M/T odorant responses are highly selective. A, Example of a neuron activated by 3 of 25 odorants. Each horizontal line represents a color-coded PSTH averaged over three trials, illustrated to the left; red and blue arrowheads indicate suprathreshold activation and suppression, respectively. Note common chemical features highlighted in red, as well as the range of response strengths and detection of weak responses. B, Suppressive responses are also frequently stimulus specific (arrowheads as in A). Note overlap in stimuli with the neuron shown above. C, Population data for 21 cells in 10 mice. Each horizontal line shows both the fraction and strength of excitatory (red) and suppressive (blue) responses for a separate M/T to each of the 25 test odorants, ordered by intensity for each cell. Trials with changes of <5 Hz or 2.5 spikes in any 500 ms bin during presentation are considered unresponsive and are shown in white. Arrows indicates the neurons shown in A and B. A small number of cells are strongly activated by particular odorants, seen at the bottom left. Overall, only 14.1% of stimuli increase M/T firing by ≥5 Hz on average, and only 9.9% produce an increase of 10 Hz (n = 21 cells in ≥10 animals, 25 odorants per cell).