How the Brain Detects, Identifies and Acts on Taste

Summary: A new EEG study sheds light on how we identify and discriminate between tastes to assess if a substance is nutritious or toxic.

Source: SfN.

Sweet and bitter flavors are identified as soon as they are tasted, according to human neural and behavioral data published in eNeuro. The study provides new insight into how the brain rapidly detects and discriminates between potentially nutritious and toxic substances.

The sense of taste, similar to that of smell, guides an organism toward stimuli that promote survival and away from stimuli that threaten it. This behavior requires detecting, identifying, and deciding to act on gustatory information.

Kathrin Ohla and Raphael Wallroth explored how this process unfolds in human adults as they detected one of four solutions — salty, sour, bitter, and sweet — and discriminated between salty versus sour and sweet versus bitter.

The researchers found strong correspondence between participants’ reaction times and their brains’ electrical activity during these tasks, suggesting that these computations take early in the taste-processing pathway. Salty and sour were more quickly detected than they were identified whereas virtually no lag between detection and discrimination was observed for sweet and bitter.

eeg output
A) Signal strength quantified as the average global field power computed within-subjects as the standard deviation of the event-related potentials over 64 electrodes for each of the tastants and water over detection trials (left) and discrimination trials (right). Salty and sour tastants show a stronger signal than sweet and bitter tastants, but less strongly so for discrimination trials. Note that the onset of the liquid stimulation (for all tastes and for water) coincided with the presentation of the fixation cross, resulting in a clear GFP response for water as well. B) Topographical voltage maps for each taste and task represent the grand-averaged mean over a 50 ms time window, early during processing (upper row) and surrounding the decoding onset (lower row) shown in Table 2 and Figure 3C relative to water. NeuroscienceNews.com image is credited to Wallroth & Ohla Fig. 2, eNeuro (2018).

As participants rated sweet and bitter tastes as more and less pleasant, respectively, and salty and sour tastes as neutral, this additional information may have facilitated the differences in processing speed.

About this neuroscience research article

Funding: German Federal Ministry of Research and Education funded this study.

Source: David Barnstone – SfN
Publisher: Organized by NeuroscienceNews.com.
Image Source: NeuroscienceNews.com image is credited to Wallroth & Ohla Fig. 2, eNeuro (2018).
Original Research: Abstract for “As soon as you taste it – evidence for sequential and parallel processing of gustatory information” by Raphael Wallroth and Kathrin Ohla in eNeuro. Published October 15 2018.
doi:10.1523/ENEURO.0269-18.2018

Cite This NeuroscienceNews.com Article

[cbtabs][cbtab title=”MLA”]SfN”How the Brain Detects, Identifies and Acts on Taste.” NeuroscienceNews. NeuroscienceNews, 15 October 2018.
<https://neurosciencenews.com/taste-detection-10025/>.[/cbtab][cbtab title=”APA”]SfN(2018, October 15). How the Brain Detects, Identifies and Acts on Taste. NeuroscienceNews. Retrieved October 15, 2018 from https://neurosciencenews.com/taste-detection-10025/[/cbtab][cbtab title=”Chicago”]SfN”How the Brain Detects, Identifies and Acts on Taste.” https://neurosciencenews.com/taste-detection-10025/ (accessed October 15, 2018).[/cbtab][/cbtabs]


Abstract

As soon as you taste it – evidence for sequential and parallel processing of gustatory information

The quick and reliable detection and identification of a tastant in the mouth regulate nutrient uptake and toxin expulsion. Consistent with the pivotal role of the gustatory system, taste category information (e.g. sweet, salty) is represented during the earliest phase of the taste-evoked cortical response (Crouzet et al., 2015) and different tastes are perceived and responded to within only a few hundred milliseconds, in rodents (Perez et al., 2013) and humans (Bujas, 1935). Currently, it is unknown whether taste detection and discrimination are sequential or parallel processes, i.e. whether you know what it is as soon as you taste it. To investigate the sequence of processing steps involved in taste perceptual decisions, participants tasted sour, salty, bitter, and sweet solutions and performed a taste-detection and a taste-discrimination task. We measured response times and 64-channel scalp electrophysiological recordings, and tested the link between the timing of behavioral decisions and the timing of neural taste representations determined with multivariate pattern analyses. Irrespective of taste and task, neural decoding onset and behavioral response times were strongly related, demonstrating that differences between taste judgments are reflected early during chemosensory encoding. Neural and behavioral detection times were faster for the iso-hedonic salty and sour tastes than their discrimination time. No such latency difference was observed for sweet and bitter, which differ hedonically. Together, these results indicate that the human gustatory system detects a taste faster than it discriminates between tastes, yet hedonic computations may run in parallel (Perez et al., 2013) and facilitate taste identification.

Significance Statement
Human response behavior reflects the culmination of multiple processing stages, so that the emergence of the commonly observed response delay between simple and more complex gustatory perceptual decisions remained unaddressed. For the first time, we show a strong correspondence between neural and behavioral task-dependent latency differences, providing evidence that this lag is represented during early chemosensory encoding, rather than resulting from higher-level cognitive processing. Moreover, we find that the processing sequence itself varies with taste contrast, likely dependent on hedonics. We suggest that taste hedonic features are processed in parallel to purely sensory computations with the potential to facilitate stimulus identification in the human gustatory sense, supporting the concept of a flexible sequence of gustatory coding states.

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