【Abstract】 Objective Using in vivo perforated whole-cell recording in adult rats, we compared the spontaneous activity of somatosensory cortical (S1) neurons that was recorded under light pentobarbital and urethane anesthesia. Methods Twenty Sprague-Dawley male rats were randomly divided into 2 groups (10 for each). Each group of rats was anesthetized with either pentobarbital or urethane, and the head of the rats was fixed with stereotaxic apparatus for surgery and the following precedures. Perforated whole-cell recording was performed in vivo in the anesthetized animals several hours after surgery. Results Twenty-seven S1 neurons recorded from each group of rats were randomly selected for analysis. There were no significant differences in the resting membrane potential (-84±4.3mV vs. -82±4.2mV; P=0.119), action-potential frequency (0.28±0.28Hz vs.0.33±0.34Hz; P=0.815), and action-potential amplitude (58±9.5mV vs. 63±8.2mV; P=0.121) between these two groups. However, the patterns of membrane-potential change were significantly different between the two groups. Under pentobarbital anesthesia, Membrane-potential changes exhibited a short duration, and their cumulative distribution fell in a unimodal curve. Under urethane anesthesia, membrane-potential changes exhibited a long duration and consist of both persistent UP and DOWN states, and their cumulative distribution fell in a bimodal curve. Conclusion Pentobarbital and urethane anesthesia lead to distinct patterns of membrane-potential changes in somatosensory cortical neurons.