Figure 7. Adaptation linearizes summation of synaptic inputs and allows surrounds to facilitate rather than suppress responses.
a, The best pairwise stimulus for each neuron was determined from the VWA and played back in isolation (unadapted, left) or embedded within random surround stimuli (adapted, right). Black, trial-averaged responses of a neuron to each of the two whiskers, R(PW) or R(SW). Circles, stimulus onset. The pairwise deflection, R(PW+SW), is shown in red (unadapted) or cyan (adapted). b, same as in panel a but for the best multi-whisker stimuli (2-9 whiskers). c, For all neurons (N = 46 unadapted in red; N = 75 adapted in blue/cyan) response to the pairwise deflection R(PW+SW) was plotted against the sum of responses to individual deflections R(PW)+R(SW). Cyan points represent neurons observed during both adapted and unadapted conditions and therefore have a red counterpart. Blue points represent neurons observed only during adaptation. Pairwise summation is nearly linear during adaptation (blue and cyan) (slope 0.723, r 0.506, p < 10−8) and sub-linear under unadapted conditions (red) (slope 0.346, r 0.738, p < 10−9). Similar behavior was observed for the optimal multi-whisker stimuli (right) (N=33 unadapted, 36 adapted; 33 matched pairs) (adapted: slope 0.491, r 0.631, p < 10−7; unadapted: slope 0.223, r 0.442, p < 10−9). d, For the same data as in c responses to pairwise deflections [R(PW+SW)] were compared to responses to the PW deflections alone [R(PW)]. Surround inputs facilitated the PW response during adaptation but suppressed the PW response without adaptation.