Lateralization Flashcards
What’s lateralization and why is it important.
Key Findings
• Lateralization refers to the functional specialization of the left and right hemispheres of the brain.
• Although both hemispheres work together, certain functions are dominantly processed in one hemisphere.
• Left Hemisphere Specialization:
• Language processing (Broca’s & Wernicke’s areas).
• Logical reasoning & analytical thinking.
• Fine motor control (e.g., right-hand movement in most right-handed individuals).
• Right Hemisphere Specialization:
• Spatial processing & face recognition.
• Emotional processing & prosody (tone of voice).
• Holistic thinking & pattern recognition.
• Importance of Lateralization:
• Allows the brain to divide tasks efficiently, improving processing speed and cognitive abilities.
• Damage to one hemisphere can lead to specific deficits (e.g., aphasia with left hemisphere damage).
Key Takeaway
• Lateralization allows the brain to specialize in different cognitive functions, with the left hemisphere dominant for language and logic, and the right hemisphere dominant for spatial abilities, emotion, and holistic thinking.
What are split-brain individuals, and what do they reveal about brain lateralization?
Key Findings
• Split-brain individuals are people who have had their corpus callosum surgically severed, typically as a treatment for severe epilepsy.
• This procedure prevents communication between the left and right hemispheres, leading to distinct behaviors when stimuli are presented to only one hemisphere.
• Key Observations from Split-Brain Studies:
• Left hemisphere (dominant for language):
• Can verbalize what it sees (when stimuli are presented to the right visual field).
• Right hemisphere (dominant for spatial processing & nonverbal communication):
• Cannot verbalize what it sees (when stimuli are presented to the left visual field).
• Can process spatial tasks and recognize objects but struggles to name them.
• Example Experiment:
• If an object is presented to the left visual field (right hemisphere), the person cannot name it but can pick it up with the left hand.
Key Takeaway
• Split-brain studies confirm brain lateralization, showing that the left hemisphere specializes in language while the right hemisphere processes spatial and nonverbal tasks.
• The corpus callosum plays a crucial role in integrating information between hemispheres.
What do split-brain studies reveal about hemispheric specialization?
Key Findings
• Left Hemisphere (LH) Specialization:
• Dominant for language processing (speech production and comprehension).
• Can verbalize stimuli presented in the right visual field (processed by the left hemisphere).
• Right Hemisphere (RH) Specialization:
• Better at spatial tasks and recognizing faces.
• Cannot verbalize what it sees but can process and respond nonverbally.
• If an object is presented in the left visual field (processed by RH), the individual cannot name it but can pick it up with the left hand.
• Key Experiment (Visual Stimuli & Responses in Split-Brain Patients):
• A word or object is flashed to one visual field:
• Right visual field (LH processing) → Patient can say the word aloud.
• Left visual field (RH processing) → Patient cannot verbalize the word but can draw or pick it up with the left hand.
• Implications:
• Confirms lateralization: LH is specialized for language, while RH handles spatial and nonverbal processing.
• Corpus callosum integrates hemispheric functions; its absence results in independent processing in each hemisphere.
Key Takeaway
• Split-brain studies demonstrate that the left hemisphere is dominant for language, while the right hemisphere excels in spatial and nonverbal tasks.
• Without the corpus callosum, the hemispheres act independently, revealing how each side of the brain contributes to cognition.
What do split-brain studies reveal about dual consciousness and confabulation?
Key Findings
• Dual Consciousness:
• Each hemisphere processes information independently and can complete tasks correctly on its own.
• Right hemisphere lacks language, so it cannot explain its choices verbally.
• Key Experiment (Shovel & Chicken Task):
• Right visual field (LH processing) → Sees chicken claw, selects chicken.
• Left visual field (RH processing) → Sees snow scene, selects shovel.
• When asked why they picked the shovel, the left hemisphere, which didn’t see the snow, confabulates, saying “The shovel is for cleaning the chicken coop.”
• Implications:
• Each hemisphere functions independently, supporting dual consciousness.
