The Fundamental Role of Memory in Olfactory Perception

REFERENCE: Wilson DA and Stevenson RJ. The fundamental role of memory in olfactory perception. Trends Neurosci 2003, 28: 243-247

REVIEWED BY: Eloy Gutierrez Sendra (TFG de CAFD, 2016)

In terms of behaviour, the olfactory processing is synthetic, in other words, it tends to reconstruct a whole from various analysed and processed elements when a smell has been detected, regardless of the physical-chemical properties of the stimulus. In this manner, olfactory perception largely depends on memory and learning.

The exposure to several smells can improve or hamper the ability to discriminate them. Therefore, memory-related disorders affect the ability to detect the presence and intensity of smells.

Physiologically, in order to detect the complex olfactory stimuli that compose a smell, the odour molecules first reach the olfactory glomeruli and then the neuronal mitral cells, which detect the characteristics of the smell and send the information received from the cilia of the olfactory bulb. In order for the information to be correctly synthesized, there should be a temporal synchronization in the binding of the smells with their receptors.

Sensorial stimulation allows to improve the cortical mechanisms of olfactory learning. It has been shown that the olfactory bulb creates temporal-spatial patterns of a specific smell that are synthesized and stored in the piriform cortex, by a process known as cortical synaptic plasticity. The experience with a specific smell allows its synthesis as a perceived whole, however, without the initial learning process, it is not possible to identify the new smell. It is possible to modify the response of the neuronal cortex through cognitive stimulation, and create new response patterns of the rapid cells and subsequent mitral cells.

Smell discrimination can be interrupted by the manipulation of normal synaptic plasticity. These manipulations of the piriform cortex put at risk smell perception. It has been shown that the olfactory system can recognize certain smells through a slower process, as piriform cortex improvement is produced when it is perceived during at least 50 seconds.

The evidence shows that olfactory perception is highly synthetic, where several components of a stimulus are perceived as a single smell, but is also inefficient in the analysis of stimuli since it has difficulty recognizing several individual components in a complex mixture of smells.