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 Syndrome Clinical 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