Plasticity in olfactory bulb circuits

Abstract

Olfaction is crucial for animal survival and human well-being. The olfactory bulb is the obligatory input station for olfactory information. In contrast to the traditional view as a static relay station, recent evidence indicates that the olfactory bulb dynamically processes olfactory information in an experience-dependent and context-dependent manner. Here, we review recent studies on experience-dependent plasticity of the main circuit components within the olfactory bulb of rodents. We argue that the olfactory bulb plasticity allows optimal representations of behaviorally-relevant odors in the continuously changing olfactory environment.

Figure 1.

Schematic of the olfactory bulb circuit. OSN: olfactory sensory neuron; PG cell: periglomerular cell; LOT: lateral olfactory tract; EPL: external plexiform layer.

Figure 2.

A model of perceptual learning-related plasticity in the olfactory bulb. Similar odorants (A and A’) evoke similar response patterns in mitral cells before learning (left). Perceptual learning induces pattern decorrelation of mitral cell representations of the learned odorants (right). The enhanced pattern separation is mediated by adaptive and selective lateral inhibition from granule cells, particularly adult-born granule cells. In addition to mitral cell inputs, granule cells also receive feedback innervation from higher brain centers, which enables context-dependent odor processing. Red circles: mitral cells with excitatory odor responses; blue circles: mitral cells with suppressive odor responses. The intensity of colors represents the strength of the responses. Yellow circles: granule cells.