Central mechanisms of pheromone information processing

An advantage of using pheromones in olfactory studies is that they are chemical signals for which receptor neurons are evolved and thus elicit biologically relevant odour-information to be processed in the brain. In many vertebrate and insect species, the olfactory system is separated into a 'main' and an 'accessory' division, the latter mediating pheromone information. In moths, the pheromone information is first processed in the brain in a large and sexually dimorphic structure, the macroglomerular complex (MGC) of the antennal lobe (AL). Also in vertebrates the pheromone information is processed in specific or modified glomerular complexes. One principle question is whether individual olfactory glomeruli are functional units, processing specific information concerning both the chemical quality and spatiotemporal features of the stimulus, like the pheromone plume. Indeed it has been shown that the axons of different pheromone-selective receptor neurons project into different MGC-glomeruli. Intracellular recordings from the AL projection (output) neurons also show that information about single components of the pheromone blend is preserved in some output pathways, whereas other output neurons respond in a unique fashion to the blend. The information about interspecific signals, which interrupts pheromone attraction, is processed in a specific MGC-glomerulus and is to a large extent kept separate from the pheromone information throughout the AL. Many of the output neurons accurately encode changes in the temporal characteristics of the stimulus.