Robust M/T activation by specific odorants. A, Composite map showing a dorsal view of recording sites, which were widely distributed on the dorsal, ventral, and medial/lateral MOB surfaces to avoid sampling bias. M/Ts have a broad range of spontaneous firing rates, from ∼0 to nearly 30 Hz; histogram shows population distribution. B, C, Both excitatory (B) and inhibitory (C) M/T responses are sustained during odorant presentation and consistent over multiple trials separated by extended time periods (B, C show separate cells). PSTHs (left) show firing rates calculated in 500 ms bins. D, Raw data for five representative ineffective odorants (methyl butyrate, cyclohexanecarboxylic acid, benzyl acetate, 2-pentanol, and 2-methylvaleraldehyde) and two odorants evoking strong responses (eucalyptol and pentyl propionate). Bottom trace shows firing on expanded timescale. Firing rates exceed 150 Hz for some stimuli, illustrating the range of sensitivity of M/Ts to different odorants. Gray bar indicates odor; all stimuli presented at 10 ppm (see Materials and Methods). A, Anterior; D, dorsal; L, lateral; P, posterior.