Somatosensory Evoked Potentials
Somatosensory evoked potentials (SEPs) represent the global responses of regions of the cortex due to electrical stimulation of the peripheral nervous system. To acquire SEP signals, the median and tibial nerves from both left and right limbs are electrically stimulated, and the response waveform is recorded from the region of the somatosensory cortex corresponding to the stimulated limb. The development of efficient signal processing methods to analyze and interpret data provided by the SEP signal is critical. Such analysis can also be used to objectively determine the efficacy of various therapeutic methods for treatment of SCI, such as human embryonic stem cells, hypothermia, and pharmaceutical agents.
Prior to injury, the characteristic peaks in the SEPs are present in the signal from each limb. Immediately after injury, however, these peaks disappear only from the hind limb signals.
Signal ProcessingWe have developed novel SEP analysis methods that go beyond the conventional analysis, in that they capture information about the morphology of the entire SEP waveform. These methods can potentially provide graphical, as well as quantitative tools for SEP monitoring and will be useful to a clinician.
Phase Space Analysis The phase space is a space of all possible states of a system. For a typical signal, for all practical purposes, a plot of the SEP waveform vs. its derivative is used to calculate the so-called phase space area. This area can then be used as a quantitative marker for the somatosensory conduction.
- Agrawal G et al. Slope analysis of somatosensory evoked potentials in spinal cord injury for detecting contusion injury and focal demyelination. J Clin Neurosci (2010), doi:10.1016/j.jocn.2010.02.005
- A. Maybhate, C. Hu, F. A. Bazley, Q. Yu, N. V. Thakor, C. Kerr, and A. All, "Potential Long Term Benefits of Acute Hypothermia after Spinal Cord Injury: Assessments with Somatosensory Evoked Potentials", Accepted for publication in Critical Care Medicine, July 2011
- Jai Madhok, Shrivats Iyer, Nitish V. Thakor, Fellow, Anil Maybhate, "Characterization of Neurologic Injury using Novel Morphological Analysis of Somatosensory Evoked Potentials". 32nd Annual International Conference of the IEEE EMBS, Buenos Aires, Argentina, Aug 31 - Sept 4, 2010.