title: Topography of Synchronization of Somatosensory Evoked Potentials Elicited by Stimulation of the Sciatic Nerve in Rat.
abstract: OBJECTIVE
  Traditionally, the topography of somatosensory evoked potentials (SEPs) is generated based on amplitude and latency. However, this operation focuses on the physical morphology and field potential-power, so it suffers from difficulties in performing identification in an objective manner. In this study, measurement of the synchronization of SEPs is proposed as a method to explore brain functional networks as well as the plasticity after peripheral nerve injury.
  
  
  METHODS
  SEPs elicited by unilateral sciatic nerve stimulation in twelve adult male Sprague-Dawley (SD) rats in the normal group were compared with SEPs evoked after unilateral sciatic nerve hemisection in four peripheral nerve injured SD rats. The characterization of synchronized networks from SEPs was conducted using equal-time correlation, correlation matrix analysis, and comparison to randomized surrogate data. Eigenvalues of the correlation matrix were used to identify the clusters of functionally synchronized neuronal activity, and the participation index (PI) was calculated to indicate the involvement of each channel in the cluster. The PI value at the knee point of the PI histogram was used as a threshold to demarcate the cortical boundary.
  
  
  RESULTS
  Ten out of the twelve normal rats showed only one synchronized brain network. The remaining two normal rats showed one strong and one weak network. In the peripheral nerve injured group, only one synchronized brain network was found in each rat. In the normal group, all network shapes appear regular and the network is largely contained in the posterior cortex. In the injured group, the network shapes appear irregular, the network extends anteriorly and posteriorly, and the network area is significantly larger. There are considerable individual variations in the shape and location of the network after peripheral nerve injury.
  
  
  CONCLUSIONS
  The proposed method can detect functional brain networks. Compared to the results of the traditional SEP-morphology-based analysis method, the synchronized functional network area is much larger. Furthermore, the proposed method can also characterize the rapid cortical plasticity after a peripheral nerve is acutely injured.
authors.affiliation: Division of the Comprehensive Epilepsy Center and Neurofunctional Monitoring Laboratory, Department of Neurology, Peking University People's Hospital Beijing, China.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Qu
authors.affiliation: School of Electrical and Control Engineering, North China University of Technology Beijing, China.
authors.forename: Jiaqing
authors.initials: J
authors.lastname: Yan
authors.affiliation: State Key Laboratory of Cognitive Neuroscience and Learning and IDG/McGovern Institute for Brain Research, Beijing Normal University Beijing, China.
authors.forename: Xiaoli
authors.initials: X
authors.lastname: Li
authors.affiliation: Department of Trauma and Orthopaedics, Peking University People's Hospital Beijing, China.
authors.forename: Peixun
authors.initials: P
authors.lastname: Zhang
authors.affiliation: Division of the Comprehensive Epilepsy Center and Neurofunctional Monitoring Laboratory, Department of Neurology, Peking University People's Hospital Beijing, China.
authors.forename: Xianzeng
authors.initials: X
authors.lastname: Liu
keywords: brain functional network; correlation matrix analysis; cortical plasticity; peripheral nerve injury; rat; somatosensory evoked potentials; surrogate resampling