title: The Brain Mechanisms Underlying the Perception of Pungent Taste of Capsaicin and the Subsequent Autonomic Responses.
abstract: In a human fMRI study, it has been demonstrated that tasting and ingesting capsaicin activate the ventral part of the middle and posterior short gyri (M/PSG) of the insula which is known as the primary gustatory area, suggesting that capsaicin is recognized as a taste. Tasting and digesting spicy foods containing capsaicin induce various physiological responses such as perspiration from face, salivation, and facilitation of cardiovascular activity, which are thought to be caused through viscero-visceral autonomic reflexes. However, this does not necessarily exclude the possibility of the involvement of higher-order sensory-motor integration between the M/PSG and anterior short gyrus (ASG) known as the autonomic region of the insula. To reveal a possible functional coordination between the M/PSG and ASG, we here addressed whether capsaicin increases neural activity in the ASG as well as the M/PSG using fMRI and a custom-made taste delivery system. Twenty subjects participated in this study, and three tastant solutions: capsaicin, NaCl, and artificial saliva (AS) were used. Group analyses with the regions activated by capsaicin revealed significant activations in the bilateral ASG and M/PSG. The fMRI blood oxygenation level-dependent (BOLD) signals in response to capsaicin stimulation were significantly higher in ASG than in M/PSG regardless of the side. Concomitantly, capsaicin increased the fingertip temperature significantly. Although there was no significant correlation between the fingertip temperatures and BOLD signals in the ASG or M/PSG when the contrast [Capsaicin-AS] or [Capsaicin-NaCl] was computed, a significant correlation was found in the bilateral ASG when the contrast [2 × Capsaicin-NaCl-AS] was computed. In contrast, there was a significant correlation in the hypothalamus regardless of the contrasts. Furthermore, there was a significant correlation between M/PSG and ASG. These results indicate that capsaicin increases neural activity in the ASG as well as the M/PSG, suggesting that the neural coordination between the two cortical areas may be involved in autonomic responses to tasting spicy foods as reflected in fingertip temperature increases.
authors.affiliation: Department of Neuroscience and Oral Physiology, Graduate School of Dentistry, Osaka UniversitySuita, Japan; Morinaga & Co., Ltd., YokohamaJapan.
authors.forename: Shinpei
authors.initials: S
authors.lastname: Kawakami
authors.affiliation: Department of Neuroscience and Oral Physiology, Graduate School of Dentistry, Osaka University Suita, Japan.
authors.forename: Hajime
authors.initials: H
authors.lastname: Sato
authors.affiliation: Division of Cerebral Integration, National Institute for Physiological SciencesOkazaki, Japan; Pathophysiological and Health Science Team, RIKEN Center for Life Science TechnologiesKobe, Japan; Department of Physiology, Graduate School of Medicine, Osaka City UniversityOsaka, Japan.
authors.forename: Akihiro T
authors.initials: AT
authors.lastname: Sasaki
authors.affiliation: Department of Psychology, Graduate School of Environmental Studies, Nagoya University Nagoya, Japan.
authors.forename: Hiroki C
authors.initials: HC
authors.lastname: Tanabe
authors.affiliation: Division of Cerebral Integration, National Institute for Physiological Sciences Okazaki, Japan.
authors.forename: Yumiko
authors.initials: Y
authors.lastname: Yoshida
authors.affiliation: Department of Neuroscience and Oral Physiology, Graduate School of Dentistry, Osaka UniversitySuita, Japan; Department of Oral Physiology, Graduate School of Medical and Dental Sciences, Kagoshima UniversityKagoshima, Japan.
authors.forename: Mitsuru
authors.initials: M
authors.lastname: Saito
authors.affiliation: Department of Neuroscience and Oral Physiology, Graduate School of Dentistry, Osaka University Suita, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Toyoda
authors.affiliation: Division of Cerebral Integration, National Institute for Physiological Sciences Okazaki, Japan.
authors.forename: Norihiro
authors.initials: N
authors.lastname: Sadato
authors.affiliation: Department of Neuroscience and Oral Physiology, Graduate School of Dentistry, Osaka University Suita, Japan.
authors.forename: Youngnam
authors.initials: Y
authors.lastname: Kang
keywords: autonomic function; capsaicin; fMRI; insular cortex; taste recognition
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