A cortical-subcortical syntax pathway linking Broca's area and the striatum

Area of Science:

• Neuroscience
• Linguistics
• Cognitive Science

Background:

• Cortical regions like Broca's area and temporal cortices, along with subcortical structures like the striatum, are known to support combinatorial syntax.
• Existing models focus on cortico-cortical tracts (e.g., arcuate fasciculus) but the striatum's integration into syntax networks remains unclear.

Purpose of the Study:

• To investigate the existence and syntactic function of a deep Broca-striatum pathway.
• To determine if this pathway contributes to syntactic processing and extends current syntax network models.

Main Methods:

• Employed a stepwise approach using voxel-based lesion-symptom mapping (VLSM) on 15 healthy controls and 12 patients with frontal/striatal lesions performing syntax tests.
• Overlapped significant VLSM clusters with probabilistic language tract maps (arcuate, extreme capsule fiber system, uncinate, aslant, Broca-striatum).
• Conducted quantitative analysis of tract-lesion overlap and correlation with syntactic processing scores.

Main Results:

• Identified a significant Broca-striatum tract linking Broca's area (BA45) with the left caudate head.
• This tract overlapped with VLSM clusters associated with complex syntax.
• Lesion load in the Broca-striatum tract correlated significantly with complex syntax scores, unlike other investigated tracts.

Conclusions:

• Established the existence and syntactic relevance of a deep Broca-caudate pathway.
• This finding extends current syntax-network models by incorporating a novel frontostriatal circuit.
• Results support functional accounts of frontostriatal circuits in language processing.