S7) 'Higher' cortical function

Question 1

What is the cerebral cortex?

Answer 1

A thin superficial layer of grey matter on the cerebral hemispheres.

Arranged as 6 layers containing cell bodies and dendrites (i.e. cortex is grey mater)

Question 2

Information is processed in the complex synaptic network found between inputs and outputs.

Describe the fine structure of the cortex in terms of inputs and outputs

Answer 2

• Most inputs (sensory) are from the thalamus and other cortical areas (the cortex can stimulate itself- there are recurrent feedback loops where the cortex provides its own input e.g. when 1 thought that arises from the cortex leads to another thought).
• Most outputs (motor) are from the axons- pyramidal cells and project to widespread areas

Question 3

Most outputs from the cortex are the axons of pyramidal neurons. Identify 3 examples of what the outputs can be.

Answer 3

– Outputs can be projection fibres going down to brainstem and cord (e.g. upper motor neurones)

– Outputs can be commissural fibres going between hemispheres (e.g. corpus callosum)

– Outputs can be association fibres connecting nearby regions of cortex in the same hemisphere (e.g. arcuate fasciculus)

Question 4

How is information processed between inputs and outputs?

Answer 4

Information is processed in the complex synaptic network found between inputs and outputs.

Interneurones connect inputs and outputs in a complex way, giving rise to behaviour, emotion, memory etc.

Question 5

What did phrenologists believe?

Answer 5

Phrenologists believed that personality traits and tendencies to crime etc. could be correlated with the size of bony prominences on the skull. This has now been discounted but was an early inspiration for cortical localisation

What we have now found is that various regions of the cortex have diff functional properties e.g. occipital lobe for vision, temporal lobe for memory

Question 6

Identify 6 functions of the frontal lobe

Answer 6

• Motor - primary role, it contains the primary motor cortex - contains the motor homunculus - has cell bodies of UMN that activate the various muscle groups
• Expression of speech (usually left hemisphere of frontal lobe) - contains Broca’s area
• Behavioural regulation / judgement
• Cognition - mathematical ability/ frontal lobe tests
• Eye movements - frontal eye field - regulates eye movement
• Continence (medial) - paracentral lobules are vital for regulation of micturition. - damage here = urinary incontinence e.g. in Alzheimer’s disease.

Question 7

The primary motor cortex - if there is damage here, what can happen?

Answer 7

Frontal lobe damage can result in contralateral weakness

Question 8

If have damage to Broca’s area found in the left frontal lobe, what can it result in?

Answer 8

Damage to left frontal lobe can result in expressive dysphasia

Question 9

Where is behaviour regulation/ judgement found specifically in the frontal lobe? What occurs if there is damage here?

Answer 9

– Prefrontal cortex

– Damage to frontal lobes can lead to (usually) impulsive, disinhibited behaviours e.g. sexual inappropriateness, aggression

Question 10

Where is cognition found specifically in the frontal lobe? What occurs if there is damage here?

Answer 10

– Prefrontal cortex

– Frontal lobe damage (particularly the right) can cause difficulty with tasks such as complex problem solving, including calculation

Question 11

The frontal lobe is important for eye movements. It contains the frontal eye fields. What occurs if there is damage here?

Answer 11

Damage can cause problems with conjugate gaze and other eye movement disturbances (however, diplopia without other cortical features would suggest brainstem/cranial nerve problem)

Question 12

The frontal lobe contains cortical areas responsible for maintenance of continence. Identify one of these areas and what can be seen if there is damage?

Answer 12

– Paracentral lobules

– Damage can cause urinary incontinence

Question 13

How might one test the higher cognitive ability of the frontal lobe?

