Updates the trace of the outgoing signal

        :param xdata: time points of recording
        :param ydata: brain potential at time points

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)