Cerebral Cortex I and Vascular Territories Flashcards
Location of the primary visual cortex
Location of the primary auditory cortex
When we say language function is usually in the left hemisphere, what we really mean to say is. . .
. . . language function is usually in the dominant hemisphere
The “where” pathway
The connections between the occipital lobe and parietal lobe.
Visual information is processed here to determine where things are in space with respect to the body. Lesions here can cause neglect.
Neglect
Caused by damage to the territory linking the occipital and temporal lobes, more commonly in the non-dominant parietal lobe, causing non-dominant-sided neglect.
Examination findings in patients with neglect may include extinction to double simultaneous stimulation, anosognosia, and sometimes unilateral asomatognosia.
Angular gyrus
Located in the dominant hemisphere.
Lesions to this area cause Gerstmann’s syndrome: Left-right confusion, inability to count (acalculia), inability to name the fingers (finger agnosia), and inability to write (agraphia).
Broca’s and Wernicke’s areas
Located in the dominant hemisphere.
Apraxia
- Difficulty performing a complex learned motor action
- Caused by lesions within the parietal lobe, often on the dominant side
- Three types:
- Limb-kinetic apraxia: difficulty performing these movements
- Ideational apraxia: inability to conceive of the idea of how to accurately perform an action
- Ideomotor apraxia: inability to convert an idea about how to do something into a motor plan.
Ideomotor ataxia explanation
Affected patients may be able to explain the intended action but are unable to perform it normally, making errors in sequencing and/or timing of the component movements of complex learned actions.
Amnesia
- Caused by lesions within the middle temporal lobes and hippocampus
- May be retrograde or anterograde
Alexia
Caused by lesions to the inferior aspect of the domintant temporal lobe
Prosopagnosia
- Inability to recognize faces
- Caused by lesions to the inferior aspect of the non-domintant temporal lobe
Inferior frontal gyrus
Houses Broca’s area!
Superior temporal gyrus
Houses Wernicke’s area, among other things.
Wernicke’s area is close to the border with the parietal lobe.
Transcortical motor aphasia
This is essentially a Broca’s aphasia with preserved repetition
The aphasia hierarchy
Aphasias in which comprehension is impaired
Receptive aphasias
Transcortical sensory aphasia
Essentially Wernicke’s aphasia with preserved repetition
Global aphasia
Production, comprehension, and repetition are all impaired.
Conduction aphasia
- Aphasia where the only focal deficit is repetition
- Caused by damage to the arcuate fasciculus
Sudden-onset aphasia is most commonly due to ___.
Sudden-onset aphasia is most commonly due to stroke in the dominant-sided MCA area.
Abulia
- Decreased initiative/motivation in speech, action, and emotion
- Can manifest as inability to make finalized decisons
- Caused by frontal lobe damage
The thalamus and basal ganglia are . . .
. . . islands of gray matter in the center of the brain, surrounded by white matter.
Thalamus
- A collection of nuclei, most of which project to one or more cortical regions
- Four basic types of circuitry pass through thalamic nuclei en route to the cortex:
- Sensory pathways
- Motor control pathways
- Consciousness/arousal pathways
- Cognition/emotion pathways
Ventral posterior lateral nucleus
- Nucleus within the thalamus
- Takes in somatosensory information from the anterolateral and dorsal column pathways and relays it to the post-central gyrus
Lateral geniculate nucleus
- Nucleus within the thalamus
- Takes in visual information from the optic tracts (so one visual field each, one on each side) and relays it through the inferior and superior radiations to the occipital lobe
The basal ganglia are part of circuits that ___.
The basal ganglia are part of circuits that initiate and coordinate movements, and dysfunction in the basal ganglia leads to movement disorders
Brain arterial supply diagram
Vascular territories of brain - lateral view
Vascular territories of brian - view along longitudinal fissure
Brain watershed territories
Anatomic and functional regions hit by MCA infarct
- Largest territory of any cerebral artery
- Parts of frontal, parietal, and temporal lobe
- Include the motor and premotor regions, somatosensory cortex, the frontal eye fields, the language areas, as well as parietal regions of spatial attention, and superior and inferior visual radiations
- Full left MCA syndrome causes right hemiplegia and hemisensory loss, aphasia, gaze deviation toward the left, and right homonymous hemianopia.
