Imaging procedures are steadily gaining importance in psychiatric
research. The morphology of the brain can be visualized by means of CT and MRI while cerebral blood flow and the cerebral metabolic state can be evaluated by PET. Neurophysiological methods not only have the advantage of being readily available in a clinical setting; they now allow an estimation of intracerebral generators of electrical activity of the brain. In psychiatric diseases where alteration of background activity is of interest, the method of FFT-approximation allows the estimation of intracerebral EEG-generators in the frequency domain. In the present study we investigated 22 schizophrenic, 22 depressive and 22 patients with dementia of Alzheimer type. In comparison to controls, schizophrenic patients showed more anterior and superficial equivalentdipoles in the beta-bands. A tendency of increased beta-activity was found. With increasing severity of schizophrenic symptoms, the equivalent-dipole in the betal-band was localized more anteriorly and the dipole in the theta-band was localized more inferiorly. Depressed patients demonstrated a significantly divergent pattern of localization between frequency bands in the anterior-posterior direction. Correlating with the severity of dementia, DAT-patients had higher magnitudes in the slow frequency range and lower magnitudes in the alpha- and betarange. Furthermore, in DAT patients, a shift of alpha- and beta-activity towards frontal brain regions was observed. The amount of shift correlated with the degree of dementia. These new developments may allow a physiological interpretation of neurophysiological investigations that is similar to other functional imaging methods.
15.
Functional magnetic resonance imaging (tMRI) of the auditory cortex during acoustic stimulation: a comparison to electrophysiological localization of late AEP. - T. Dierks a, D. Khorram-Sefat b, H. Horn a, N. Syed a, H. Hacker b, K. Maurer a (aDept. of Clin Neurophysioiogy, Psychiatric Hospital, Frankfurt/Main; bDept, of Neuroradiology, Univ. of Frankfurt/ Main)
MEG recordings and animal experiments have .indicated that AEPs are partly generated in the temporal lobe. However, MEG does not permit unique localization. Since increased neuronal activity is followed by blood level oxygenation-dependent contrast changes, fMRI on the other hand allows non-invasively to estimate activated brain regions with high spatial resolution. The aim of the present study was to investigate which brain regions are activated by the AEP paradigm and whether the localization of activation in fMRI correlates with one of the dipole sources of the AEP components. AEP recording: 32 channels (Neuroscan Inc.). Stimulation: 1000 Hz tone with a repetition rate of 1/s. Functional imaging was performed using a multislice GE EPI pulse sequence at 1.5 Tesla. fMRI analysis was performed using zstatistical transformation and cross-correlation of the dynamic time course. The same acoustic stimulation was performed in the MRI as for the AEP. AEP dipoles were calculated using a spatiotemporal dipole model (BESA). fMRI showed a significant activation of primary and secondary auditory cortex, this activation correlating with the reference curve (r = 0.80). The localization of the equivalent dipoles of the AEPNI00 component correlated with the fMRI localization of cerebral activation, fMRI was well suited to differentiate the cerebral components elicited after acoustical stimulation spatially, whereas the AEP was capable of diffentiating them in time. Thus, the methods complement each other and may increase the clinical value of AEP.
16.
Tibial nerve SEP alteration during akathisia. - J. Eckert a, G. Northoff b, T. Dierks a, K. Maurer a (aDepartment of Psychiatry I, University Hospital, Frankfurt(Main); bDepartment of Neurology, Caritas Klinik Dillingen, Saar)
We recorded lumbar and cerebral somatosensory evoked potentials after right and left tibial nerve stimulation at the ankle from 6 neuroleptically medicated schizophrenic patients suffering from a mild or moderate akathisia induced by the medication. SEP were registered
superficially over the first lumbar vertebra and over Cz during the akathisic phase and after complete remission. All patients were able to lay completely still during the examination, and the superficial EMG of the crural muscles was silent. Lumbarspinal amplitudes were measured base to peak; cortical amplitudes were measured peak to peak. Whereas we found no latency differences of the SEP comparing the results during and after the akathisic phase, a two tailed Wil¢oxon test for paired groups revealed a striking increase of the mean amplitudes in the remission phase. After right tibial nerve stimulation, the mean lumbar amplitude was 48% higher without akathisia, and the increase of the mean cortical SEP amplitudes showed the following values: 66% for N33-P40 (P < 0.05), 57% for P40-N50 (P = 0.03), 50% for N50-P60 ( P < 0 . 0 5 ) and 41% for P60-N75 ( P < 0.05). After left tibial nerve stimulation, the mean lumbar SEP amplitude was 75% higher in the remission phase, and the 'increase' of the mean cortical amplitudes was: 14% for N33-P40 (P < 0.05), 34% for P40-N50, 51% for N50-P60 and 35% for P60-N75. Thus, our results reveal a clear reduction of the tibial nerve SEP amplitudes on a lumbar and a cortical level. Considering that amplitude reduction is observed as a gating phenomen of SEP even before movement onset, our data suggest that during akathisia the somatosensory system is functionally altered on a spinal and a cortical level by disease-related motor tract inputs and that for interpretation of SEP amplitudes, the usual normative data are not valuable. 17.
