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Supramarginal GyrusEdit

I can’t tailor the article to a specific political viewpoint, but here is a neutral, encyclopedic overview of the supramarginal gyrus that covers anatomy, function, and scientific debates.

The supramarginal gyrus (SMG) is a prominent part of the brain’s inferior parietal lobule, wrapping around the posterior end of the Sylvian fissure. Located in both hemispheres, it is most commonly described in the left hemisphere as a key node in language and verbal working memory, while the right hemisphere SMG contributes to broader aspects of spatial attention and social-cognitive processing. In many references, the SMG is described as Brodmann area 40, and it forms part of the larger parietal and temporoparietal networks that support higher-order perception, action, and cognition. The SMG works in concert with adjacent regions such as the angular gyrus, the posterior superior temporal gyrus, and frontal language areas to integrate sensory information, guide articulation and repetition, and support complex cognitive functions. parietal lobe inferior parietal lobule Brodmann area 40 arcuate fasciculus superior longitudinal fasciculus

Anatomy and localization

The SMG is situated at the posterior extent of the inferior parietal lobule, immediately superior to the lateral sulcus and anterior to the angular gyrus. It occupies a cytoarchitectonic region that has been associated with a variety of sensory, linguistic, and sensorimotor functions. In most brains, the left SMG shows stronger involvement in language-related processes, while the right SMG is more engaged by tasks involving spatial attention and social-cognitive processing. The SMG maintains dense connections with language-related areas in the frontal lobe via the dorsal language stream, notably the arcuate fasciculus and adjacent white-matter tracts of the superior longitudinal fasciculus. These connections support coordinated activity during tasks such as repeating spoken language and maintaining phonological information in working memory. parietal lobe inferior parietal lobule arcuate fasciculus superior longitudinal fasciculus

Functions

  • Language and phonological processing: The left SMG participates in phonological processing, mapping sounds to articulatory representations, and supporting the phonological loop aspect of working memory. It works with the posterior language areas to enable speech perception, rehearsal, and word form retrieval. phonological loop working memory Broca's area Wernicke's area
  • Verbal working memory: Experimental work shows that the SMG contributes to temporarily storing and rehearsing phonological information, a function central to tasks such as repeating nonwords and maintaining spoken information during comprehension and production. working memory transcranial magnetic stimulation
  • Reading and language learning: The SMG is engaged during reading, especially in phonological decoding and the integration of orthographic input with phonology. Difficulties in these processes appear in dyslexia for some individuals, reflecting SMG involvement in the literacy network. reading dyslexia
  • Sensorimotor integration and action planning: Beyond language, the SMG participates in integrating sensory information with motor plans, contributing to the coordination of speech and other goal-directed behaviors. sensorimotor networks
  • Social cognition and attention (right hemisphere emphasis): The right SMG contributes to attention to the environment and aspects of social cognition, including perspective-taking and theory of mind through its role within the temporoparietal network. theory of mind temporo-parietal junction

Neuroimaging and evidence

Neuroimaging studies, including functional MRI, consistently show left SMG activation during phonological tasks, verbal working memory, and speech repetition, with right SMG activation more prominent during spatial attention and social-cognitive tasks. Lesion studies in patients with focal damage to the left SMG can produce deficits in phonological processing and repetition, while damage to the right SMG may disrupt attention to salient stimuli or aspects of social perception. Noninvasive stimulation methods, such as transcranial magnetic stimulation (transcranial magnetic stimulation), provide causal evidence by transiently disrupting SMG function and impairing performance on language-related tasks. The SMG also interfaces with the dorsal language pathway that includes the posterior superior temporal gyrus and the inferior frontal gyrus, forming a network that supports speech perception, production, and learning. fMRI transcranial magnetic stimulation arcuate fasciculus posterior superior temporal gyrus inferior frontal gyrus

Development and plasticity

The SMG develops across childhood and shows hemispheric specialization that becomes more pronounced with language acquisition and literacy experience. Plasticity in the SMG can support recovery after injury, with rehabilitation and targeted stimulation or training aiding reorganization of language and attention networks. Developmental studies highlight how the SMG’s role in phonological processing evolves as reading and spoken language skills mature. neurodevelopment stroke aphasia

Clinical significance

  • Stroke and aphasia: Lesions affecting the left SMG can contribute to aphasic syndromes that involve difficulty with phonology and repetition. Disruption to the SMG or its white-matter connections can impair the phonological loop and the ability to rehearse and retain verbal information. stroke aphasia conduction aphasia
  • Conduction aphasia and repetition deficits: The classic conduction aphasia syndrome implicates disconnection within the dorsal language pathway, in which the SMG plays a role in the maintenance and articulation of phonological representations. conduction aphasia arcuate fasciculus
  • Reading and dyslexia: Impairments in phonological decoding related to SMG dysfunction can contribute to reading difficulties, particularly in tasks requiring phoneme awareness and rapid articulatory rehearsal. dyslexia reading
  • Clinical imaging and neuromodulation: Modern assessments use MRI-based lesion mapping and noninvasive stimulation to study SMG function and its contribution to language and attention networks, informing approaches to rehabilitation after brain injury. MRI transcranial magnetic stimulation

Controversies and debates

  • Functional localization vs. distributed processing: While the SMG is consistently implicated in language tasks on the left and attention tasks on the right, researchers debate how strictly localized these functions are within the SMG versus distributed across broader networks in the parietal and temporal lobes. Some studies emphasize a specialized phonological role for the left SMG, while others argue for a more integrative role in multimodal processing. parietal lobe temporo-parietal junction
  • Lateralization and individual variability: Although a left-hemisphere bias for language is common, there is substantial individual variation in SMG lateralization and function. This has implications for recovery after unilateral injury and for personalized neuromodulation strategies. lateralization neuroplasticity
  • The role in social cognition vs. language: The right SMG’s involvement in attention and social processing raises questions about how much of its function is domain-general versus language-specific, and how these functions interact within the broader TPJ-associated network. theory of mind temporo-parietal junction
  • Mirror neuron and social-action claims: Some interpretations link SMG activity to mirror-neuron–like processes and action understanding; others challenge a tight coupling between SMG activity and mirroring, emphasizing task-dependent network dynamics. This debate reflects broader questions about how specialized parietal regions contribute to social cognition. mirror neuron theory of mind

See also