We trained naive or trained mice to associate odor cues with outcome (water, air puff or no outcome), and recorded dopamine cell body activity in the vetral tegmental area (VTA), dopamine axon activity in the ventral striatum (VS) or dopamine release in VS with optic fiber fluorometry (photometry). In different set of mice, single dopamine neuron activiy was recorded with 2-photon microscope. In some of these mice, we reversed odor-outcome contingency so that an odor that was associated with no outcome or air puff became associated with water reward. Licking pattern was also recorded.

Fiber-fluorometry 

The noise from the power line in the voltage signal was cleaned by removing 58-62Hz signals through a band stop filter. Z-score was calculated from signals in an entire session smoothed with moving average of 50 ms. To average data using different sessions, signals were normalized as follows. The global change of signals within a session was corrected by linear fitting of signals and time and subtracting the fitted line from signals. The baseline activity for each trial (F0_each) was calculated by averaging activity between -1 to 0 sec before a trial start (odor onset for odor trials and water onset for free water trials), and the average baseline activity for a session was calculated by averaging F0_each of all trials (F0_average). dF/F was calculated as (F - F0_each)/F0_average. dF/F was then normalized by dividing by average responses to free water (0 to 1 sec from water onset). 

2-photon imaging

Acquired images were preprocessed in the following manner: 1) movement correction was performed using phase correlation image registration implemented in Suite2P⁵⁹; 2) region-of-interest (ROI) selection was performed manually from the mean and standard deviation projections of a subset of frames from the entire acquisition, as well as a movie of the frames used to build those projections; 3) Neuropil decontamination was performed with FISSA⁶⁰ using four regions around each ROI. The decontaminated signal extracted from these regions was then flattened (to correct for drifts caused by photobleaching), and z-scored across the entire session. The preprocessed and z-scored fluorescence were resampled to 30 Hz and used for further analysis. The first one was used to calculate ∆F/F0 in which F0 was the mean fluorescence before odor delivery. When the z-scored fluorescence was used for analysis, the mean z-score value before odor delivery was subtracted.