• The left hemisphere fills in missing information with logical but false explanations (confabulation).
Key Takeaway
• Split-brain patients demonstrate dual consciousness, where the right hemisphere makes correct nonverbal choices but cannot explain them, while the left hemisphere confabulates to maintain a coherent narrative.
What is callosal agenesis, and how does it differ from surgical split-brain patients?
Key Findings
• Callosal Agenesis:
• Occurs in 1 in 4000 people, where individuals are born partially or completely lacking a corpus callosum (hemisphere not connected).
• Unlike surgically split-brain patients, they do not exhibit severe neuropsychological deficits.
• Neural Compensation:
• During development, the nervous system adapts by strengthening alternative interhemispheric connections.
• Other brain pathways (e.g., anterior commissure) may help compensate for the lack of direct corpus callosum communication.
• Implications:
• The brain has a remarkable ability to reorganize itself when disruptions occur early in development.
• Highlights the difference between developmental vs. acquired brain changes—early deficits allow for adaptation, while sudden lesions (like in split-brain surgery) do not.
Key Takeaway
• People with callosal agenesis often lack the cognitive impairments seen in split-brain patients because the developing brain compensates by strengthening alternative connections between hemispheres.
What is dichotic presentation, and why do some people show an ear advantage?
Dichotic Presentation:
• A method where different auditory stimuli are played simultaneously into each ear.
• Used to study hemispheric dominance in auditory processing.
• Right Ear Advantage (REA):
• Most people show better recognition of verbal stimuli (e.g., words, numbers) in the right ear.
• This happens because the right ear projects directly to the left hemisphere, which is dominant for language processing.
• Left Ear Advantage (LEA):
• Some individuals may have a left ear advantage for nonverbal sounds (e.g., music, environmental sounds).
• The left ear projects to the right hemisphere, which specializes in spatial and emotional auditory processing.
• Implications:
• Ear advantage reflects hemispheric specialization, with the right ear favoring language (left hemisphere) and the left ear favoring nonverbal sounds (right hemisphere).
Key Takeaway
• Dichotic listening tasks reveal hemispheric dominance, with a typical right ear advantage for language and a left ear advantage for nonverbal sounds.
What is the tachistoscope test, and what does it reveal about hemispheric dominance?
Key Findings
• Planum Temporale:
• A cortical area in the superior temporal lobe, adjacent to the primary auditory cortex.
• Larger in the left hemisphere in most individuals.
• Asymmetry and Language:
• Leftward asymmetry is present before birth, supporting the idea that language lateralization is innate rather than purely experience-based.
• The larger left planum temporale is linked to language dominance in the left hemisphere.
• Variation in Asymmetry:
• Most right-handed people have a larger left planum temporale.
• Some left-handed people show more symmetrical or reversed asymmetry, though many still have a leftward bias.
Perfect Pitch and Planum Temporale:
• Musicians with perfect pitch tend to have an even more pronounced leftward asymmetry in the planum temporale.
• Suggests a connection between auditory processing specialization and structural differences in the brain.
• Implications: • Planum temporale asymmetry is an early structural marker of language lateralization, supporting the biological basis of hemispheric dominance.
Key Takeaway
• The planum temporale is typically larger in the left hemisphere, reinforcing the left hemisphere’s role in language processing, with this asymmetry evident before birth.
What is the planum temporale, and why is it important?
Key Findings
• Planum Temporale:
• A cortical area in the superior temporal lobe, adjacent to the primary auditory cortex.
• Larger in the left hemisphere in most individuals.
• Asymmetry and Language:
• Leftward asymmetry is present before birth, supporting the idea that language lateralization is innate rather than purely experience-based.
• The larger left planum temporale is linked to language dominance in the left hemisphere.
• Variation in Asymmetry:
• Most right-handed people have a larger left planum temporale.
• Some left-handed people show more symmetrical or reversed asymmetry, though many still have a leftward bias.