Masseter silent period evoked by painful laser stimuli. - J. Ellrich a, H.C. Hopf b, R.-D. Treede a (aInstitute of Physiology and Pathophysiology, Johannes Gutenberg-University, Saarstr. 21, D-55099 Mainz; bDepartment of Neurology, Langenbeckstr. 1, D-55101 Mainz)
Electrical stimulation of the n. mentalis evokes two silent periods in masseter muscle bilaterally. The latencies of these silent periods SPI and SP2 are 10-15 ms and 40-55 ms, respectively. It is still unclear whether the masseter silent periods (MSP) are mediated by tactile (Cruccu et al., Exp. Brain Res., 1989, 77: 447-450) or nociceptive fibers (Miles et al., Exp. Brain Res., 1987, 65: 331-336). We investigated 10 healthy volunteers (20-26 years old) using an infrared laser (Th:YAG-Laser, A = 2/~m, r = 3 ms, 600 mJ, A = 20 m m 2) that selectively activates nociceptors in hairy skin. Perceptual and pain thresholds of n. mentalis area were determined by the method of limits. While volunteers clenched the teeth at maximum strength, 20 laser stimuli of 600 mJ were applied every 30 s. Latencies of MSP were measured from the rectified and averaged signal of 20 trials. A MSP was defined as more than 50% suppression of the background EMG, measured in a 100 ms pretrigger interval. Latencies and durations of MSP were measured at the point when EMG activity reached 80% of the background level. MSP was also elicited by electrical pulses (200,us) with intensities twice the individual pain threshold. With a mean pain threshold of 366 _+68 mJ (range: 260-460 m J) the chosen stimulus intensity of 600 mJ was certainly painful for all volunteers. In 9 of 10 subjects the MSP could bilaterally be elicited by painful laser stimuli. The onset latency was 46.9 ms, the duration 58.8 ms. In only one subject MSP consisted of two separate periods. The electrical thresholds were: detection, 1.3 mA; SPI, 9 mA; SP2, 4.7 mA; and pain, 11.6 mA. The onset latencies and durations were 11.8 ms and 20.9 ms for SPI, and 44.9 ms and 43.2 ms for SP2. When comparing the onset latencies of laser and electrically evoked MSP, one must consider the nociceptor activation latency of about 40 ms. The adjusted latency of laser evoked MSP agrees well with those of the electrically evoked SP1, but not SP2. The high electrical threshold of SPI of nearly twice that of SP2 may be an additional hint that this suppression period is mediated by nociceptive afferents. Supported by the Deutsche Forschungsgemeinschaft Tr 236/6-1. 18.
Monitoring of patients with transjugular intrahepatic portosystemic shunt (tips) by event-related potentials. - S. Evers a, J. Menzel b, B. Bauer a, I.W. Husstedt a (aDept. of Neurology,
DC-neuromagnetometry of injury currents from human nerve and muscle specimens. - G. Curio a, F. Armbrust a, B.-M. Mackert a, J. Mackert a, M. Burghoff c, L. Trahms c, K.-D. Wolff b, P. Marx a (Depts. of aNeuroiogy and bplastic Surgery, University Klinikum Benjamin Franklin, Berlin; Cphysikalisch-Technische Bundesanstalt, Berlin)
Superconducting Quantum Interference Devices (SQUIDs) allow remote recordings of injury-related neuromagnetic near-DC fields from rat nerve and muscle specimens (Curio et al., EEG 89, 1993:154 160). Here. a recording protocol for potential clinical applications is introduced. Mechanical oscillation of a DC-current source shifts its signal to a higher frequency range containing lower external noise; additionally, narrow band filtering at the modulation frequency can improve the signal-to-noise ratio. A vertical motion was achieved by a nonmagnetically manufactured scissors lift, hydraulically driven via pipelines from outside the magnetically shielded room. Using technical dipoles driven by a DC-current, a system drift of only 60 tT over 15 rain was found. First recordings of human nerve and muscle injury fields generated by specimens freshly resected during tumor operations could easily be performed with sufficient signal-to-noise ratio for at least 90 rain after the resection and showed an approximately exponential decay (time constant: 120 min) which agrees with theoretical predictions and rcsults from anmml studies. Inside a magnetically shielded room in a clinical environment, human nerve and muscle injury currents can be detected. DC-currents due to nerve trauma or after brain ischemia ('peri-inthrct depolarizations') are clinically important perspectives for this DC-neuromagnetometry. 11.
