The expressive power of language lies in its ability to construct an infinite array of ideas out of a finite set of pieces. Surprisingly, few neurolinguistic investigations probe the basic processes that constitute the foundation of this ability, choosing instead to focus on relatively complex combinatorial operations. Contrastingly, in the present work, we investigate the neural circuits underlying simple linguistic composition, such as required by the minimal phrase "red boat." Using magnetoencephalography, we examined activity in humans generated at the visual presentation of target nouns, such as "boat," and varied the combinatorial operations induced by its surrounding context. Nouns in minimal compositional contexts ("red boat") were compared with those appearing in matched noncompositional contexts, such as after an unpronounceable consonant string ("xkq boat") or within a list ("cup, boat"). Source analysis did not implicate traditional language areas (inferior frontal gyrus, posterior temporal regions) in such basic composition. Instead, we found increased combinatorial-related activity in the left anterior temporal lobe (LATL) and ventromedial prefrontal cortex (vmPFC). These regions have been linked previously to syntactic (LATL) and semantic (vmPFC) combinatorial processing in more complex linguistic contexts. Thus, we suggest that these regions play a role in basic syntactic and semantic composition, respectively. Importantly, the temporal ordering of the effects, in which LATL activity (ϳ225 ms) precedes vmPFC activity (ϳ400 ms), is consistent with many processing models that posit syntactic composition before semantic composition during the construction of linguistic representations.

Language is experienced primarily through one of two mediums--spoken words and written text. Although substantially different in form, these two linguistic vehicles possess similar powers of expression. Consequently, one goal for the cognitive neuroscience of language is to determine where, if anywhere, along the neural path from sensory stimulation to ultimate comprehension these two processing streams converge. In the present study, we investigate the relationship between basic combinatorial operations in both reading and listening. Using magnetoencephalography, we measured neural activity elicited by the comprehension of simple adjective-noun phrases (red boat) using the same linguistic materials and tasks in both modalities. The present paradigm deviates from previous cross-modality studies by investigating only basic combinatorial mechanisms--specifically, those evoked by the construction of simple adjective-noun phrases. Our results indicate that both modalities rely upon shared neural mechanisms localized to the left anterior temporal lobe (lATL) and left angular gyrus (lAG) during such processing. Furthermore, we found that combinatorial mechanisms subserved by these regions are deployed in the same temporal order within each modality, with lATL activity preceding lAG activity. Modality-specific combinatorial effects were identified during initial perceptual processing, suggesting top-down modulation of low-level mechanisms even during basic composition.

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Human language, as well as birdsong, relies on the ability to arrange vocal elements in novel sequences. However, little is known about the ontogenetic origin of this capacity. We tracked the development of vocal combinatorial capacity in three species of vocal learners, combining an experimental approach in zebra finches with an analysis of natural development of vocal transitions in Bengalese finches and pre-lingual human infants and found a common, stepwise pattern of acquiring vocal transitions across species. In our first study, juvenile zebra finches were trained to perform one song and then the training target was altered, prompting the birds to swap syllable order, or insert a new syllable into a string. All birds solved these permutation tasks in a series of steps, gradually approximating the target sequence by acquiring novel pair-wise syllable transitions, sometimes too slowly to fully accomplish the task. Similarly, in the more complex songs of Bengalese finches, branching points and bidirectional transitions in song-syntax were acquired in a stepwise manner, starting from a more restrictive set of vocal transitions. The babbling of pre-lingual human infants revealed a similar developmental pattern: instead of a single developmental shift from reduplicated to variegated babbling (i.e., from repetitive to diverse sequences), we observed multiple shifts, where each novel syllable type slowly acquired a diversity of pair-wise transitions, asynchronously over development. Collectively, these results point to a common generative process that is conserved across species, suggesting that the long-noted gap between perceptual versus motor combinatorial capabilities in human infants1 may arise from the challenges in constructing new pair-wise transitions.

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