Brain Regions Involved in Dysarthria
Dysarthria results from damage to multiple brain regions that control speech musculature, with the most commonly implicated areas being the pons, corona radiata, cerebellum, and posterior insula 1, 2.
Primary Neuroanatomical Locations
The brain regions causing dysarthria vary by lesion location and can be categorized into supratentorial and infratentorial structures:
Infratentorial Lesions (Most Common)
- Pons: The most frequently affected region (n=142 in systematic review), causing dysarthria through damage to corticobulbar pathways that control speech musculature 2
- Cerebellum: Second most common infratentorial site (n=64), particularly:
- Lobulus simplex and lobulus quadrangularis in the upper cerebellum are critical for coordinated speech production 3
- Cerebellar lesions produce ataxic dysarthria with characteristic irregular articulatory breakdowns
Supratentorial Lesions
- Corona radiata: Second most common overall location (n=104), disrupting descending motor pathways to bulbar musculature 2
- Posterior insula (bilateral): Voxel-lesion behavior mapping demonstrates that both right and left posterior insular cortex damage directly causes dysarthria through disruption of extensive somatosensory and motor connections involved in speech motor execution 4
- Left middle frontal gyrus: Small cortical infarctions here can cause pure dysarthria by secondarily compromising cortical areas connected to the corticobulbar tract 5
Cortical Morphological Changes
Recent advanced neuroimaging reveals specific cortical alterations in dysarthric patients 6:
- Bilateral insula: Increased fractal dimension and gyrification
- Superior temporal gyrus: Elevated gyrification bilaterally
- Precentral gyrus: Increased gyrification bilaterally
- Right supramarginal gyrus: Gyrification correlates with respiratory and reflex components of speech (ρ > 0.3)
Affected Neural Subsystems
Dysarthria affects five subsystems of speech production through damage to their controlling neural pathways 1:
- Respiratory system (breath support)
- Laryngeal system (phonation)
- Velopharyngeal system (resonance)
- Oral-articulatory system (articulation)
- Prosodic control (rhythm and intonation)
The specific dysarthria type and characteristics depend on which neural pathways are damaged and lesion severity.
Clinical Implications
Approximately 20% of stroke patients present with dysarthria, with lesion location determining the specific motor speech characteristics 1. The systematic review of 420 dysarthric patients with isolated lesions demonstrates that both supratentorial and infratentorial pathways contribute to speech motor control 2.
Common Pitfall
Do not assume dysarthria only results from brainstem lesions. While the brainstem contains critical pathways for articulation and phonation 7, cortical lesions (particularly posterior insula and middle frontal gyrus) can independently cause dysarthria through disruption of motor planning and execution networks 4, 5.
The posterior insula appears particularly critical, as it serves as an integration hub connecting cortical motor planning regions with subcortical execution pathways 4. This explains why relatively small insular lesions can produce significant speech deficits.