Lecture 21 - Higher Cortical Function PDF

Higher Cortical Function Dr. Kelly Roballo Types of Cerebral Cortex Blumenfeld, Neuroanatomy Frontal Lobe § Makes up 1/3 of all cerebral cortex Precentral gyrus Central sulcus § Primary motor, Premotor, Frontal eye Field, Supplementary motor, Prefrontal, & Broca’s area § Motor Homunculus...

Higher Cortical Function Dr. Kelly Roballo Types of Cerebral Cortex Blumenfeld, Neuroanatomy Frontal Lobe § Makes up 1/3 of all cerebral cortex Precentral gyrus Central sulcus § Primary motor, Premotor, Frontal eye Field, Supplementary motor, Prefrontal, & Broca’s area § Motor Homunculus Exhibits somatotopic organization Primary Motor Cortex: Brodmann 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 Brodmann’s Areas Frontal Eye Field: Inferior Part of Area 8 n Stimulation produces conjugate eye movement to contralateral side n Lesion produces transient deviation of eyes to ipsilateral side and paralysis of contralateral gaze Supplementary Motor Area: Parts of Areas 6 and 8 n Medial surface n Programming for complex movements involving several parts of the body Brodmann’s Areas Prefrontal Cortex: Areas 9, 10, 11, 12, 32, 46, and 47 n Nearly 1/4 of all cortex n Orbitofrontal area functions in visceral and emotional activities n Dorsolateral area functions in intellectual activities such as planning, judgement, problem solving and conceptualizing Broca’s Area: Areas 44 & 45 • Part of the inferior frontal gyrus • Functions in speech Frontal Lobe - Prefrontal Cortex • 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 • Lobotomy: surgical severance of nerve fibers connecting the frontal lobes to the thalamus for relief of some mental disorders • Area of brain damaged in “Phineas Gage” Phineas Gage, who was an industrious, responsible, considerate young railroad construction foreman in 1848. Then a blasting accident shot a meter-long, 3-cm-wide iron tamping rod through his brain. The tamping iron entered Gage’s head below his left eye, passed through his frontal lobe, and exited the top of his head Gage survived this terrible accident, but he was a completely different person. He was quarrelsome, bad-tempered, lazy, and irresponsible. He was impatient and obstinate, and he used profane language, which he had never done before. He spent the rest of his days as a drifter, earning money by telling his story, exhibiting his scars and the tamping iron. Main Functional Areas of the Frontal Cortex Parietal Lobe • Makes up 1/5 of total cortex • Primary and secondary somatosensory, Gustatory, Association Central sulcus Postcentral gyrus § Sensory Homunculus Exhibits somatotopic organization Primary Somatosensory Area: 3,1,2 n Somatotopically organized n Areas of cortex proportional to sensory discrimination of the area not to the amount of surface area Secondary Somatosensory Area: Posterior part of area 43 • Somatotopy poorly defined Primary Gustatory Cortex: Area 43 Anterior part of parietal operculum n Lesion results in ipsilateral (mostly) ageusia (the absence or impairment of the sense of taste) Parietal Lobe Parietal Lobe Parietal Association Cortex : Areas 5,7,39,40 • 7: input from visual and motor cortex • 39&40: input from all association areas • function in hand performance • neglect syndrome • astereognosis Astereognosis: Loss of the ability to recognize the shapes of the objects by handling them Parietal Neglect Syndrome • 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 Hemispheric Asymmetry in Attention Lesions Causing Left: Hemineglect Temporal Lobe • • • • • 1/4 of total cortex Primary auditory Auditory association Visual association Limbic Primary Auditory Cortex: Areas 41 &42 n Tonotopic organization n High frequency sounds posteromedial, and low frequency sounds anterolateral n Lesion causes difficulty in recognizing distance and direction of sound, especially when the sound comes from the contralateral side Superior temporal gyrus Sylvian fissure Auditory Association Cortex: Area 22 n Wernicke’s area (posterior part of 22) n Language understanding and formulation n Damage can result in aphasia (slow speech, impaired articulation) Limbic Temporal Cortex: Visceral function, emotions, behavior, memory • Stimulation can elicit past events • Bilateral lesion of 20,21 causes prosopagnosia (a form of visual agnosia) inability to recognize faces. Often damaged in Alzheimer’s disease Temporal Lobe Occipital Lobe Area 