2. Anatomy Of Cerebral Connections
• 3 major types of fiber connections of the neocortex:
A. Association fibers,
B. Projection fibers,
C. Commissural fibers
A. Association fibers- unite different parts of the same cerebral hemisphere.
1. Long fiber bundles that connect distant neocortical areas.
2. Short subcortical U-fibers that connect adjacent neocortical areas.
B. Projection fibers- consist of efferent and afferent fibers uniting the cortex with the lower parts of the
brain and with the spinal cord.
C. Commissural fibers- function primarily to join the two hemispheres and include principally the
Corpus Callosum, the Anterior Commissure, and the Commisure of Fornix, and the Habenular
Commissure.
Intrahemispheric
Interhemispheric
4. Viviana Siless. Multi-modal registration of T1 brain image and geometric descriptors of white matter tracts. Medical Imaging.
cingulate gyrus to entorhinal cortex
Association fibre
7. ANTERIOR COMMISURE
interconnects various regions of the
two temporal lobes and frontal lobes.
It contributes to the role of memory,
emotion, speech and hearing.
It also is involved in olfaction, instinct,
and sexual behavior
The superior lamina or stalk of the
pineal body is called the HABENULAR
COMMISSURE, it connects the
habenular nuclei of the two cerebral
hemispheres.
The POSTERIOR COMMISSURE
attaches the pineal gland to the
posterior wall of the third ventricle.
It connects the language processing
centres of both cerebral hemispheres.
Closely related in function to the
splenium of the corpus callosum.
Commissural fibers
8. Commisure of Fornix
Hippocampal Commissure, Or
Commissure Of Fornix, is a bundle of
fibres interconnecting the Hippocampi of
the two cerebral hemispheres.
Via Crus (part of body of fornix)
9. Disconnection syndrome
◦ Coined in 1965 by Neurologist Norman Geschwind (1926–1984)
◦ As higher function deficits that result from white matter lesions or lesions of the association
cortices, the latter acting as relay stations between primary motor, sensory, and limbic areas.
◦ A condition in which information transfer between parts of the brain is interrupted or blocked.
◦ Collection of neurological symptoms c/b lesions to Association or Commissural nerve fibres.
◦ 1) Interhemispheric disconnection syndrome:
due to involvement of commissural fibres
◦ 2) Intrahemispheric disconnection syndrome:
due to association fibres involvement
David Myland Kaufman (2007). Clinical Neurology for Psychiatrists. pg. 171.
11. Superior Longitudinal fascilculus
◦ Bundle of tracts passes from the frontal lobe
through the operculum to the posterior end
of the lateral sulcus where they either radiate
to and synapse on neurons in the occipital
lobe, turn downward and forward around the
putamen and then radiate to and synapse on
neurons in anterior portions of the temporal
lobe.
Hemineglect without Hemioanopia.
12. Inferior Longitudinal fasciculus
◦ Visual information from the occipital lobes from
can’t reach the left hemisphere (language areas).
◦ Can copy drawings but can’t recognize it.
◦ Patient can identify the same object presented in
the tactile or auditory modality.
◦ Inability to match an internal visual percept with
representations of visual objects;
◦ Perceive visual stimuli normally but failed to assign
meaning or identity.
Associative Visual Agnosia
13. ◦ The Left Hemisphere is dominant for LINGUISTIC FUNCTIONS, and
usually for MOTOR PRAXIS.
◦ The Right Hemisphere is dominant for VISUOSPATIAL and
VISUOCONTRUCTIVE ABILITIES, but has only a moderate capacity for
the Comprehension Of Auditory And Visual Verbal Material (Written
Text).
NO CAPACITY to produce oral or written language.
Saj, A., & Vuilleumier, P. (2012). Agnosias, apraxias, and callosal disconnection syndromes. In L. Caplan & J. Van Gijn (Eds.), Stroke Syndromes, 3ed (pp. 267-286).
15. Classification of CALLOSAL DISCONNECTION SYNDROMES.
Verbal Disconnection:-
Left visual anomia.
Left hemialexia.
Left auditory anomia.
Left tactile anomia.
Right olfactory anomia.
Motor Disconnection :-
Crossed optic ataxia
Left unilateral motor apraxia.
Agraphia of the left hand.
Right unilateral constructional apraxia.
Alien hand syndrome.
Saj, A., & Vuilleumier, P. (2012). Agnosias, apraxias, and callosal disconnection syndromes. In L. Caplan & J. Van Gijn (Eds.), Stroke Syndromes, 3ed (pp. 267-286).
16. Left visual anomia (Hemianomia):-
◦ Images seen in the Right Visual Hemifield (LEFT HEMISPHERE) are normally named or described, while those
shown in the Left Hemifield (RIGHT HEMISPHERE) cannot (or are even not reported).
◦ When no verbal response is required, the patient can recognize the object or perform matching tasks with the
left hand (but not with the right) and draw it with the left hand.