Perfect Pitch and Planum Temporale:
• Musicians with perfect pitch tend to have an even more pronounced leftward asymmetry in the planum temporale. Music activates the right hemisphere more than the left, and musical perception is damaged when right hemisphere damaged.
• Suggests a connection between auditory processing specialization and structural differences in the brain.
• Implications: • Planum temporale asymmetry is an early structural marker of language lateralization, supporting the biological basis of hemispheric dominance.
Key Takeaway
• The planum temporale is typically larger in the left hemisphere, reinforcing the left hemisphere’s role in language processing, with this asymmetry evident before birth.
What is the Wada test, and what does it reveal about brain lateralization?
Key Findings
• Wada Test:
• A procedure used to determine which hemisphere is dominant for language.
• Involves injecting a fast-acting anesthetic (sodium amobarbital) into one carotid artery, temporarily inactivating one hemisphere.
• Procedure & Observations:
• If the left hemisphere is anesthetized (in most people):
• Speech production is impaired or lost, confirming left hemisphere dominance for language.
• If the right hemisphere is anesthetized:
• Speech is typically unaffected, unless the person has right hemisphere language dominance (rare).
• Uses of the Wada Test:
• Pre-surgical evaluation for epilepsy patients before brain surgery.
• Helps determine language dominance and memory function to avoid damaging critical areas.
• Implications:
• Confirms that the left hemisphere is dominant for language in most people.
Key Takeaway
• The Wada test temporarily disables one hemisphere to assess language dominance, confirming left hemisphere specialization in most individuals.
What is prosopagnosia, and what causes it?
Key Findings
• Definition:
• Prosopagnosia, or face blindness, is the inability to recognize familiar faces, despite normal vision and intelligence.
• Causes:
• Acquired Prosopagnosia:
• Results from brain damage, often due to stroke, trauma, or neurodegeneration.
• Typically linked to lesions in the fusiform face area (FFA) of the right temporal lobe.
• Congenital (Developmental) Prosopagnosia:
• Present from birth with no obvious brain damage.
• May result from abnormal development of face-processing networks.
• Symptoms:
• Difficulty recognizing familiar faces, even close friends or family.
• May rely on voice, clothing, or other cues to identify people.
• In severe cases, individuals may fail to recognize their own face in a mirror.
• Implications:
• Prosopagnosia highlights the specialized role of the fusiform gyrus in facial recognition.
Key Takeaway
• Prosopagnosia is a disorder affecting face recognition, usually due to damage in the fusiform face area (FFA), demonstrating the brain’s specialized system for processing faces.
What does FMRI reveal about prospagnosia and the fusiform face area (FFA)?
Key Findings
• Study Overview:
• Researchers examined face-selective activation in the fusiform gyrus (FFA) using fMRI.
• Patients with prosopagnosia showed weaker or absent FFA activation compared to control participants.
• Key Results:
• Healthy individuals:
• Strong activation in the right fusiform gyrus (FFA) when viewing faces.
• Prosopagnosia patients:
• Significantly reduced or absent FFA activation, correlating with their inability to recognize faces.
• Implications:
• Confirms that the FFA is crucial for face recognition.
• Damage or dysfunction in the FFA leads to prosopagnosia, reinforcing the specialized role of this brain region in face processing.
Key Takeaway
• Prosopagnosia results from impaired fusiform face area (FFA) function, as demonstrated by fMRI studies showing weaker activation in affected individuals.
What is congenital prosopagnosia, and what does the “Greenies” study reveal about it?
Key Findings
• Congenital Prosopagnosia (Developmental Prosopagnosia):
• A lifelong inability to recognize faces, despite normal vision and no history of brain injury.
• May result from abnormal development or weaker connectivity in the fusiform face area (FFA) and its network.
• Individuals may rely on other cues (e.g., voice, hairstyle) to recognize people.
• The “Greenies” Study (Face Learning in Prosopagnosia):
• Researchers created a fictional alien species (“Greenies”), which had two genders and five families, requiring participants to learn to recognize them.
