Generalizing fear

The association between a neutral sound and an unpleasant outcome may make it more difficult to distinguish among similar sounds, according to a paper published online this week in Nature Neuroscience. This finding suggests one possible reason why individuals with post-traumatic stress disorder often react reflexively to innocuous stimuli that are similar to those that they have associated with unpleasant outcomes in the past. Rony Paz and colleagues had participants listen to a specific frequency tone paired with an odor. When the odor was pleasant, the participants were very good at differentiating that tone from other similar ones. However, Paz and colleagues found that when a tone is paired with an unpleasant odor, people become much worse at discriminating the tone from other similar ones. This effect was still observed when the tones were paired with other sounds, instead of odors, and persisted the day after training.