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P78. Feasibility and safety aspects of retinofugal alternating current stimulation
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Society Proceedings / Clinical Neurophysiology 126 (2015) e63–e170
For instance, it has been assumed that comprehension of time-compressed speech involves mesial frontal brain structures including SMA-proper and pre-SMA, which buffer phonological materials (Vagharchakian et al., 2012). In line with this notion, left pre-SMA was strongly activated when subjects were trained to understand ultra-fast speech at high syllable rates, likely by providing a prosodic interface for the time-critical encoding of speech with respect to its syllabic structure (Dietrich et al., 2013). Here, we tested the functional role of the pre-SMA for ultra-fast speech comprehension by inducing a transient ‘virtual lesion’ using continuous theta burst magnetic stimulation (cTBS; 3 stimuli at 50 Hz, repeated every 200 ms, 600 pulses in total, stimulation intensity equaling 120% of resting motor threshold for the right abductor pollicis brevis muscle). Pre-SMA as defined individually by functional MRI was targeted using a frameless neuro-navigation system. Nineteen healthy subjects performed a sentence repetition task comprising of sentence utterances synthesized at five distinct syllable rates (8, 10, 12, 14, 16 syl/s) prior to stimulation (pre-stimulation baseline), 10 min after stimulation (assumed maximum of the TMS effect), and 60 min after cTBS procedure (post-stimulation baseline), respectively. Speech comprehension was quantified by the percentage of correctly reproduced words. Compared to baseline speech comprehension was decreased at high speech rates of 12 syl/s or faster at 10 min, but not at 60 min after stimulation. This transient impairment of speech comprehension following cTBS suggests that pre-SMA, indeed, contributes to time-critical encoding of phonetic-linguistic information. Our results further lend support to the notion that TBS can be used as a tool for transient interference with pre-SMA cognitive function (Fig. 1).
References Dietrich S, Hertrich I, Ackermann H. Training of ultra-fast speech comprehension induces functional reorganization oft he central-visual system in late-blind humans. Front Hum Neurosci 2013;7:701. doi:10.3399/fnhum.2013.00701. Vagharchakian L, Dehaene-Lambertz G, Pallier C, Dehaene S. A temporal bottleneck in the language comprehension network. J Neurosci 2012;32(26):9089–102. doi:10.1523/jneurosci.5685-11.2012. doi:10.1016/j.clinph.2015.04.209
P77. Effects of high resistance muscle training on cortico-spinal output during motor fatigue. A study using transcranial magnetic stimulation—K. Rösler, F. Marti, O. Scheidegger (Inselspital, Neurologische Universitätsklinik, Bern, Switzerland) Objective: To compare responses to transcranial magnetic brain stimulation during a fatiguing exercise before and after a 3 weeks lasting resistance training, in healthy subjects. Methods: The triple stimulation technique (TST, Magistris et al., 1998) was used to quantify a central conduction index (CCI = amplitude ratio of central conduction response and peripheral nerve response, obtained simultaneously by the TST). The CCI removes effects of peripheral fatigue from the quantification of the responses to brain stimulation. It allows a quantification of the percentage of the entire target muscle motor unit pool driven to discharge by a transcranial magnetic stimulus. Subjects (n = 15) performed a 3 weeks training regimen (2 min twice per day) of repetitive isometric maximal voluntary contractions (MVC) of abductor digiti minimi (ADM; duration 1 s, frequency 0.5 Hz). Before and after this training, TST recordings were obtained every 15 s during an 2 min exercise, where subjects performed repetitive contractions of the ADM, and repeatedly during a recovery
period of 7 min, using stimulation intensities and facilitatory maneuvers sufficient to excite all cortical motor neurons. Results: There was a consistent decrease of force to approximately 40% of MVC in all experiments and in all subjects, before and after training. In all subjects, CCI decreased during exercise. While before training, the CCI decreased to 49% (SD 23.7%) after 2 min of exercise, it decreased after training only to 79% (SD 26.4%) (p < 0.01). Thus, training resulted in a smaller decrease of the CCI during exercise. Discussion: The training regimen increased the proportion of target motor units that could be activated by transcranial magnetic stimulation during a fatiguing exercise. Possible underlying mechanisms at spinal and supraspinal sites are discussed. doi:10.1016/j.clinph.2015.04.210