• Key Findings:
• Individuals with congenital prosopagnosia struggled to learn and distinguish Greenies, similar to their difficulty recognizing human faces.
• They performed normally on non-face object recognition tasks, suggesting a face-specific deficit rather than a general visual impairment.
Key Takeaway
• Congenital prosopagnosia is a lifelong impairment in face recognition, likely due to atypical FFA development. The “Greenies” study confirms that individuals with this condition struggle with face learning, reinforcing that their deficit is specific to facial processing, not general vision.
What are super-recognizers, and what makes them different from the general population?
Key Findings
• Definition:
• Super-recognizers are individuals with exceptional face recognition ability, far above the average person.
• They can effortlessly remember and identify faces, even after brief encounters or long time gaps.
• Key Characteristics:
• Can recognize faces even with changes in age, hairstyle, or lighting.
• Perform extremely well on face recognition tests, such as identifying people from low-quality security footage.
• May notice subtle differences between similar-looking individuals that others miss.
• Neural Basis:
• fMRI studies suggest super-recognizers have stronger activation in the fusiform face area (FFA) compared to average individuals.
• Implications:
• Demonstrates that face recognition ability exists on a spectrum, with prosopagnosia on one end and super-recognizers on the other.
• Some law enforcement agencies recruit super-recognizers for surveillance and security work.
Key Takeaway
• Super-recognizers have exceptional face recognition skills, likely due to enhanced FFA function, highlighting the variability in human facial processing abilities.
What do studies comparing self and celebrity face recognition reveal?
Key Findings
• Study Overview:
• Compared recognition of one’s own face vs. celebrity faces using fMRI.
• Measured brain activation in response to self-faces, familiar faces (celebrities), and unfamiliar faces.
• Key Results:
• Right Hemisphere Dominance for Self-Recognition:
• Greater activation in the right hemisphere when viewing one’s own face, particularly in the right fusiform gyrus and right frontal regions.
• Left Hemisphere Involvement in Familiar Face Recognition:
• Celebrity face recognition showed more balanced activation across both hemispheres.
• Self-Face Recognition is More Robust:
• People tend to recognize their own face faster and more accurately than celebrity faces.
• Key Takeaway
• Self-face recognition relies more on the right hemisphere, while celebrity face recognition involves both hemispheres, suggesting the brain processes personal identity and familiar faces differently.
What are the fundamental components of language, and what do they mean?
Key Findings
1. Phonemes (音素):
• The smallest unit of sound in a language that distinguishes meaning.
• Example: /p/ and /b/ in “pat” vs. “bat” change the word’s meaning.
2. Morphemes (语素):
• The smallest meaningful unit of language.
• Example: “un-”, “happy”, and ”-ness” in “unhappiness” each contribute to the word’s meaning.
3. Syntax (句法):
• The rules governing sentence structure and word order.
• Example: In English, “The cat chased the dog” is different from “The dog chased the cat”.
4. Semantics (语义学):
• The meaning of words and sentences.
• Example: “Colorless green ideas sleep furiously” is syntactically correct but lacks clear meaning.
5. Pragmatics (语用学):
• The social rules of language use in context.
• Example: “Could you pass the salt?” is a request, not a literal yes/no question.
Key Takeaway
• Language is structured into different levels—phonemes (sounds), morphemes (meaningful units), syntax (structure), semantics (meaning), and pragmatics (social context)—all working together for communication.
What is aphasia, what are its symptoms, and what causes it?
Key Findings
• Aphasia is a language disorder caused by brain damage, affecting speech production, comprehension, reading, or writing.
• 90-95% of aphasias result from left-hemisphere damage, typically due to stroke, brain injury, tumors, or neurodegenerative diseases.
• Common Symptoms of Aphasia:
• Nonfluent speech – Difficulty forming words and sentences (e.g., Broca’s aphasia).
• Fluent but nonsensical speech – Words flow but lack meaning (e.g., Wernicke’s aphasia).
• Impaired comprehension – Difficulty understanding spoken or written language.
