Reworking the language network

Abstract

Prior investigations of functional specialization have focused on the response profiles of particular brain regions. Given the growing emphasis on regional covariation, we propose to reframe these questions in terms of brain 'networks' (collections of regions jointly engaged by some mental process). Despite the challenges that investigations of the language network face, a network approach may prove useful in understanding the cognitive architecture of language. We propose that a language network plausibly includes a functionally specialized 'core' (brain regions that coactivate with each other during language processing) and a domain-general 'periphery' (a set of brain regions that may coactivate with the language core regions at some times but with other specialized systems at other times, depending on task demands). Framing the debate around network properties such as this may prove to be a more fruitful way to advance our understanding of the neurobiology of language.

Keywords: cognitive control; domain generality; domain specificity; fMRI; language network.

Figure 1. Hypothetical network configurations

A schematic illustration of several hypothetical network configurations (for b and d, we show network configurations at two different time points). Single-color nodes represent functionally specific brain regions (i.e., regions that are selectively engaged by a particular mental process); multiple-color nodes represent domain-general brain regions (i.e., regions with functionally diverse responses). 1a. Two networks composed of functionally specific brain regions, and one network composed of domain-general brain regions, with no interaction between the networks. 1b. No functionally specific brain regions; all brain regions are domain-general but combine in different ways to solve different tasks. 1c. Two networks composed of functionally specific brain regions, and one network composed of domain-general brain regions, with one node of the latter serving as a “hub” via which the specialized networks can interact with the domain-general network. 1d. Two networks composed of functionally specific brain regions, and one network composed of domain-general brain regions. The latter can combine with either of the two specialized networks at different times, thus becoming the “periphery” of the pink network at t=1, and of the green network at t=2.

Figure 2. The language network under different definitions

a) A schematic depiction of five sets of brain regions that are sometimes included in the language network: red = the classic high-level language processing regions; yellow = speech perception regions; green = visual word-form area; pink = speech articulation regions; and blue = cognitive control regions. b) A schematic illustration of possible definitions of the language network, ranging from very liberal (1) to more conservative (2 and 3).