Gut Taste Stimulants Alter Brain Activity in Areas Related to Working Memory: a Pilot Study

Abstract

Background/Aims: Taste perception is one of the most important primary oral reinforcers, driving nutrient and energy intake as well as toxin avoidance. Taste receptors in the gastrointestinal tract might as well impact appetitive or aversive behavior and thus influence learning tasks and a close relation of neural taste processing and working memory networks seems plausible. Methods: In the present pilot study, we determined the effects of five taste qualities “bitter” (quinine), “sweet” (glucose), “sour” (citric acid), “salty” (NaCl) and “umami” (monosodium glutamate, MSG) on working memory processing using functional MRI and their effect on plasma insulin and glucose levels. On six separate occasions, subjects received one of the following test substances dissolved in 200 mL tap water via a nasogastric tube (to circumvent the oral cavity): 1) 2g citric acid corresponding to 52 mM, 2) 2g NaCl; 171 mM, 3) 0.017g quinine; 0.26 mM, 4) 1g monosodium glutamate; 30 mM, 5) 25g glucose; 694 mM and 6) 200 mL tap water (placebo). Results: The taste qualities “bitter” and “umami” significantly altered brain activation patterns in the primary gustatory cortex as well as in subcortical structures, previously reported to be involved in emotional learning and memory. In contrast, glucose did not reveal any statistically significant brain activation difference. Working memory performance was not different over the six treatments. Plasma insulin and glucose levels were not affected by the different taste substances (MSG, quinine, NaCl and citric acid). Conclusions: in this pilot trial, we demonstrate that acute intragastric administration of different taste substances does not affect working memory performance in humans. However, “umami” and “bitter” have effects on brain areas involved in neural working memory, overpowering the effects of “sweet”, “salty” and “sour” reception.

Free l-glutamate-induced modulation in oxidative and neurochemical profile contributes to enhancement in locomotor and memory performance in male rats

“…Present findings showed that chronic supplementation of free Glu at adequate amount enhances memory performance leading to improved spatial, recognition and associative memory processes. These findings are in agreement with the recent study which observed that umami taste in GI is responsible for stimulation of cortical and sub-cortical brain areas that are linked to working memory 40 . Moreover, studies showed that the effect of Glu depends upon its dosage.…”

A Review of the Alleged Health Hazards of Monosodium Glutamate

“…An existing relation between neural taste processing and working memory networks was hypothesized (Meyer‐Gerspach et al., ). Administration of 1 g MSG as a 30 mM solution, via a nasogastric tube, significantly altered brain activation patterns in the primary gustatory cortex, as well as in subcortical structures, previously reported to be involved in emotional learning and memory.…”

“…Nevertheless, working memory performance was unaffected (Meyer-Gerspach et al, 2016). This aspect is important in establishing whether flavor enhancers have some bearing on affective responses and possibly behavior, thereby causing food overconsumption (Meyer-Gerspach et al, 2016).…”

Brain Imaging of Taste Perception in Obesity: a Review

“…While chemosensory stimuli interact with TRCs in the tongue to generate taste perception in the brain, taste also results from the interaction of chemosensory stimuli with extraoral TRCs, including those in the gastrointestinal (GI) tract [ 128 – 130 ]. Although their function continues to be explored, GI taste receptors (i.e., sweet, bitter, fat, and amino acid receptors) appear to modulate satiety hormones [ 131 – 135 ].…”

“…Intragastric administration of quinine and/or MSG can alter brain activation patterns in regions (insula, subcortical limbic and memory structures, homeostatic and hedonic centers) that regulate food intake [ 129 , 130 ]. Further, intragastric administration of quinine can lead to lower hunger scores and hedonic eating, which were associated with changes in orexigenic and satiety gut hormone levels [ 128 , 138 , 139 ].…”