• Word-finding difficulties (Anomia) – Struggling to recall words.
• Repetition deficits – Difficulty repeating phrases, especially in conduction aphasia.
Key Takeaway
• Aphasia is a language disorder, typically caused by left-hemisphere damage (90-95% of cases), leading to deficits in speech production, comprehension, reading, and writing.
What additional symptoms can appear in aphasia?
Key Findings
• Aphasia can also involve other language-related deficits, depending on the brain areas affected.
• Common Additional Symptoms:
• Agraphia (书写障碍) → Impaired ability to write, even when motor skills are intact.
• Alexia (失读症) → Impaired reading ability, often co-occurring with aphasia.
• Apraxia (失用症) → • Speech Apraxia → Difficulty with motor planning for speech, leading to slow, effortful articulation. • Limb Apraxia → Difficulty performing purposeful movements, despite normal strength and coordination. • **Damage to the angular gyrus is often associated with agraphia and alexia.
Key Takeaway
• Aphasia is often accompanied by agraphia (writing impairment), alexia (reading impairment), and in some cases, apraxia (motor planning difficulties), depending on the extent of brain damage.
What is the difference between fluent and nonfluent aphasia?
Key Findings
• Fluent Aphasia (Wernicke’s Aphasia):
• Speech is fluent but lacks meaning (“word salad”).
• Poor comprehension of both spoken and written language.
• Unaware of their deficits and often not frustrated by their speech.
• Example: Speaking in long, grammatically correct sentences, but with nonsensical or irrelevant content.
• Nonfluent Aphasia (Broca’s Aphasia): • Speech is slow, effortful, and grammatically impaired. • Good comprehension but struggles to express thoughts verbally. • Aware of their impairment and often frustrated by their difficulty in speaking. • Example: “Want… coffee… now” instead of “I want some coffee now.”
Key Takeaway
• Fluent aphasia (Wernicke’s) allows speech but impairs comprehension, while nonfluent aphasia (Broca’s) preserves comprehension but makes speech effortful and broken.
What brain regions are affected in fluent and nonfluent aphasia?
Key Findings
• Broca’s Aphasia (Nonfluent Aphasia):
• Location: Broca’s area (left inferior frontal gyrus).
• Function: Responsible for speech production and articulation.
• Damage Effects:
• Impaired speech production (slow, effortful, nonfluent).
• Comprehension remains intact.
• Patients are aware of their deficits and sometime frustrated.
• Wernicke’s Aphasia (Fluent Aphasia):
• Location: Wernicke’s area (left superior temporal gyrus).
• Function: Critical for language comprehension.
• Damage Effects:
• Fluent but nonsensical speech (word salad).
• Severe comprehension deficits (both spoken and written language).
• Patients are unaware of their impairment and not frustrated.
Key Takeaway
• Broca’s aphasia is caused by damage to Broca’s area (left frontal lobe) and affects speech production, while Wernicke’s aphasia results from damage to Wernicke’s area (left temporal lobe) and impairs language comprehension.
What do dichotic listening, split-brain studies, Broca’s aphasia, and somatosensory involvement tell us about language processing?
Key Findings:
• Lateralization & Dichotic Listening
• Right ear inputs (processed by the left hemisphere) are recognized faster, supporting left hemisphere dominance for language.
• Split-Brain & Split-Screen Tasks
• Left visual field (right hemisphere) → Cannot verbalize but can identify objects with the left hand.
• Right visual field (left hemisphere) → Can name and describe objects, confirming left hemisphere’s role in language production.
• Broca’s Aphasia
• Damage to Broca’s area (left frontal lobe) causes nonfluent, effortful speech but spares comprehension.
• Patients are often aware of their deficits, leading to frustration.
• Somatosensory Language Involvement
• The somatosensory system may support speech perception by linking mouth/tongue movements to sounds.
• Suggests that language processing is not purely abstract but involves sensorimotor integration.
