Fig. 4. (A ) Joint-interval graphs for four subthalamic neurons demonstrating the consistent depression of short interval discharge activity (less than 10 ms; boxes ). Also note that each neuron exhibited a unique discharge pattern, although mean discharge frequencies were very similar for each cell. Propofol did not appear to alter the overall discharge pattern of any of these neurons, except for the selective depression of high frequency discharge. The neurons exhibited various degrees of cardioballistic pulse artifact. (B ) Joint-interval graphs showing the time course of effects on a subthalamic neuron. Short latency spike intervals (arrow; <10 ms; boxes ) were depressed after a bolus administration of propofol (0.3 mg/kg intravenously). Indicated times are from the start of the bolus. The sedative had a rapid onset, peaking at 2.0 min and a gradual recovery that required approximately 10 min after administration.