Saj, A., & Vuilleumier, P. (2012). Agnosias, apraxias, and callosal disconnection syndromes. In L. Caplan & J. Van Gijn (Eds.), Stroke Syndromes, 3ed (pp. 267-286).
Tested by:- Presenting images
to each hemisphere separately
briefly presentation.
Lesions are typically located in
the most Posterior And Dorsal
Portion Of The Splenium
17.
18. Left Hemialexia
◦ Anomia for words shown in the Left visual field.
◦ Can read words presented in their Right visual hemifield,
◦ But are unable to read aloud or write down words presented on the Left Side.
Lesions are usually located in the
more Ventral Portion Of The
Splenium
19. Pure Alexia
◦ Inability to recognize written words
◦ In the absence of language disturbance, Without Agraphia.
◦ Aka Pure Word Blindness.
◦ Recognition and naming of individual letters is preserved.
Lesion in the LEFT PCA Territory, involving
The Left Inferomedial Temporooccipital
Region And (Ventroposterior) Splenium of
the corpus callosum
20. Left Auditory Anomia
◦ Lack of transfer from the right hemisphere to the language system of the left hemisphere
prevents any verbal report of auditory stimuli.
◦ Dichotic Listening Test is required to demonstrate the deficit.
Lesions affecting
interhemispheric auditory
transfer are located in the
Posterior Inferior Trunk Of The
Corpus Callosum or Isthmus.
21. Left Tactile Anomia
◦ Can describe and name objects palpated with the Right Hand (without vision), but not with the
Left Hand.
◦ Patient can still point to, match, or even draw the object when using only the Left Hand.
Incorrect naming of the object does not
prevent normal manipulation and use.
E.g., a patient palpating a spoon with his
left hand claims that this is a pin, yet
when asked to use it, shows an
appropriate grasp and movement.
Lesion at :- Posterior Trunk Of The
Corpus Callosum.
22. Right Olfactory Anomia
◦ Odors presented to the Right Nostril (Right Hemisphere) are not named, while those presented
to the Left Nostril (Left Hemisphere) are named.
◦ No anosmia.
Lesion :- Mostly d/t involvement of Anterior Commissure,
but some fibers connecting anterior cingulate areas and
posterior orbitofrontal areas are located in the Rostral
Corpus Callosum.
23. Crossed Optic Ataxia
◦ When an object is presented in the peripheral visual field of a patient, the patient can get it with
the ipsilateral but not the contralateral hand.
◦ Results from disconnection between motor reaching systems in one hemisphere and
visuospatial information in the other.
24. Left Unilateral Motor Apraxia
◦ Results from disconnection of the Right Motor Cortex from Left Hemisphere areas involved in the
representation of skillful gestures and limb postures.
◦ Inability to perform purposeful gestures on demand without any motor or sensory deficit.
◦ Impairment is observed in response to verbal command, imitation, or both.
◦ Visual presentation or tactual manipulation of objects can often elicit a normal gesture.
◦ Lesions are always located in the left hemisphere, particularly in the left inferior frontal gyrus
(Anterior Superficial MCA Territory), extending to subcortical white matter
and/or
◦ Involving the Anterior Corpus Callosum.
25. Agraphia Of The Left Hand
◦ Two Forms
1. Unilateral Apraxic Agraphia.
2. Unilateral Aphasic Agraphia.
Apraxic Agraphia:-
◦ C/B Badly Drawn Letters And Scribbles.
◦ Disconnection Of The Right Motor Cortex From Left Hemisphere Language Areas May Produce Two Distinct
Forms Of Writing Problems Selectively Affecting The Left Hand.
◦ Typing And Writing With Block Letters Are Preserved
◦ D/T Impaired Transfer Of Graphomotor Information.
Unilateral Aphasic Agraphia :-
◦ Verbal-motor Disconnection
◦ Disruption Of The Transfer Of Linguistic Information.
◦ Impaired Two-hand Writing And Typing.
Posterior Trunk Of The Corpus Callosum
Anterior Splenium / Isthmus
26. Right Unilateral Constructional Apraxia
◦ Difficulties in Drawing and Constructive Abilities when using the Right but NOT Left hand.
◦ Disconnection of the Left Motor Cortex from Right Hemisphere visuospatial skills.
◦ when a model is shown to the left hemisphere (using tachistoscopic methods), both the right and left
hands fail in copying.
◦ Lesion:- Posterior Corpus Callosum
27. Pure Callosal Alien Hand Syndrome
◦ Damage restricted to the Midtrunk Of The Corpus Callosum
◦ Two major aspects that may also occur alone:
(i) Left Hand makes Unintended movements during purposeful actions. These movements can
Intermanual conflict, e.g., closing a drawer opened with the right hand).
Irrelevant but nonantagonistic (e.g., slapping on the table while drawing with the right)
Mirroring the right (e.g., reaching for the same object);
(ii) Left hand does not move despite an intention to use it during voluntary actions.
