1

2

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

Disconnection Syndromes (DS)

3

‘The Classical associationist era’ Paradigm based on two central tenets:

1) Localization of function in discrete cortical areas

2) Connections between areas through white matter association pathways

DS before Geschwind

4

Franz Joseph Gall (1758-1828): White matter Grey matter Phrenology (England)

DS before Geschwind

5

Theodor Meynert (1833-1892): White matter fibers:

1) Projection fibers

2) Commissural fibers

3) Association fibers

DS before Geschwind

6

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

7

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

DS before Geschwind

8

Motor component (Broca) Sensory component (Wernicke) Lesions:

Broca Pure motor aphasia Wernicke Pure sensory aphasia Arcuate Fasciculus Conduction aphasia

Conduction Aphasia

9

Lesions:

Cortical (Visual cortex)

Apperceptive agnosia

Trans-Cortical (associative

fiber connections) Associative agnosia

Visual Agnosia

10

Hugo Liepmann (1863-1925)

Higher movement disorders Spontaneous movements Planned gestures

Disconnection of visual, auditory and somatosensory areas from motor area

The apraxias

11

Left hemisphere dominant for complexmovements control

Lesions: Left parietal lobe bilateral apraxia

Anterior portion of corpus callosum Unilateral apraxia (left)

Left motor area (not shown)

bilateral apraxia + right paresis

The apraxias

12

Jules Déjérine (1849-1917)

Left angular gyrus = visual verbal centre

Lesions: Left angular gyrus Alexia + Agraphia Left central white matter occipital lesion

Pure alexia

Pure Alexia

13

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)

The fall of the classical era

14

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

15

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)

Geschwind’s neo-associationism

16

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 limbic cortex

17

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 Wernicke’s area

18

Left hemisphere disconnections:

Hand motor cortex from posterior sensory areas Apraxia

Broca’s area from Wernicke’s Conduction aphasia

Disconnections between sensory areas and motor cortex

19

20

Geschwind contribution:1. Association cortex as an obligatory relay2. Hierarchies of associations within the IPL3. Importance of IPL in phylogeny and ontogeny of

language

Two research paths: Damasio (CT, PET, SPET) Mesulam (Tracing neural connections, computation

theory etc.)

DS After Geschwind

21

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

22

Two key elements underlie higher function deficits:1. Loss of specialized cortical function2. Damage to connecting pathways

Recent techniques enable research of disorders caused by hyperconnection and cortical hyperfunction

Contemporary neuroanatomical basis of higher brain functions

23

Territories composed of specialized subregions Intra-territorial connections (U-shaped) Inter-territorial connection (Long)

Hodotopic framework of clinicopathological correlations

24

Topological mechanism (Topos = place) Prosopagnosia, face hallucinations

Hodological mechanism (Hodos = road / path) Conduction aphasia, autism

Hodotopic framework of clinicopathological correlations

25

Hodotopic framework of clinicopathological correlations

26

Direct (Long segment) Indirect (Anterior, Posterior)

Pure hodological mechanism: Long segment Conduction

aphasia Long, anterior, posterior

Global aphasia

Language network disorders

27

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

28

Direct (Long segment) Indirect (Anterior, Posterior)

Hyperfunction: Indirect Semantically based

sympthoms

Direct Excessive repetition ( e.g. echolalia)

Language network disorders

29

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

Praxis network disorders

30

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

31

Direct (Inferior longitudinal fasciculus, green) Indirect (U-shaped occipito-temporal, red)

Hyperfunction: Indirect Visual hallucinations

Hyperconnectivity: Indirect / Direct Unclear

( Synaesthesia? Phobia)?

Visual network disorders