Functional Areas of Cerebral Cortex 1

• Anatomically the cortex is divided into 6 lobes: frontal, parietal, temporal, occipital, limbic and insular

• Each lobe has several gyri• Functionally the cortex is

divided into numbered areas first proposed by Brodmann in 1909

• Brodmann’s areas were described based on cytoarchitecture; later they were found to be functionally significant

Functional Areas of Cerebral Cortex 2

• Cytoarchitecture is based on the density of different cortical neurons and thickness of layers

Frontal Lobe

• Makes up 1/3 of all cerebral cortex

• Primary motor• Premotor• Frontal eye field• Supplementary motor• Prefrontal• Broca’s area

Primary Motor Cortex: Area 4

• Somatotopic organization

• Size of areas is proportional to the degree of skill involved with movement

• Lesions of motor cortex result in paralysis/paresis of contralateral body area

Premotor Cortex: Area 6

• Contains programming for movements

• Electrical stimulation produces slower movements of larger groups of muscles compared to area 4

• Lesion produces apraxia - inability to perform voluntary movement in the absence of paralysis

Frontal Eye Field: Inferior Part of Area 8

• Stimulation produces conjugate eye movement to contralateral side

• Lesion produces transient deviation of eyes to ipsilateral side and paralysis of contralateral gaze

Supplementary Motor Area: Parts of Areas 6 and 8

• Medial surface• Stimulation

produces posturing responses such as turning head and eyes toward moving arm

• Programming for complex movements involving several parts of the body

Prefrontal Cortex: Areas 9, 10, 11, 12, 32, 46, and 47

• Nearly 1/4 of all cortex• Orbitofrontal area

functions in visceral and emotional activities

• Dorsolateral area functions in intellectual activities such as planning, judgement, problem solving and conceptualizing

Prefrontal Cortex 2

• Lesions cause loss of initiative, careless dress, loss of sense of acceptable social behavior

• Prefrontal leucotomy or prefrontal lobotomy were once common surgical procedures to treat patients with severe behavioral disorders

• Now drugs are used

Broca’s Area: Area 44 & 45

• Part of the inferior frontal gyrus

• Functions in speech

Parietal Lobe

• Includes over 1/5 of total cortex

• Primary somatosensory• Secondary

somatosensory• Gustatory• Association

Primary Somatosensory Area: 1,2,3

• Somatotopically organized• Areas of cortex

proportional to sensory discrimination of the area not to amount of surface area

• Stimulation produces contralateral tingling or numbness but never pain

• Lesions cause contralateral loss of tactile discrimination and position sense but no relief of pain

Secondary Somatosensory Area

• Parietal operculum into posterior insula; posterior part of area 43

• Bilateral input• Somatotopy poorly

defined• Pain is perceived

here

Primary Gustatory Cortex: Area 43

• Anterior part of parietal operculum

• Lesion results in contralateral (mostly) ageusia

Parietal Association Cortex : Areas 5,7,39,40

• 5 input from S1• 7 input from visual

and motor cortex• 39&40 input from all

association areas– function in hand

performance– neglect syndrome– astereognosis

Parietal Neglect SyndromeClinical Illustration

• Failure to recognize side of body contralateral to injury

• May not bathe contralateral side of body or shave contralateral side of face

• Deny own limbs• Objects in contralateral

visual field ignored

Temporal Lobe

• 1/4 of total cortex• Primary auditory• Auditory association• Visual association• Limbic

Primary Auditory Cortex: Areas 41 &42

• Transverse temporal gyrus

• Tonotopic organization• High freq posteromedial

and low freq anterolateral

• Lesion causes difficulty in recognizing distance and direction of sound, especially when the sound comes from the contralateral side

Auditory Association Cortex: Area 22

• Wernicke’s area (posterior part of 22)• Language understanding and formulation• Damage can result in aphasia

Limbic Temporal Cortex: Areas 20,21, 27,28,29,30, 34,36,38

• Visceral function, emotions, behavior, memory

• Stimulation can elicit past events

• Left posterior area memory of verbal info

• Right posterior area memory of visual info

• Bilateral lesion of 20,21 causes prosopagnosia, loss of facial recognition

• Often damaged in Alzheimer’s disease

Occipital Lobe: Areas 17,18,19

• 17 striate cortex, primary visual cortex

• Macular vision in posterior part

• Lesion causes homonymous hemianopsia

Occipital Lobe: Areas 18 & 19

• 18 parastriate cortex• 19 peristriate cortex• Receive visual info from 17 bilaterally• Complex processing for color, movement,

direction, visual interpretation• Lesion can cause visual agnosia

Hemispheric Lateralization of Function

• Hemisphere with language function is termed “dominant”• 10% of population is left-handed• 13% male, 9% female are left-handed• 95% of right-handers have language in left hemisphere• 75% of left-handers have language in left hemisphere• Handedness and language dominance develop before speech

begins• Dominant hemisphere also excels in analytical thinking and

calculation

• Nondominant hemisphere excels in sensory discrimination, emotional/nonverbal thinking, artistic skill, music, spatial perception and perhaps face recognition

Language Areas of the Brain 1

• Broca’s area, 44 & 45 is the motor speech center

• Motor programs for speech production

• Projects to motor cortex areas controlling vocal cords, tongue and lips

• Lesion causes expressive aphasia with poor articulation, short sentences, slow speech

Language Areas of the Brain 2

• Wernicke’s area, posterior part of 22

• Functions in comprehension and formulation of language

• Lesion causes receptive aphasia with defective use of words, meaningless verbiage, lack of comprehension

Spoken Description of Visualized Scene

• Visual input to 17 with further processing in 18 & 19

• On to area 39 where objects named and recognized

• Then to 22 where words are assembled into sentences

• Then to Broca’s area 44 & 45

• Then to adjacent motor cortex for expression