Key Takeaway:
• Language is strongly lateralized to the left hemisphere, as shown in dichotic listening and split-brain studies. Broca’s aphasia highlights the role of the frontal lobe in speech production, while somatosensory areas may support speech perception and articulation.
How do Broca’s and Wernicke’s aphasia differ in terms of brain region, speech fluency, and comprehension?
Key Findings:
• Broca’s Aphasia
• Region: Broca’s area in the left premotor/frontal region.
• Speech: Nonfluent, slow, effortful speech with poor grammar.
• Comprehension: Largely preserved.
• Other: Patients are often aware of their difficulty.
• Wernicke’s Aphasia
• Region: Wernicke’s area in the left superior temporal gyrus.
• Speech: Fluent but nonsensical (word salad).
• Comprehension: Severely impaired.
• Other: Patients are often unaware of their impairment.
Key Takeaway:
• Broca’s aphasia results in nonfluent speech with preserved comprehension, while Wernicke’s aphasia produces fluent but meaningless speech with poor comprehension, reflecting damage to different language areas.
What is fluent aphasia, what does word deafness indicate, and how are anomia and the angular gyrus involved?
Key Findings:
• Fluent Aphasia (Wernicke’s Aphasia)
• Speech: Fluent but lacks meaning (word salad).
• Comprehension: Impaired, especially for spoken language.
• Cause: Damage to Wernicke’s area in the left superior temporal gyrus.
• Word Deafness
• Inability to comprehend spoken words, despite normal hearing and intact speaking, reading, and writing.
• Indicates damage to the superior temporal lobe, often bilateral or deep in the left hemisphere.
• Suggests that hearing words and understanding them rely on distinct neural mechanisms.
• Anomia (Word-Finding Difficulty)
• A common symptom in many types of aphasia, including Wernicke’s aphasia.
• Patients struggle to recall words, often using circumlocutions (e.g., “the thing you sit on” instead of “chair”).
• Angular Gyrus and Language Processing
• Located in the parietal lobe, crucial for language-related functions, including reading and writing.
• Damage can cause alexia (reading impairment) and agraphia (writing impairment).
• Plays a role in word retrieval, contributing to anomia when damaged.
Key Takeaway:
• Fluent aphasia disrupts comprehension despite smooth speech, word deafness reflects auditory-language processing deficits, and damage to the angular gyrus can impair reading, writing, and word retrieval (anomia).
Global Aphasia – Meaning, Symptoms, and Causes
Key Findings:
• Definition:
• Global aphasia is the most severe form of aphasia, affecting both speech production and comprehension.
• Patients have very limited communication ability, often only producing a few words or sounds.
• Symptoms:
• Nonfluent speech – Severe difficulty forming words or sentences.
• Severely impaired comprehension – Cannot understand spoken or written language.
• Difficulty repeating words – Unable to echo spoken phrases.
• Cause:
• Extensive damage to the left hemisphere, affecting both Broca’s area (speech production) and Wernicke’s area (comprehension).
• Often caused by a large stroke in the middle cerebral artery (MCA) territory, leading to widespread language deficits.
Key Takeaway:
• Global aphasia results from extensive left-hemisphere damage, causing severe impairments in speech production, comprehension, and repetition, making communication extremely limited.
What are the key models of the brain’s language circuitry, and what does the connectionist model of aphasia propose?
Key Findings:
• Classical Model (Wernicke-Geschwind Model)
• Broca’s area: Controls speech production.
• Wernicke’s area: Responsible for language comprehension.
• Angular gyrus: Involved in reading and writing.
• Arcuate fasciculus: A bundle of axons connecting Wernicke’s and Broca’s areas.
• Critical for repetition of heard speech.
• Damage leads to conduction aphasia: fluent speech and good comprehension, but impaired repetition.
• Connectionist Model of Aphasia
• Views the brain’s language system as a network of interconnected regions, rather than isolated centers.
• Emphasizes the importance of connections (e.g., arcuate fasciculus) for integrating comprehension and production.
• Explains how different types of aphasia result from disruption in specific nodes or connections in the language network.
