Neural representation of word categories is distinct in the temporal lobe: An activation likelihood analysis

Abstract

The distinction between nouns and verbs is a language universal. Yet, functional neuroimaging studies comparing noun and verb processing have yielded inconsistent findings, ranging from a complete frontal(verb)-temporal(noun) dichotomy to a complete overlap in activation patterns. The current study addressed the debate about neural distinctions between nouns and verbs by conducting an activation likelihood estimation (ALE) meta-analysis of probabilistic cytoarchitectonic maps. Two levels of analysis were conducted: simple effects (Verbs vs. Baseline, Nouns vs. Baseline), and direct comparisons (Verbs vs. Nouns, Nouns vs. Verbs). Nouns were uniquely associated with a left medial temporal cluster (BA37). Activation foci for verbs included extensive inferior frontal (BA44-47) and mid-temporal (BA22, 21) regions in the left hemisphere. These findings confirm that the two grammatical classes have distinct neural architecture in supra-modal brain regions. Further, nouns and verbs overlapped in a small left lateral inferior temporal activation cluster (BA37), which is a region for modality-independent, grammatical class-independent lexical representations. These findings are most consistent with the view that as one acquires language, linguistic representations for a lexical category shift from the modality specific cortices which represent prototypical members of that category (e.g., motion for verbs) to abstract amodal representations in close proximity to modality specific cortices.

Keywords: Broca's area; fusiform gyrus; middle temporal; nouns; semantics; verbs.

Figure 1

ALE foci for the five analyses at a threshold of p < .01. (a) Nouns minus baseline, (b) verbs minus baseline, (c) nouns minus verbs, (d) verbs minus nouns, and (e) conjunction of nouns and verbs. The MNI coordinates for each analysis are given in Table 1 and the z coordinates are noted on each figure panel. The figure was generated using mango image viewer (Lancaster & Martinez, 2015) [Color figure can be viewed at http://wileyonlinelibrary.com]

Figure 2

A three‐dimensional view of the left hemisphere showing the relative location of the activation clusters of the direct effects (a) and conjunction (b) analyses. Green = verbs vs. nouns, clusters are in BA44/45 and BA 21, blue = nouns vs. verbs, showing cluster in BA 37, red/yellow = conjunction of verbs and nouns, showing a cluster in BA 37. A comparison of noun (a) and conjunction (b) clusters shows that noun cluster (x = −50) is medial to the conjunction cluster (x = −29.2). The figure was generated using mango image viewer (Lancaster & Martinez, 2015) [Color figure can be viewed at http://wileyonlinelibrary.com]