P78. Feasibility and safety aspects of retinofugal alternating current stimulation—L. Haberbosch, A. Jooß, R. Fleischmann, M. Rönnefarth, S. Brandt, S. Schmidt (Charité Universitätsmedizin Berlin, Klinik für Neurologie, Berlin, Germany) Introduction: Non-invasive Brain Stimulation is now widely used, yet little is known about its mechanisms of action and its safety. The more critical aspect of the two is safety. An assessment of stimulation parameters and measures such as charge density, impedances, amplitudes and thresholds as well as a sufficient investigation of side effects deem necessary. Here we compare the novel retinofugal transorbital alternating current stimulation (rtACS) and the well-known Photic Stimulation (PS, ‘‘Photic Driving’’) regarding their safety aspects and conclude on the feasibility of rtACS. Methods: We stimulated 21 healthy subjects with rtACS as well as PS at a frequency of 10 Hz. Prior to stimulation, we assessed phosphene thresholds (rtACS) or light thresholds (PS). The stimulation intensity was set to 120% threshold in both cases. Post-stimulation, pain and other side effects were reported via questionnaire. We also recorded electrode impedances and calculated the resulting charge density. Results: We noted an average phosphene threshold at 290.24 lV (±44.16), impedances at 12.57 kX (±1.8). The charge density amounted to a mean 47.90 C/cm2 (±12.37). The mean light threshold for PS was 1.24 (±0.44). The most common side effect for rtACS was a tingling sensation (67%), followed by fatigue (33%). PS evoked mostly fatigue (19%) and headache (14%). Pain was reported in 30% of the subjects during rtACS (mean intensity 2.5 ± 1.85 on a numeric rating scale) and in 25% during PS (2.75 ± 0.96). In direct comparison, rtACS showed no significant difference in pain, a significantly (p < 0.05) higher rate of fatigue after stimulation and a significantly (p < 0.05) lower rate of headache. Tingling, itching and burning occurred only in rtACS. Conclusions: Firstly, the theoretical stimulation parameters calculated from amplitude and impedance are well below the damage limits found in the animal model. Secondly, the subjective measures showed no strong feelings of discomfort. The intensity of pain experienced by stimulation did not differ significantly between rtACS and the well-established, safe PS. This reassures the safety and feasibility of rtACS. To complete these findings, we will to perform neuron specific enolase (NSE) and MRI measurements pre- and post-stimulation. doi:10.1016/j.clinph.2015.04.211
Society Proceedings / Clinical Neurophysiology 126 (2015) e63–e170
For instance, it has been assumed that comprehension of time-compressed speech involves mesial frontal brain structures including SMA-proper and pre-SMA, which buffer phonological materials (Vagharchakian et al., 2012). In line with this notion, left pre-SMA was strongly activated when subjects were trained to understand ultra-fast speech at high syllable rates, likely by providing a prosodic interface for the time-critical encoding of speech with respect to its syllabic structure (Dietrich et al., 2013). Here, we tested the functional role of the pre-SMA for ultra-fast speech comprehension by inducing a transient ‘virtual lesion’ using continuous theta burst magnetic stimulation (cTBS; 3 stimuli at 50 Hz, repeated every 200 ms, 600 pulses in total, stimulation intensity equaling 120% of resting motor threshold for the right abductor pollicis brevis muscle). Pre-SMA as defined individually by functional MRI was targeted using a frameless neuro-navigation system. Nineteen healthy subjects performed a sentence repetition task comprising of sentence utterances synthesized at five distinct syllable rates (8, 10, 12, 14, 16 syl/s) prior to stimulation (pre-stimulation baseline), 10 min after stimulation (assumed maximum of the TMS effect), and 60 min after cTBS procedure (post-stimulation baseline), respectively. Speech comprehension was quantified by the percentage of correctly reproduced words. Compared to baseline speech comprehension was decreased at high speech rates of 12 syl/s or faster at 10 min, but not at 60 min after stimulation. This transient impairment of speech comprehension following cTBS suggests that pre-SMA, indeed, contributes to time-critical encoding of phonetic-linguistic information. Our results further lend support to the notion that TBS can be used as a tool for transient interference with pre-SMA cognitive function (Fig. 1).