Changes of heart rate variability in the assessment of autonomic dysfunction in Parkinson's disease. - Th. Deiseroth a, W. Greulich a, W. Gehlen b (aKlinik fiir Neurologie, Universit~it Witten/Herdecke, Klinik Ambrock, Hagen; bNeurologische Univcrsitiitsklinik, Ruhr-Universitiit, Knappschaftskrankenhaus, Bochum~
Parkinson's disease is often associated with autonomic dysfunction. The study investigates the frequency of disturbed heart rate variability in Parkinson's disease compared to other neurological dysfunctions and to the dependence of aging. We tested 30 patients with Parkinson's disease aged 39-84 years without any sign of polyneuropathy compared to age-matcbed groups of 30 patients with signs of different kinds of polyneuropathy and 40 healthy persons. The variability of heart rate was observed during the valsalva manouver and deep breathing. A significant correlation to age was found in all groups during valsalva manouver and deep breathing. Also, there were significant differences between the different patients and the patients compared with the healthy persons while deep breathing. The dimensions an the frequency
41P
of autonomoic dysfunction depends on kind and dimension of neurological dysfunction and the progress of aging. Consequently, elderly patients with Parkinson's disease have a double risk in getting autonomic dysfunctions. 12.
Effects from increased doses of carbamazepine on neuropsychological and posturographic parameters of brain function. A. Delcker, S. Neumiiller, H. Wilhelm, H.C. Diener (Department of Neurology, University of Essen, Essen)
Particularly at the beginning of treatment and with increasing doses of carbamazepine, side effects occur. Our aim was to test neurophysiological and neuropsychological side effects of carbamazepine. Twenty-two patients with a trigeminal neuralgia were included for a lollow-up study with a monotherapy of increasing carbamazepine doses (0-600 rag). Patients had a normal neurological examination and a normal cranial computed tomography. The effect of carbamazepine on postural stability was quantified by posturography. Different neuropsychological tests to study cognitive effects of carbamazepine were performed. In sensory analysis the somatosensory ratio was significantly influenced by increased doses (beginning with 400 mg) of carbamazepine during the study. Mean reaction time of tonic alertness and phasic alertness varied significantly with different doses of carbamazepine. An increase in doses of carbamazepine influenced patients' attention during trail-making tests and divided attention tests significantly. Our observations further support that the rate of change of carbamazepine doses is an important determinant of psychomotorical effects. It influences the posture stability in the phase of increasing doses. Somatosensory afferent system is really preferred in reducing use. 13.
Changes in cerebral blood flow velocities following Radermecker complexes in a patient with subacute sclerosing panencephalitis (SSPE): a case report. - B. Diehl a, M. Deppe a, W. Hammacher b, H. Henningsen a, S.R.G. Stodieck a (aDept. of Neurology, University Hospital, AIbert-Schweitzer-Str. 33, 48129 Miinster, Germany; bDept, of Neuropediatrics, Krankenhaus der Stadt Hagen)
The EEG in subacute sclerosing panencephalitis (SSPE) is characterized by generalized periodic high amplitude complexes recurring at intervals of 5-12 s. Little is known about the pathophysiology of this pattern. Most authors favour a brain stem origin.There are no data on the changes in cerebral perfusion following Radermecker complexes. The case of a 15 year old girl who was diagnosed with SSPE 9 months after onset of symptoms with personality changes is presented. Radermecker complexes were first detected on EEG in a late stage (coma) after injection of midazolam and did not ocurr spontaneously until 2 weeks later. In one recording session, 21 Radermecker complexes were monitored simultaneously by scalp EEG and transcranial Doppler sonography (TCD). No motor symptoms were noticed during the recording. Heart cycle integration and baseline correction were applied to minimize spontaneous fluctuations of the TCD signal. Following transformation into percentage units, cerebral blood flow velocities (CBFV) in both middle cerebral arteries (MCA) were averaged time-locked to the occurrence of the complex. Relative to the CBFV before the Radermecker complexes, an increase of max. 4.2% was measured in both MCAs peaking 4.5 s after occurrence of the complex. Then CBFV decreased within the following 5 s, reaching nearly baseline values 10 s after the Radermecker complex. Radermecker complexes, characteristic EEG features of SSPE, were immediately followed by an increase in cerebral perfusion lasting for several seconds. We suggest that this perfusion increase reflects neuronal activation.
