Hockenbury Discovering Psychology 5th txtbk

Specialization in the Cerebral Hemispheres73Language and the Left HemisphereThe Early Work of Broca and WernickeBy the end of the 1700s it had already been well establishedthat injury to one side of the brain could produce muscleparalysis or loss of sensation on the opposite side of thebody. By the early 1800s, animal experiments had shownthat specific functions would be lost if particular brainareas were destroyed. And, as discussed in the ScienceVersus Pseudoscience box on page 63, phrenology triggeredscientific debates about cortical localization, orlocalization of function—the idea that particular brain areasare associated with specific functions.In the 1860s, more compelling evidence for cortical localization was presentedby a French surgeon and neuro anatomist named Pierre Paul Broca. Broca treateda series of patients who had great difficulty speaking but could comprehend writtenor spoken language. Subsequent autopsies of these patients revealed a consistentfinding—brain damage to an area on the lower left frontal lobe. Today, this area onthe left hemisphere is referred to as Broca’s area, and it is knownto play a crucial role in speech production (Figure 2.20).About a decade after Broca’s discovery, a young Germanneurologist named Karl Wernicke discovered anotherarea in the left hemisphere that, when damaged, produceda different type of language disturbance. Unlike Broca’s patients,Wernicke’s patients had great difficulty understandingspoken or written communications. They could speakquickly and easily, but their speech sometimes made nosense. They sometimes used meaningless words oreven nonsense syllables, though their sentencesseemed to be grammatical. In response to the question“How are you feeling?” a patient might saysomething like, “Don’t glow glover. Yes, uh, ummm,bick, bo chipickers the dallydoe mick more work mittle.”Autopsies of these patients’ brains revealed consistentdamage to an area on the left temporal lobe that todayis called Wernicke’s area (see Figure 2.20).The discoveries of Broca and Wernicke provided the first compelling clinical evidencethat language and speech functions are performed primarily by the left cerebralhemisphere. If similar brain damage occurs in the exact same locations on the righthemisphere, these severe disruptions in language and speech are usually not seen.The notion that one hemisphere exerts more control over or is more involvedin the processing of a particular psychological function is termed lateralization offunction. Speech and language functions are lateralizedon the left hemisphere. Generally,the left hemisphere exerts greatercontrol over speech and languageabilities in virtually all righthandedand the majority of lefthandedpeople.The language disruptions demonstratedby Broca’s and Wernicke’s patientsrepresent different types ofaphasia. Aphasia refers to the partialor complete inability to articulate ideasor understand spoken or written languageBroca’s areabecause of brain injury or damage. There aremany different types of aphasia.Wernicke’s areaPaul Broca (1824–1880): Evidence for theLocalization of Speech Paul Broca was alreadya famous scientist and surgeon whenhe announced in 1861 that he had discoveredsolid evidence for the localization oflanguage functions in the human brain.His patient was an unpleasant middle-agedman universally known as Tan becausethat was the only word he could speak—aside from a single swear word when angered.Of normal intelligence, Tan couldcomprehend the speech of others butcould not produce language himself. AfterTan’s death, an autopsy revealed a distinctlesion on the lower left frontal lobe. Thisarea is still known as Broca’s area.Karl Wernicke (1848–1905): Evidence forthe Localization of Language ComprehensionBorn in Poland but educated in Germany,psychiatrist and neurologist KarlWernicke was only 26 when he publishedhis findings on a type of aphasia that differedfrom that identified by Paul Broca.Wernicke’s patients were unable to comprehendwritten or spoken language,although they could produce speech. Wellknownfor his research in clinical neurology,Wernicke published many articles andbooks, including a comprehensive textbookon psychiatry.Figure 2.20 Broca’s and Wernicke’sAreas of the Cerebral Cortex Broca’s area,located in the lower frontal lobe, is involvedin the production of speech. Wernicke’sarea, found in the temporal lobe, isimportant in the comprehension of writtenor spoken language. Damage to eitherof these areas will produce different typesof speech disturbances, or aphasia. In mostpeople, both areas are found on the lefthemisphere.