Fore Brain

Medial View

Lateral Brain cerebrum cerebellum brainstem

A. The Cerebrum

Central Sulcus

Lateral Sulcus

Longitudinal Fissure LEFT RIGHT

Cerebral Hemispheres

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 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

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

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

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 & 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

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.

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.

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.

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.