Full left MCA syndrome
Full left MCA syndrome causes right hemiplegia and hemisensory loss, aphasia, gaze deviation toward the left, and right homonymous hemianopia.
Full right MCA syndrome
A full right MCA syndrome causes left hemiplegia and hemisensory loss, left-sided neglect, gaze deviation to the right, and left-sided homonomyous hemianopia.
M1 segment of the MCA
The MCA’s stem
Gives off the lenticulostriate penetrating branches that supply the basal ganglia and internal capsule before dividing into superior and inferior branches known as the M2 segments.
M2 segments of the MCA
- The superior M2 branch of the MCA supplies Broca’s area (most commonly on the left), the motor cortex, and the superior visual radiation,
- whereas the inferior M2 branch supplies Wernicke’s area (most commonly on the left) and the inferior visual radiation
Anatomic and function regions hit by ACA infarct
- ACAs supply the anterior, superior, and medial frontal lobes and the superior and medial parietal lobes—essentially all of the frontal and parietal lobes not supplied by the MCAs
- ACA strokes cause contralateral leg weakness and sensory loss more so than face and arm weakness and sensory loss
- ACA strokes can also cause cognitive changes such as abulia
MCA, ACA, arms, and legs
One typically learns that the MCA supplies the face and arm areas on the lateral surface of the homunculus and the ACA supplies the leg area, so that MCA strokes cause contralateral face and arm weakness much more so than leg weakness, and ACA strokes cause contralateral leg weakness much more so than face and arm weakness.
This is true for the gray matter on the cortex surface, but of course, if white matter pathways are affected, this can cause a complete contralateral hemiparesis or hemiplegia affecting the face, arm, and leg
Anatomic and functional regions hit by PCA infarction
- The PCAs supply the occipital lobes, inferior medial temporal lobes, and the thalami
- Deficits can include contralateral homonymous hemianopia or superior quadrantanopia, impaired short-term memory (with medial temporal or hippocampal involvement), alexia without agraphia (if dominant temporal lobe), prosopagnosia (if non-dominant lobe temporal lobe), and/or changes in cognition and/or level of arousal (if thalamus is involved)
Lacunar strokes
- Caused by occlusion of small penetrating arteries affecting the subcortical white matter (internal capsule), subcortical gray matter (basal ganglia, thalamus or anterior pons)
- Syndromes include:
- Pure motor stroke - posterior internal capsule or anterior pons
- Pure sensory stroke - VPL/VPM nuclei of thalamus\
- Ataxia-hemiparesis - internal capsule or anterior pons, involving the corticospinal tract and corticopontocerebellar fibers
- Dysarthria–clumsy hand - internal capsule or anterior pons
MCA-ACA watershed stroke
- Infarction in the MCA-ACA borderzone can cause proximal arm and leg weakness with preserved strength distally in the hands and feet
MCA-PCA watershed stroke
- MCA-PCA watershed region is at the parieto-occipital junction
- When the MCA-PCA watershed region is affected bilaterally, the patient will often have deficits in visual attention that can include some or all of the elements of Balint’s syndrome: optic ataxia, ocular apraxia, and simultanagnosia
ACA, MCA, PCA stroke summary image
Lacunar stroke summary image
Area of the brain associated with spatial reasoning, calculation, and attention
Area of the brain associated with recognition memory
Why is it that profound cases of neglect tend to be left-sided or non-dominant sided?
Both the right and left hemispheres can attend to the right, but only the right hemisphere can attend to the left.
Limbic system summary image
Ataxia vs Apraxia
Ataxia is a neurological sign wherein there is loss of coordination of muscles. It is a type of movement disorder. Apraxia, on the other hand, is the inability to execute complex, purposeful movements which have already been learnt by the person.
