177. does navigated transcranial magnetic stimulation (tms) decrease the variability of...

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subtest 5 (affect matching) of the TAB in a second trial. In an addi- tional run, subjects viewed 180 photographs of faces, animals and neutral objects in order to evaluate if the discrimation of faces was intact. All faces were taken from the Karolinska Directed Emotional Faces (KDEF) and consisted of neutral, angry, happy, sad, and fearful facial expressions. Images of animals and neutral objects were se- lected from the International Affective Picture System (IAPS). ERPs elicited by faces and control stimuli were measured using a dense sensor EEG (129 channels) and analyzed with EMEGS, a MATLAB- based software package. Clinical and electrophysiological data were analyzed by repeated measures ANOVAs. Results: All participants showed an augmented N170 to faces compared to other objects (animals, household). While all three groups showed a comparable N170 for paired faces with a congruent or an incongruent emotional expression over occipito-temporal areas in subtest two, patients with an emotion recognition deficit in the TAB (MS I) showed a reduced right-lateralized N170 ampli- tude in all five conditions (neutral, angry, happy, sad or fearful faces) in subtest five. Moreover, patients with a low emotion recognition accuracy revealed an increased reaction time for incorrect responses. No correlations were found between neurophysiological data and le- sion load in MRI or clinical scores (MSFC). Conclusions: The impaired N170 in MS patients with clinical def- icits in recognizing emotional facial expressions in the affect match- ing task may contribute an interesting neurophysiological correlate of disturbed explicit social cognition already on the early stage of structural encoding within the temporo-occipital network. doi:10.1016/j.clinph.2008.07.174 177. Does navigated transcranial magnetic stimulation (TMS) decrease the variability of MEP-amplitudes?—N. Jung, N. Kuhnke, S. Stolle, I. Delvendahl, V. Mall (Universität Freiburg, Neuropädi- atrie, Freiburg, Germany) Introduction: One major attribute of transcranial magnetic stim- ulation (TMS) is the variability of the MEP-amplitudes. Navigated TMS allows the investigator to retrieve the stimulation site with an accuracy of 2.5 mm (Schönfeldt-Lecuona et al., 2005). The purpose of this study was to investigate the variability and reproducibility of MEP-amplitudes with and without navigated TMS at one point in time as well as the reproducibility between different points in time. Methods: We investigated n = 8 healthy subjects (w: n = 4 m: n = 4; age: 22–25; mean age 23.8 ± 1.24) at three different points in time (interval between investigation was at least 24 hours) with and without an optically tracked frameless navigational device (Brainview, Fraunhofer Institut (IPA), Stuttgart, Germany). Dose- recruitment curves ( 5% to +30% stimulator output of resting motor threshold (rMT)), MEP-amplitudes of 1 mV (SI 1 mV ) and of 120% rMT (SI 120MT ) were recorded. Parameters of statistical spread were the standard deviation (SD), range and the coefficient of variation (CV). Results: SD, range and CV of the MEP-amplitudes did not show a significant difference between navigated and non-navigated TMS in dose-recruitment curves, SI 1 mV and SI 120MT . This was the case for variability at one point in time as well as for reproducibility at differ- ent points in time. In dose-recruitment curves, the CV showed a trend towards a decrease in the navigated sessions. Discussion: Our results do not support the hypothesis that spa- tial accuracy reduces the variability and heightened the reproduc- ibility of MEP-amplitudes. Other factors such as spinal desynchronisation might be responsible for this effect. doi:10.1016/j.clinph.2008.07.175 178. Monitoring of facial nerve motor function during skull base surgery using transcranial electrocortical stimulation—M.A. Aci- oly de Sousa, G. Feigl, M. Liebsch, M. Tatagiba (Uniklinikum Tübingen, Neurochirurgie, Tübingen, Germany) Objective: Transcranial electrocortical stimulation (TES) is used routinely in neurosurgery to monitor major motor pathways intra- operatively. Monitoring of facial nerve (FN) function is usually per- formed either by using free running electromyography (EMG) or by direct stimulation of the FN. TES has only recently been used to also monitor FN function; however, the technique and parameters for FN MEP monitoring are so far not standardized. It was the goal of this study to develop a TES protocol for reliable monitoring of FN MEPs. Methods: FN MEPs were recorded intra-operatively from 63 pa- tients undergoing surgeries in the cerebellopontine angle and skull base between August 2006 and August 2007. TES was performed using corkscrew electrodes positioned at CZ and C3 or C4, respec- tively. The contralateral abductor pollicis brevis muscle was used as a control to ensure that the FN was not stimulated extracranially. Stimulation was always applied contralaterally to the affected side for 2 ms using 1, 3 and/or 5 pulses ranging from 200 to 600 V with 50 ms between stimuli. FN potentials were recorded from needles placed in the orbicularis oculi and oris muscles. Results: FN MEP from the orbicularis oris and oculi muscles could reliably be monitored in 93.7 and 88.9% of the patients, respectively. Only when using 3–5 train pulses extracranial FN stimulation could be avoided. Artifacts were occasionally observed in MEPs recordings of the orbicularis oculi muscle preventing continuous data acquisition. Conclusion: FN MEPs can be obtained reliably using TES with 3–5 train pulses. Stable intra-operative FN MEPs predict a good post- operative outcome of FN function. However, further refinements of this technique are still necessary in order to minimize artifacts and to make this method even more reliable. doi:10.1016/j.clinph.2008.07.176 179. Pure intraoperative MEP losses: Assessment of neurological and neuroradiological postoperative outcome—A. Szelényi 1 , E. Hattingen 2 , S. Weidauer 3 , R. Gerlach 1 , V. Seifert 1 ( 1 Klinikum der JWG Universität, Klinik und Poliklinik für Neurochirurgie, Frankfurt a.M, Germany, 2 Klinikum der JWG Universität, Institut für Neuroradiologie, Frankfurt a.M, Germany, 3 Katharinenkran- kenhaus, Klinik für Neurologie, Frankfurt a.M, Germany) Introduction: In supratentorial surgery, the cortical depth of excitation of the pyramidal neurons by transcranial electric stimula- tion (TES) is critical to detect even the most superficial cortical le- sions affecting the motor cortex. An excitation caudally to a lesion consequences false negative results. Exclusive (i.e. no changes in other modalities as SEPs) mMEP changes were correlated to clinical and neuroradiological outcome to evaluate their significance. Methods: MMEPs (all elicited with TES; in 14 patients also direct cortical stimulation) were elicited with a train of 5 anodal rectangu- lar pulses (0.5 ms pulse width, interstimulus interval of 2-4 ms; rep- etition rate of up to 1 Hz; stimulation intensity of 10% above motor threshold). Out of a prospective neuromonitoring database (1900 pa- tients), patients were analyzed for the type of exclusive mMEP dete- rioration (loss; >50% amplitude decrement; increment of motor threshold; duration), for lesions affecting the motor cortex or motor pathways in postoperative MRI (T2, T2 * , DWI) and postoperative mo- tor status (<24 h postoperatively, 6 months). e74 Society Proceedings / Clinical Neurophysiology 120 (2009) e9–e88

