<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def updateSignal(self, xdata, ydata, plotname=None):
 """Updates the trace of the outgoing signal :param xdata: time points of recording :param ydata: brain potential at time points """

        if plotname is None:
            plotname = self.responsePlots.keys()[0]
        self.responsePlots[plotname].updateData(axeskey='stim', x=xdata, y=ydata)