Failure to initiate or interrupt an action (e.g., grasping or releasing an object held in the hand).
The execution of an incorrect movement, inconsistent with verbally stated purposes (e.g., drawing circles
instead of a line).
A combination of Intermanual Conflict and Difficulties In Initiating Willed Actions with the left hand
has been termed Diagonistic Apraxia
Loss of Transcallosal Inhibition of Parietal Areas and/or Premotor Areas (particularly the SMA) in the nondominant
(right) hemisphere, By Left (dominant hemisphere)
28. Alien Hand Syndrome
Frontal Type Callosal type Sensory type
(Posterior AH )
Site of lesion Medial Frontal Cortex Combined
With Anterior Callosal
Disconnection
Midtrunk Of The Corpus Callosum Thalamus (Ventroposterolateral
And Ventrolateral Nuclei) And
Subthalamic Region,
Superior Posterior Parietal Lobes
Vascular
terrirtory
ACA Pericallosal Arteries PCA / MCA
Side involved Either the DOMINANT or
NONDOMINANT hand (or
sometimes BOTH).
Always involves the
LEFT/NONDOMINANT hand.
LEFT/NONDOMINANT hand
C/f Forced Grasping
of objects impulsive reaching
and Groping toward objects
in near sight compulsive
manipulation of tools
Intermanual conflict,
Failure to initiate
or interrupt an action
Spontaneous non-goal oriented
motor activities such as Levitation,
Drifting, Or Repetitive Scratching
Or Tapping. Unintentional and
uncontrollable movements of
limbs.
Associated
findings
Transcortical motor
aphasia
Feeling of foreignness of the limb
(Asomatognosia), Hemispatial
Neglect, or Anosognosia are
frequently associated.
29.
30. References :-
◦ David Myland Kaufman (2007). Clinical Neurology for Psychiatrists. pg. 171.
◦ Saj, A., & Vuilleumier, P. (2012). Agnosias, apraxias, and callosal disconnection syndromes. In
L. Caplan & J. Van Gijn (Eds.), Stroke Syndromes, 3ed (pp. 267-286).
◦ Arnaud Saj and Patrik Vuilleumier. Agnosias, apraxias, and callosal disconnection syndromes.
Stroke Syndromes, Third Edition, ed. Louis R. Caplan and Jan van Gijn.
◦ S. E. Seymour et al. The disconnection syndrome. Basic findings reaffirmed. Brain (1994), 117,
105-115.
◦ Gary J. Schummer et al, The Disconnection Syndrome. Biofeedback Volume 36, Issue 4, pp. 157–
162.
◦ John R. Absher et al, Disconnection syndromes: An overview of Geschwind’s contributions.
NEUROLOGY 1993;43:862-86.
◦ Bradley, 8th Edition.
31.
32. ◦ The most classical disconnection signs observed in practice follow lesions of the posterior half of
the corpus callosum, that is, the trunk (vascularized by the ACA) and the splenium (vascularized
by the PCA). Effects of more anterior disconnection in the genu (ACA territory) are poorly known
and presumably involve higher-level executive functions as well as motor intentional processes
33. Disconnection due to involvement of Corpus Callosum
Shozawa H, Futamura A, Saito Y, Honma M, Kawamura M, Miller MW and Ono K (2018) Diagonistic Apraxia: A Unique Case of Corpus Callosal Disconnection Syndrome and Neuromyelitis Optica Spectrum Disorder. Front. Neurol. 9:653.
Diagonistic apraxia, in which a patient’s hands are uncoordinated, and the left hand has to be verbally
instructed to follow a patient’s will .
Disconnection of right superior parietal lobule from left results in problems with volitional control of
movements of the left hand.
Crossed Tactile Anomia And Tactile
Disorientation.
Alexia Of Left Visual Field
Impaired prosody in speech
Auditory Extinction Of The Left Ear
And Crossed Optic Ataxia
Editor's Notes
David Myland Kaufman (2007). Clinical Neurology for Psychiatrists. Elsevier Health Sciences. pp. 171–. ISBN 978-1-4160-3074-4
with a tachistoscope or computerized display
Pseudoasterognosia:- patient can still point to, match, or even draw the object when using only the left hand.
A failure to recognize one’s own hand (versus the examiner’s hand) when held by the other hand (with eyes closed or behind one’s back) was termed alien hand sign
LEFT PARIETAL REGIONS around the supramarginal gyrus and angular gyri (posterior MCA territory) are more often associated with impaired imitation (both meaningful and meaningless gestures) without deficits in gesture production on command, and typically accompanied by conduction aphasia (anterior parietal branches of MCA).
Superior parietal lobule is concerned with selection of movement based on integration of visual and somatosensory information.
For the pupillary light reflex, the olivary pretectal nucleus innervates both Edinger-Westphal nuclei. To reach the contralateral Edinger-Westphal nucleus, the axons cross in the posterior commissure.