Differences in Brain Responses to Food or Tastants Delivered with and Without Swallowing: a Meta-analysis on Functional Magnetic Resonance Imaging (fMRI) Studies

Introduction This study aimed to meta-analyze the functional magnetic resonance imaging (fMRI) data and compare the brain activations from gustatory studies with different stimulus delivery methods. Methods Published fMRI studies were included into the analysis if they evaluated the brain responses to liquid tastants or food among healthy subjects. Studies were coded into three groups: stimulus removed from the mouth by suction without the need to swallow, swallowing without controlling for its confounds, and swallowing with controlling for its confounds. Results Forty-five studies that comprised of a total of 1498 participants fulfilled the inclusion criteria. Suction studies activated the posterior cingulate. Swallowing studies covered multiple brain regions including the anterior and middle insula, the precentral gyrus, and the postcentral gyrus. Conclusions For the contrast analysis between swallowing studies with and without controlling for the confounds, the former group had larger brain activation mainly at the anterior and middle insula and the thalamus, whereas the latter group had larger brain activation mainly at the anterior cingulate, precentral gyrus, and postcentral gyrus. Implications Compared to studies that did not control for confounds of swallowing, studies that controlled for swallowing demonstrated heightened responses at the insula and reduced responses at the sensorimotor cortex.