Figure 5. Input magnitude asymmetries show that the pre-synaptic cells were directionally selective.

(a–c) Input magnitude asymmetries of conductance sets for 3 cells. Left column: preferred (left) and null (right) conductance traces, excitation (ge, red) and inhibition (gi, blue). Sweep timing shown below traces. Right: total evoked conductance magnitudes (normalized areas under the curves, preferred (P) and null (N)). The preferred ge is significantly larger than the null ge in each set. (a) Preferred inhibition is smaller than the null. (b) Preferred and null inhibition are equal. (c) Preferred inhibition is larger than the null. (** p < 0.01, * p < 0.05, Student’s t test). (d) The preferred/ null ratios (P/N) for all 17 conductance sets. For excitation, all 17 P/N ratios were significantly greater than one, indicating a magnitude asymmetry that favored the preferred sweep (filled red circles, mean 1.79 ± 0.11). In contrast, the inhibitory P/N ratios varied around ~ 1.0 (mean 1.07 ± 0.08), and only 8 were significantly different from one (filled blue circles). 5/17 P/N ratios for inhibition were less than one, favoring the preferred sweep. 9/17 were not different from one (open blue circles), favoring neither direction, and 3/17 were greater than one, favoring the null direction. Lines connect the excitatory and inhibitory conductance sets evoked by the same FM set.