Cortical Response to Fat Taste.

We sense fat by its texture and smell, but it is still unknown whether we also taste fat despite evidence of both candidate receptors and distinct fat taste sensations. One major reason fat is still not recognized as a basic taste quality is that we first need to demonstrate its underlying neural activity. To investigate such neural fat taste activation, we recorded evoked responses to commercial cow milk products with 0.1%, 4%, and 38 % fat via high-density electroencephalography (EEG) from 24 human participants. The experimental design ensured that the products would only be discriminable via their potential fat taste; all stimuli were carefully controlled for differences in viscosity, lubrication, odor, temperature, and confounding tastes (sweetness, acidity, and "off-taste") and were delivered directly onto the tongue using a set of computer-controlled syringe pumps. Advanced topographical pattern analysis revealed different neural activation to the milk products 85-134 ms after stimulus onset, which, as expected, best discriminated the two milk fat extremes (0.1% and 38% fat). Notably, this time period has previously been shown to also encode basic taste qualities, such as sweet or salty. By adding to the evidence of cortical fat taste processing in response to staple food, our finding not only substantiates that we taste fat but also highlights its potential relevance during our everyday lives with possible large-scale impacts on motivational eating behavior to explain overconsumption of energy-dense foods.

EEG discrimination of perceptually similar tastes.

Perceptually similar stimuli, despite not being consciously distinguishable, may result in distinct cortical brain activations. Hypothesizing that perceptually similar tastes are discriminable by electroencephalography (EEG), we recorded 22 human participants' response to equally intense sweet-tasting stimuli: caloric sucrose, low-caloric aspartame, and a low-caloric mixture of aspartame and acesulfame K. Time-resolved multivariate pattern analysis of the 128-channel EEG was used to discriminate the taste responses at single-trial level. Supplementing the EEG study, we also performed a behavioral study to assess the participants' perceptual ability to discriminate the taste stimuli by a triangle test of all three taste pair combinations. The three taste stimuli were found to be perceptually similar or identical in the behavioral study, yet discriminable from 0.08 to 0.18 s by EEG analysis. Comparing the participants' responses in the EEG and behavioral study, we found that brain responses to perceptually similar tastes are discriminable, and we also found evidence suggesting that perceptually identical tastes are discriminable by the brain. Moreover, discriminability of brain responses was related to individual participants' perceptual ability to discriminate the tastes. We did not observe a relation between brain response discriminability and calorie content of the taste stimuli. Thus, besides demonstrating discriminability of perceptually similar and identical tastes with EEG, we also provide the first proof of a functional relation between brain response and perception of taste stimuli at individual level.

A new gustometer: Template for the construction of a portable and modular stimulator for taste and lingual touch.

Taste research has been hampered by technical difficulties, mostly because liquid taste stimuli are difficult to control in terms of timing and application area. Exact stimulus control requires a gustometer, but the existing devices are either not well-documented or rather inflexible. We designed a gustometer based on a computer-controlled, modular pump system, which can be extended via additional hardware modules-for example, for heating of the stimuli or sending and receiving triggers. All components are available for purchase "off the shelf." The pumps deliver liquids through plastic tubing and can be connected to commercially available or custom-made mouthpieces. We determined the temporal precision of the device. Onset delays showed minuscule variation within pumps (SD < 3 ms) and small differences between pumps (< 4.5 ms). The rise time was less than 2 ms (SD < 2 ms), and the dosage volume bias was only 2%. To test whether hemitongues could be stimulated independently, we conducted a behavioral experiment. A total of 18 participants received tasteless stimuli to the left, right, or both sides of the tongue. The side of stimulation was correctly identified on 91% of trials, indicating that the setup is suitable for lateralized stimulation. Electroencephalographic responses to water and salty stimuli were recorded from two participants; the stimulation successfully evoked event-related responses, demonstrating the suitability of the device for use in electrophysiological investigations. We provide a Python-based open-source software package and a Web interface to easily operate the system. We thereby hope to facilitate access to state-of-the-art taste research methods and to increase reproducibility across laboratories.