S3: Injury to the Cerebral Hemispheres and Cognitive Function Flashcards
1
Q
What is the first question a neurologist is going to ask (for injury in the brain)?
A
Q: where is the lesion in the brain? The key to answering this question are two part, firstly the findings of the clinical examination and observation and secondly a rudimentary understanding of neuroanatomy.
2
Q
Describe hemispheric structure
A
- The cerebral cortex is the outer layer of folded grey matter of the brain and consists of cell bodies, dendrites and myelinated axons.
- The hemispheres are divided in two by the corpus callosum, which contains fibres that project into the white matter of both hemispheres, this allows communication between the two.
3
Q
What does the left and right hemispheres of the brain tend to do?
A
- The left hemisphere controls the right side of the body and right hemisphere the left.
- Left hemisphere also deals with verbal info while right with spatial.
- Left (usually) contains the apparatus that deals with expressive speech and comprehension while the right deals with nonverbal aspects of communication.
- Left appears to deal with arithmetic while right number estimation. Linking on with this it seems that left deals with linear reasoning while the right much more wider holistic problem solving.
4
Q
How is the frontal lobe divided?
A
The frontal lobe can be divided up into a number of sub-regions.
- Starting from the back we have the motor, premotor and supplementary motor areas (SMA).
- We also have the inferior frontal cortex (inferior frontal gyrus) which deals with language.
- Finally we have the prefrontal cortex which is divided into dorsolateral, ventromedial and orbital.
5
Q
Describe role of the motor areas in frontal lobe
A
- The primary motor cortex is for voluntary motor activity of limbs with somatotopic organisation in the cortex.
- The premotor area appears to provide voluntary motor activity to the trunk.
- The supplementary motor area (SMA) has a role in more complex and bimanual movements.
- The motor strip is controlling voluntary movements of the opposite side of the body.
6
Q
Describe how damage to primary motor areas is easiest to spot
A
- Damage to the primary motor areas will lead to difficulties with voluntary motor activity of limbs.
- The more medial the lesion, the more it will affect the lower limb. The more lateral, it will affect the face and upper limb.
- Remember the motor strip controls opposite side of the body.
- These two facts allow us to infer where the lesion may be.
- For example, if weakness is on the right hand-side we can assume the damage is to the left hemisphere. The particular part the weakness is in allows us to infer where the lesion is on the motor strip, due to its somatotopic organisation. A meningioma of the falx, may just affect the legs and lower extremity, whereas a lesion more lateral may produce problems with speech.
7
Q
Describe the inferior frontal regions in the frontal lobe
A
- The left inferior frontal gyrus (trangular area and opercular region) is associated with Broca’s area which is critical for speech output.
- A lesion here will produce Broca’s aphasia, where the patient has severely reduced verbal output, with halting and effortful articulation but preserved comprehension.
8
Q
Describe the prefrontal regions in the frontal lobe
A
- Dorsolateral frontal complex which is important for self monitoring (how far you’ve got in achieving you goal), planning and problem solving. It makes sure everything is going to plan and it is referred to as ‘executive function’. This is particularly on the left hemisphere and a lesion here could result in patient being disordered and unorganised.
- Polar and orbitofrontal cortex which are areas of the brain critical for personal interaction, understanding social norms and creating our own personality. Although our personalities are different, we still know there are certain ground rules we shouldn’t break e.g. swearing at random people. A lesion in this area could cause a patient to act completely differently, swearing and insulting people as well as being nice to people they don’t know.
9
Q
Describe parietal lobe and how lesions may affect it
A
- Split into the dominant parietal lobe (usually left) and non-dominant parietal lobe (usually right).
- Anatomically split into superior parietal lobule and inferior parietal lobule.
- The parietal lobe is heavily involved in sensations of touch, smell and taste. So a loss could lead to lack of sensation on the contralateral side of the body.
- However, as there are many aspects e.g. going through the thalamus, generally parietal lesions doesn’t lead to hemiloss sensation.
- The parietal lobe works a lot in multimodal integration, this is integrating primary sense modalities particularly touch, smell and taste.
10
Q
Describe the dominant parietal lobe of frontal cortex
A
- This is usually left.
- The parietal lobe is involved in numeracy and goal-directed movement (called ‘praxis’).
- An individual who has a lesion in the dominant parietal lobe they may find they can’t get manipulate their hands properly (apraxia).
11
Q
Describe the nondominant parietal lobe of frontal cortex
A
- This is usually right.
- It is involved in understanding spatial relations.
- So someone with a nondominant parietal lesion may have difficulty understanding spatial relations. A common symptom of a non-dominant parietal lobe is dressing apraxia, this isn’t a real apraxia (due to not being able to move limbs in a goal-directed manner), rather it is a confusion in the spatial relations of things leading to struggling to put clothes on (as an example).
They may also say they get lost or can’t remember when they leave the house to go left or right. - Nondominant parietal lobe lesions are also associated with another phenomenon called hemispatial neglect. The left hemisphere is very focused, its spotlight of attention is on the right side of the visual space. The right hemisphere takes in everything. If you shut down the left hemisphere the brain would still take in everything in the visual field. If you shut down the right hemisphere, the attention would be focused on one side, this is hemispatial neglect.
12
Q
Describe the occipital lobe
A
- The occipital lobe is the visual lobe of the brain, it is the final destination of the visual pathway.
- Different aspects of the visual world are processed by different parts of the occipital lobe.
- Visual information is transmitted from the retinal photoreceptors in the optic nerve via the thalami.
13
Q
How is the cortical processing in the occipital lobe hierarchiacal?
A
- Cortical processing is hierarchical, area V1 (striate cortex) is at the top of this hierarchy so damage to V1 gives rise to loss of all visual information coming into the cortex. This leads to cortical blindness or hemianopia.
- V2, V3 in front, the prestriate cortex are sensitive to/process different visual primitives (certain aspects of vision) e.g. colour or motion.
- Features of the visual world are processed by different parts of the visual cortex. This gives rise to a number of unusual clinical syndromes such as acquired colour blindness (achromatopsia) or even akinetopsia (patient can only see stationary objects but cannot see motion).
14
Q
Describe the temporal lobe
A
- The temporal lobe is important for hearing, it contains the primary auditory cortex located inside the lateral sulcus.
- It is also involved in language comprehension, this occurs in Wernicke’s area.
- A patient who has a lesion in Wernicke’s area will not understand what is said to them but will speak fluently. However their speech is nonsensical, often containing meaningless word-like sounds (neologisms). This is because they are unable to self-monitor their speech.
15
Q
What is the limbic system?
A
- The limbic lobe comprises a group of interconnected structures in the temporal lobe and midbrain. It includes the hippocampus, cingulate gyrus, mammillary bodies etc.
- This system is important in encoding new information and memories. Most people’s limbic systems are very active.
- Damage to critical parts of the limbic lobe can give rise to an “amnestic syndrome”, this is an inability to store new information, whilst fully aware of their surroundings.
- Patients with damage to their limbic lobe due to alcohol will talk meaningfully and informatively but things that they say will be false and made-up, but they are unaware what they are saying is false this is called confabulation e.g. I flew in from Beijing this morning on my private jet with Joe Gatto.
Patients continuously repeat the same statements or questions.
