SYNTAX

Neurophysiology of birdsong syntax perception

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 Obiettivo del progetto (Objective)

'Like human language, birdsong is hierarchically organized according to particular syntactic constraints (phonological syntax). Interestingly, birds have also been shown to posses impressive capabilities in recognizing syntactic patterns, even artificial ones, which makes them an attractive, but as yet virtually unexplored, model for research into the neural underpinnings of syntax perception. To address this issue at the neurophysiological level, I propose to apply a high-density electrical neuroimaging technique, based on an array of intracerebral electrodes that measure action potential activity from 64 sites simultaneously, to record activity in auditory and song system nuclei during stimulation with artificial, song-like sequences. First, I will identify cortical areas that are sensitive to short term history of syllables and investigate whether the time scales at which such sensitivity is observed, matches with those necessary for syntax recognition. Second, I will test which types of short-term history sensitivity are involved. I hypothesize the involvement of both acoustic feature-specific adaptation and a distinctly different syllable-specific form of adaptation, where the former may be a causal factor in enabling the latter. Furthermore, I will test for a third form of short-term history sensitivity that has been proposed to be responsible for deviance detection as reflected in mismatch negativity (MMN) in human EEG, and that has been linked to syntactic processing of language. Together, the results may provide support for the hypothesis that phonological syntax is in part represented in activation signatures that reflect time-varying, short-term predictability of syllable occurrence within a sequence. This highly interdisciplinary project lies at the intersection of behavioural neurobiology and linguistics, and should yield an animal model system for the study of neural processes that may also underlie syntax processing in the human brain.'

Introduzione (Teaser)

Birdsong exhibits phonological syntax in which sounds are put together in an organised syntactic structure that produces meaning. The first use of electrodes to study sequence rule learning in non-human animals has shed light on neural mechanisms.

Descrizione progetto (Article)

Birds are particularly adept at recognising syntactic patterns. Scientists set out to investigate potential similarities in neuronal processing of syntax between birds and humans with EU funding of the project SYNTAX (Neurophysiology of birdsong syntax perception). Using an array of 64 intracerebral electrodes, researchers recorded electrical activity from populations of neurons in auditory and song system nuclei during stimulation with artificial song-like sequences.

The team used the zebra finch, a widely studied animal model of speech and language-related neural mechanisms. Due to the nature of the experiment, it was performed under anaesthesia, specifically isoflurane. This anaesthetic induces a sleep-like state in which primary and secondary cortical areas still respond in a stimulus-specific way to complex sequences, including natural song.

Unexpectedly, researchers identified spontaneous travelling waves of both individual (action potential) and population (field potential) activity throughout most of the forebrain, both inside and external to auditory areas. This activity has also been seen in the cerebral neocortex.

Researchers then investigated changes in this activity in auditory cortex as a result of stimulation using artificial sound sequences based on natural song syllables. One of the most important project results was the finding that the zebra finch exhibits both memory-based stimulus-specific adaptation and rule learning. Until now, the sequence rule learning that is key for human syntax capabilities has only been studied behaviourally in non-human animals with highly controversial results.

SYNTAX went on to identify neural response patterns consistent with neural processes that involve prediction of future input based on short-term rule learning. In other words, this activity could reflect short-term predictability of syllable occurrence within a sequence.

The results expand the utility of the zebra finch animal model to include a role as a comparative neural model system for syntactic rule learning. They could also lead to better understanding of changes in evoked responses reflecting a change in expected stimulus sequence (mismatch negativity). The phenomenon has been implicated in a number of cognitive functions and has been linked to disorders including dyslexia and psychiatric diseases. Establishment of an animal model of syntactic rule learning will no doubt have broad-reaching impact.