Figure 3. PCx Firing Emerges When Multiple Glomeruli Are Coactive.

(A) Example M/T neuron in MOB tested with a series of multisite patterns encompassing increasing numbers of glomeruli. M/T responses were independent of pattern size. Traces, raw single-trial data. Rasters, repeated presentations. Histograms, spike probability in 10 ms bins. See also Figure S3.

(B) Mean firing rates for all M/Ts tested with multisite patterns, quantified for the most effective individual site (1, left) and for the set of patterns containing this site (2–16, right; n = 11 cells).

(C) Mean M/T spike count is independent of number of uncaging sites in the stimulus pattern (n = 11 cells).

(D) Example PCx neuron tested with a series of multisite patterns. Firing emerged only when several glomeruli were coactive.

(E) Mean firing rates for all PCx neurons in response to patterns of increasing size. Spiking appeared only when patterns contained ≥3–4 sites (n = 14 – 53 cells for various pattern sizes).

(F) PCx input-output function showing the dependence of firing on the number of MOB uncaging sites. Asterisks show significant difference relative to rest (p < 0.05, t-test; n = 14 – 53 cells).

(G) Cumulative plot of PCx neuron activation with additional MOB uncaging sites. For 3-site stimuli (light blue), most cells were unresponsive or driven by a small set of patterns (left), while a few cells responded to many patterns (right). For stimuli with additional sites (darker blue traces, indicated by number labels), a greater proportion of cells was activated, and cells reponded to a greater fraction of patterns.

(H) Mean PCx spike count for different sized patterns, divided by number of uncaging sites to normalize for total cortical input. The ‘per glomerulus’ contribution rose steeply for patterns of 3 or more sites.

(I) Comparison of PCx responses to composite patterns and component sites. For an effective 4-site pattern, there was little or no response to individual sites stimulated 4 times at 20 Hz.

(J) Population analysis shows patterns are consistently more effective than repeated stimulation of components (n = 10 cells). Dark blue, mean firing rate for effective 4-site stimuli. Light blue, firing for component sites activated 4 times at 20Hz. Gray, resting activity. Vertical lines, uncaging pulses.