Cerebral Cortex 2 Heteromodal Association Cortex Multimodal association

Cerebral Cortex 2

Heteromodal Association Cortex • Multimodal association cortical areas – Integration of sensory information for multiple modalities • Most of neocortex in humans • NO direct motor or sensory areas – Do not receive direct sensory input – Do not project to LMN

• Bidirectional connections with – Motor and sensory association cortex – Limbic cortex

Association Cortex • Involved in higher intellectual functions – Abstract reasoning – Complex planning – Personality – Processing of memory – Generation of emotions

Higher Cortical Functions • Hemispheric specialization – Some functions located on one side of the cerebral cortex – May speed up processsing if it is all done on one side

Handedness • 90% right-handed – left cerebral hemisphere is dominant • Simple movements – contralateral hemisphere • Skilled, complex tasks – dominant hemisphere – Lesions of left hemisphere more often associated with apraxia – difficulties formulating skilled movements

Language • Left hemisphere is usually dominant for verbal communication – R- > 95% – L – 60 -70% • Language function may be more bilateral • Tend to recover language faster

Language • Non-dominant side – Non-verbal communication – Emotional aspects of events and language – Musical perception

Attention • Both sides involved in attention for the contralateral side • Right side attends to both sides – R side stroke will produce inattention to the left

Dominant hemisphere (usually L) Language Non-dominant hemisphere (Usually R) Prosody (emotion conveyed by tone of voice) Skilled motor formulation Visual-spatial analysis (praxis) and spatial attention Arithmetic: sequential Arithmetic: ability to and analytical calculating correctly line up columns skill of numbers on a page

Dominant hemisphere (usually L) Non-dominant hemisphere (Usually R) Musical ability: in sequential and analytical untrained persons. skills in trained persons Complex musical pieces in trained musicians Direction: following a set Direction: finding one’s of written directions in way by overall sense of sequence spatial orientation

Higher Order Cerebral Function • • • Language Attention and spatial processing Frontal lobes Visual processing Attention and Awareness

Language • Brain regions involved – Primary auditory cortex – Wernicke’s area (part of auditory association cortex) – Primary motor cortex for the face – Broca’s area (association cortex) – Connections between Broca’s and Wernicke’s areas • Arcuate fasciculus

Wernicke’s Area • Primarily involved in language comprehension • Maps sounds to meaning in order to produce meaningful language (lexicon) – Comprehension – Production

Broca’s area • Higher level aspects of speech formulation and planning – Correct syntax of language comprehension and production

Language – Non-dominant hemisphere • Connected with dominant hemisphere through corpus callosum – May have difficulty aspects of language imparted by tone of voice – May have difficulty producing emotionally appropriate expression

Aphasia • Deficit in language processing – Injury to language dominant hemisphere • Affects both spoken and written language

Broca’s Aphasia • Damage to Broca’s area or surrounding structures • Decreased fluency of spontaneous speech – Phrase length of fewer than 5 words – More content words (nouns) than function words (prepositions, articles, etc. ) – Can be tested by word generation tasks • FAS (12 or more words) • Prosody is frequently lacking

• Naming difficulties • Impaired repetition – “No ifs, ands or buts” • Comprehension usually relatively intact – Difficulties where syntax matters – passive voice • Writing and reading aloud – similar to speaking difficulties – slow, agrammatical, and effortful

• Frustration and depression common • Associated problems – Dysarthria – Hemiplegia on R side – Apraxia • Often affects left-side and oral-buccal-lingual structures • Stroke – MCA (superior division)

Wernicke’s Aphasia • Lesion – Wernicke’s area and adjacent structures • Stroke – MCA (inferior division) • Impaired comprehension – Do not respond appropriately to questions or commands – May respond to some commands about axial muscles

• Normal fluency, prosody and grammatical structure • Sentences do not have meaning – Paraphasic errors • Replace word with one of a similar meaning • Replace part of a word with a similar sound – Neologisms – make up new word • Impaired naming

• Disconnect from Broca’s area – Impaired repetition • Reading and writing – similar deficits

• Associated dysfunctions – Contralateral visual field cut – Apraxia may be present – difficult to assess due to aphasia – Often appear unaware of disorder – May exhibit angry or paranoid behavior

Syndromes related to aphasia • • • Alexia and agraphia Apraxia Aphemia Cortical deafness Pure word deafness Nonverbal auditory agnosia

Alexia and agraphia • Reading and writing impairments • Deficits in central language processing • Patients with aphasia have agraphia • Deficits in patients with aphasia tend to mirror the aphasia

• Writing – With Broca’s aphasia • Effortful, agrammatical and sparse – With Wernicke’s aphasia • Fluent, paraphasic and largely incomprehensible

Apraxia • Ideomotor apraxia – inability to carry out an action in response to a verbal command, in the absense of any comprehension deficit, motor weakness or incoordination • Ask patient to carry out an imaginary action – Awkward looking attempts – Perform tasks ineffectually

• 1/3 rd of patients with aphasia have some apraxia • Different regions of the body (orofacial, proximal, or distal limb) may be affected differently

Aphemia (Verbal apraxia) • • Small lesion in Broca’s area Motor speech deficits Writing is intact Verbal apraxi – aphemia that occurs as a developmental disorder in children

Cortical deafness • Lesion to bilateral auditory corex

Pure Word Deafness • • AKA verbal auditory agnosia Can identify non-verbal sounds Cannot understand spoken words Can read and write normally • Lesion to auditory cortex of dominant hemisphere which extends deep to the subcortical white matter

Non-dominant hemisphere Attention and spatial processing • Usually Right side • Global Attention – Vigilance, Concentration, Generalized Behavioral Arousal • Selective or Directed Attention – Focusing attention on a specific domain

Cerebral Hemispheres and Attention • Involves both cerebral hemispheres • Right cerebral hemisphere is more important for most people – L side – responds to R – R side – responds to L and R • Opposite role of premotor cortex – R side – Left hand – L side – L and R hand

• Slight left attentional bias

Effects of Injury on Attention • Right hemisphere lesion – Severe left neglect • Left hemisphere lesion – Minimal right neglect • Bilateral hemisphere lesion – Severe right neglect