Spinal cord direct current stimulation: finite element analysis of the electric field and current density

Applied low-intensity direct current (DC) stimulates and directs axonal growth in models of spinal cord injury (SCI) and may have therapeutic value in humans. Using higher electric strengths will probably increase the beneficial effects, but this faces the risk of tissue damage by electricity or toxic reactions at the electrode–tissue interface. To inform the optimisation of DC-based therapeutics, we developed a finite element model (FEM) of the human cervical spine and calculated the electric fields (EFs) and current densities produced by electrodes of different size, geometry and location. The presence of SCI was also considered. Three disc electrodes placed outside the spine produced low-intensity, uneven EFs, whereas the EFs generated by the same electrodes located epidurally were about three times more intense. Changes in electrical conductivity after SCI had little effect on the EF magnitudes. Uniformly distributed EFs were obtained with five disc electrodes placed around the dura mater, but not with a paddle-type electrode placed in the dorsal epidural space. Replacing the five disc electrodes by a single, large band electrode yielded EFs > 5 mV/mm with relatively low current density (2.5 μA/mm2) applied. With further optimisation, epidural, single-band electrodes might enhance the effectiveness of spinal cord DC stimulation.

[1]  W A Wesselink,et al.  Analysis of current density and related parameters in spinal cord stimulation. , 1998, IEEE transactions on rehabilitation engineering : a publication of the IEEE Engineering in Medicine and Biology Society.

[2]  M. Nieto‐Sampedro,et al.  Olfactory glia transplantation into cervical spinal cord contusion injuries. , 2005, Journal of neurosurgery. Spine.

[3]  R. Bunge,et al.  Observations on the pathology of several types of human spinal cord injury, with emphasis on the astrocyte response to penetrating injuries. , 1997, Advances in neurology.

[4]  G. Wallace,et al.  Conducting polymers for neural interfaces: challenges in developing an effective long-term implant. , 2008, Biomaterials.

[5]  M. Cohen,et al.  Modification of retrograde degeneration in transected spinal axons of the lamprey by applied DC current , 1983, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[6]  J. Cook,et al.  Effects of applied electric fields on clinical cases of complete paraplegia in dogs. , 1993, Restorative neurology and neuroscience.

[7]  M. Nitsche,et al.  Excitability changes induced in the human motor cortex by weak transcranial direct current stimulation , 2000, The Journal of physiology.

[8]  Q. Hogan.  Epidural Anatomy Examined by Cryomicrotome Section: Influence of Age, Vertebral Level, and Disease , 1996, Regional Anesthesia & Pain Medicine.

[9]  K. Fountas,et al.  Cervical Spinal Cord‐Smaller Than Considered? , 1998, Spine.

[10]  J. B. Ranck,et al.  THE SPECIFIC IMPEDANCE OF THE DORSAL COLUMNS OF CAT: AN INISOTROPIC MEDIUM. , 1965, Experimental neurology.

[11]  J. L. Polo,et al.  Bioelectrochemical control of neural cell development on conducting polymers. , 2010, Biomaterials.

[12]  Electrical stimulation as therapy for neurological disorder. , 2006, IEEE engineering in medicine and biology magazine : the quarterly magazine of the Engineering in Medicine & Biology Society.

[13]  Daniel R. Merrill,et al.  Electrical stimulation of excitable tissue: design of efficacious and safe protocols , 2005, Journal of Neuroscience Methods.

[14]  R. Hurlbert,et al.  Characterization of longitudinal field gradients from electrical stimulation in the normal and injured rodent spinal cord. , 1994, Neurosurgery.

[15]  Lumbar dura mater biomechanics: experimental characterization and scanning electron microscopy observations. , 1999, Anesthesia and analgesia.

[16]  Barry Coburn,et al.  A Theoretical Study of Epidural Electrical Stimulation of the Spinal Cord - Part II: Effects on Long Myelinated Fibers , 1985, IEEE Transactions on Biomedical Engineering.

[17]  M. Fehlings,et al.  The effect of direct-current field on recovery from experimental spinal cord injury. , 1988, Journal of neurosurgery.

[18]  C H Tator,et al.  Dose-response study of the pathological effects of chronically applied direct current stimulation on the normal rat spinal cord. , 1993, Journal of neurosurgery.

[19]  Min Zhao,et al.  Controlling cell behavior electrically: current views and future potential. , 2005, Physiological reviews.

[20]  Markus Zahn,et al.  Transcranial direct current stimulation: A computer-based human model study , 2007, NeuroImage.

[21]  Jiping He,et al.  Paresthesia thresholds in spinal cord stimulation: a comparison of theoretical results with clinical data , 1993 .

[22]  Mark S. Greenberg,et al.  Handbook of Neurosurgery , 1993 .

[23]  M Nissan,et al.  Sagittal evaluation of elemental geometrical dimensions of human vertebrae. , 1985, Journal of anatomy.

