The Supramarginal Gyrus: Anatomical and Functional Characteristics
The supramarginal gyrus (SMG) is a distinct region of the inferior parietal lobule that plays critical roles in language processing, sensory integration, and higher cognitive functions.
Anatomical Location and Structure
The supramarginal gyrus (Brodmann Area 40) is located in the inferior parietal lobule, specifically:
- Situated around the posterior end of the lateral (Sylvian) fissure
- Arches over the ascending posterior segment of the lateral sulcus
- Bordered anteriorly by the postcentral gyrus and posteriorly by the angular gyrus (Brodmann Area 39) 1
- Forms part of the ventral portion of the parietal lobe
Connectivity and Fiber Pathways
The SMG has extensive white matter connections that contribute to its functional significance:
- Projects to the ventrolateral prefrontal cortex via the superior longitudinal fasciculus III (SLF III) and arcuate fasciculus (AF) 1, 2
- Contains dense subcortical connections forming a complex network with surrounding regions 2
- Connects with auditory and language processing areas through multiple fiber pathways
- Shows hemispheric differences in connectivity patterns that support specialized functions 3
Functional Divisions
The SMG is not functionally homogeneous but contains multiple specialized subregions:
Ventral SMG:
- Anterior portion: Associated with articulatory sequencing
- Posterior portion: Involved in auditory short-term memory 4
Dorsal SMG:
- Posterior portion: Integrates sublexical and lexical cues, particularly for word processing
- Anterior portion: Supports executive functions during complex language tasks 4
Functional Roles
Language Processing
The SMG plays crucial roles in language, particularly:
- Phonological processing and phoneme manipulation
- Kana alexia (phonological dyslexia) and kana agraphia (phonological agraphia) result from left SMG damage 1
- Verbal short-term memory, essential for language comprehension 1
- Articulatory planning and speech production 4
Other Cognitive Functions
Beyond language, the SMG contributes to:
- Part of the network involved in Gerstmann's syndrome (finger agnosia, left-right disorientation, agraphia, and acalculia) when damaged 1
- Sensory integration and spatial processing
- Tool use and action understanding (particularly in the left hemisphere)
- Mathematical cognition (particularly in the right hemisphere) 3
Clinical Significance
Damage to the SMG can result in various deficits:
- Phonological processing impairments affecting reading and writing
- Verbal short-term memory deficits
- Components of Gerstmann's syndrome
- Language production difficulties when part of larger lesions affecting perisylvian regions 5
Hemispheric Specialization
The SMG shows notable hemispheric differences:
- Left SMG: More involved in language processing, tool use, and phonological functions
- Right SMG: More involved in spatial attention and mathematical cognition 3
Relationship to Surrounding Structures
The SMG functions in concert with surrounding structures:
- Works with the angular gyrus as part of the inferior parietal lobule
- Connects with frontal language areas through white matter pathways
- Participates in multiple functional networks depending on task demands 3
Understanding the complex structure and function of the supramarginal gyrus is important for interpreting neuroimaging findings and predicting outcomes following brain injury or surgical interventions in this region.