Spatiotemporal dynamics of word retrieval in speech production revealed by cortical high-frequency band activity

ABSTRACT

Word retrieval is core to language production and relies on complementary processes: the rapid activation of lexical and conceptual representations and word selection, which chooses the correct word among semantically related competitors. Lexical and conceptual activation is measured by semantic priming. In contrast, word selection is indexed by semantic interference and is hampered in semantically homogeneous (HOM) contexts. We examined the spatiotemporal dynamics of these complementary processes in a picture naming task with blocks of semantically heterogeneous (HET) or HOM stimuli. We used electrocorticography data obtained from frontal and temporal cortices, permitting detailed spatiotemporal analysis of word retrieval processes. A semantic interference effect was observed with naming latencies longer in HOM versus HET blocks. Cortical response strength as indexed by high-frequency band (HFB) activity (70–150 Hz) amplitude revealed effects linked to lexical-semantic activation and word selection observed in widespread regions of the cortical mantle. Depending on the subsecond timing and cortical region, HFB indexed semantic interference (i.e., more activity in HOM than HET blocks) or semantic priming effects (i.e., more activity in HET than HOM blocks). These effects overlapped in time and space in the left posterior inferior temporal gyrus and the left prefrontal cortex. The data do not support a modular view of word retrieval in speech production but rather support substantial overlap of lexical-semantic activation and word selection mechanisms in the brain.

AUTHORS

• Stephanie Ries

• Rhummit K. Dhillon

• Alex Clarke

• David King-Stephens

• Kenneth Laxer

• Peter Weber

• Rachel A. Kuperman

• Kurtis I. Auguste

• Peter Brunner

• Gerwin Schalk

• Jack J. Lin

• Josef Parvizi

• Nathan E. Crone

• Nina F. Dronkers

• Robert T. Knight

Date: 2017

DOI: 10.1073/pnas.1620669114

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Direct brain recordings reveal hippocampal rhythm underpinnings of language processing

ABSTRACT

Language is classically thought to be supported by perisylvian cortical regions. Here we provide intracranial evidence linking the hippocampal complex to linguistic processing. We used direct recordings from the hippocampal structures to investigate whether theta oscillations, pivotal in memory function, track the amount of contextual linguistic information provided in sentences. Twelve participants heard sentences that were either constrained (“She locked the door with the”) or unconstrained (“She walked in here with the”) before presentation of the final word (“key”), shown as a picture that participants had to name. Hippocampal theta power increased for constrained relative to unconstrained contexts during sentence processing, preceding picture presentation. Our study implicates hippocampal theta oscillations in a language task using natural language associations that do not require memorization. These findings reveal that the hippocampal complex contributes to language in an active fashion, relating incoming words to stored semantic knowledge, a necessary process in the generation of sentence meaning.

AUTHORS

• Vitoria Piai

• Kristopher L. Anderson

• Jack J. Lin

• Callum Dewar

• Josef Parvizi

• Nina F. Dronkers

• Robert T. Knight

Date: 2016

DOI: www.pnas.org/cgi/doi/10.1073/pnas.1603312113

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