The pattern of summation in the low monoaminergic state depends on the type of stimulus. In cells where Ia inhibition and Ia excitation were combined (open symbols), regression slope was significantly <1.0 (y = 0.39x +1.16 for the hyperpolarized window, open squares; y = 0.34x + 1.09 for the depolarized window, open triangles). The 95% confidence intervals for these slopes did not include the line y = x. In cells where CP inhibition was combined with Ia excitation (filled symbols), the 95% confidence intervals for regression slopes did include the y = x line (y = 0.91x + 0.14 for the hyperpolarized window, filled squares; y = 1.22x + 0.07 for the depolarized window).