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

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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 investigated how the brain creates "gustatory imagery"—the ability to imagine the taste of food. They specifically wanted to see the timing of brain activity to determine if the "thinking" part of the brain tells the "tasting" part of the brain what to do.

How They Studied It

The study involved 9 participants who underwent brain scans using magnetoencephalography (MEG), a tool that measures magnetic fields produced by brain activity with millisecond precision. Participants were shown either words (like "Lemon") or pictures of food and were asked to imagine the taste. They also performed a control task where they looked at non-food items (like "Glass" or a picture of a tennis ball) and were asked to imagine their appearance.

What They Found

The researchers discovered a specific sequence in the brain during taste imagery. When participants saw a word and imagined a taste, a region called the prefrontal cortex (associated with complex thought and memory retrieval) activated first. About 85 milliseconds later, the insular cortex (the primary area for processing actual taste) became active. This pattern occurred in over 70% of the participants who showed brain activity in both regions. Interestingly, words were much more effective at triggering this "top-down" brain signal than pictures were.

What This Might Mean

This suggests that imagining a taste isn't just a random spark in the brain's taste center. Instead, it appears to be a controlled process where the front of the brain retrieves a memory and then "signals" the taste center to recreate the sensation. While this study used a small group of healthy participants, it helps explain the biological pathway for internal sensations. For those with aphantasia (who may lack various types of mental imagery), this research provides a map of which brain connections might be functioning differently.

One Interesting Detail

The brain's taste center (the insular cortex) reacted much faster to real tastes in previous studies than it did to imagined tastes in this one. When imagining a taste from a word, it took about 400 milliseconds for the taste center to "light up," showing that the brain takes extra time to build a flavor from memory.

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

Abstract

Authors

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

Abstract

Authors

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

Abstract

Authors

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

Abstract

Authors

What This Study Is About

How They Studied It

What They Found

What This Might Mean

One Interesting Detail

What This Study Is About

How They Studied It

What They Found

What This Might Mean

One Interesting Detail

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