The lateralization of gustatory function and the flow of information from tongue to cortex

Controversy surrounds whether crossed and/or uncrossed fibers carry taste information from tongue to cortex and whether there is hemispheric specialization for gustatory processing. The current study examined these issues in 14 patients with unilateral insula lesions, seven with right-sided and seven with left-sided damage, and in 42 healthy controls. Two tasks were carried out, with tastants applied unilaterally to the tongue tip: (1) taste discrimination; and (2) stimulus sampling followed by judgments of quality, intensity, hedonics and name-recognition, for sweet, salty, bitter and sour tastants. Controls were better at discriminating tastants applied to their right tongue tip relative to their left, and better at taste quality judgments when tastants were applied to their left tongue tip relative to their right. Insula lesions to the left or right side resulted in bilateral impairments in discrimination, quality judgments and naming, when compared to controls. However, the Left insula group was poorer on tasks involving salt, and for ipsilateral hedonic judgments, relative to controls and the Right insula group. These findings are consistent with gustatory information ascending from tongue to cortex both ipsilaterally and contralaterally, and provide preliminary support for hemispheric gustatory specialization.