Imaging and Genomic Classification of Brain Alteration Induced By Gustatory Bitter Stimulus, A Pilot Study

Objectives: Despite the exhaustive information concerning the role of physiological structures involved in gustatory stimuli, there is still a need to clarify as to whether the gustatory sense is processed in the human brain and how different kind of gustatory stimuli affect brain areas involved in taste processing. To characterize the networks that can be involved in shaping the properties of the gustatory pathways. Materials and Methods: In this fMRI study we investigated two populations characterized by their opposite response (sensitive/non-sensitive) to bitter gustatory stimulus induced by propylthiouracil molecule (PROP). In the MRI experiment PROP was delivered to the subjects by an impregnated filter paper disk. The individuals recruited for this study are 5 super-testers and 8 non-testers to the bitter stimulus. The procedure defines two different groups of subjects “non-taster” and super-taster” which take part to the fcMRI experimental stud Functional data, acquired by a GE Medical Signa 1.5Tesla HD Optima Scanner, were processed with SPM12 toolbox and network pathways were analysed using the CONN toolbox. The general linear model (GLM) technique was applied by allowing for statistical evaluation of activation. Low oscillation of Bold signals [0.09:0.9 Hz] time series were processed by calculating the semi partial correlation index between voxels; the integrated connectivity contrast measure was applied for connectivity map calculation. All contrasts were examined with a voxel wise t-test (p<0.05 uncorrected). We examined activations using the four hubs of the Default Mode Network of the brain, as crucial seeds for the connectivity analysis. A dissimilarity contrast matrix between non-taster e super-tester subjects (between-subjects contrast) and between the two conditions of the bitter stimulus submission and no stimulus submission adopted in the fMRI experiment was created. DMN ROIs projection towards the Brodmann areas were detected with t-test significance test. Results: In our fMRI study the areas of Insula, Cingulate Cortex, Somatosensory Associative Cortex, Entorhinal Cortex, Premotor Cortex Area are correlated to the four DMN areas during the bitter stimuli processing more in super tester than in the control population. Discussion: The bitter taste is differently processed by the two groups of supertasters and non-testers and our results suggests further tests, increasing the population and making different hypothesis in order to encompass the main gustatory pathways and their correlations and differentiation in processing and interpreting gustatory information. Conclusion: It seems likely that further studies are needed to address the possible reasons of this difference between these population. A working hypothesis can privilege an evolutionary differentiation between these two populations, as the correct appreciation of bitter taste can be an advantageous step in peering through possible dangerous tastes in a primitive setting.