Lateralisation and language

• The forebrain is where the two sides of the brain are relatively separate, but they can communicate through the corpus callosum.
• In 1861 Broca described a patient with specific language difficulties.
• Following a series of strokes, the patient was only able to utter the nonsense word “tan”, but however he could understand what was spoken to him (comprehension was intact).
• The damage was in the left frontal lobe, known as Broca’s area, which is responsible for speech production.
• Broca’s aphasia is a type of language disorder that occurs when there is damage to Broca’s area in the brain.
• The deficit in Broca’s aphasia is in speech production, which can lead to difficulty in speaking fluently and struggle to find the right words.
• Speech comprehension appears intact in Broca’s aphasia.
• The damage to Broca’s aphasia is always on the left side of the brain, usually in an anterior location.
• Wernicke described patients with different language problems to Broca’s aphasia in 1874.
• Wernicke’s aphasia is characterized by a deficit in speech comprehension, while speech production appears intact.
• Wernicke’s aphasia may cause individuals to speak fluently but their speech may be nonsensical and lack meaning.
• The damage to Wernicke’s aphasia is always on the left side of the brain, usually in a posterior location in the temporal lobe.
• Paraphasia is a language error in which individuals substitute or produce incorrect words or sounds while speaking.
• Phonemic paraphasia involves substituting similar sounds.
• Semantic paraphasia involves substituting words with similar meanings.
• Broca’s area stores articulatory images of words, characterized by difficulty in producing speech, while comprehension remains relatively intact.
• Wernicke’s area stores images of how word sound, involves fluent speech production but with impaired comprehension.
• These two conditions demonstrate a double dissociation, as they show opposite patterns of impairment in speech production and comprehension.
• Wernicke proposed that there's a connection between the posterior and anterior speech areas in the brain, facilitating the process of speaking.
• Conduction aphasia is a language disorder characterized by difficulty in repeating words or phrases, despite intact comprehension and speech production, typically caused by damage to the arcuate fasciculus, a bundle of nerve fibers that connects Broca's area and Wernicke's area.
• Strokes that affect both Broca’s and Wernicke’s areas will produce global aphasia, both comprehension and production affected.
• Historically, brain damage is the most important source of evidence regarding brain behaviour relationships, however, not without problems of interpretation.
• Damage to different regions of the left temporal lobe affects naming people, animals or tools to different extent.
• Attempting “reverse engineering” involves determining the function of a component by seeing what the rest of the system can and can’t do when that component has been removed, involves examining the effects of specific brain lesions or injuries to understand the functions of the affected brain regions.
• Brain damage is not typically confined to neuroanatomical boundaries, the physical divisions or borders between different regions or structures in the brain.
• It is very rare that we know what the performance would have been prior to the brain damage.
• By observing the symptoms and deficits that arise from brain damage, researchers can work backwards to infer the normal functions of those areas.
• A person is impaired performing a certain psychological task following brain damage to area A.
• It is too simplistic to say that the psychological process necessary for a task is located ‘in’ area A, or that the purpose of area A is to implement that psychological process.
• Other areas might also contribute to the psychological process and area A might contribute to other functions.
• Therefore, area A plays an essential role in some aspect of that psychological process.
• Neuropsychology approach involves finding a patient who has a deficit in one task but performs normally on another task, by comparing these two tasks, researchers can infer that the brain damage selectively affects the cognitive function related to the impaired task.
• The first psychological task/process might be more difficult to perform and so more easily disrupted than the second psychological task/process.
• Single dissociation is a research method used in neuropsychology to examine the effects of brain damage on specific cognitive functions, it helps us understand the functional specialization of different brain regions.
• The brain is incredibly complex, and language processing is a distributed process that relies on the coordination and interaction of multiple brain regions.
• Lesions restricted to either Broca’s or Wernicke’s areas typically produce only mild deficits in language abilities, suggesting that these specific brain regions play a crucial role in language processing, but other brain areas can compensate to some extent when these regions are damaged.
• Stronger evidence for double dissociation includes if brain damage in a different area in another patient disrupts the second psychological task/process, but not the first psychological task/process.
• Recognition stage aphasias include word deafness, phonemic processing, and semantic processing.
• Damage that affects different stages of processing will produce different types of input aphasias, such as word deafness, phonemic processing, and semantic processing.
• By studying these dissociations, researchers can gain insights into the underlying cognitive processes and the specific areas of the brain that are affected.