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Gustatory Imagery Reveals Functional Connectivity from the Prefrontal to Insular Cortices Traced with Magnetoencephalography

DOI: 10.1371/journal.pone.0021736
Kobayashi, M., Sasabe, T., Shigihara, Y., Tanaka, M., & Watanabe, Y. (2011). Gustatory imagery reveals functional connectivity from the prefrontal to insular cortices traced with magnetoencephalography. PLoS ONE, 6(7), e21736. doi:10.1371/journal.pone.0021736

Abstract

Our experience and prejudice concerning food play an important role in modulating gustatory information processing; gustatory memory stored in the central nervous system influences gustatory information arising from the peripheral nervous system. We have elucidated the mechanism of the "top-down" modulation of taste perception in humans using functional magnetic resonance imaging (fMRI) and demonstrated that gustatory imagery is mediated by the prefrontal (PFC) and insular cortices (IC). However, the temporal order of activation of these brain regions during gustatory imagery is still an open issue. To explore the source of "top-down" signals during gustatory imagery tasks, we analyzed the temporal activation patterns of activated regions in the cerebral cortex using another non-invasive brain imaging technique, magnetoencephalography (MEG). Gustatory imagery tasks were presented by words (Letter G-V) or pictures (Picture G-V) of foods/beverages, and participants were requested to recall their taste. In the Letter G-V session, 7/9 (77.8%) participants showed activation in the IC with a latency of 401.7±34.7 ms (n = 7) from the onset of word exhibition. In 5/7 (71.4%) participants who exhibited IC activation, the PFC was activated prior to the IC at a latency of 315.2±56.5 ms (n = 5), which was significantly shorter than the latency to the IC activation. In the Picture G-V session, the IC was activated in 6/9 (66.7%) participants, and only 1/9 (11.1%) participants showed activation in the PFC. There was no significant dominance between the right and left IC or PFC during gustatory imagery. These results support those from our previous fMRI study in that the Letter G-V session rather than the Picture G-V session effectively activates the PFC and IC and strengthen the hypothesis that the PFC mediates "top-down" control of retrieving gustatory information from the storage of long-term memories and in turn activates the IC.

Authors

  • Masayuki Kobayashi2
  • Tetsuya Sasabe2
  • Yoshihito Shigihara1
  • Masaaki Tanaka2
  • Yasuyoshi Watanabe2

What This Study Is About

Researchers wanted to find the "GPS route" the brain takes when we imagine a taste. They aimed to see if the brain’s "executive office" (the part that handles thinking and memory) sends a signal to the "tasting center" to trigger a mental flavor.

How They Studied It

The team worked with nine volunteers. To track the brain's activity in real-time, they used a MEG scanner—a high-tech helmet that measures magnetic fields produced by your brain. It’s like a super-fast stopwatch that can see changes happening in milliseconds (thousandths of a second).
Participants were shown words (like "Lemon" or "Chocolate") and pictures of food. Their job was to use gustatory imagery—which is the ability to "taste" something in your mind without actually eating it. For comparison, they also looked at non-food items like "Glass" or "Tennis ball."

What They Found

The researchers discovered a clear "top-down" chain of command. When someone imagined a taste:
1. The Prefrontal Cortex (the brain's "Boss") lit up first.
2. About 100 milliseconds later, the Insular Cortex (the "Tasting Center") activated.
Think of it like a light switch: the Boss flips the switch, and a split-second later, the Tasting Center turns on. Interestingly, seeing the *word* for a food was actually better at triggering this "brain-taste" than seeing a *picture* of the food.

What This Might Mean

This study suggests that mental imagery isn't just a random spark; it’s a deliberate signal sent from the front of the brain to the sensory areas.
For people with aphantasia—the inability to create mental "pictures" or other sensory experiences in the mind—this research is a big clue. It suggests that if someone can’t "taste" a lemon in their head, the issue might be a "disconnection" on this highway. Either the "Boss" isn't sending the signal, or the "Tasting Center" isn't receiving it.
*Note: This was a very small study with only nine people, so we need more research to see if these results hold true for everyone, especially those with aphantasia.*

One Interesting Detail

The entire process of "thinking" a taste happens incredibly fast—the signal travels from the front of the brain to the tasting center in about 0.08 seconds. That’s faster than the blink of an eye!
This summary was generated by AI and may contain errors. Always refer to the original paper for accuracy.