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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

Understanding How Our Brain Processes Taste: A Study on Gustatory Imagery

Overview/Introduction

Have you ever wondered how your brain processes the taste of your favorite food even when you're not eating it? This study explores how our brain imagines tastes using words and pictures, and how different parts of the brain work together during this process. Researchers used advanced brain imaging techniques to understand the "top-down" control—how our brain uses past experiences and memories to influence how we perceive taste.

Methodology

To investigate how the brain processes imagined tastes, researchers used a technique called magnetoencephalography (MEG). This method allows scientists to see which parts of the brain are active and when. Participants were shown either words or pictures of foods and asked to imagine their taste. The study focused on two key brain areas: the prefrontal cortex (PFC), which is involved in decision-making and memory, and the insular cortex (IC), which processes taste.

Key Findings

  • In sessions where participants imagined tastes from words, the insular cortex was activated in about 78% of participants.
  • The prefrontal cortex was activated before the insular cortex in 71% of these cases, suggesting that the PFC might initiate the process of recalling taste memories.
  • When participants imagined tastes from pictures, the insular cortex was activated in 67% of participants, but the prefrontal cortex was rarely involved.
  • There was no significant difference in activation between the left and right sides of the brain for these tasks.

Implications

These findings suggest that when we imagine tastes, our brain uses a "top-down" approach where the prefrontal cortex helps retrieve taste memories, which then activate the insular cortex. This could help us understand how our experiences and memories influence our perception of taste, even when we're not actually eating.

Limitations

While the study provides valuable insights, it had a small sample size, which might limit the generalizability of the findings. Additionally, the study focused on specific brain regions, and other areas might also play a role in gustatory imagery.
In summary, this research sheds light on the complex processes our brain uses to imagine tastes, highlighting the important roles of the prefrontal and insular cortices. Understanding these processes could have implications for how we approach taste-related experiences and conditions.