The olfactory bulb (Latin: bulbus olfactorius) is a neural structure of the vertebrate forebrain involved in olfaction, the sense of smell.

It sends olfactory information to be further processed in the amygdala, the orbitofrontal cortex (OFC) and the hippocampus where it plays a role in emotion, memory and learning.

Processing occurs at each level of the main olfactory bulb, beginning with the spatial maps that categorize odors in the glomeruli layer.

[6] A well known model[7] is that the bulbar neural circuit transforms the odor information in the receptors to a population pattern of neural oscillatory activities[8] in the mitral cell population,[7] and this pattern is then recognized by the associative memories of olfactory objects in the olfactory cortex.

[citation needed] The interneurons in the external plexiform layer perform feedback inhibition on the mitral cells to control back propagation.

[4] It is not clear what the functional role of lateral inhibition would be, though it may be involved in boosting the signal-to-noise ratio of odor signals by silencing the basal firing rate of surrounding non-activated neurons.

This may contribute to a more specific output from the olfactory bulb that would closer resemble the glomerular odor map.

[17] It has been hypothesized that, in order for the vomernasal pump to turn on, the main olfactory epithelium must first detect the appropriate odor.

Vomeronasal sensory neurons provide direct excitatory inputs to AOB principle neurons called mitral cells[19] which are transmitted to the amygdala and hypothalamus and therefore are directly involved in sex hormone activity and may influence aggressiveness and mating behavior.

[20] Axons of the vomeronasal sensory neurons express a given receptor type which, differently from what occurs in the main olfactory bulb, diverge between 6 and 30 AOB glomeruli.

Mitral cell dendritic endings go through a dramatic period of targeting and clustering just after presynaptic unification of the sensory neuron axons.

This appears as a clear functional specialization, given the differential role of the two populations of sensory neurons in detecting chemical stimuli of different type and molecular weight.

A clear difference of the AOB circuitry, compared to the rest of the bulb, is its heterogeneous connectivity between mitral cells and vomeronasal sensory afferents within neuropil glomeruli.

AOB mitral cells indeed contact through apical dendritic processes glomeruli formed by afferents of different receptor neurons, thus breaking the one-receptor-one-neuron rule which generally holds for the main olfactory system.

Accordingly, AOB mitral cells show clearly different firing patterns compared to other bulbar projection neurons.

These connections are indicative of the association between the olfactory bulb and higher areas of processing, specifically those related to emotion and memory.

Similar to the process in the amygdala, an odor is associated with a particular reward, i.e. the smell of food with receiving sustenance.

[26] In lower vertebrates (lampreys and teleost fishes), mitral cell (principal olfactory neurons) axons project exclusively to the right hemisphere of Habenula in an asymmetric manner.

It is reported that dorsal Habenula (Hb) are functional asymmetric with predominant odor responses in right hemisphere.

These spontaneous active Hb neurons are organized into functional clusters which were proposed to govern olfactory responses.

et al. 2014, Current Biology) Further evidence of the link between the olfactory bulb and emotion and memory is shown through animal depression models.

[citation needed] In most mammals, new neurons are born from neural stem cells in the sub-ventricular zone and migrate rostrally towards the main [30] and accessory[31] olfactory bulbs.

The survival of immature neurons as they enter the circuit is highly sensitive to olfactory activity and in particular associative learning tasks.

[citation needed] The olfactory lobe is a structure of the vertebrate forebrain involved in olfaction, or sense of smell.

Comparing the structure of the olfactory bulb among vertebrate species, such as the leopard frog and the lab mouse, reveals that they all share the same fundamental layout (five layers containing the nuclei of three major cell types; see "Anatomy" for details), despite being dissimilar in shape and size.

A similar structure is shared by the analogous olfactory center in the fruit fly Drosophila melanogaster, the antennal lobe.

Three-dimensional geometric morphometric analyses of endobasicranial shape reveal previously undocumented details of evolutionary changes in Homo sapiens.

Such brain reorganization, beside physical consequences for overall skull shape, might have contributed to the evolution of H. sapiens' learning and social capacities, in which higher olfactory functions and its cognitive, neurological behavioral implications could have been hitherto underestimated factors.