Human brain language areas identified by functional magnetic resonance imaging

Abstract

Functional magnetic resonance imaging (FMRI) was used to identify candidate language processing areas in the intact human brain. Language was defined broadly to include both phonological and lexical-semantic functions and to exclude sensory, motor, and general executive functions. The language activation task required phonetic and semantic analysis of aurally presented words and was compared with a control task involving perceptual analysis of nonlinguistic sounds. Functional maps of the entire brain were obtained from 30 right-handed subjects. These maps were averaged in standard stereotaxic space to produce a robust "average activation map" that proved reliable in a split-half analysis. As predicted from classical models of language organization based on lesion data, cortical activation associated with language processing was strongly lateralized to the left cerebral hemisphere and involved a network of regions in the frontal, temporal, and parietal lobes. Less consistent with classical models were (1) the existence of left hemisphere temporoparietal language areas outside the traditional "Wernicke area," namely, in the middle temporal, inferior temporal, fusiform, and angular gyri; (2) extensive left prefrontal language areas outside the classical "Broca area"; and (3) clear participation of these left frontal areas in a task emphasizing "receptive" language functions. Although partly in conflict with the classical model of language localization, these findings are generally compatible with reported lesion data and provide additional support for ongoing efforts to refine and extend the classical model.

Fig. 1.

Top. FMRI activation map for the tone decision–rest comparison. The data are presented as sequential sagittal sections from left to right, with the stereotaxic coordinate x-axis,L–R given for each section (see Talairach and Tournoux, 1988). The anteroposterior commissural line (y-axis) and vertical AC line (z-axis) are shown in green. Activated voxels are shown superimposed on stereotaxically averaged anatomical brain images. Probability values for these voxels are coded using the color scale at bottom. One centimeter tick marks are provided to help relate the large activation regions to Talairach and Tournoux (1988). Structures showing bilateral activation include the STG and planum temporale, the supramarginal gyrus, premotor cortex and SMA, midanterior cingulate gyrus, anterior insula, anterior putamen, thalamus, midbrain, and posterior cerebellum. Modest right hemisphere lateralization is evidenced by right unilateral activation in the IFG and MTG and by relative rightward asymmetry in most of the other activated regions.

Fig. 3.

Top. Language areas identified in a 26-year-old male subject. Activated areas in the left hemisphere include STS and MTG (L56), ITG (L56-44), fusiform gyrus (L44), angular gyrus (L56-32), IFG (L56-44), rostral and caudal middle frontal gyrus (L44-32), superior frontal gyrus (L20-8), anterior cingulate (L8), and perisplenial cortex/precuneus (L8). The right posterior cerebellum is activated, as are small foci in right dorsal prefrontal cortex and right angular gyrus.