Journal of the K. S. C. N. Vol. 1, No. 2 Electrical Stimulation Cerebral Cortex Joong-Koo Kang, M.D. Department of Neurology, University of Ulsan, Asan Medical Center - Abstract - Electrical cortical stimulation has been used clinically for more than 40 years for the localization of eloquent brain area such as language and sensori-motor area, in patients with intractable epilepsy for whom resections are considered. Extraoperative mapping has been performed more recently. This paper discusses the principle and methods of electrical cortical stimulation. 191
Figure 1. Interrelationships between the basic and derived stimulus parameters Table 1. Stimulus-induced injury Mechanism Parameter Safety measure Charge Transfer Change density Biphasic pulse Electrolysis Voltage Constant-voltage stimulator Thermal deposition Energy Chronaxies-convergent paradigm Miscellaneous altered homeostass, organelle damage, Multiple Brief, intermittent trials with minimum repetition rate sequestration 192 Journal of the K. S. C. N. 1999
Figure 4. Strength-duration curves of myelinated and nonmyelinat - ed fibers with chronoaxies of 0.4 ms(b) and 0.1 ms(a), respectively Figure 2. Changes in TMP produced by different constant current pulses. A. An anodal pulse hyperpolarizes the mem - brance. B. A weak cathodal pulse produces a subthresh - old depolarization. C. A stronger current reaches thresh - old. D. Stimulation is most efficient at the briefer pulse duration. E. Stimulation becomes once again ineffective at very brief duration Figure 3. Strength-duration curve showing the threshold current intensity required for stimulation as a function of pulse duration 193
Figure 5. How a response may be elicited following monopolar stimulation from a nontarget tissue lying within the cur - rent pathway. B: Why bipolar stimulation fails to elicit a response from the target tissue because of shunting of current. 194 Journal of the K. S. C. N. 1999
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Figure 6. A typical AD following cortical stimulation. The numbers correspond to phase described in the text. Figure 7. Various morphologies of ADs 196 Journal of the K. S. C. N. 1999
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Figure 8. Motor and sensory homunculi. The lateral convexity homunculi were simplified from Penfield and Jasper. The SSMA homunculus was prepared using the relative fre - quency of the body parts that were involved during stim - ulation. The contralateral extremity representation is bigger than the ipsilateral counterpart in SSMA. The proximal extremity representation is much bigger than the distal. The reverse is the case for the primary sensory motor area. PNMA, primary negative motor area. SI, primary sensory area. 198 Journal of the K. S. C. N. 1999
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01. Barry FE, Walter MS, Gallistel CR. On the optimal pulse duration in electrical stimulation of the brain. Physiology and behavior 1974;12:749-754 02. Berger MS, Kincaid J, Ojemann GA, Lettich E. Brain map- ping techiniques to maximmize resection, safety, and seizure control in children with brain tumors. N e u r o s u r g e r y 1989 ; 25:786-792 03. Engel JJ. Surgical Treatment of the Epilepsies. 2nd ed. Raven Press. pp 399-414 04. Gordon B, Lesser RP, Rance NE, et al. Parameters for direct cortical electrical stimulation in human brain: histopathologic conformation. electroencephalogr Clin Neurophysiol 1990;75: 371-377 05. Jayakar P, Resnick TJ, Duchowny MS, Alvarenz LA. A safe and effective paradigm to functionally map the cortex in childhood. J Clin Neurophysiol 1992;9:288-293 06. Lesser RP. Luders H, Klem GN, et al. Extraoperative cortical functional localization in patients with epilepsy. J Clin Neurophysiol 1987;4:27-53 07. Luders H. Epilepsy Surgery. Raven Press. pp 399-408 08. Orrin D, Beric A, Dogali M. Electrical and Magnetic Stimulation of the Brain and Spinal Cord. Advances in Neurology Vol 63, Raven Press 201