Functional Areas of the Cerebral Cortex

Diagram: Motor and Sensory Functional Areas

I. Motor Areas (Anterior to the Central Sulcus)

1. Primary Motor Cortex (Brodmann Area 4)

• Located on the precentral gyrus, immediately anterior to the central sulcus
• Contains the motor homunculus - a somatotopic map of the body where face and hand areas are on the lateral convexities and the leg area dips into the interhemispheric fissure
• More than half the primary motor cortex is devoted to controlling the hands and muscles of speech
• Stimulation of a single neuron usually causes contraction of a group of muscles ("a specific movement rather than one specific muscle")
• Output travels via the corticospinal (pyramidal) tract to the spinal cord

2. Premotor Area (Brodmann Area 6)

• Lies 1-3 cm anterior to the primary motor cortex
• Generates complex "patterns" of movement - e.g., positioning the shoulder and arm before hand use
• Contains mirror neurons (active both when performing a task and when observing someone else perform it)
• The anterior part creates a "motor image" of the total movement; the posterior part executes it sequentially, sending signals either directly to the primary motor cortex or via the basal ganglia-thalamic circuit

3. Supplementary Motor Area (also Brodmann Area 6)

• Located on the medial surface, just above the premotor area, extending into the longitudinal fissure
• Works with the premotor area to plan bimanual and complex sequential movements
• Important for initiating voluntary movement (lesions cause akinesia)

4. Frontal Eye Field (Brodmann Area 8)

• Located anterior to the premotor area in the prefrontal cortex
• Controls voluntary conjugate eye movements (turning the eyes)
• Stimulation causes eyes to deviate to the contralateral side

II. Sensory Areas (Posterior to the Central Sulcus)

5. Primary Somatosensory Cortex - Somatosensory Area I (Brodmann Areas 3, 1, 2)

• Located on the postcentral gyrus, immediately posterior to the central sulcus
• Receives cutaneous, proprioceptive, and kinesthetic signals relayed via the ventrobasal thalamus
• Has high-degree somatotopic organization (sensory homunculus) - face and hand have disproportionately large representation
• Sensory input arrives at layer IV; output leaves via layers V and VI
• Area 3a - deep muscle/joint sensation; Area 3b - cutaneous touch; Areas 1 and 2 - texture and size discrimination

6. Somatosensory Area II (Brodmann Area 40, lateral parietal)

• Smaller secondary somatosensory area located in the upper wall of the Sylvian fissure
• Also has body representation but less precise; important for bilateral sensory integration

7. Somatosensory Association Area (Brodmann Areas 5, 7)

• Located in the posterior parietal lobe, posterior to the primary somatosensory cortex
• Interprets the meaning of somatosensory signals - stereognosis (recognizing objects by touch), shape, texture
• The nondominant (usually right) parietal association cortex is critical for attention to the contralateral body and space - its damage causes hemispatial neglect

8. Primary Visual Cortex (Brodmann Area 17)

• Located along the calcarine fissure of the occipital lobe (medial surface)
• Receives visual signals from the contralateral visual hemifield via the optic radiations (Meyer's loop passes under the temporal lobe; superior fibers pass under the parietal lobe)
• Highly organized retinotopic map; responds to contralateral visual field
• Damage causes contralateral homonymous hemianopia

9. Visual Association Cortex (Brodmann Areas 18, 19)

• Surrounds the primary visual cortex
• Processes color, form, movement, and spatial relationships
• Two main pathways:
  • Dorsal stream ("where/how"): to posterior parietal cortex for spatial processing
  • Ventral stream ("what"): to inferior temporal lobe for object and face recognition

10. Primary Auditory Cortex (Brodmann Areas 41, 42)

• Located in the superior temporal gyrus (Heschl's gyri), within the lateral/Sylvian fissure
• Receives input from the medial geniculate body of the thalamus
• Has at least 6 tonotopic maps - low frequencies anteriorly, high frequencies posteriorly
• Determines pitch, loudness, and sound localization

11. Auditory Association Cortex (Brodmann Area 22 and surroundings)

• Located adjacent and posterior to the primary auditory cortex
• Processes patterns of sound, sequences of tones, and auditory memory
• Extends into the parieto-occipital junction where it can associate auditory with somatosensory information
• Destruction causes inability to distinguish different sound patterns despite intact hearing

III. Association Areas

12. Parieto-Occipito-Temporal Association Area

• Located at the junction of the parietal, occipital, and temporal lobes (Brodmann areas 5, 7, 39, 40)
• The major "integrative" area of the brain - combines visual, auditory, and somatosensory inputs
• Functions include: analysis of spatial coordinates, language, reading, and complex object recognition
• Provides preanalyzed sensory input to the prefrontal cortex for planning

13. Wernicke's Area (Brodmann Area 22 posterior / Areas 39, 40)

• Located in the posterior superior temporal gyrus of the dominant (usually left) hemisphere, adjacent to the primary auditory cortex
• The "language comprehension" center - interprets the meaning of spoken and written words
• Receives input from visual and auditory cortices; integrates language comprehension
• Damage causes Wernicke's (receptive) aphasia: fluent but meaningless speech; poor comprehension

14. Prefrontal Association Area (Brodmann Areas 9, 10, 11, 12, 46)

• Located in the anterior frontal lobe, anterior to the premotor area
• Functions:
  • "Elaboration of thought" - storing working memory for combining new thoughts
  • Planning complex sequences of actions
  • Executive functions: judgment, impulse control, social behavior, abstract reasoning
• Receives massive input from the parieto-occipito-temporal association area via a subcortical fiber bundle
• Output to motor system passes through the caudate-thalamic circuit

15. Broca's Area (Brodmann Areas 44, 45)

• Located in the inferior frontal gyrus of the dominant hemisphere, just anterior to the primary motor cortex face area
• Contains the neural circuits for word formation and speech production - planning the articulatory motor program
• Works closely with Wernicke's area via the arcuate fasciculus
• Damage causes Broca's (expressive/non-fluent) aphasia: comprehension intact, speech is labored and reduced

16. Limbic Association Area

• Located in the anterior temporal pole, ventral frontal lobe, and cingulate gyrus (deep in the longitudinal fissure)
• Concerned primarily with behavior, emotions, and motivation
• Part of the broader limbic system that provides emotional drive and motivational impetus for learning

17. Facial Recognition Area

• Located on the inferior medial surface of the occipital and temporal lobes
• Specialized for recognition of faces
• Damage causes prosopagnosia (inability to recognize familiar faces)

Summary Table

Key Concepts to Remember

1. The central sulcus is the key landmark - motor anterior, sensory posterior
2. Dominance: Language areas (Broca's + Wernicke's) are in the dominant (left) hemisphere in ~95% of right-handed people; spatial/attentional areas are in the nondominant (right) hemisphere
3. Thalamocortical unity: Each cortical area works in concert with a specific thalamic nucleus - cutting thalamic connections nearly abolishes cortical function in that area
4. Layer specificity: Sensory signals arrive at layer IV; motor output leaves from layers V-VI
5. Lesion consequences: Understanding which area is damaged predicts the neurological deficit (aphasia type, neglect, visual field defect, apraxia, etc.)