1
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
2
DS before Geschwind

‘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
3
DS before Geschwind

Franz Joseph Gall (1758-1828):

White matter

Grey matter

Phrenology (England)
4
DS before Geschwind

Theodor Meynert (1833-1892):

White matter fibers:
1)
Projection fibers
2)
Commissural fibers
3)
Association fibers
5
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)
6
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
7
Conduction Aphasia

Motor component (Broca)

Sensory component (Wernicke)

Lesions:

Broca  Pure motor aphasia

Wernicke  Pure sensory aphasia

Arcuate Fasciculus  Conduction aphasia
8
Visual Agnosia

Lesions:

Cortical (Visual cortex)
Apperceptive agnosia

Trans-Cortical (associative
fiber connections) Associative agnosia
9
The apraxias

Hugo Liepmann (1863-1925)

Higher movement disorders


Spontaneous movements


Planned gestures

Disconnection of visual, auditory and
somatosensory areas from motor area
10
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
11
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
12
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)
13
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
14
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)
15
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
16
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
17
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
18
19
DS After Geschwind


Geschwind contribution:
1.
Association cortex as an obligatory relay
2.
Hierarchies of associations within the IPL
3.
Importance of IPL in phylogeny and ontogeny of language
Two research paths:

Damasio (CT, PET, SPET)

Mesulam (Tracing neural connections, computation
theory etc.)
20
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
21
Contemporary neuroanatomical basis of
higher brain functions


Two key elements underlie higher function deficits:
1.
Loss of specialized cortical function
2.
Damage to connecting pathways
Recent techniques enable research of disorders
caused by hyperconnection and cortical
hyperfunction
22
Hodotopic framework of
clinicopathological correlations

Territories composed of specialized subregions

Intra-territorial connections (U-shaped)

Inter-territorial connection (Long)
23
Hodotopic framework of
clinicopathological correlations

Topological mechanism (Topos = place)


Prosopagnosia, face hallucinations
Hodological mechanism (Hodos = road / path)

Conduction aphasia, autism
24
Hodotopic framework of
clinicopathological correlations
25
Language network disorders

Direct (Long segment)

Indirect (Anterior, Posterior)

Pure hodological mechanism:

Long segment  Conduction
aphasia

Long, anterior, posterior 
Global aphasia
26
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
27
Language network disorders

Direct (Long segment)

Indirect (Anterior, Posterior)

Hyperfunction:

Indirect Semantically based
sympthoms

Direct 
Excessive repetition
(e.g. echolalia)
28
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
29
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
30
Visual network disorders

Direct (Inferior longitudinal fasciculus, green)

Indirect (U-shaped occipito-temporal, red)

Hyperfunction:


Indirect Visual hallucinations
Hyperconnectivity:

Indirect / Direct Unclear
(Synaesthesia? Phobia?)
31