Cerebral Cortex

Lecture 10

What are the six layers of the neocortex?

I: molecular, II: granular, III: small pyramidal, IV: granular, V: large pyramidal, VI: fusiform pyramidal.

Which neocortical layer receives most thalamic sensory input?

Layer IV.

Which layers send corticocortical projections?

Layers II and III.

Which layer sends major subcortical motor outputs (e.g., CST)?

Layer V.

Which layer sends corticothalamic projections?

Layer VI.

What are the two types of corticocortical pathways?

Association (same hemisphere) and commissural (contralateral hemisphere).

What is the major commissural pathway connecting hemispheres?

Corpus callosum.

What are U-fibers?

Short association fibers connecting adjacent gyri.

What is the superior longitudinal fasciculus?

A long association fiber connecting frontal, parietal, and occipital lobes.

What are Brodmann areas based on?

Cytoarchitecture (cellular organization).

Where is primary somatosensory cortex located?

Postcentral gyrus (S1).

Which nucleus projects visual input to the primary visual cortex?

LGN → area 17.

Which nucleus projects auditory input to primary auditory cortex?

MGN → area 41.

What is the functional role of the prefrontal cortex?

Executive function: planning, insight, personality, inhibition.

What deficit results from right posterior parietal damage?

Contralateral neglect.

Compare short vs. long association fibers with examples.

• Short (U-fibers): connect adjacent gyri; form local circuits.

• Long association: connect distant lobes:
  -Superior longitudinal fasciculus (arcuate fasciculus): speech areas.
  -Cingulum: connects limbic areas.
  -Uncinate fasciculus: connects orbitofrontal cortex ↔ temporal pole.

Give key Brodmann areas and their functions relevant for exams.

• 4: primary motor cortex (M1).

• 6: premotor + supplementary motor areas.

• 1–3: primary somatosensory cortex (S1).

• 5,7: somatosensory association.

• 17: primary visual cortex (V1).

• 18,19: visual association.

• 41: primary auditory cortex.

• 42: auditory association.

• 22: auditory/language (Wernicke).

• 44/45: Broca’s area.

Describe the functional organization of the parietal lobe and how lesions present.

• Inputs: VPL/VPM (somatosensory pathways).

• S1 (postcentral gyrus): somatotopic homunculus.

• S2 + association areas (5,7): integration and higher-order processing.

• Lesions:

  • Agnosia: inability to recognize objects with intact sensation.

  • Right parietal = contralateral neglect.

  • Apraxia: inability to perform learned movements despite intact motor ability.

Describe the visual cortical hierarchy and lesion effects.

• LGN → V1 (17): retinotopic map; destruction = cortical blindness.

• V2–V5: higher-order visual processing (motion, color, recognition).

• Lesions to association areas → agnosias (e.g., prosopagnosia, movement blindness).

Describe auditory cortical organization.

• MGN → area 41: tonotopic.

• Area 42 + area 22 (Wernicke): comprehension.

• Lesions → impaired language comprehension or difficulty localizing sound.

Describe the motor hierarchy in the frontal lobe.

• M1 (4): executes movement.

• PMC (lateral 6): planning based on external cues.

• SMA (medial 6): internally generated movements.

Describe dorsolateral vs. ventromedial PFC.

• DLPFC: working memory, planning.

• VMPFC: emotional regulation via limbic connections.

• Damage → impulsivity, inappropriate behaviour, poor emotional regulation.