OLFACTORY PATHWAYS - TASTE + SMELL
Flavour refers to a combination of taste and smell. The connections of the taste and olfactory (smell) pathways in primates suggest that the necessary convergence may also occur in the orbitofrontal cortex. Consistent with this, Rolls and Baylis (1994) showed that some neurons in the orbitofrontal cortex (10 per cent of those recorded) respond to both taste and olfactory inputs. Some of these neurons respond equally well to, for example, both a glucose taste and a fruit odour. Interestingly, others also respond to a visual stimulus representing, say, sweet fruit juice. This convergence of visual, taste and olfactory inputs produced by food could provide the neural mechanism by which the colour of food influences what we taste. For example, experimental participants reported that a red solution containing sucrose may have the flavour of a fruit juice such as strawberry, even when there was no strawberry flavour present; the same solution coloured green might subjectively taste of lime. There is also another olfactory area in the orbitofrontal cortex. Some of these olfactory neurons respond to food only when the monkey is hungry, and so seem to represent the pleasantness or reward value of the smell of food. These neurons therefore function in a similar manner with respect to smell as the secondary taste neurons function with respect to taste. The orbitofrontal cortex also contains neurons that respond to the texture of fat in the mouth. Some of these fat-responsive neurons also respond to taste and smell inputs, and thus provide another type of convergence that is part of the representation of the flavour of food. A good example of a food that is well represented by these neurons is chocolate, which has fat texture, sweet taste and chocolate smell components.
Flavour refers to a combination of taste and smell. The connections of the taste and olfactory (smell) pathways in primates suggest that the necessary convergence may also occur in the orbitofrontal cortex. Consistent with this, Rolls and Baylis (1994) showed that some neurons in the orbitofrontal cortex (10 per cent of those recorded) respond to both taste and olfactory inputs. Some of these neurons respond equally well to, for example, both a glucose taste and a fruit odour. Interestingly, others also respond to a visual stimulus representing, say, sweet fruit juice. This convergence of visual, taste and olfactory inputs produced by food could provide the neural mechanism by which the colour of food influences what we taste. For example, experimental participants reported that a red solution containing sucrose may have the flavour of a fruit juice such as strawberry, even when there was no strawberry flavour present; the same solution coloured green might subjectively taste of lime. There is also another olfactory area in the orbitofrontal cortex. Some of these olfactory neurons respond to food only when the monkey is hungry, and so seem to represent the pleasantness or reward value of the smell of food. These neurons therefore function in a similar manner with respect to smell as the secondary taste neurons function with respect to taste. The orbitofrontal cortex also contains neurons that respond to the texture of fat in the mouth. Some of these fat-responsive neurons also respond to taste and smell inputs, and thus provide another type of convergence that is part of the representation of the flavour of food. A good example of a food that is well represented by these neurons is chocolate, which has fat texture, sweet taste and chocolate smell components.
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