Fig. 3. Objective determination of CTmax, using the residuals
of the linear regressions vs. time of the absolute difference sums
(ADS) of 
CO2 and
of activity. Each ADS is a cumulative sum of the absolute differences between
adjacent sample points in the respective data channel; the residuals of the
linear regressions of each ADS vs. time clearly shows an inflection
point for each ADS at which spiracular control (in the case of
CO2) or motor
control (in the case of activity) ceases. See
Fig. 2 for reference. We
operationally define the inflection point, as measured using our methodology,
as the theta point and consider it to be congruent with behavioral measures of
CTmax. See text for details.