Answer 13

Ask a patient to count down in 7s from 100

Question 14

Identify 5 functions of the parietal lobe

Answer 14

• Sensory - contains the primary sensory cortex
• Comprehension of speech (usually left hemisphere) - Wernicke’s area
• Body image (usually right hemisphere) - lesions here can lead to body dysmorphic disorders
• Awareness of external environment (attention)
• Calculation and writing
• The visual pathways projecting through white matter - superior optic radiations pass through the parietal lobe on their way from the thalamus to occipital lobes

Question 15

What occurs if there is damage to the primary sensory cortex at the parietal lobe?

Answer 15

Damage might result in contralateral anaesthesia affecting all modalities (modalities converge at the cortex)

Question 16

Which part of the parietal lobe is comprehension of speech found and what can occur if there is damage here?

Answer 16

– The parietal lobe contains part of Wernicke’s area

– Damage to left parietal lobe can cause a receptive dysphasia

Question 17

Body image and awareness of external environment is a function of the parietal lobe. What can occur if there is damage to the right parietal lobe?

Answer 17

Damage to right parietal lobe can lead to neglect.

Question 18

Calculation and writing is a function of the parietal lobe. It works with the frontal lobe to perform these tasks. What can occur if there is damage to the left parietal lobe?

Answer 18

Damage to left parietal lobe can affect calculation ability (but maybe also frontal lobe)

Question 19

What is hemispatial neglect?

Answer 19

• Hemispatial neglect is a neuropsychological condition occurring due to damage to one hemisphere of the brain
• There is a deficit in attention to/awareness of one side of the visual field and the patient is unable to process and perceive stimuli on one side of the body or environment

Question 20

Although not cortical function, remember that the superior optic radiation projects through the parietal
lobe! Knowing this, if damage occurs here, what can it result in?

Answer 20

Damage here can cause a contralateral inferior homonymous quadrantanopia

Question 21

Identify 4 functions of the temporal lobe

Answer 21

• Hearing - contains the primary auditory cortex - superior surface of temporal lobe, near to Wernicke’s area
• Olfaction - contains the primary olfactory cortex - infero-medial surface of temporal lobe
• Memory - deep to temporal lobe = hippocampus (lays down new memories)
• Emotion
• Visual pathways projecting through white matter - contains 3rd visual fibres going from Lateral geniculate nucleus to the occipital lobe .: temporal lobe lesion can lead to a visual field defect.

Question 22

What can occur if there is damage/ lesion to the primary auditory cortex?

Answer 22

Damage can lead to a number of complex effects on hearing which are not the remit of the unit.

Auditory hallucinations may be a feature of temporal lobe lesions

Question 23

What can occur if there is damage to the primary olfactory cortex?

Answer 23

Damage can lead to a number of complex effects on smell which are not the remit of the
unit.

Olfactory hallucinations may be a feature of temporal lobe lesions

Question 24

Which part of the temporal lobe is vital for consolidating declarative memories and what can occur if there is damage here?

Answer 24

– The hippocampus is a crucial structure for consolidating declarative memories

– Damage may lead to amnesia (but remember that there are two hippocampi, one in each temporal lobe)

– Also, some pathologies such as temporal lobe epilepsy can trigger memories, leading to a feeling of deja vu

Question 25

Which part of the temporal lobe is responsible for emotion? What are the effects of lesions found here?

Answer 25

– Temporal lobes contain a number of **limbic system structures** such as the **hippocampus and amygdala** – Effects of lesions are **complex**, but may be related to **pathogenesis of some psychiatric disorders**

Question 26

Although not a cortical function, remember that the inferior optic radiation projects through the temporal lobe. If damage occurs here, what can it cause?

Answer 26

Damage here can cause a **contralateral superior homonymous quadrantanopia**

Question 27

**A caveat about interpreting clinical data concerning brain lobe function**

Answer 27

Question 28

What can give us clues about ‘global’ cortical function?