17: striate cortex, primary visual cortex • Macular vision in posterior part • Lesion causes homonymous hemianopsia: blindness in one half of the visual field of one or both eyes • Patient will constantly look over to their blind side, aware of all they may miss otherwise Parietooccipital sulcus lingual gyrus Occipital Lobe: Areas 18 & 19 n Receive visual info from area-17 bilaterally n Complex processing for color, movement, direction, visual interpretation n Lesion can cause visual agnosia (loss of the ability to recognize familiar objects or stimuli) Inferior Occipitotemporal Cortex Hemispheric Lateralization of Function • Hemisphere with language function is termed “dominant” • 10% of population is 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 skills, music, spatial perception and perhaps face recognition * Clinical Correlation Language Areas of the Brain • 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 * Clinical Correlation Language Processing & Related Functions • Wernicke’s area • initial steps of language processing that enable particular sequences of sounds to be identified/comprehended as meaningful words • Wernicke’s area >> corresponds to Broadmann’s area 22 n Broca’s area >> articulation of the sounds that constitute speech >>> primary motor area n the motor program that activates particular sequences of sounds to produce words is formulated in Broca’s area n Broca’s area >> corresponds to Broadmann’s 44-45 * Clinical Correlation * Clinical Correlation Broca’s Aphasia • • • • (Mostly) Infarct in the left middle cerebral artery (MCA) superior division Decreased frequency of spontaneous speech Phrase length fewer than 5 words More nouns than prepositions • Lacking prosody (melodious intonation for the meaning of sentence) • Repetition is impaired • Comprehension is (relatively) intact • Right hemiparesis (affecting face & arm, more than leg) • frustration & depression Frontal Lobe: Speech Production VIDEOS: https://www.youtube.com/watch?v=IP8hkopObvs https://www.youtube.com/watch?v=JWC-cVQmEmY * Clinical Correlation Wernicke’s Aphasia • Infarct in the left middle cerebral artery (MCA) inferior division territory • impaired comprehension • has normal fluency, prosody, and grammatical structure • “empty”, meaningless, nonsensical paraphasic errors • Impaired repetition • contralateral visual field cut (especially right upper quadrant) • apraxia • unaware of their deficit (contrast to Broca’s aphasia) Temporal Lobe: Speech Comprehension VIDEO: https://www.youtube.com/watch?v=3oef68YabD0 * Clinical Correlation Vascular Territories of Language Areas Wernicke Disease • Due to Vitamin B1 (thiamine) deficiency • Is uncommon in individuals who have a varied diet, but individuals with a history of chronic alcoholism may not have a well-balanced diet (Korsakoff syndrome). • Capillary proliferation, hemorrhage, necrosis, and hemosiderin deposition are often found in the mamillary bodies and the periaqueductal gray matter, resulting in paralysis of the extraocular muscles. • If memory problems with confabulation are observed add to the scenery, the diagnosis is Wernicke-Korsakoff syndrome. * Clinical Correlation Korsakoff’s psychosis • Is characterized by retrograde memory loss, the inability to form new memories, and a tendency for confabulation (exaggerating) to compensate for these losses. • It is caused by thiamine deficiency and commonly accompanies chronic alcoholism. Thiamine is a coenzyme for transketolase, which participates in the pentose monophosphate pathway of glucose metabolism. • Chronic alcoholism damages Dorsomedial nucleus of thalamus (memory formation), which is believed to play a role in memory formation • TEST: A thiamine deficiency is indicated by a change in erythrocyte transketolase activity. • If enzyme activity increases by more than 15% when thiamine diphosphate is added to the culture medium, then the thiamine deficiency is considered significant enough to indicate Korsakoff’s psychosis. * Clinical Correlation Alexia & Agraphia • impairments in reading and writing • caused by deficits in central language processing/ not by simple sensory or motor deficits Alexia without agraphia • Visual Information 1. Dorsal Pathways: project to parieto-occipital association cortex >> answer the question where? 2. Ventral Pathways: project to occipito-temporal association cortex >> what? (analyze form, color, faces, letters) Thank you