The researchers further showed that the auditory, visual and olfactory cortices each store memories related to the specific sense they process. Lesions in the olfactory cortex did not prevent trained rats from remembering to associate a sound with the fear memory.
Experiments even revealed that the sensory cortices store information specific to the emotional meaning of the sound, sight, or smell.
Rats startle when they first hear a sound, regardless of whether it's linked to a scary event. But eventually, in a process called habituation, they grow accustomed to it. The team wanted to find out if these sensory memories that didn't involve fear were still stored in the secondary cortices. So they habituated the rats to a sound with no electric shock. One month later, lesions were made on the rats' secondary cortices for all senses. The lesioned rats still didn't startle upon hearing the sound, suggesting the secondary cortices only store memories if the stimulus is tied to an emotion. These sensory memories must be stored in another brain region, the researchers figure.
The researchers note the secondary cortices are likely not the only regions involved in storing emotion memories tied to the senses. Other areas, such as the amygdala, thought to play a key role in processing fear, could participate as well.