Figure 4.

TTX reduced the SNR in both the center and surround response. A, Graded potential and spike responses of a representative cell increased with bath application of STR and PTX. Addition of TTX to the bath reversibly abolished the spike response and reduced the graded potential response. B, The diameter–response function of ganglion cell graded potential responses showed a weak but consistent surround inhibition (open circles). Addition of STR and PTX removed this inhibition (filled circles). C, With surround inhibition blocked, TTX reduced both signal (left graph) and noise (right graph). The mean reduction in signal was slightly more pronounced (28%) than in noise (21%). Curve fits were generated with a modified Naka–Rushton function (Eq. 3). D, As a result of the larger reduction in the signal, TTX reduced SNR in the graded potential response over the entire range of contrasts.