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Intracranial SEPs recordings – The new way to go?
Clinical Neurophysiology 126 (2015) 2251–2252
Contents lists available at ScienceDirect
Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph
Editorial
Intracranial SEPs recordings – The new way to go? See Article, pages 2366–2375
Somatosensory evoked potentials (SEPs) are a standard clinical procedure to test sensory pathways. Their application was first description in 1947 by George Dawson over 60 years ago (Mauguiere, 2004). Although SEPs inherently contain numerous information about somatosensory afferents, mainly components, phase-locked to the electrical stimulus, are usually used in clinical routines. Changes in SEPs latency and amplitudes together with pathological side differences indicate pathological states within the peripheral nerve, spinal cord, brain stem, midbrain and cortex and help the clinician to localize dysfunctions in the sensory pathway. Furthermore, SEPs have become a useful tool in monitoring sensory and cortical functions during vascular and spinal cord operations. However, signals conveyed after electrical nerve branch stimulation contain more information than stimulus phase locked evoked potentials. For example, high frequency responses in different cortical and subcortical areas (Eisen et al., 1984; Curio et al., 1994) can be observed following nerve stimulation and may be helpful to investigate and understand sensory-motor functions. The integration of sensory-motor information is essential for accurate movement control. For example, playing an instrument not only replicates a rehearsed preset movement, but also needs online sensory information and multi sensory integration to get the task done. Sensory feedback about the string tension or keyboard pressure is gating precise motoric movements and adjusting these movements to achieve an optimal result, which must be performed within milliseconds by the sensory-motor network of the brain. Although the sensory-motor interplay sometimes results in perfect results, pathophysiological states as observed in movement disorders can result in inability to perform accurate movements or even in abasia. Important targets to investigate and modulate movement disorders are the basal ganglia and the thalamus. Over the last decades, implantation of deep brain electrodes for the treatment of Parkinson’s disease, movement disorders, depression and chronic pain has given new and important insights in the function of the basal ganglia and the thalamus in sensory-motor processing. The physiology of these structures and their connection to the sensory-motor cortex is an important topic in current electrophysiological research, which may help to develop better treatment of sensory-motor disorders in the future. Insola and colleagues (2015) in this issue of Clinical Neurophysiology applied a paradigm in which they used electrical
stimulation of the median nerve to investigate the effect of pure passive movement on both cortical and subcortical somatosensory evoked responses. However, they did not restrict the analysis on the phase locked part of the signal, which only is one small correlate of the afferent volley but also analyzed high frequency oscillations above 1000 Hz in deep brain structures such as the Nucleus ventralis intermedius of the thalamus (VPN), the nucleus subthalamicus (STN) and the pedunculopontine tegmental nucleus (PPTg). Interestingly, besides a reduction of the SEPs amplitude after passive movement of the hand, the authors reported a decrease in power of high frequency oscillations after passive hand movements, which raises the possibility of a functional connection between deep brain oscillations, deep brain SEPs and cortical SEPs. However, one small drawback is that the authors did not analyze oscillations at the cortical level to calculate a functional connectivity between the somatosensory cortex and deep brain structures. Still, it would have been a challenge to record high frequency oscillations from surface scalp EEG electrodes, because the recordings were made in the operating room. Why does this finding represent useful information for a better understanding of sensory-motor information processing in health and disease, substantiated by further research? The information of sensory input and its gating function may be useful in the development of new and sophisticated algorithms for deep brain stimulations. Actually, the newest generation of deep brain stimulators uses multisite contacts and electrodes for more complex stimulation pattern. The identification of physiological sensory-motor information processing is obligatory to develop new opportunities in the treatment of sensory-motor disorders and can therefore be helpful for the application of deep brain stimulation or other neuro-stimulation procedures. Conflict of interest statement None. References Curio G, Mackert BM, Burghoff M, Koetitz R, Abraham-Fuchs K, Harer W. Localization of evoked neuromagnetic 600 Hz activity in the cerebral somatosensory system. Electroencephalogr Clin Neurophysiol 1994;91:483–7. Eisen A, Roberts K, Low M, Hoirch M, Lawrence P. Questions regarding the sequential neural generator theory of the somatosensory evoked potential raised by digital filtering. Electroencephalogr Clin Neurophysiol 1984;59: 388–95.
http://dx.doi.org/10.1016/j.clinph.2015.04.051 1388-2457/Ó 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
2252
Editorial / Clinical Neurophysiology 126 (2015) 2251–2252
Insola A, Padua L, Mazzone P, Valeriani M. Low- and high-frequency subcortical SEP amplitude reduction during pure passive movement. Clin Neurophysiol 2015;126:2366–2375. Mauguiere F. Somatosensory evoked potentials: normal responses, abnormal waveforms, and clinical applications in neurological diseases. In: Niedermeyer Ernst, Lopes da Silva Fernando, editors. Electroencephalography: basic principles, clinical applications, and related fields. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2004. p. 1067–120.
