Lecture 8: Functional Organisation of the Cortex

Question 1

Look at the following case study:

• 20 year old woman fainted, unconscious for several hours.
• Once awake, unable to speak apart from saying ‘damn’ repeatedly due to frustration of loss of speech.
• Able to print words with L hand. R hand limp and paralysed.
• Months later: Loss of speech persisted, R arm and hand weak.

Locate the lesion. Structures involved? Vessel involved?

Answer 1

There may be a lesion in Broca’s area - loss of speech but she is able to interpret the meaning of words. This is also near the motor areas of the brain and so could explain why her right hand is limp.

Broca’s area is found in the left hemisphere.

The vessel involved may be the MCA.

Question 2

By how much does the thickness of the cerebral cortex vary?

Answer 2

2-4mm

The cerebral cortex is heavily folded to increase the surface area. There is a laminar arrangement I-VI layers.

Question 3

What are the additional sulci and gyri of the frontal and temporal lobe?

Answer 3

In addition to the pre-central gyrus, there is also a superior gyri, middle gyri and inferior gyri of the frontal lobe. These are seperated by the superior and inferior sulci.

In the temporal lobe there is a superior, middle and inferior gyri separated by the superior and inferior sulci.

Question 4

What are the sulci of the occipital lobe?

Answer 4

• The Pareto-occipital sulcus

- The calcarine sulcus (more inferior)

Question 5

What are the gyri and sulci of the limbic lobe?

Answer 5

The cingulate sulcus creates the cingulate gyrus. The collateral sulcus and the parahippocampal gyrus form the uncus (in the temporal lobe).

Question 6

What is the result of an uncle herniation?

Answer 6

The uncus is closely related to the midbrain. Any increased cranial pressure can cause herination. If the uncus herniates below the tentorium cerebelli we get an uncal herination. It therefore compresses on the midbrain. Here there is the origin of the oculomotor nerve.

Question 7

What is Broadmann’s areas?

Answer 7

Cortical map - divided into 46 areas. Specific areas of the cortex are believed to carry our specific functions. Some of these numbers remain today.

Question 8

What are the primary projection areas?

Answer 8

This is where the specific sensory pathways end. They are in charge or perceiving sensation such as touch and hearning.

General sensation - post central gyrus.

Visual - Either side of calcarine sulcus and the occipital pole.

Auditory - Heschl’s Gyrus (superior temporal gyrus)

Olfactory - Uncus

Gustatory - Inferior post-central gyrus

Primary motor cortex - Pre-central gyrus. This is where motor pathways originate.

Question 9

What is the role of secondary sensory and motor areas?

Answer 9

These areas are involved in interpretation.

Secondary sensory areas - involved in interpretation and understanding of sensation. Receive input form primary sensory areas. 
Secondary motor areas - organises patterns of movement

Question 10

Give the secondary sensory areas.

Answer 10

• General sensation (somaesthetic) - superior parietal lobe
• Visual - Pre-striate area
• Auditory - Lateral fissure / superior temporal gyri

Question 11

Give the secondary motor areas.

Answer 11

Pre-motor areas - Anterior to the pre-central sulcus on the lateral surface

Supplementary motor area - Anterior to the pre-central sulcus on the medial surface.

In these area learned complex motor activities are stored.

Frontal eye field - Anterior to the pre-motor. This area is involved control of voluntary scanning movements of the eyes.

Broca’s area - Found in the inferior frontal gyrus in the dominant hemisphere (the left in most people). It regulates the pattern if breathing and vocalisation needed for normal speech.

Question 12

How is the primary motor cortex organised?

Answer 12

Somatopically organised

Question 13

How is the primary somatosensory cortex organised?

Answer 13

Specific areas of the body are projected and displayed in specific areas of the cortex. Information that moves the toes for example starts in the very midline. This is the same for sensory information. It travels form the body to the thalamus and projected to the corrected area in the post central gyrus e.g. for toes in the midline. For the face, it will be projected more laterally.

Face is more laterally, then the arms, trunk, the legs then the toes.

Question 14

What is the result of a defect in the the association somatosensory areas?

Answer 14

Agnosia - inability to interpret sensation.

	Superior parietal lobe involved in interpretation, undressing and recognition. It give spatial analysis. It tells you what type of sensation it is - pinching, burning etc. Injury to the primary somatosensory areas we either get reduced (hypaesthesia) or aesthesia - diminished sensation.

Question 15

How is the primary auditory cortex organised?

Answer 15

Tonotopically organised

Question 16

What is the role of the association auditory cortex?

Answer 16

This gives meaning and significance to sound. It surrounds the primary auditory area.

Wernicke’s area is found in the dominant hemisphere and is involved in interpretation of written or spoken word.

Question 17

How is the primary visual cortex organised?

Answer 17

Retinotopically organized

- Area around calcarine sulcus and occipital pole.

Question 18

What is prosoagnosia as a result of?

Answer 18

Lesion in the associated areas of the visual cortex.

Prosoagnoisa is the inability to recognise faces.

Question 19

Where is the taste cortex found?

Answer 19

Inferior margin of the post-central gyrus and extends into the insula. The insula is found between the frontal, parietal and temporal bone. This area perceives taste

Question 20

What is the role of the prefrontal cortex?

Answer 20

Prefrontal cortex: anterior to all the other areas, regulates mood and feelings. It is involved in higher order cognitive function. Important in judgment, planning and conceptualisation. Important in personality and character.

Question 21

What is the role of the Parieto-temporal cortex?

Answer 21

Parietotemporal cortex - spans parts of the parietal and temporal lobe. Integrates information from different modalities such as vision, hearing, touch and gives it all meaning. It is also involved in memory. An example is when you hear and taste things that you associate with a memory it will store it and send it to activate the memory.

Question 22

What precedes conduction aphasia?

Answer 22

Damage to the Arcuate fasciculus. This connects Wernicke’s area and Broca’s area in the dominant hemisphere. It is an association area. A lesion means there is no connection between the area that produces language and the area that understands it. Conduction aphasia occurs if the pathway is disrupted.

This leads to to impaired repetition, but comprehension and fluency is intact.

Question 23

Which is the dominant hemisphere?

Answer 23

Left - found here is linguistic function and numerical skills

Question 24

What is found in the non-dominant hemisphere?

Answer 24

Spatial awareness

Question 25

What is the term given to: “Inability to perform purposeful/learned skilled movements.”

What can cause this?

Answer 25

Apraxia

Injury to the associated motor areas. Injury to the pre-central gyrus itself can lead to paresis or paralysis is severe enough.

Question 26

How is the thalamus involved in sensation?

Answer 26

Sensory information stops in the associated area of the thalamus before being projected. It is also somatotopically organised.

	The thalamus is divided into specific nuclei:
	• Lateral Ventral posterolateral receives input from leg projects to midline 
	• Medial Ventral posteromedial  receives input from arm project to lateral region

	• VPM receives inputs from face projects  to lateral region