The olfactory bulb is a neural structure of the vertebrate forebrain involved in olfaction, or the sense of smell.
In humans the olfactory bulb is on the inferior side of the brain. The olfactory bulb is supported and protected by the cribriform plate of the ethmoid bone, which in mammals separates it from the olfactory epithelium, and which is perforated by olfactory nerve axons. The bulb is divided into two distinct structures: the main olfactory bulb and the accessory olfactory bulb.
The olfactory bulb transmits smell information from the nose to the brain, and is thus necessary for a proper sense of smell.
As a neural circuit, the olfactory bulb has one source of sensory input, and one output. As a result, it is generally assumed that it functions as a filter, as opposed to an associative circuit that has many inputs and many outputs. However, the olfactory bulb also receives "top-down" information from such brain areas as the amygdala, neocortex, hippocampus,locus coeruleus, and substantia nigra.