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The brain, speech and language pt 1 Yr 1 LCSC06 2015 Six layers of cells in the cortex: Brodmann’s areas C Y T O A R C H I T E C T U R E Hemispheric differences Left hemisphere typically contains general interpretive and speech centers and is responsible for language based skills Right hemisphere is typically responsible for spatial relationships and analyses The right hemisphere and communication • Right hemisphere plays a role in pragmatics • And prosody: – Understanding the tone of voice, interpreting emotion – Using intonation to express emotions • Face recognition – prosopagnosia Cortical areas and processing: the role of association cortex • Primary cortex: • Deals exclusively with a particular function eg vision, hearing, sensation, movement • Ascending/descending tracts from spinal cord, brain stem, special sense organs – originate or terminate in the primary cortical areas. • Higher order areas further process this information Unimodal association cortex: • higher order integration of information • extracts and processes information received and puts it together with other info at a modality level. • Unimodal each of these areas deal with one modality only ie sight, hearing, movement, sensation • this is to ensure that processing of sensory information at this stage is not mixed up with other sensory information Association areas: • Multimodal association cortex: • highest level of information/cognitive processing • highest form of human thought occurs here. • Information flows between these processing sites • So inter-modality processing: cognitive and intellectual function, memory, learning, and language Association cortices involved in language processing include: • • • • • The pre-frontal cortex The perisylvian zone Posterior parietal cortex Lateral temporal cortex Parahippocampal region • Be sure you can locate these areas Association cortex involved in planning / initiation and sequencing of motor movements: Revision: white matter pathways • Association fibres transmit nerve impulses between gyri in the same hemisphere • Commisural fibres transmit impulses from the gyri on one hemisphere to the corresponding gyri in the opposite hemisphere • Projection fibres form descending and ascending tracts that transmit impulses from the cerebrum and other parts of the brain to the spinal cord or from spinal cord to the brain Association White Matter Pathways • Connect cerebral areas within each hemisphere. • …and are generally bidirectional. • Contain short association fibres known as "U" or arcuate fibres that link adjacent cortical gyri. • Long association fibres, all of which terminate in the frontal lobe, include 5 types: the cingulate, the arcuate fasciculus, the superior and the inferior occipitofrontal fasciculi, and the uncinate fasciculus. Resources.med.fsu.edu Conduction aphasia: • Difficulty or inability to repeat, in the presence of fairly fluent but paraphasic speech. • Difficulty naming objects and cannot read aloud accurately. • May also have an impairment of voluntary movement Commissural White Matter Pathways • Commissural white matter pathways connect the 2 hemispheres. • The largest is the corpus callosumCorpus callosum has been described as the ‘information superhighway’ of the brain • Ensures that each hemisphere ‘knows’ what the other is doing • Connected by myelinated fibres www.cea1.com Projection White Matter Pathways • White matter projections consist of long tracts that both ascend and descend. • Projections that ascend are called corticopetal tracts, while those that descend are called corticofugal tracts. • Names of specific projections include the thalamo-cortical radiations, and the corticospinal and corticobulbar tracts. www.leonidzhukov.net Occipital lobes • Area 17 is the primary visual area. • Areas 18 and 19 are the secondary visual areas. • Fusiform gyrus (Brodmann’s area 37) – part of the visual association cortex. Possibly responsible for visual letter/word form recognition • Damage results in letter-by-letter reading Temporal lobes Temporal lobes • Virtually all the temporal cortex is involved in language processing in one form or another • The area known as Wernicke’s area (WA) is not as clearly defined anatomically as Broca’s area. • WA found the superior margin of the temporal lobe posterior to the primary auditory cortex extending around the posterior margin of the lateral fissure Brain regions involved in language processing Auditory cortical areas Auditory processing • Auditory association cortex (adjacent to the primary auditory cortex) is only activated by speech sounds (and other human sounds such as laughter, coughing) or writing (not other visual symbols) • The LEFT anterior auditory association cortex distinguishes speech from other background noise, writing from other visual symbols • The LEFT posterior auditory association cortex is activated during semantic tasks and retrieval of words from semantic memory • RIGHT anterior auditory association cortex is activated by strong dynamic pitch variation (as found in music and speech prosody) • Middle temporal gyrus activated during semantic processing, and possibly arranged in a ‘semantotopic’ fashion • Posterior inferior temporal gyrus anterior to the cerebellum is concerned with visual recognition or words and pictures, thereby connecting the semantic areas with the visual ones. • Anterior inferior temporal area involved in semantic decision making and may be involved in analysing the phonemic content of words. Comprehension • Can be for written or spoken language • If former, visual input received at primary visual cortex; if latter, primary auditory cortex • Further processed by relevant adjacent higher order and association cortices • Same areas of cortex involved in linguistic processing, no matter the modality of input ie auditory or written, or output ie spoken or written Temporal planum The insula Broca’s area Broca’s aphasia • Results from damage to more extensive area than the classical Broca’s area (BA) • If confined to BA, pure apraxia of speech (AoS) can result • Anterior insula almost always involved • As is the left frontal association cortex • Right hemiparesis and right hemianopia is common Brain regions involved in language processing Thebrain.mcgill.ca Supramarginal gyrus • Involved in the phonological and articulatory storage/processing of words ie motor plan • And formulation of written language The Angular gyrus Angular gyrus • Area of cortex above and below the upward extension of the middle temporal gyrus • Activated in complex semantic tasks such as spoken and written sentence comprehension • And in metaphorical thinking eg “It’s raining cats and dogs” Acquired dyslexia • If due to small, circumscribed lesions at the junction between temporal, parietal and occipital lobes, can occur without disturbance to speech/language • Graphemic-phonological conversion affected • Deep dyslexia has been reported when this area is lesioned in dominant hemisphere Transcortical aphasias • Transcortical sensory aphasia results when pathways between the association cortex and the classical language areas are damaged. Lesions lie in the tertiary association cortex around the junction of the parietal, temporal and occipital lobes, or inferior parts of left temporal lobe and left thalamus • Repetition is intact as BA and WA are still functionally connected by the arcuate fasciculus • Transcortical motor aphasia • BA is disconnected from the SMA and other areas of the frontal association cortex • Non-fluent aphasia • Preserved repetition • May be a right-sided hemiparesis if connections to adjacent motor areas are involved Subcortical structures with a role in language • Basal ganglia: • Damage to the left caudate nucleus /putamen results in a fluent aphasia with neologisms • The thalamus: • Different types of aphasia can result, with anomia, poor comprehension, intact repetition ..and the cerebellum also has a role in regulating behaviour and affect, due to connections with the frontal lobes Thalamus • Key relay station between major sensory inputs – vision, hearing , touch, proprioception etc –and the cerebral cortex. • Processes some info before passing it on. • Receives input back from the cortex, allowing some control over the stream of information Normal direct/indirect loops of basal ganglia Green = excitatory pathways, Red = inhibitory pathways Premotor/motor cortex (Glutamate) Striatum (GABA, ENK) (GABA, SP) External globus pallidus (GABA) Subthalamic nucleus (glutamate) Indirect loop Substantia nigra (dopamine) Internal globus pallidus (GABA) Direct loop Thalamus (glutamate) Typical exam questions: 1)Describe the location and function of ‘mirror’ neurons 2) What is meant by ‘association cortex’? Name one such area with relevance to language processing. 3) On the diagram of the brain supplied, locate the following: Heschl’s gyrus, the supramarginal gyrus, Broca’s area, primary visual cortex