[24]  Anthony Sances,et al.  Spinal Cord Implant Studies , 1976, IEEE Transactions on Biomedical Engineering.

[25]  L. Geddes,et al.  The specific resistance of biological material—A compendium of data for the biomedical engineer and physiologist , 1967, Medical and biological engineering.

[26]  A. Straube,et al.  Spinal DC stimulation in humans modulates post-activation depression of the H-reflex depending on current polarity , 2010, Clinical Neurophysiology.

[27]  D. Miklavčič,et al.  ELECTRIC PROPERTIES OF TISSUES , 2006 .

[28]  R. Borgens,et al.  Electrically mediated regeneration and guidance of adult mammalian spinal axons into polymeric channels , 1999, Neuroscience.

[29]  E. Buchser,et al.  Neurostimulation technology for the treatment of chronic pain: a focus on spinal cord stimulation , 2007, Expert review of medical devices.

[30]  P. Nelson,et al.  Oscillating field stimulation for complete spinal cord injury in humans: a phase 1 trial. , 2005, Journal of neurosurgery. Spine.

[31]  V. M. Soto,et al.  Motoneuron loss associated with chronic locomotion impairments after spinal cord contusion in the rat. , 2005, Journal of neurotrauma.

[32]  L. Dai,et al.  Three-Dimensional Finite Element Model of the Cervical Spinal Cord: Preliminary Results of Injury Mechanism Analysis , 2009, Spine.

[33]  R. Yeasting,et al.  The quantitative anatomy of the laminas of the spine. , 1999, Spine.

[34]  Barry Coburn,et al.  A Theoretical Study of Epidural Electrical Stimulation of the Spinal Cord Part I: Finite Element Analysis of Stimulus Fields , 1985, IEEE Transactions on Biomedical Engineering.

[35]  Manohar M. Panjabi,et al.  Clinical Biomechanics of the Spine , 1978 .

[36]  M. Suh,et al.  The control of neural cell-to-cell interactions through non-contact electrical field stimulation using graphene electrodes. , 2011, Biomaterials.

[37]  B. Coburn,et al.  Electrical stimulation of the spinal cord: a further analysis relating to anatomical factors and tissue properties , 1983, Medical and Biological Engineering and Computing.

[38]  M. Poo,et al.  Perturbation of the direction of neurite growth by pulsed and focal electric fields , 1984, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[39]  M. Tuszynski,et al.  Human spinal cord retains substantial structural mass in chronic stages after injury. , 1999, Journal of neurotrauma.

[40]  A. Blight,et al.  Transected dorsal column axons within the guinea pig spinal cord regenerate in the presence of an applied electric field , 1986, The Journal of comparative neurology.

[41]  P. Stypulkowski,et al.  Electrical stimulation as therapy for neurological disorders , 2006, IEEE Engineering in Medicine and Biology Magazine.

[42]  Metin Akay,et al.  Wiley encyclopedia of biomedical engineering , 2006 .

[43]  H. Ramsey,et al.  Comparative morphology of fat in the epidural space. , 1959, The American journal of anatomy.

[44]  B. Quinio,et al.  Cervical cord compression due to delayed scarring around epidural electrodes used in spinal cord stimulation. , 2010, Journal of neurosurgery. Spine.

[45]  J Myklebust,et al.  Electrical field distribution within the injured cat spinal cord: injury potentials and field distribution. , 1994, Journal of neurotrauma.

[46]  David R. Wozny,et al.  The electrical conductivity of human cerebrospinal fluid at body temperature , 1997, IEEE Transactions on Biomedical Engineering.

[47]  K. R. Robinson,et al.  The distribution of free calcium in transected spinal axons and its modulation by applied electrical fields , 1990, The Journal of neuroscience : the official journal of the Society for Neuroscience.

[48]  J. Myklebust,et al.  Electric field distribution within normal cat spinal cord. , 1994, Journal of neurotrauma.

[49]  B. Coburn,et al.  Electrical stimulation of the spinal cord: two-dimensional finite element analysis with particular reference to epidural electrodes , 1980, Medical and Biological Engineering and Computing.

[50]  Kenneth R. Robinson,et al.  Electric field effects on human spinal injury: Is there a basis in the in vitro studies? , 2008, Developmental neurobiology.

[51]  H. Yao,et al.  Anisotropic Ion Diffusivity in Intervertebral Disc: An Electrical Conductivity Approach , 2006, Spine.

[52]  J. Volkmann.  DEEP BRAIN STIMULATION II Deep Brain Stimulation for the Treatment of Parkinson’s Disease , 2004 .

[53]  J. Holsheimer,et al.  Epidural spinal cord stimulation: calculation of field potentials with special reference to dorsal column nerve fibers , 1991, IEEE Transactions on Biomedical Engineering.