On the pursuit of the brain network for proto-syntactic learning in non-human primates: conceptual issues and neurobiological hypotheses

Songbirds have become impressive neurobiological models for aspects of human verbal communication because they learn to sequence their song elements, analogous, in some ways, to how humans learn to produce spoken sequences with syntactic structure. However, mammals such as non-human primates are considered to be at best limited-vocal learners and not able to sequence their vocalizations, although some of these animals can learn certain 'artificial grammar' sequences. Thus, conceptual issues have slowed the progress in exploring potential neurobiological homologues to language-related processes in species that are taxonomically closely related to humans. We consider some of the conceptual issues impeding a pursuit of, as we define them, 'proto-syntactic' capabilities and their neuronal substrates in non-human animals. We also discuss ways to better bridge comparative behavioural and neurobiological data between humans and other animals. Finally, we propose guiding neurobiological hypotheses with which we aim to facilitate the future testing of the level of correspondence between the human brain network for syntactic-learning and related neurobiological networks present in other primates. Insights from the study of non-human primates and other mammals are likely to complement those being obtained in birds to further our knowledge of the human language-related network at the cellular level.