"Correlating brain activation with the volatile release and perception of various formulations can improve fundamental knowledge on the perceptual mechanisms of taste and aroma and more importantly, on the perceptual interactions between the two," explained lead author Luca Marciana in the Journal of Neuroscience Methods (doi: 10.1016/j.jneumeth.2006.05.035).
Indeed, taste is a key driver in the €3.2 trillion global food industry and a greater understanding of the physiology of consumers, could lead to strong market advantages.
Imaging of the brain's responses during food tasting is not a new technique and has been used extensively. However, the most common techniques, namely positron emission tomography (PET), functional magnetic resonance imaging (fMRI), and magnetoencephalography (MEG), have several technical limitations.
All three techniques, fMRI, PET and MEG, often require subjects to be lying down, which restricts movement, allows only a limited volume of tastants to be presented, and delays swallowing.
But, in the case of fMRI, the latter two limitations could be eliminated to produce a more "natural" image of brain activity, according to the Nottingham researchers.
The subjects would still however be required to be supine.
The scientists adopted a three-pronged approach to improve the technique of fMRI by incorporating an automated, sprayed stimulus delivery system providing a larger volume of liquid sample to achieve more extensive stimulation of the taste receptors. Secondly, the model was adjusted to achieve prompt swallowing, the so-called pseudo-natural delivery. Finally, the brain coverage area was extended and a double-echo technique used to improve sensitivity.
To test the effectiveness of the improvements the researchers recruited 12 healthy right-handed subjects to undergo a taste-aroma test. The flavour stimulus consisted of a mixture of sucrose (three per cent), and banana/pear aroma volatiles (0.1 per cent isoamyl acetate) in water.
The results of these tests showed that the sprayed delivery system allowed for a extensive covering of the oral cavity, previously unobtainable with fMRI.
The pseudo-natural delivery also allowed the researchers to measure the response to tasting that was "closer to real consumption of liquid beverages."
Numerous brain areas were found to be activated, said the researchers, including the insula, frontal operculum, dorsolateral prefrontal cortex, anterior cingulate cortex, ventro-medial thalamus, hippocampus and medial orbitofrontal cortex.
"This study validates the use of the pseudo-natural delivery protocol using a combined taste and aroma solution as a stimulus, sucrose sweet taste and banana/pear aroma," wrote the researchers.
"This protocol offers conditions closer to real consumption of liquid foods within the limitation of having to lie supine and still inside the MRI scanner," they concluded.
The work comes hot on the heels of other attempts to improve brain imaging, with scientists in Japan pioneering the use of functional near-infrared spectroscopy (fNIRS) (Appetite, on-line ahead of print, doi: 10.1016/j.appet.2006.04.003).
This technique, said the researchers from Japan's National Food Research Institute, could prove to be more valuable than the standard techniques since the subjects are not required to be lying down, but allows tasting a mouthful of sample in an upright position with little oral movement restriction.