Higher Cortical Function

Question 1

What is the structure of the cortex?

Answer 1

There are six layers of pyramidal cells. The cortex receives input from the thalamus, from other parts of the cortex and from monoaminergic neurons – which have a role as neuromodulators. The cortex has outputs to widespread areas, including other parts of the cortex, the brainstem and basal ganglia, the reticular formation and the spinal cord.

It is made up of 4 association lobes: frontal, parietal, temporal and occipital

Question 2

Give functions of the frontal lobes.

Answer 2

o	Motor output
o	Higher intellect
o	Personality
o	Social conduct
o	Expression of speech (left hemisphere - dominant)
o	Behavioural regulation, judgement and inhibition
o	Cognition
o	Eye movements
o	Continence

Question 3

Describe frontal lobe lesion

Answer 3

Personality and behavioural changes

Despite knowing the appropriate response to a situation they respond inappropriately as they are unable to regulate behaviours. They also struggle to express emotions so may be happy but not articulate this in facial expressions or speech. They may exhibit depressive symptoms and show personality changes with a lack of motivation and inability to plan for the future.

Question 4

Give parietal lobe functions

Answer 4

o Sensation – sensory cortex in postcentral gyrus
o Body image (usually right hemisphere – non-dominant)
o Awareness of external environment (usually right hemisphere – non-dominant)
o Calculation and writing (usually left hemisphere – dominant)
o Visual pathways project through the white matter

Question 5

Describe parietal lobe lesion

Answer 5

Attention deficits (associated with contralateral neglect syndrome)

Can present with hemineglect where the patient neglects half of their environment and so despite their visual pathway remaining intact they are only able to see half of the world around them. Sensory inattention can also present with the patient losing the ability to determine 3-D shapes and read words using only touch in the contralateral side. They can also have aphasia, dyslexia, dyscalculia and apraxia. They may have a contralateral lower homonymous quadrantanopia because of the projecting fibres.

Question 6

Give temporal lobe function

Answer 6

o Hearing
o Comprehension of speech (usually left hemisphere – dominant)
o Olfaction
o Memory
o Emotion
o Visual pathways project through the white matter

Question 7

Describe temporal lobe lesion

Answer 7

Recognition deficits (agnosia, prosopagnosia)

They can have word agnosia and aphasia (unable to understand language). Dyslexia and impaired memory can also present. They may have a contralateral upper homonymous quadrantanopia because of the projecting fibres.

Question 8

Give occipital lobe function

Answer 8

Vision

Question 9

What are the function of limbic association areas?

Answer 9

Attaches emotional connotations to our sensory input and consequent behaviour. It rewards appropriate behaviours with pleasure sensations and negative sensations to inappropriate behaviours. These reward/punishment centres of the limbic system are closely associated with the ability to learn.

Question 10

What is lateralisation?

Answer 10

Individuals can be described as having a dominant and non-dominant hemisphere, whereby certain functions are carried out using one side of the brain and others on the other side, known by a process ‘lateralisation’. The left hemisphere is dominant in 95% of the population.

Question 11

What is the left (dominant) hemisphere responsible for? Right?

Answer 11

The left (dominant) hemisphere is responsible for sequential processing, including language, and mathematics/logic.

The right (non-dominant) hemisphere is responsible for processing the “whole picture” – functions include perception of body image, visuospatial awareness, emotion and music.

Question 12

How do the hemispheres communicate?

Answer 12

The two hemispheres communicate mainly via the corpus callosum (there are other connections like the anterior commissure) – severing the corpus callosum leads to odd signs – like differential ability to name an object depending on whether it is seen on the left or the right (the optic chiasm remains in tact).

Question 13

Where are language pathway’s found? What are the output and input areas for language? How are they connected?

Answer 13

Language pathways are lateralised. They are found in the dominant hemisphere.

Broca’s area (output), which is found in the inferior lateral part of the frontal lobe, is responsible for formulation of language components and production of speech.

Wernickes area (input), which is found in the superior temporal lobe, is responsible for interpretation of language, written and spoken.

They are connected to each other by the arcuate fasciculus.

Question 14

Describe the pathway for repeating a heard word.