References Dietrich S, Hertrich I, Ackermann H. Training of ultra-fast speech comprehension induces functional reorganization oft he central-visual system in late-blind humans. Front Hum Neurosci 2013;7:701. doi:10.3399/fnhum.2013.00701. Vagharchakian L, Dehaene-Lambertz G, Pallier C, Dehaene S. A temporal bottleneck in the language comprehension network. J Neurosci 2012;32(26):9089–102. doi:10.1523/jneurosci.5685-11.2012. doi:10.1016/j.clinph.2015.04.209
P77. Effects of high resistance muscle training on cortico-spinal output during motor fatigue. A study using transcranial magnetic stimulation—K. Rösler, F. Marti, O. Scheidegger (Inselspital, Neurologische Universitätsklinik, Bern, Switzerland) Objective: To compare responses to transcranial magnetic brain stimulation during a fatiguing exercise before and after a 3 weeks lasting resistance training, in healthy subjects. Methods: The triple stimulation technique (TST, Magistris et al., 1998) was used to quantify a central conduction index (CCI = amplitude ratio of central conduction response and peripheral nerve response, obtained simultaneously by the TST). The CCI removes effects of peripheral fatigue from the quantification of the responses to brain stimulation. It allows a quantification of the percentage of the entire target muscle motor unit pool driven to discharge by a transcranial magnetic stimulus. Subjects (n = 15) performed a 3 weeks training regimen (2 min twice per day) of repetitive isometric maximal voluntary contractions (MVC) of abductor digiti minimi (ADM; duration 1 s, frequency 0.5 Hz). Before and after this training, TST recordings were obtained every 15 s during an 2 min exercise, where subjects performed repetitive contractions of the ADM, and repeatedly during a recovery
period of 7 min, using stimulation intensities and facilitatory maneuvers sufficient to excite all cortical motor neurons. Results: There was a consistent decrease of force to approximately 40% of MVC in all experiments and in all subjects, before and after training. In all subjects, CCI decreased during exercise. While before training, the CCI decreased to 49% (SD 23.7%) after 2 min of exercise, it decreased after training only to 79% (SD 26.4%) (p < 0.01). Thus, training resulted in a smaller decrease of the CCI during exercise. Discussion: The training regimen increased the proportion of target motor units that could be activated by transcranial magnetic stimulation during a fatiguing exercise. Possible underlying mechanisms at spinal and supraspinal sites are discussed. doi:10.1016/j.clinph.2015.04.210
P78. Feasibility and safety aspects of retinofugal alternating current stimulation—L. Haberbosch, A. Jooß, R. Fleischmann, M. Rönnefarth, S. Brandt, S. Schmidt (Charité Universitätsmedizin Berlin, Klinik für Neurologie, Berlin, Germany) Introduction: Non-invasive Brain Stimulation is now widely used, yet little is known about its mechanisms of action and its safety. The more critical aspect of the two is safety. An assessment of stimulation parameters and measures such as charge density, impedances, amplitudes and thresholds as well as a sufficient investigation of side effects deem necessary. Here we compare the novel retinofugal transorbital alternating current stimulation (rtACS) and the well-known Photic Stimulation (PS, ‘‘Photic Driving’’) regarding their safety aspects and conclude on the feasibility of rtACS. Methods: We stimulated 21 healthy subjects with rtACS as well as PS at a frequency of 10 Hz. Prior to stimulation, we assessed phosphene thresholds (rtACS) or light thresholds (PS). The stimulation intensity was set to 120% threshold in both cases. Post-stimulation, pain and other side effects were reported via questionnaire. We also recorded electrode impedances and calculated the resulting charge density. Results: We noted an average phosphene threshold at 290.24 lV (±44.16), impedances at 12.57 kX (±1.8). The charge density amounted to a mean 47.90 C/cm2 (±12.37). The mean light threshold for PS was 1.24 (±0.44). The most common side effect for rtACS was a tingling sensation (67%), followed by fatigue (33%). PS evoked mostly fatigue (19%) and headache (14%). Pain was reported in 30% of the subjects during rtACS (mean intensity 2.5 ± 1.85 on a numeric rating scale) and in 25% during PS (2.75 ± 0.96). In direct comparison, rtACS showed no significant difference in pain, a significantly (p < 0.05) higher rate of fatigue after stimulation and a significantly (p < 0.05) lower rate of headache. Tingling, itching and burning occurred only in rtACS. Conclusions: Firstly, the theoretical stimulation parameters calculated from amplitude and impedance are well below the damage limits found in the animal model. Secondly, the subjective measures showed no strong feelings of discomfort. The intensity of pain experienced by stimulation did not differ significantly between rtACS and the well-established, safe PS. This reassures the safety and feasibility of rtACS. To complete these findings, we will to perform neuron specific enolase (NSE) and MRI measurements pre- and post-stimulation. doi:10.1016/j.clinph.2015.04.211