Ultra-high-field fMRI study of insular discrimination of taste quality and perceived taste valence

The human primary gustatory cortex (hPGC) resides in the insula. How this region processes and represents taste stimuli is still under investigation. Here we use ultra-high field (7 Tesla) fMRI to investigate whether the insular cortex discriminates the five basic tastes (quality) and the perceived valence of the tastes. Eight healthy young volunteers rated the valence (positive, negative and neutral) of a series of tastants delivered as small liquid boluses via a gustometer during a preliminary off-line intake session. Functional acquisition was set up to fully cover the insular cortex at high isometric spatial resolution. Using multivariate analyses and the searchlight method, multi-class discrimination accuracy for all basic tastes and their rated valence were assessed separately for each participant. Distinct patterns representing each basic taste could be decoded above chance across several clusters within the middle and posterior insular bilaterally, despite a high degree of spatial variability across participants. Overall, valence decoding was weaker, and the resulting significant clusters showed generally low overlap with those obtained from taste-quality decoding. In agreement with prior reports, these results suggest that taste quality might be encoded in the insular cortex according to individual functional response patterns rather than to an anatomically consistent chemotopic arrangement. Albeit preliminary, this analysis extends this notion by proposing that taste quality and valence are represented by distinct insular cortical clusters.