How brain deciphers what smells good or bad

A new study provided a deeper insight into how the brain can distinguish between good and bad smells.

Scientists from the BMBF Research Group Olfactory Coding at the Max Planck Institute for Chemical Ecology in Jena, Germany, have now found that in fruit flies, the quality and intensity of odors can be mapped in the so-called lateral horn.

Whether an odor is pleasant or disgusting to an organism is not just a matter of taste. Often, an organism's survival depends on its ability to make just such discrimination, because odors can provide important information about food sources, oviposition sites or suitable mates.

They have created a spatial map of this part of the olfactory processing system in the fly brain and showed that the lateral horn can be segregated into three activity domains, each of which represents an odor category.

The categories are good versus bad, as well as weak versus strong smells. These categorizations have a direct impact on the behavior of the flies, suggesting that the function of the lateral horn is similar to that of the amygdala in the brains of vertebrates. The amygdala plays a crucial role in the evaluation of sensory impressions and dangers and the lateral horn may also.

Animals use their senses, such as vision and olfaction, to perceive visual cues or odors in their surroundings and to process and evaluate the information that is sent via these senses to their brains. They must be able to tell good from bad odors.

Good odors are important signals when animals search for food or a mating partner. Female insects also use olfactory signals to select a good oviposition place. Bad smells, on the other hand, can signal danger, for example, rotten and toxic food.

The researchers believe that the function of the lateral horn in fruit flies can be compared to that of the amygdale, two almond- shaped nuclei, in the brain of vertebrates. In humans, the amygdala plays a primary role in the emotional evaluation of situations and the assessment of risks. If the amygdala was damaged, humans fail to show fear or aggression. However, lesions in the amygdala also prevent vital flight or defense reactions from being triggered.

The scientists hypothesize that damage to the lateral horn might have similar effects on fruit flies. However, this assumption was so far speculative because the lateral horn could not be selectively inactivated.