Unveiling the brain's spatio-temporal processing of salt habituation using high-density EEG

Better understanding the multifactorial facets of salt perception over the course of a meal is crucial to set novel daily consumption strategies and formulate recommendations. We investigated whether habituation to salt (NaCl) and adaptation would occur within a controlled design, ideal to observe habituation (2 min of short pulses) and within a second more realistic design closer to bites time-frame (20 s continuous in-mouth stimulation) using High-Density Electroencephalography in healthy human adults. In the first design, a slight habituation to salt occurred as saltiness intensity decreased after 20 stimulations of 500 ms every 3 s. However, habituation was not complete after 40 repetitions and perceived saltiness intensity only slightly decreased, although one minute to recover full taste capacities was given. The EEG analysis showed that the mean and max amplitude of early ERP components P1, identified using microstate analysis (130-350 ms after the stimulation onset), were higher before than after habituation over the frontal ROI and were associated with reduced activity in the middle temporal gyrus. These results demonstrated that habituation leads to reduced activity in early processing stages likely in temporal areas adjacent to the primary gustatory cortical areas. In the second design, the frequency analysis revealed that slow oscillations could be associated with NaCl adaptation as we identified a decrease of delta oscillations through time (from 1 to 10 s approximately after the stimulation onset) for both frontal and central midline areas. Source estimation suggests that adaptation is associated with an overall decrease of both frontal and temporal cortical generator activities. Combined with the absence of a clear late ERP component in the first design, taste habituation processing could have both a peripheral and central origin.