Lateralization of Lateralization of FunctionFunction

Contralateral ControlCorpus CallosumSet of axons which allow the 2 hemispheres to exchange informationCutting the corpus callosum prevents sharing of this informationSome are born without a corpus callosum

LateralizationEach hemisphere specializes in certain behavior & cognitive abilitiesE.g., language is mainly in the left hemisphere

Lateralization of Lateralization of FunctionFunction

Visual InputLight from the right visual field shines onto the left half of both retinas

This is relayed to the left hemisphere

The right half of each retina connects to the right hemisphere which sees the left visual field

Lateralization of Lateralization of FunctionFunction

Split-brain ResponsesWith a severed corpus callosum can point to objects with the left hand, but not the rightWith visual information presented to the right visual field can name or describe what is seenRight hemisphere: is better than the left at perceiving emotions in gestures & tone of voiceWith right hemisphere damage can speak with less inflection & expressionRight is more adept at compre-hending spatial relationshipsAlso better at perceiving patterns instead of details

Lateralization of Lateralization of FunctionFunction

Planum TemporaleA section of the temporal cortex larger in the left hemisphere in 65% of the population

The difference in size is apparent at 3 months

Children with the biggest ration of left to right planum temporale are better on language tests

Lateralization of Lateralization of FunctionFunction

Corpus CallosumSlowly develops over the first 5 to 10 yearsNeurons connected to the corpus callosum take years to develop their mature adult patternThose born without a corpus callosum seem to have larger than normal hemispheric connections elsewhere

Anterior CommisureConnects the hemispheres around the anterior parts of the cerebral cortexThe hippocampal commisure connects the left hippocampus to the right hippocampus

Lateralization of Lateralization of FunctionFunction

Speech & Hemispheric Dominance90% of people are right handed & left hemisphere dominance for speech

Others are either right hemisphere dominant or mixed

Corpus callosum is larger in left handers than right handers

Recovery from InjuryRecovery of speech after brain injury depends on the damaged hemisphere & how speech is lateralized

Children with left-hemisphere damage recover more language than adults with similar damage, but the cause of the damage is more important with age

Human Human LanguageLanguageUniqueness

Productivity creates uniquenessAbility to produce new signals to represent new ideas

Chimp CommunicationsCannot learn to talk but can learn some language skills using ASL or other visual systemsUse of language-related skills differ from human language

Bonobo CommunicationsUses symbols in several ways that more resemble humansUse of language-related skills similar in several ways

Evolution of Human Evolution of Human LanguageLanguage

A Product of Overall IntelligenceBrain-to-body ratio relationship can’t explain language

Is it a dominant gene?

Language development is unclear

Special ModuleLanguage Acquisition Device

Language evolved as an extra brain module

Language has a critical period; if language isn’t learned during childhood development it leads to disadvantages

Brain Damage & Brain Damage & LanguageLanguage

AphasiaAphasiaSevere language impairment

Broca’s AreaBroca’s AreaSmall part of the left frontal cortex when damaged leads to language impairments

Wernicke’s AreaWernicke’s AreaNear the auditory part of the left temporal lobe

Brain Damage & Brain Damage & LanguageLanguage

Broca’s AphasiaBroca’s AphasiaNonfluent aphasiaMost prominent symptom: deficit in language productionDamage to Broca’s areaCan speak meaningfully but omits pronouns, prepositions, conjunctions & qualifiersSome trouble understanding the same kinds of words

Brain Damage & Brain Damage & LanguageLanguage

Wernicke’s Wernicke’s AphasiaAphasiaFluent aphasia

Difficulty in understanding verbal & written communications, can speak smoothly but speech is often nonsensical

Anomia: difficulty recalling the names of objects

Language Language ActivationActivationLanguage requires activation of many different areas of the frontal & temporal cortex

DyslexiaDyslexiaInability to Read ProperlyHas adequate intelligence & visionMany underlying causes

Bilateral Symmetrical Cerebral CortexHave left & right hemisphere structures the same size

HypothesesUnresponsive magnocellular path to the visual systemA subtle hearing impairmentProblem converting vision to sound & vice-versaFunction of attentional differencesProblem communicating between hemispheres