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Page 1: 177. Does navigated transcranial magnetic stimulation (TMS) decrease the variability of MEP-amplitudes?

subtest 5 (affect matching) of the TAB in a second trial. In an addi-tional run, subjects viewed 180 photographs of faces, animals andneutral objects in order to evaluate if the discrimation of faces wasintact. All faces were taken from the Karolinska Directed EmotionalFaces (KDEF) and consisted of neutral, angry, happy, sad, and fearfulfacial expressions. Images of animals and neutral objects were se-lected from the International Affective Picture System (IAPS). ERPselicited by faces and control stimuli were measured using a densesensor EEG (129 channels) and analyzed with EMEGS, a MATLAB-based software package. Clinical and electrophysiological data wereanalyzed by repeated measures ANOVAs.

Results: All participants showed an augmented N170 to facescompared to other objects (animals, household). While all threegroups showed a comparable N170 for paired faces with a congruentor an incongruent emotional expression over occipito-temporalareas in subtest two, patients with an emotion recognition deficitin the TAB (MS I) showed a reduced right-lateralized N170 ampli-tude in all five conditions (neutral, angry, happy, sad or fearful faces)in subtest five. Moreover, patients with a low emotion recognitionaccuracy revealed an increased reaction time for incorrect responses.No correlations were found between neurophysiological data and le-sion load in MRI or clinical scores (MSFC).

Conclusions: The impaired N170 in MS patients with clinical def-icits in recognizing emotional facial expressions in the affect match-ing task may contribute an interesting neurophysiological correlateof disturbed explicit social cognition already on the early stage ofstructural encoding within the temporo-occipital network.

doi:10.1016/j.clinph.2008.07.174

177. Does navigated transcranial magnetic stimulation (TMS)decrease the variability of MEP-amplitudes?—N. Jung, N. Kuhnke,S. Stolle, I. Delvendahl, V. Mall (Universität Freiburg, Neuropädi-atrie, Freiburg, Germany)

Introduction: One major attribute of transcranial magnetic stim-ulation (TMS) is the variability of the MEP-amplitudes. NavigatedTMS allows the investigator to retrieve the stimulation site with anaccuracy of 2.5 mm (Schönfeldt-Lecuona et al., 2005). The purposeof this study was to investigate the variability and reproducibilityof MEP-amplitudes with and without navigated TMS at one point intime as well as the reproducibility between different points in time.