Answer 28

Question 29

In terms of cerebral dominance, state which form of processing is over-represented in the different cerebral hemispheres (in 95% of people)

Answer 29

- **Left**: sequential processing - **Right**: 'whole picture' processing Knowledge of cerebral dominance allows us to predict the effects of lobe lesions (e.g. a dysphasia is likely to have arisen from left hemisphere damage)

Question 30

Sequential processing is dominant in the left hemisphere. Which two functions does this include?

Answer 30

- Language - Mathematics/logic

Question 31

Whole picture processing is dominant in the right hemisphere. Which four functions does this include?

Answer 31

- **Body image** - **Visuospatial awareness** (related to the disorder: neglect. where if you have a right parietal lobe lesion → fail to acknowledge existence of left ½ of the world -because the right parietal lobe tends to both halves of the space whereas the left parietal lobe only tends to the right ½ of the space. Damage to the right parietal lobe → loss of attention to the left half of the space) - **Emotion** - **Musical ability**

Question 32

In 95% people, which hemisphere is dominant? How do the 2 hemispheres differ in terms of which half they control?

Answer 32

**Left hemisphere** is **dominant in 95% of people** (think about how it **controls the right hand in most people**) The **right hemisphere ‘attends’ to both halves of space** but the **left hemisphere only ‘attends’** to the **right half of space**

Question 33

What is the corpus callosum?

Answer 33

A **huge bundle of white matter** **connecting the two hemispheres.** An early **surgical treatment for severe epilepsy** was to **cut the corpus callosum** to **prevent seizure activity from propagating through the whole brai**n. This had some interesting neuropsychological consequences for those patients…

Question 34

What could happen if there was damage to the corpus callosum?

Answer 34

Strangely, we don't get major obvious deficits - it is possible that other pathways can take over from it. Destruction of the corpus callosum can cause some interesting deficits such as alien hand syndrome and subtle effects on language processing

Question 35

**Language pathways** are **primarily found in the left hemisphere.** In light of this, where is Broca's area and what does it do?

Answer 35

**Broca's area** - inferolateral frontal lobe– site of **speech production** (**sits near to the mouth/ pharynx area of primary motor cortex**- close to the facial regions of the homunculus to economise the amount of wiring needed to connect the two together)

Question 36

If there is damage to the Broca's area, what can it cause?

Answer 36

Damage can cause **staccato speech**, where the **patient still understands what is being said to them (Broca’s / expressive dysphasia)**

Question 37

Language pathways are primarily found in the left hemisphere. In light of this, where is Wernicke's area and what does it do?

Answer 37

**Wernicke’s area** - superior temporal lobe/ at the **parieto-temporal junction** – **interpretation of language/ comprehension of speech - sits near the primary auditory cortex in the temporal lobe**

Question 38

If there is damage to Wernicke's area, what can it cause?

Answer 38

Damage can cause **fluent, nonsensical speech** where the patient **does not appear to understand** **what is being said to them** (**Broca’s /receptive dysphasia**)

Question 39

What can a large middle cerebral artery infarct result in terms of the Broca's and Wernicke's area?

Answer 39

**Large middle cerebral artery infarcts** can cause **global aphasia** where **both areas** are **destroyed** leading to **virtually no verbal language function**

Question 40

How are Broca's area and Wernicke's area connected?

Answer 40

Broca's area and Wernicke's area are connected to each other via the **arcuate fasciculus**

Question 41

Describe the arcuate fasciculus.

Answer 41

**White matter which connects Broca's and Wernicke's area.** **Most unidirectional from Wernicke's to Broca's area.** but can be bidirectional.

Question 42

Damage to the arcuate fasciculus can lead to ….

Answer 42

Damage to this white matter pathway can cause the **inability to repeat heard words**

Question 43

Language pathways overall summary

Answer 43

Question 44

Describe the pathway for repeating a heard word

Answer 44

Cochlea → auditory cortex → Wernicke's area → arcuate fasciculus → Broca's area → primary motor cortex

Question 45

Describe the pathway for speaking a written word

Answer 45

Eyes → visual cortex → Wernicke's area → arcuate fasciculus → Broca's area → primary motor cortex

Question 46

Describe the pathway for speaking a thought

Answer 46

All over the brain → Wernicke's → arcuate fasciculus → Broca's area → motor cortex

Question 47

What is Wernicke's aphasia (aka receptive aphasia)?

