Abstract
Purpose: 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.Method: 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.Conclusion: 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.
Highlights
To map the topography of the rat somatosensory cortex, traditionally, microscopic and histological techniques have been applied
Craniotomy was performed on the 12 normal rats and on the four peripheral nerve injured rats
No significant difference in N1-P1 interval was found between the two groups
Summary
To map the topography of the rat somatosensory cortex, traditionally, microscopic and histological techniques have been applied. Fluorescent dyes, which can be used individually or combined with HRP, have served as methods for the mapping of fiber connections. Electrophysiological techniques, such as somatosensory and motor evoked potentials (SEPs and MEPs; Agrawal et al, 2010; Sherman et al, 2010; Cloud et al, 2012; Hua et al, 2012; Pan et al, 2012), have been used to reliably assess the integrity and functionality of sensory pathways and to perform systematic investigation of central or peripheral nervous injury, though with some difficulty in interpretation. Histological, electrophysiological, and neuroimaging methods, independently or combined, comprise the toolbox for modern neuroscience research
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