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Disconnection Syndromes (DS). Higher function deficits resulted from lesions of white matter or the association cortices ‘Functional’ disorders such as schizophrenia, autism, dyslexia Founded on: Anatomy, post-mortem dissections, monkeys. More recently: DTI, Tractography.
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Disconnection Syndromes(DS) • Higher function deficits resulted from lesions of white matter or the association cortices • ‘Functional’ disorders such as schizophrenia, autism, dyslexia • Founded on: Anatomy, post-mortem dissections, monkeys. • More recently: DTI, Tractography
DS before Geschwind • ‘The Classical associationist era’ • Paradigm based on two central tenets: • Localization of function in discrete cortical areas • Connections between areas through white matter association pathways
DS before Geschwind • Franz Joseph Gall (1758-1828): • White matter • Grey matter • Phrenology (England)
DS before Geschwind • Theodor Meynert (1833-1892): • White matter fibers: • Projection fibers • Commissural fibers • Association fibers
DS before Geschwind • Karl Wernicke (1848-1904): • The father of Disconnection theory • ‘fundamental psychic elements’ / ‘memory images’ • “… mediated by means of their manifold connections via the association fibres” (Wernicke, 1885)
DS before Geschwind • Karl Wernicke (1848-1904): • Higher functions arise through associative connections, Disorders of higher function from their breakdown • Critisizm: • No cortical specialization other than motor/sensory • Theoretical framework explained classical DS
Conduction Aphasia • Motor component (Broca) • Sensory component (Wernicke) • Lesions: • Broca Pure motor aphasia • Wernicke Pure sensory aphasia • Arcuate Fasciculus Conduction aphasia
Visual Agnosia • Lesions: • Cortical (Visual cortex) Apperceptiveagnosia • Trans-Cortical (associative fiber connections) Associative agnosia
The apraxias • Hugo Liepmann (1863-1925) • Higher movement disorders • Spontaneous movements • Planned gestures • Disconnection of visual, auditory and somatosensoryareas from motor area
The apraxias • Left hemisphere dominant for complex movements control • Lesions: • Left parietal lobe bilateral apraxia • Anterior portion of corpus callosum Unilateral apraxia (left) • Left motor area (not shown) bilateral apraxia + right paresis
Pure Alexia • Jules Déjérine (1849-1917) • Left angular gyrus= visual verbal centre • Lesions: • Left angular gyrus Alexia + Agraphia • Left central white matter occipital lesion Pure alexia
The fall of the classical era • Déjérine model suggested • Higher functions located in cortex • An area specialized for higher visual function outside the visual cortex • Wernicke’s opposition to higher functional centers • The early 20th century (holistic, anti-localizationist) • 1965 (localization theory, DS)
Geschwind’s neo-associationism • Flechsig’s rule • Include sensory and motor cortices and interhempispheric connections • Association cortex acted as an obligatory relay station • Phylogenetic perspective • Higher-order association area in the parietal lobe • Connections that did not depend on the limbic system
Geschwind’s neo-associationism • The role of the angular gyrus: • Déjérine visual memories of letters and words • Geschwind forming multimodality associations • Geschwind focused on DS caused by lesions of association cortex (parietal lobe) • “…A ‘disconnexion lesion’ will be a large lesion either of association cortex or of the white matter leading from association cortex” (Geschwind, 1965)
Disconnections between sensory areas and limbic cortex • Failure of a stimulus to evoke memories/affective response • Disconnections between limbic lobe and - • Somatosensory cortex pain asymbolia • Auditory cortex verbal learning impairment etc. • Visual system (indirect connections) no symptoms
Disconnections between sensory areas and Wernicke’s area • Modality-specific language deficits • Disconnections can be direct or indirect (through the angular gyrus) • Four syndromes: • Tactile aphasia/Anomia • Pure word deafness • Pure alexia • Modality-specific agnosia
Disconnections between sensory areas and motor cortex • Left hemisphere disconnections: • Hand motor cortex from posterior sensory areas Apraxia • Broca’s area from Wernicke’s Conduction aphasia
DS After Geschwind • Geschwind contribution: • Association cortex as an obligatory relay • Hierarchies of associations within the IPL • Importance of IPL in phylogeny and ontogeny of language • Two research paths: • Damasio (CT, PET, SPET) • Mesulam (Tracing neural connections, computation theory etc.)
Contemporary neuroanatomical basis of higher brain functions • Functional subdivision of the association cortex • ‘Extended territories’ composed of specialized cortical subregions serving different but related functions • Parallel, bidirectional, distributed processing
Contemporary neuroanatomical basis of higher brain functions • Two key elements underlie higher function deficits: • Loss of specialized cortical function • Damage to connecting pathways • Recent techniques enable research of disorders caused by hyperconnectionand cortical hyperfunction
Hodotopic framework of clinicopathological correlations • Territories composed of specialized subregions • Intra-territorial connections (U-shaped) • Inter-territorial connection (Long)
Hodotopic framework of clinicopathological correlations • Topological mechanism (Topos = place) • Prosopagnosia, face hallucinations • Hodological mechanism (Hodos = road / path) • Conduction aphasia, autism
Language network disorders • Direct (Long segment) • Indirect (Anterior, Posterior) • Pure hodological mechanism: • Long segment Conduction aphasia • Long, anterior, posterior Global aphasia
Language network disorders • Direct (Long segment) • Indirect (Anterior, Posterior) • Pure topological mechanism: • Anterior portions of Geschwind’s Non-fluent aphasia • All of Geschwind’s Mixed trans-cortical aphasia • All of Geschwind’s + deep white matter Global aphasia
Language network disorders • Direct (Long segment) • Indirect (Anterior, Posterior) • Hyperfunction: • Indirect Semantically based sympthoms • Direct Excessive repetition (e.g. echolalia)
Praxis network disorders • Med. Frontal Med. Parietal (DMPF, yellow) • Motor SPL (DLFP, green) • Motor IPL(VLFP, red) • Lesions: • SPL Depends on which praxic subfunctions are affected • SPL + White matter Additional abnormalities
Visual network disorders • Indirect (U-shaped occipito-temporal, red) • Direct (Inferior longitudinal fasciculus, green) • Lesions: • Direct specific deficits related to the cortical specializations lost • Indirect + medial white matter Visual hypo-emotionality / Visual amnesia
Visual network disorders • Direct (Inferior longitudinal fasciculus, green) • Indirect (U-shaped occipito-temporal, red) • Hyperfunction: • Indirect Visual hallucinations • Hyperconnectivity: • Indirect / Direct Unclear (Synaesthesia? Phobia?)