Answer 47

**Wernicke's aphasia** is form of aphasia wherein the ability to grasp the meaning of spoken words and sentences is impaired, while the ease of producing connected speech is not very affected

Question 48

How does a person with Wernicke's aphasia present?

Answer 48

* speaks very fluently * no hesitations * but what they say makes no sense * the person does not understand what others say * have an intact Broca's area .: able to produce speech and speak fluently * but non intact Wernicke's area where they are not able to understand what is being said hence the answers were nonsensical.

Question 49

What is Broca's aphasia (aka expressive aphasia)?

Answer 49

**- Broca's aphasia** is a form of aphasia wherein a patient has trouble speaking fluently but their comprehension can be relatively preserved - Patients have difficulty producing grammatical sentences and their speech is limited mainly to short utterances of less than four words

Question 50

How does a person with Broca's aphasia present?

Answer 50

* Hesitation, paucity of words * not able to say the words - struggling to get answers → problems with Broca's area (speech production problem) * No problem with understanding the questions being asked .: Wernicke's area intact

Question 51

What types of memory are there?

Answer 51

- **Declarative** – explicit, factual information - **Non declarative** – implicit, motor skills and emotions Both types of memory are stored in different areas .: a lesion in one, would mean sparing of the other.

Question 52

Where in the brain is memory stored?

Answer 52

Memories are thought to be stored in a **relatively ‘distributed’ fashion** throughout **large areas of the brain** - **Declarative** – cerebral cortex (in a distributive fashion) - **Non declarative** – tends to be stored in subcortical structures: cerebellum + basal ganglia

Question 53

How are memories stored?

Answer 53

**Short term memory** (seconds to minutes) becomes **long term memory** (up to a lifetime) when it is consolidated. **Consolidation** depends on emotional **context** (e.g. traumatic events - less recall), **rehearsal** (e.g. revising using flashcards/ notes) and **association**

Question 54

Consolidation is needed to convert short term memories into long term memories. What are the factors influencing consolidation?

Answer 54

o **Emotional context** (if an event has strong emotional content, then it tends to be remembered better) o **Rehearsal** (you are all familiar with this idea) o **Association** (if you can associate a piece of knowledge with something you already know it tends to be more easily remembered)

Question 55

How is short term memory vs long term memory stored?

Answer 55

**Short term memory:** Stored for **seconds to minutes** as a **‘reverberation’ or ‘echo’ in cortical circuit** **Long term memory:** Stored for **very long periods** in the **cerebral cortex, cerebellum** etc. (up to a lifetime) following consolidation

Question 56

Which part of the brain is responsible for declarative memory consolidation?

Answer 56

The **hippocampus** is crucial for consolidating declarative memories

Question 57

The hippocampus receieves multiple inputs. What are they?

Answer 57

Visual system Auditory system Somatosensory system Limbic system .: It has multimodal inputs from many brain systems (making it good at associating stimuli)

Question 58

The hippocampus also has a role as an ‘oscillator’, facilitating consolidation of memories in the cortex via its output pathways. What is the pathway?

Answer 58

primarily the fornix → mammillary bodies → thalamus → cortex)

Question 59

Neuroplasticity: the molecular and cellular mechanisms of memory .. What is the key molecular mechanism of memory consolidation?

Answer 59

**Long term potentiation** (LTP) is the key molecular mechanism of memory consolidation → Causes **changes in glutamate receptors** in synapses leading to **synaptic strengthening** **→ New physical connections** can also **form between neurone**s to **further strengthen connections (**axonal sprouting)

Question 60

Learn this table.

Answer 60