[Paper Review] Amygdala and insula contributions to dorsal-ventral pathway integration in the prosodic neural network

David I. Leitman, Chris J. Edgar+4 more|arXiv (Cornell University)|Nov 5, 2016

Phonetics and Phonology Research23 references3 citations

TL;DR

This study demonstrates that the amygdala and insula play critical roles in integrating dorsal (speech motor/articulation) and ventral (emotional prosody perception) pathways within the prosodic neural network. Using magnetoencephalography and diffusion MRI, it reveals dynamic amygdala-cortical functional connectivity, direct structural pathways from amygdala to STG/IFG via a ventral route, and robust amygdala-insula functional and structural connections that may integrate emotional prosody into speech planning systems.

ABSTRACT

Speech prosody enables communication of emotional intentions via modulation of vocal intonations. Reciprocal interactions between superior temporal (STG) and inferior frontal gyri (IFG) have been shown to anchor a neural network for prosodic comprehension, which we refer to as the Prosody Neural Network (PNN). Although the amygdala is critical for socio-emotional processing, its integral functional and structural role in processing social information from speech prosody as well as its role in the PNN is largely unexplored including inconsistent recent empirical findings. Here, we used magnetoencephalography and diffusion magnetic resonance imaging of white-matter pathways to establish that the PNN is characterized by (1) a robust amygdala-cortical functional connectivity that dynamically evolves as prosodic interpretation progresses, (2) direct structural fiber connections between amygdala and STG/IFG traversing a ventral white-matter pathway, and (3) robust amygdala-insula functional connectivity and structural insula fiber projections to arcuate STG-IFG connections. These findings support a role for functional and structural amygdala-centric ventral pathways in combining speech features to form prosodic percepts. They also highlight insula contributions to prosodic comprehension, potentially via vertical integration of amygdala-centric ventral processing into dorsal pathways responsible for prosodic motor articulation and speech planning.

Motivation & Objective

• To clarify the functional and structural roles of the amygdala in processing emotional prosody within the prosodic neural network (PNN).
• To investigate the existence and significance of direct white-matter pathways connecting the amygdala to key prosody regions (STG and IFG).
• To examine the contribution of the insula to integrating emotional processing (via amygdala) with motor and articulatory systems in prosodic comprehension.
• To resolve inconsistencies in prior empirical findings on amygdala involvement in prosodic processing.

Proposed method

• Employed magnetoencephalography (MEG) to measure dynamic functional connectivity between the amygdala, insula, STG, and IFG during prosodic comprehension tasks.
• Used diffusion magnetic resonance imaging (dMRI) to map white-matter structural pathways connecting the amygdala to STG and IFG via a ventral pathway.
• Analyzed functional connectivity patterns over time to assess how amygdala-cortical interactions evolve during prosodic interpretation.
• Mapped structural fiber tracts from the insula to the arcuate fasciculus, linking it to dorsal pathway components (STG-IFG connections).
• Combined neuroimaging data to test hypotheses about ventral pathway integration of emotional prosody into speech motor systems.
• Applied advanced image processing and tractography techniques to identify and validate subcortical-cortical connections.

Experimental results

Research questions

• RQ1 Does the amygdala exhibit dynamic functional connectivity with cortical regions during prosodic comprehension, and how does this evolve over time?
• RQ2 Are there direct structural white-matter pathways connecting the amygdala to the superior temporal gyrus and inferior frontal gyrus?
• RQ3 What is the role of the insula in linking amygdala-mediated emotional processing with dorsal pathway systems for speech articulation?
• RQ4 How do functional and structural connections between the amygdala, insula, and dorsal-ventral pathway hubs support prosodic perception?
• RQ5 To what extent does the insula serve as a vertical integrator of emotional prosody into motor planning networks?

Key findings

• The amygdala shows robust, time-evolving functional connectivity with the STG and IFG during prosodic interpretation, indicating dynamic integration into the PNN.
• Direct structural fiber tracts were identified connecting the amygdala to the STG and IFG through a ventral white-matter pathway, supporting a structural basis for emotional prosody processing.
• The insula exhibits strong functional connectivity with the amygdala, suggesting a role in emotional salience integration.
• Structural projections from the insula to the arcuate fasciculus were confirmed, linking insular processing to dorsal pathway systems for speech planning.
• The findings support a model in which the amygdala and insula form a ventral pathway that integrates emotional prosody into dorsal motor and articulatory systems.
• The study provides neuroanatomical and functional evidence for a dual-pathway integration model in prosodic processing, resolving prior inconsistencies in amygdala function.