Methods: We investigated n = 8 healthy subjects (w: n = 4 m:n = 4; age: 22–25; mean age 23.8 ± 1.24) at three different pointsin time (interval between investigation was at least 24 hours) withand without an optically tracked frameless navigational device(Brainview, Fraunhofer Institut (IPA), Stuttgart, Germany). Dose-recruitment curves (�5% to +30% stimulator output of resting motorthreshold (rMT)), MEP-amplitudes of 1 mV (SI1 mV) and of 120% rMT(SI120MT) were recorded. Parameters of statistical spread were thestandard deviation (SD), range and the coefficient of variation (CV).

Results: SD, range and CV of the MEP-amplitudes did not show asignificant difference between navigated and non-navigated TMS indose-recruitment curves, SI1 mV and SI120MT. This was the case forvariability at one point in time as well as for reproducibility at differ-ent points in time. In dose-recruitment curves, the CV showed atrend towards a decrease in the navigated sessions.

Discussion: Our results do not support the hypothesis that spa-tial accuracy reduces the variability and heightened the reproduc-ibility of MEP-amplitudes. Other factors such as spinaldesynchronisation might be responsible for this effect.

doi:10.1016/j.clinph.2008.07.175

178. Monitoring of facial nerve motor function during skull basesurgery using transcranial electrocortical stimulation—M.A. Aci-oly de Sousa, G. Feigl, M. Liebsch, M. Tatagiba (UniklinikumTübingen, Neurochirurgie, Tübingen, Germany)

Objective: Transcranial electrocortical stimulation (TES) is usedroutinely in neurosurgery to monitor major motor pathways intra-operatively. Monitoring of facial nerve (FN) function is usually per-formed either by using free running electromyography (EMG) orby direct stimulation of the FN. TES has only recently been used toalso monitor FN function; however, the technique and parametersfor FN MEP monitoring are so far not standardized. It was the goalof this study to develop a TES protocol for reliable monitoring ofFN MEPs.

Methods: FN MEPs were recorded intra-operatively from 63 pa-tients undergoing surgeries in the cerebellopontine angle and skullbase between August 2006 and August 2007. TES was performedusing corkscrew electrodes positioned at CZ and C3 or C4, respec-tively. The contralateral abductor pollicis brevis muscle was usedas a control to ensure that the FN was not stimulated extracranially.Stimulation was always applied contralaterally to the affected sidefor 2 ms using 1, 3 and/or 5 pulses ranging from 200 to 600 V with50 ms between stimuli. FN potentials were recorded from needlesplaced in the orbicularis oculi and oris muscles.

Results: FN MEP from the orbicularis oris and oculi muscles couldreliably be monitored in 93.7 and 88.9% of the patients, respectively.Only when using 3–5 train pulses extracranial FN stimulation couldbe avoided. Artifacts were occasionally observed in MEPs recordingsof the orbicularis oculi muscle preventing continuous dataacquisition.

Conclusion: FN MEPs can be obtained reliably using TES with 3–5train pulses. Stable intra-operative FN MEPs predict a good post-operative outcome of FN function. However, further refinements ofthis technique are still necessary in order to minimize artifacts andto make this method even more reliable.

doi:10.1016/j.clinph.2008.07.176

179. Pure intraoperative MEP losses: Assessment of neurologicaland neuroradiological postoperative outcome—A. Szelényi 1, E.Hattingen 2, S. Weidauer 3, R. Gerlach 1, V. Seifert 1 (1 Klinikum derJWG Universität, Klinik und Poliklinik für Neurochirurgie,Frankfurt a.M, Germany, 2 Klinikum der JWG Universität, Institutfür Neuroradiologie, Frankfurt a.M, Germany, 3 Katharinenkran-kenhaus, Klinik für Neurologie, Frankfurt a.M, Germany)

Introduction: In supratentorial surgery, the cortical depth ofexcitation of the pyramidal neurons by transcranial electric stimula-tion (TES) is critical to detect even the most superficial cortical le-sions affecting the motor cortex. An excitation caudally to a lesionconsequences false negative results. Exclusive (i.e. no changes inother modalities as SEPs) mMEP changes were correlated to clinicaland neuroradiological outcome to evaluate their significance.

Methods: MMEPs (all elicited with TES; in 14 patients also directcortical stimulation) were elicited with a train of 5 anodal rectangu-lar pulses (0.5 ms pulse width, interstimulus interval of 2-4 ms; rep-etition rate of up to 1 Hz; stimulation intensity of 10% above motorthreshold). Out of a prospective neuromonitoring database (1900 pa-tients), patients were analyzed for the type of exclusive mMEP dete-rioration (loss; >50% amplitude decrement; increment of motorthreshold; duration), for lesions affecting the motor cortex or motorpathways in postoperative MRI (T2, T2*, DWI) and postoperative mo-tor status (<24 h postoperatively, 6 months).

e74 Society Proceedings / Clinical Neurophysiology 120 (2009) e9–e88