Answer 14

• Action potential encoding a sound arrives in auditory cortex, primary auditory area
• Projections are sent to Wernicke’s area – interpret the sound
• Projections along the arcuate fasciculus are sent to Broca’s area – produce speech
• Which then sends projections to the motor cortex to coordinate the production of speech

Question 15

Describe the pathway for speaking written word

Answer 15

• Visual inputs are processed in the visual cortex
• Which then send neurons to synapse in Wernicke’s area to interpret the visual input
• Which then projects along the arcuate fasciculus to Broca’s area
• Which then communicates with the motor cortex to produce speech

Question 16

Describe the pathway for speaking a thought

Answer 16

• Wernickes area receives inputs from throughout the cortex
• Which are carries to Brocas area along the arcuate fasciculus
• And then projected to the motor cortex.

Question 17

Describe Wernicke’s aphasia. What else can damage to Wernicke’s area cause?

Answer 17

• Wernicke’s aphasia (receptive/central/sensory aphasia) is a fluent aphasia, where the speech is unintelligible but is produced fluently (jargon aphasia). Damage to Wernicke’s area also impairs comprehension of language – which may be both written and spoken.

Question 18

Describe Broca’s aphasia.

Answer 18

• Broca’s aphasia (expressive/motor aphasia) results from damage to Broca’s area. People are able to understand language, but production of language is severely affected and speech may be very hesitant and stilted.

Question 19

What are the two types of memory?

Answer 19

Memory can either be declarative (the explicit recall of facts) or non-declarative/procedural (the implicit learning and performance of motor skills and emotions).

Question 20

Describe declarative memory.

Answer 20

Concerned with naming of objects, recognition of places, remembering events etc. They are assessed consciously, can be rapidly learned but also rapidly forgotten, depending upon connections between the hippocampus and widespread regions of the cerebral cortex.

It can be further subdivided into short-term and longer-term memory.

Question 21

Describe procedural memory

Answer 21

Involves the performance of motor skills that are learnt and perfected by practice, such as riding a bike. They are difficult to form yet once formed are long lasting and can be performed without conscious recollection.

Question 22

Describe the formation of memories. With reference to parts of the brain.

Answer 22

Memories are initially placed in the short-term memory, and then consolidated (consolidation depends on the emotional context, rehearsal and association), after which they may become part of the long-term memory, which can store memories for up to a lifetime.

Memories form via synaptic links between the cortical sensory areas (inputting into the region), amygdala and hippocampus (where memory occurs and structural changes develop), and the diencephalon, basal forebrain, and the prefrontal cortex (organises the memory for storage).

Question 23

What part of the brain is important for the consolidation of declarative memory?

Answer 23

The hippocampus is important for the consolidation of declarative memory. It receives inputs from the auditory and visual systems, the somatosensory system and the limbic system, and “repeats” them to the cortex.

Question 24

Describe long term potentiation.

Answer 24

LTP is a long-lasting enhancement in signal transmission between two neurons that results from stimulating them synchronously; LTP makes a memory stronger by allowing circuits to adapt to allow more presynaptic messengers to be present.

This is the strengthening (more dendritic terminals, more receptors) or pruning of synapses in order to reinforce certain connections – in response to repeated use or disuse.

Question 25

What is long term depression?

Answer 25

The opposite of LTP is long-term depression, where there is a weakening of infrequently used synapses, causing gradual loss of memory.

Question 26

What are the types of amnesia?

Answer 26

Pathological forgetting:
Anterograde amnesia
Retrograde amnesia.

Question 27

Describe anterograde amnesia. What causes it?

Answer 27

Unable to form new memories often due to damage to temporal lobes, particularly hippocampal gyrus – this is often temporary and can last from around the time of an accident to some point after this, the shorter the duration of this the better prognosis

Question 28

Describe retrograde Amnesia. Causes?

Answer 28

Unable to recall events prior to an incident (this can be due to an accident such as a car crash or conditions such as Alzheimer’s)

Question 29

What can cause amnesia?

Answer 29

Vascular interruptions, tumours, trauma, infections, or vitamin B deficiency (Korsakoff’s syndrome, commonly seen in chronic alcoholics).