14.
Equivalent dipole generators of electrical brain activity in psychiatric diseases. - T. Dierks, K. Maurer (Dept. of Psychiatry I, Univ. of Frankfurt/Main)
42P
Society proceedings Imaging procedures are steadily gaining importance in psychiatric
research. The morphology of the brain can be visualized by means of CT and MRI while cerebral blood flow and the cerebral metabolic state can be evaluated by PET. Neurophysiological methods not only have the advantage of being readily available in a clinical setting; they now allow an estimation of intracerebral generators of electrical activity of the brain. In psychiatric diseases where alteration of background activity is of interest, the method of FFT-approximation allows the estimation of intracerebral EEG-generators in the frequency domain. In the present study we investigated 22 schizophrenic, 22 depressive and 22 patients with dementia of Alzheimer type. In comparison to controls, schizophrenic patients showed more anterior and superficial equivalentdipoles in the beta-bands. A tendency of increased beta-activity was found. With increasing severity of schizophrenic symptoms, the equivalent-dipole in the betal-band was localized more anteriorly and the dipole in the theta-band was localized more inferiorly. Depressed patients demonstrated a significantly divergent pattern of localization between frequency bands in the anterior-posterior direction. Correlating with the severity of dementia, DAT-patients had higher magnitudes in the slow frequency range and lower magnitudes in the alpha- and betarange. Furthermore, in DAT patients, a shift of alpha- and beta-activity towards frontal brain regions was observed. The amount of shift correlated with the degree of dementia. These new developments may allow a physiological interpretation of neurophysiological investigations that is similar to other functional imaging methods.
15.
Functional magnetic resonance imaging (tMRI) of the auditory cortex during acoustic stimulation: a comparison to electrophysiological localization of late AEP. - T. Dierks a, D. Khorram-Sefat b, H. Horn a, N. Syed a, H. Hacker b, K. Maurer a (aDept. of Clin Neurophysioiogy, Psychiatric Hospital, Frankfurt/Main; bDept, of Neuroradiology, Univ. of Frankfurt/ Main)
MEG recordings and animal experiments have .indicated that AEPs are partly generated in the temporal lobe. However, MEG does not permit unique localization. Since increased neuronal activity is followed by blood level oxygenation-dependent contrast changes, fMRI on the other hand allows non-invasively to estimate activated brain regions with high spatial resolution. The aim of the present study was to investigate which brain regions are activated by the AEP paradigm and whether the localization of activation in fMRI correlates with one of the dipole sources of the AEP components. AEP recording: 32 channels (Neuroscan Inc.). Stimulation: 1000 Hz tone with a repetition rate of 1/s. Functional imaging was performed using a multislice GE EPI pulse sequence at 1.5 Tesla. fMRI analysis was performed using zstatistical transformation and cross-correlation of the dynamic time course. The same acoustic stimulation was performed in the MRI as for the AEP. AEP dipoles were calculated using a spatiotemporal dipole model (BESA). fMRI showed a significant activation of primary and secondary auditory cortex, this activation correlating with the reference curve (r = 0.80). The localization of the equivalent dipoles of the AEPNI00 component correlated with the fMRI localization of cerebral activation, fMRI was well suited to differentiate the cerebral components elicited after acoustical stimulation spatially, whereas the AEP was capable of diffentiating them in time. Thus, the methods complement each other and may increase the clinical value of AEP.
16.
