Olfactory bulb

The olfactory bulb is a part of the vertebrate forebrain. It works in olfaction, or the sense of smell.

The olfactory bulb has one source of sensory input (axons from olfactory receptor neurons, and one output (mitral cell axons). It is thought that it functions as a filter. However, the olfactory bulb also gets "top-down" information from brain areas like the amygdala, neocortex, hippocampus, locus coeruleus, and substantia nigra.

Its range of functions probably include:

discriminating between odors
enhancing sensitivity of odor detection
filtering out background odors 
permitting higher brain areas involved in arousal and attention to modify the detection or discrimination of odors.

 References 

Category:Anatomy of the brain
Category:Sensory system