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Michael Hauck Department of Neurology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany Department of Neurophysiology, University Medical Center Hamburg-Eppendorf, Germany ⇑ Tel.: +49 40 7410 53770, +49 40 7410 56170; fax: +49 40 7410 56721, +49 40 7410 57752. Available online 18 April 2015
Contents lists available at ScienceDirect
Clinical Neurophysiology journal homepage: www.elsevier.com/locate/clinph
Editorial
Intracranial SEPs recordings – The new way to go? See Article, pages 2366–2375
Somatosensory evoked potentials (SEPs) are a standard clinical procedure to test sensory pathways. Their application was first description in 1947 by George Dawson over 60 years ago (Mauguiere, 2004). Although SEPs inherently contain numerous information about somatosensory afferents, mainly components, phase-locked to the electrical stimulus, are usually used in clinical routines. Changes in SEPs latency and amplitudes together with pathological side differences indicate pathological states within the peripheral nerve, spinal cord, brain stem, midbrain and cortex and help the clinician to localize dysfunctions in the sensory pathway. Furthermore, SEPs have become a useful tool in monitoring sensory and cortical functions during vascular and spinal cord operations. However, signals conveyed after electrical nerve branch stimulation contain more information than stimulus phase locked evoked potentials. For example, high frequency responses in different cortical and subcortical areas (Eisen et al., 1984; Curio et al., 1994) can be observed following nerve stimulation and may be helpful to investigate and understand sensory-motor functions. The integration of sensory-motor information is essential for accurate movement control. For example, playing an instrument not only replicates a rehearsed preset movement, but also needs online sensory information and multi sensory integration to get the task done. Sensory feedback about the string tension or keyboard pressure is gating precise motoric movements and adjusting these movements to achieve an optimal result, which must be performed within milliseconds by the sensory-motor network of the brain. Although the sensory-motor interplay sometimes results in perfect results, pathophysiological states as observed in movement disorders can result in inability to perform accurate movements or even in abasia. Important targets to investigate and modulate movement disorders are the basal ganglia and the thalamus. Over the last decades, implantation of deep brain electrodes for the treatment of Parkinson’s disease, movement disorders, depression and chronic pain has given new and important insights in the function of the basal ganglia and the thalamus in sensory-motor processing. The physiology of these structures and their connection to the sensory-motor cortex is an important topic in current electrophysiological research, which may help to develop better treatment of sensory-motor disorders in the future. Insola and colleagues (2015) in this issue of Clinical Neurophysiology applied a paradigm in which they used electrical
stimulation of the median nerve to investigate the effect of pure passive movement on both cortical and subcortical somatosensory evoked responses. However, they did not restrict the analysis on the phase locked part of the signal, which only is one small correlate of the afferent volley but also analyzed high frequency oscillations above 1000 Hz in deep brain structures such as the Nucleus ventralis intermedius of the thalamus (VPN), the nucleus subthalamicus (STN) and the pedunculopontine tegmental nucleus (PPTg). Interestingly, besides a reduction of the SEPs amplitude after passive movement of the hand, the authors reported a decrease in power of high frequency oscillations after passive hand movements, which raises the possibility of a functional connection between deep brain oscillations, deep brain SEPs and cortical SEPs. However, one small drawback is that the authors did not analyze oscillations at the cortical level to calculate a functional connectivity between the somatosensory cortex and deep brain structures. Still, it would have been a challenge to record high frequency oscillations from surface scalp EEG electrodes, because the recordings were made in the operating room. Why does this finding represent useful information for a better understanding of sensory-motor information processing in health and disease, substantiated by further research? The information of sensory input and its gating function may be useful in the development of new and sophisticated algorithms for deep brain stimulations. Actually, the newest generation of deep brain stimulators uses multisite contacts and electrodes for more complex stimulation pattern. The identification of physiological sensory-motor information processing is obligatory to develop new opportunities in the treatment of sensory-motor disorders and can therefore be helpful for the application of deep brain stimulation or other neuro-stimulation procedures. Conflict of interest statement None. References Curio G, Mackert BM, Burghoff M, Koetitz R, Abraham-Fuchs K, Harer W. Localization of evoked neuromagnetic 600 Hz activity in the cerebral somatosensory system. Electroencephalogr Clin Neurophysiol 1994;91:483–7. Eisen A, Roberts K, Low M, Hoirch M, Lawrence P. Questions regarding the sequential neural generator theory of the somatosensory evoked potential raised by digital filtering. Electroencephalogr Clin Neurophysiol 1984;59: 388–95.
http://dx.doi.org/10.1016/j.clinph.2015.04.051 1388-2457/Ó 2015 International Federation of Clinical Neurophysiology. Published by Elsevier Ireland Ltd. All rights reserved.
2252
Editorial / Clinical Neurophysiology 126 (2015) 2251–2252
Insola A, Padua L, Mazzone P, Valeriani M. Low- and high-frequency subcortical SEP amplitude reduction during pure passive movement. Clin Neurophysiol 2015;126:2366–2375. Mauguiere F. Somatosensory evoked potentials: normal responses, abnormal waveforms, and clinical applications in neurological diseases. In: Niedermeyer Ernst, Lopes da Silva Fernando, editors. Electroencephalography: basic principles, clinical applications, and related fields. 5th ed. Philadelphia: Lippincott Williams & Wilkins; 2004. p. 1067–120.
⇑
Michael Hauck Department of Neurology, University Medical Center Hamburg-Eppendorf, Martinistrasse 52, 20246 Hamburg, Germany Department of Neurophysiology, University Medical Center Hamburg-Eppendorf, Germany ⇑ Tel.: +49 40 7410 53770, +49 40 7410 56170; fax: +49 40 7410 56721, +49 40 7410 57752. Available online 18 April 2015