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Fore Brain
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Medial View
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Lateral Brain cerebrum cerebellum brainstem
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A. The Cerebrum
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Central Sulcus
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Lateral Sulcus
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Longitudinal Fissure LEFT RIGHT
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Cerebral Hemispheres
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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
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Functional Areas of Cerebral Cortex 2
Cytoarchitecture is based on the density of different cortical neurons and thickness of layers
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Frontal Lobe Makes up 1/3 of all cerebral cortex Primary motor
Premotor Frontal eye field Supplementary motor Prefrontal Broca’s area
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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
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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
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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
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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
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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
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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 Now drugs are used
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Broca’s Area: Area 44 & 45 Part of the inferior frontal gyrus
Functions in speech
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Parietal Lobe Includes over 1/5 of total cortex Primary somatosensory
Secondary somatosensory Gustatory Association
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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
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Clinical Case After his wife had a stroke, a husband notices that his wife's hair is always tangled and uncombed on the left side of her head, although on the right her hair is straightened and orderly. The left side of her face is usually dirty from food remaining there, but the right face is always clean. She has stopped putting her ring and watch on her left hand. When eating, she never uses her fork on the left side of her plate and, surprisingly, she often asks why she was not given a fork to eat with. This woman's stroke most likely damaged the:
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Clinical Case 2 In a particular case, one woman lost her concept of left, with regard to her body and surroundings. For example when applying lipstick, she completely neglects the left side of her face. When eating she complains that her portions are too small, because she only eats from the right side of her plate. Where is her lesion? in the right frontal lobe in the left parietal cortex in the right parietal cortex in the left frontal lobe
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Secondary Somatosensory Area
Parietal operculum into posterior insula; posterior part of area 43 Bilateral input Somatotopy poorly defined Pain is perceived here
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Primary Gustatory Cortex: Area 43
Anterior part of parietal operculum Lesion results in contralateral (mostly) ageusia
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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
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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
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• Temporal association cortex
the ability to pay attention to, identify and plan meaningful responses to external stimuli or internal motivations involves association areas of cerebral cortex association areas are responsible for information processing between sensory input and motor output Association cortex has three major divisions: • Parietal association cortex – paying attention to complex stimuli in the external and internal environment: “where is it- pay attention” • Temporal association cortex – identification of stimuli: “what is it” • Frontal association cortex – planning responses: “ what are you going to do about it”
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Contralateral Neglect Syndrome
Most often seen after large areas of damage to right side parietal lobe – frequent consequence of stroke on right side of brain and thus neglect of everything on the left Patients ignore everything on side opposite to lesion – not blindness: patients can recognize and name objects Doctor wiggles a finger; patient sees the finger If doctor doesn’t move the finger, patient is oblivious – may even believe that the left side of one’s body is someone else’s
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Temporal Lobe 1/4 of total cortex Primary auditory
Auditory association Visual association Limbic
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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
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Auditory Association Cortex: Area 22
Wernicke’s area (posterior part of 22) Language understanding and formulation Damage can result in aphasia
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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
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Occipital Lobe: Areas 17,18,19 17 striate cortex, primary visual cortex Macular vision in posterior part Lesion causes homonymous hemianopsia
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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
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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
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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
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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
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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
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Aphasia Broca's Aphasia
A type of nonfluent aphasia, so called because speech production is halting and effortful. Damage is typically in the anterior portion of the left hemisphere. The dominant feature is agrammatism (impaired syntax). Content words (nouns, verbs) may be preserved but sentences are difficult to produce due to the problems with grammar, resulting in "telegraphic speech." In its more severe form, spoken utterances may be reduced to single words. Comprehension is typically only mildly to moderately impaired, and impairments are primarily due to difficulty understanding complex grammar. Repetition of words and sentences is usually poor.
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Aphasia Wernicke's Aphasia type of fluent aphasia.
Damage is typically in the posterior portion of the left hemisphere. Comprehension is poor and the person often produces jargon, or nonsensical words and phrases when attempting to speak. These utterances typically retain sentence structure but lack meaning. The person is usually unaware of how they are speaking and may continue to talk even when they should pause to allow others to speak; this is often referred to as "press of speech." Repetition of words and sentences is poor.
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Conduction Aphasia Conduction Aphasia type of fluent aphasia with a prominent impairment with repetition. Damage typically involves the arcuate fasciculus and the left parietal region. The patient may be able to express him- or herself fairly well, with some word-finding issues, and comprehension can be functional. However, the patient will show significant difficulty repeating phrases, particularly as the phrases increase in length and complexity and as they stumble over words they are attempting to pronounce. This type of aphasia is rare.
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Aphasia Transcortical Sensory Aphasia type of fluent aphasia similar to Wernicke's with the exception of a strong ability to repeat words and phrases. The person may repeat questions rather than answer them ("echolalia"). Transcortical Motor Aphasia type of nonfluent aphasia similar to Broca's aphasia, but again with strong repetition skills. The person may have difficulty spontaneously answering a question but can repeat long utterances without difficulty. Global Aphasia type of nonfluent aphasia with severe impairment of both expressive and receptive skills. Usually associated with a large left hemisphere lesion. People are often alert and may be able to express themselves through facial expressions, intonation, and gestures.
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Clinical Case 3 A 59-year-old woman had a cerebrovascular accident 9 months ago. Her past medical history is remarkable for hyperthyroidism and atrial fibrillation. She initially presented with slurred speech and right hemiparesis. The hemiparesis resolved, but her speech is still agrammatic and nonfluent, and she has difficulty finding words and completing sentences. Her comprehension is intact, and she appears frustrated when she attempts to speak. The remainder of the neurologic examination is normal. A lesion which areas would most likely account for her deficits?
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Clinical Case 4 A 77-year-old right-handed man with a history of atrial fibrillation and diabetes mellitus is brought to the emergency department by his family. His son describes that when his father awoke that morning, he was unable to use words or sentences that made any sense. On examination, the patient has spontaneous, fluent speech, with normal grammatical constructs and prosody. However, the majority of what he says is meaningless. He is unable to follow commands, except to close his eyes. When asked to identify objects, he uses inappropriate substitutions of words. He also fails to repeat words and is unable to read. A lesion which areas would most likely account for his language deficits?
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