Mapping “phantom taste” in thermal tasters
Sally Eldeghaidy1, Martha Skinner2, Rebecca Ford2, Joanne Hort2, and Susan Francis 1

1Sir Peter Mansfield Imaging Centre, University of Nottingham, Nottingham, United Kingdom, 2Sensory Science Centre, School of Biosciences, University of Nottingham, Nottingham, United Kingdom


Thermal taster status refers to a new taste phenotype in which thermal stimulation of the tongue elicits a “phantom” taste in individuals. The mechanism behind thermal taste is not yet known, but hypothesised to arise from entwined gustatory and trigeminal nerves. Here, we use fMRI to perform the first study to investigate whether cortical areas respond to phantom taste. Subjects underwent fMRI to warming/cooling thermal stimulation. Thermal tasters reported a sweet taste as the taste most prevalent during warming/cooling trials. We show that this “phantom” taste elicits significant activation of primary gustatory cortex including anterior insula and anterior cingulate cortex.


Recently, a taste phenotype termed thermal taster status has been described1. Thermal taster status refers to the fact that, in some individuals, thermal stimulation of the tongue elicits a phantom taste. Little is known regarding the mechanism behind this, but behavioural data2 has led to the hypothesis of cross-wiring between taste and temperature receptors co-innervating papillae on the tongue. Here, we use fMRI to perform the first study to determine whether cortical areas respond to the perception of phantom taste.


21 subjects were screened for thermal taster status (8 male, 26± 4yrs). 9 subjects (3 male, 27± 4yrs) were classified as thermal tasters (TTs) and took part in the fMRI study.

Thermal Taster screening was performed using an intra-oral thermode (Medoc Pathway) to deliver warming and cooling thermal stimuli to the anterior tongue tip1,2, Fig1. Subjects were asked whether they perceived a taste during heating and/or cooling thermal stimulation, and if so, to describe the taste quality (sweet, salty, bitter, sour, umami, ‘metallic’, etc.), and using a rollerball to indicate the time point(s) they perceived the taste and to rate its intensity on a general Labelled Magnitude Scale (gLMS). Thermal tasters were classified as those who perceived a taste during warming or cooling.

fMRI Protocol:

Subjects were scanned during blocks of warming trials followed by cooling trials (Fig. 1), with 10 repetitions of each trial. During fMRI, subjects indicated using a rollerball, the time point(s) they perceived a taste and its intensity for each warming/cooling trial on a gLMS. A control task was employed to model confounding effects (e.g., due to motor activation) of the rollerball rating in which subjects were not exposed to any thermal stimuli, but were instructed to rate using the rollerball.

fMRI Data Acquisition and Analysis:

fMRI data was acquired on a Philips 3T Achieva scanner with 32-channel receive coil using 36 transverse dual-echo GE-EPI images (TE: 20/45ms, TR: 2.5s, 3x3x3mm3, SENSE 2), and an MPRAGE image was collected to aid registration of functional maps to MNI space. Weighted fMRI data were slice timing corrected, realigned, normalised to MNI space, and spatially smoothed (6 mm) and temporally filtered using SPM12. A GLM was formed for each subject to identify cortical activation to phantom taste. For each individual, the onset and duration of the phantom taste was determined from the continuous rollerball taste intensity ratings collected during the fMRI acquisition. This rollerball time series was convolved with a canonical haemodynamic response function, and motion parameters included as covariates of no interest. Thermal tasters who responded to warming or cooling trials were pooled, with maps combined at the 2nd level random effects group (RFX) analysis


During thermal stimulation of the tongue, the intensity of the “phantom” taste reported was between weak and strong on the gLMS, with an average intensity rating of above moderate. TTs reported perceiving tastes during warming trials, cooling trials or both, with sweet taste reported being most often perceived during warming trials, and sweet/minty during cooling trials, Fig 2. Behavioural rollerball data collected during the fMRI session indicated consistency in onset of the perceived phantom taste across the 10 repetition, Fig 3. RFX maps from thermal tasters showed that phantom taste perceived during thermal stimulation of the tongue activated taste areas including anterior insula [(-36, 16, 4), T=5.12, P<0.001], frontal operculum [(-48, 14, 8), T=5.52, P<0.001] and ACC [(4, 26, 44), T=4.83, P<0.001], Fig. 4. Maps in response to the control task, to assess rollerball movements, were limited to a small region of somatosensory areas with no activation in taste areas.


Behaviourally thermal tasters have been shown to be more sensitive to pure taste stimuli at supra-threshold levels2, and the temperature of warm and cold stimuli3 compared with thermal non-tasters (TnTs). The mechanism for this increase in sensitivity in TTs has been hypothesised to be due to a temperature sensitive chemosensory pathway1. A hypothesis supported by the discovery that the TRPM5 cation channel, which responds to sweet, bitter and umami tastes is also heat activated and highly temperature sensitive4. We demonstrate that thermal stimulation applied to the anterior of the tongue can elicit a clear “phantom” taste response in thermal tasters generating a cortical response in primary gustatory cortex. Recently, fMRI studies have shown a heightened cortical response in TTs compared with TnT to taste, aroma flavour and trigeminal stimuli5,6, again supporting a mechanism of entwined gustatory and trigeminal nerves in thermal tasters.


This work was funded by the BBSRC and Unilever


[1] Cruz A. and Green B. G. Thermal stimulation of taste. Nature, 2000; 403 (6772) :889-892.

[2] Bajec M. R. and Pickering G. J. Thermal taste, PROP responsiveness, and perception of oral sensations. Physiology & Behavior, 2008; 95, (4):581-590.

[3] Yang Q, Hollowood T, Hort J. Phenotypic variation in oronasal perception and the relative effects of PROP and Thermal Taster Status. Food Quality and Preference, 2014; 38:83-91.

[4] Talavera K, Yasumatsu K, Yoshida R et al. The taste transduction channel TRPM5 is a locus for bitter-sweet taste interactions. FASEB Journal, 2008; 22: 1343-1355.

[5] Eldeghaidy S, Hort, J, Yang Q, et al. Impact of Thermal Taster Status on Cortical Response to Flavour and Temperature Stimuli, Proceedings OHBM meeting, Hawaii, USA, 2015.

[6] Eldeghaidy S, Hort J, Clark RA, et al. Cortical processing in thermal tasters: evidence for cross-modal integration, Proceeding OHBM meeting, Hawaii, USA, 2015.


Fig.1: A) Graphical representation of the thermal taster screening protocol. (i) warming trial: cooling to 15˚C before warming to 40˚C, (ii) cooling trial: cooling to 5˚C before returning to body temperature 35˚ C. (iii) The thermode probe applied to the anterior tongue tip, and gLMS to rate taste intensity. B) fMRI Protocol: A block paradigm of warming trials followed by cooling trials and then a control task.

Fig. 2: Tastes perceived during: A) warming trials and B) cooling trials

Fig. 3: Example time and intensity rating of phantom taste perceived through a block of 10 repetitions using the rollerball. A) warming trial, and B) cooling trial during fMRI acquisition.

Fig. 4: RFX group maps in response to “phantom” taste elicited in thermal tasters during warming and cooling trials. Maps are overlaid on T1 images and threshold at P<0.005.

Proc. Intl. Soc. Mag. Reson. Med. 24 (2016)