[In vivo extracellular neural recording for the study of cortical plasticity]

Neural network plasticity is fundamental for learning and memory. Its abnormal change underlies some neural diseases. Measurement of the plasticity of cortex can help understand the mechanism of plasticity, and provide a quantitative way to observe the neural process of natural aging and neurodegenerative diseases, which may lead to a new approach for evaluation of anti-aging drugs and new medical treatments for neurodegenerative diseases. In this study, a systematic method was established based on whisker pairing (WP) experiment to measure the network plasticity in the barrel cortex in rat. WP experiment is a classical experiment to study the effect of innocuous bias of the flow of sensory activity from the whiskers for certain periods in awake and behaving rats on the receptive field organization in S1 barrel cortex neurons. In the experiment, one pair of adjacent whiskers D2 and D3 remained intact while others were being trimmed throughout a certain period. After that, receptive fields of single cells in the contralateral barrel were analyzed by post-stimulus time histogram after certain days of WP and compared with the controls. In the control group, response magnitudes to surrounding whiskers D1 and D3 deflection were not significantly different. However, after WP, a bias occurred in response to paired surrounding whisker D3 relative to the opposite trimmed surrounding whisker D1. In this study, by comparing the bias degree in rats in different groups after WP, a quantitative method was established to compare cortical plasticity. Example of corical plasticity comparison between adolescent and mature rats was employed in this paper to illustrate our method. The key techniques of this method such as the identification of D2 barrels, supragranular (L2-3) and barrel layer (L4) in real-time were described in details. The feasibility of this approach was further verified by compendious report of results and our previous study regarding cortical plasticity comparison between adolescent and mature rats.