Tibial nerve SEP alteration during akathisia. - J. Eckert a, G. Northoff b, T. Dierks a, K. Maurer a (aDepartment of Psychiatry I, University Hospital, Frankfurt(Main); bDepartment of Neurology, Caritas Klinik Dillingen, Saar)
We recorded lumbar and cerebral somatosensory evoked potentials after right and left tibial nerve stimulation at the ankle from 6 neuroleptically medicated schizophrenic patients suffering from a mild or moderate akathisia induced by the medication. SEP were registered
superficially over the first lumbar vertebra and over Cz during the akathisic phase and after complete remission. All patients were able to lay completely still during the examination, and the superficial EMG of the crural muscles was silent. Lumbarspinal amplitudes were measured base to peak; cortical amplitudes were measured peak to peak. Whereas we found no latency differences of the SEP comparing the results during and after the akathisic phase, a two tailed Wil¢oxon test for paired groups revealed a striking increase of the mean amplitudes in the remission phase. After right tibial nerve stimulation, the mean lumbar amplitude was 48% higher without akathisia, and the increase of the mean cortical SEP amplitudes showed the following values: 66% for N33-P40 (P < 0.05), 57% for P40-N50 (P = 0.03), 50% for N50-P60 ( P < 0 . 0 5 ) and 41% for P60-N75 ( P < 0.05). After left tibial nerve stimulation, the mean lumbar SEP amplitude was 75% higher in the remission phase, and the 'increase' of the mean cortical amplitudes was: 14% for N33-P40 (P < 0.05), 34% for P40-N50, 51% for N50-P60 and 35% for P60-N75. Thus, our results reveal a clear reduction of the tibial nerve SEP amplitudes on a lumbar and a cortical level. Considering that amplitude reduction is observed as a gating phenomen of SEP even before movement onset, our data suggest that during akathisia the somatosensory system is functionally altered on a spinal and a cortical level by disease-related motor tract inputs and that for interpretation of SEP amplitudes, the usual normative data are not valuable. 17.
Masseter silent period evoked by painful laser stimuli. - J. Ellrich a, H.C. Hopf b, R.-D. Treede a (aInstitute of Physiology and Pathophysiology, Johannes Gutenberg-University, Saarstr. 21, D-55099 Mainz; bDepartment of Neurology, Langenbeckstr. 1, D-55101 Mainz)
Electrical stimulation of the n. mentalis evokes two silent periods in masseter muscle bilaterally. The latencies of these silent periods SPI and SP2 are 10-15 ms and 40-55 ms, respectively. It is still unclear whether the masseter silent periods (MSP) are mediated by tactile (Cruccu et al., Exp. Brain Res., 1989, 77: 447-450) or nociceptive fibers (Miles et al., Exp. Brain Res., 1987, 65: 331-336). We investigated 10 healthy volunteers (20-26 years old) using an infrared laser (Th:YAG-Laser, A = 2/~m, r = 3 ms, 600 mJ, A = 20 m m 2) that selectively activates nociceptors in hairy skin. Perceptual and pain thresholds of n. mentalis area were determined by the method of limits. While volunteers clenched the teeth at maximum strength, 20 laser stimuli of 600 mJ were applied every 30 s. Latencies of MSP were measured from the rectified and averaged signal of 20 trials. A MSP was defined as more than 50% suppression of the background EMG, measured in a 100 ms pretrigger interval. Latencies and durations of MSP were measured at the point when EMG activity reached 80% of the background level. MSP was also elicited by electrical pulses (200,us) with intensities twice the individual pain threshold. With a mean pain threshold of 366 _+68 mJ (range: 260-460 m J) the chosen stimulus intensity of 600 mJ was certainly painful for all volunteers. In 9 of 10 subjects the MSP could bilaterally be elicited by painful laser stimuli. The onset latency was 46.9 ms, the duration 58.8 ms. In only one subject MSP consisted of two separate periods. The electrical thresholds were: detection, 1.3 mA; SPI, 9 mA; SP2, 4.7 mA; and pain, 11.6 mA. The onset latencies and durations were 11.8 ms and 20.9 ms for SPI, and 44.9 ms and 43.2 ms for SP2. When comparing the onset latencies of laser and electrically evoked MSP, one must consider the nociceptor activation latency of about 40 ms. The adjusted latency of laser evoked MSP agrees well with those of the electrically evoked SP1, but not SP2. The high electrical threshold of SPI of nearly twice that of SP2 may be an additional hint that this suppression period is mediated by nociceptive afferents. Supported by the Deutsche Forschungsgemeinschaft Tr 236/6-1. 18.
Monitoring of patients with transjugular intrahepatic portosystemic shunt (tips) by event-related potentials. - S. Evers a, J. Menzel b, B. Bauer a, I.W. Husstedt a (aDept. of Neurology,