Areas of the brain that interpret our sense of taste may also provide a representation of oral textures such as how fat feels in the mouth, according to new review.
The paper, published in Journal of Texture Studies and authored by Professor Edmund Rolls – a leading expert in neural networks and computational neuroscience – aimed to describe how oral texture, including fat, is represented in the brain.
“This is an important issue, for it is not yet clear how oral fat is sensed […] evidence from neuroscience is providing indications about this by showing what must have been transduced by receptors in the mouth, in order to produce the neuronal responses found in the brain,” wrote Prof Rolls.
The review reports that fat in the mouth is represented by its texture in the primary taste areas of the brain such as the cortex of the insula, the orbitofrontal cortex, the amygdala and in the anterior cingulate cortex.
“The neurons that respond to fat also respond to silicone and paraffin oil, indicating that the sensing is texture- not chemo-specific,” explained. Rolls.
“This research has implications for understanding how fat in the mouth is sensed … It therefore has implications for the design of foods that may mimic the mouthfeel of fat, but not its energy content,” said Rolls.
Texture in the mouth is an important indicator of whether fat is present in a food, which is important not only as a high-value energy source, but also as a potential source of essential fatty acids.
Previous research discovered a group of neurons in the orbitofrontal cortex that respond to the texture of fat in the mouth.
Rolls explained that the brain's representation of oral fat is frequently in terms of combinations with other sensory aspects of food, including taste, texture and olfactory inputs. He said that such combinations “are important for understanding the full impact of the fat in food in the mouth on the pleasantness of food,”
“Fat in the diet may be pleasant, yet its intake must be controlled, and understanding the rules by which the pleasantness of fat is regulated is important,” he added.
Rolls explained that fat texture-sensitive neurons are found in the primary taste cortex, the secondary taste cortex in the orbitofrontal cortex where the pleasantness of food is represented, and in the amygdala.
He noted that neurons increase firing rates to cream, but responded to texture rather than the chemical structure of the fat. However, the same neurones also responded to silicone oil and paraffin oil stimulus, and did not have a taste input.
“Different neurons respond to different combinations of texture, taste, oral temperature, and in the orbitofrontal cortex to olfactory and visual properties of food,” he explained.
The review notes that some neurons also respond to fats in terms of their viscosity, and the extent that different fats have different viscosities, adding that “this is one way that fats may be perceptually different.”
“Another factor that could allow discrimination between different fats in the mouth is of course their odour, with butyrate content associated with some fatty foods (such as butter) being one example,” said Rolls.
He concluded that such discoveries “may have important applications, including in the prevention and treatment of obesity, and in producing highly palatable yet nutritious food.”
Source: Journal of Texture Studies
Volume 42, Issue 2 , Pages 137–156, doi: 10.1111/j.1745-4603.2011.00296.x
“The neural representation of oral texture including fat texture”
Author: E.T. Rolls