Neuroimaging of Language: Why Hasn't a Clearer Picture Emerged?

Abstract

Two broad questions have driven dozens of studies on the neural basis of language published in the last several decades: (i) Are distinct cortical regions engaged in different aspects of language? (ii) Are regions engaged in language processing specific to the domain of language? Neuroimaging has not yet provided clear answers to either question. In this paper, we discuss one factor that is a likely contributor to the unclear state of affairs in the neurocognition of language, and that, in our opinion, has not received sufficient attention in the recent literature. In particular, fMRI studies of language have relied, almost exclusively, on group analyses, in which data from multiple individuals are co-registered to and analyzed in a common space. We argue that this approach can obscure functional specificity because of the anatomical variability across individual brains, and we advocate the use of an alternative approach -the functional localization approach -that circumvents this problem.

Functional specificity in the human brain: A window into the functional architecture of the mind

“…Already, the evidence is strong for cortical regions that are selectively engaged in the perception of faces, places, bodies, and words and another region for thinking about what other people are thinking. Possible cortical specializations for other domains, including aspects of number (100), music (101), and language (70), are under active investigation. The possibility is within reach of obtaining a cognitively precise parts list for the human brain.…”

“…Group analyses underestimate functional specificity, because different individuals' brains are anatomically quite different from each other, so alignment across brains is necessarily imperfect. As a result, functionally different regions will sometimes be aligned to the same location in the group space (70,71). Fedorenko and I are now revisiting the question of functional specificity of the language system using the same individual-subject ROI method that has enabled us to discover the functional specificity of the other regions described above.…”

Functional specificity for high-level linguistic processing in the human brain

“…Nonlinguistic tasks. In experiment 1 (math), participants (n = 11) saw a number (11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(30) and added three addends to it (of sizes two to four or six to eight in the easy and hard conditions, respectively). † After each trial, participants had to choose the correct sum in a two-choice forced choice question (the incorrect sum deviated by one to two).…”

“…Even when two tasks are compared in the same group of subjects, standard functional MRI group analysis methods can be deceptive: two different mental functions that activate neighboring but nonoverlapping cortical regions in every subject individually can produce overlapping activations in a group analysis, because the precise locations of these regions vary across subjects (24)(25)(26), smearing the group activations. Definitively addressing the question of neural overlap between linguistic and nonlinguistic functions requires examining overlap within individual subjects (27,28), a data analysis strategy that has almost never been applied in neuroimaging investigations of high-level linguistic processing.…”

Processing structure in language and music: a case for shared reliance on cognitive control

“…Although musical manipulations do activate "language regions" in frontal cortex (e.g., Koelsch et al, 2005b;Minati et al, 2008;Seger et al, 2013;Tillmann et al, 2006;Vuust et al, 2011), these fMRI studies have not examined musical and linguistic manipulations in the same participants, and thus do not necessarily show that the same neural regions are involved in the processing of musical and linguistic structure (cf. Fedorenko & Kanwisher, 2009). In fact, most of the few recent studies that have included within-subjects comparisons of linguistic and musical manipulations have not found substantial overlap between neural regions implicated in the processing of language and music (but see Abrams et al, 2011).…”