Key Takeaway:
• The brain’s language circuitry involves Broca’s and Wernicke’s areas, connected by the arcuate fasciculus. The connectionist model views language as a network, where damage to regions or connections leads to different types of aphasia.
What is the Wernicke-Geschwind Model (Connectionist model of Aphasia) of Language Processing
The Wernicke-Geschwind model outlines a serial pathway for how the brain processes language. It proposes that:
• Spoken language comprehension begins in the auditory cortex, then moves to Wernicke’s area, where the meaning of words is extracted.
• To respond verbally, information is sent via the arcuate fasciculus to Broca’s area, which is responsible for speech planning and production.
• Broca’s area then sends motor instructions to the motor cortex, which controls the mouth and vocal tract.
For reading aloud:
• Visual input goes to the visual cortex, then the angular gyrus, which translates visual words into an auditory code before sending it to Wernicke’s area for comprehension, and then follows the same pathway for speech output.
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This model emphasizes a left-lateralized, step-by-step flow between specialized regions, particularly Wernicke’s area (comprehension), Broca’s area (production), and the arcuate fasciculus (connection)—a foundational view of language processing in the brain.
What is the motor theory of language, and what evidence supports it?
Key Findings:
• Motor Theory of Language:
• Proposes that speech perception and speech production share the same neural circuits.
• Understanding spoken language involves mapping sounds onto the motor programs used to produce those same sounds.
• Key Idea:
• We perceive speech by simulating the articulatory gestures (e.g., movements of lips, tongue) in our own motor system.
• Supporting Evidence:
1. Premotor Cortex Activation:
• Brain imaging shows activation in Broca’s area and premotor regions during speech perception, not just production.
2. Mirror Neurons:
• Found in Broca’s area, these neurons fire both when performing and observing speech movements, supporting perception-action linkage.
3. Disruption Studies:
• TMS (transcranial magnetic stimulation) over motor speech areas impairs speech perception, showing motor regions contribute to understanding speech.
Key Takeaway:
• The motor theory of language suggests we understand speech by engaging the brain’s motor systems involved in producing it, supported by imaging, mirror neuron, and brain stimulation studies.
How is language represented in bilingual people, and what do brain imaging studies show?
Key Findings:
• Overlap vs. Separation:
• In early bilinguals (learned both languages during childhood), the same brain areas are typically used for both languages, especially in Broca’s area.
• In late bilinguals (learned second language in adulthood), there is less overlap—the two languages may activate adjacent but distinct regions.
• fMRI Study Findings:
• Bilingual individuals were asked to speak or think in both of their languages during scanning.
• Broca’s area showed shared activation for early bilinguals, but more separated activation in late bilinguals.
• This suggests that age of acquisition influences whether the brain integrates or separates language systems.
Key Takeaway:
• Bilinguals show more overlapping brain activation if both languages were learned early, while late learners often use distinct areas, highlighting how brain plasticity and language experience shape language representation.
What is Silbo Gomero, and what does it reveal about language processing in the brain?
Key Findings:
• Silbo Gomero:
• A whistled version of Spanish spoken on La Gomera, one of Spain’s Canary Islands.
• Used to communicate across long distances, with whistles mimicking the pitch and rhythm patterns of spoken language.
• Brain Activation Study:
• fMRI scans showed that when fluent Silbo users heard the whistles, they activated Broca’s and Wernicke’s areas—the same regions used in spoken language processing.
• Non-speakers of Silbo only activated auditory regions, not language areas.
• Implication:
• The brain recognizes Silbo as a linguistic system—language regions respond based on linguistic structure, not the sound type (spoken or whistled).
Key Takeaway:
• Silbo Gomero shows that the brain’s language areas can process non-verbal linguistic systems, reinforcing that language is about structure and meaning—not just speech sounds.
What have studies on babies revealed about early language development, and what do we know about the origins of language?
Key Findings:
• Universal Sound Discrimination at Birth:
• Babies are born able to discern all phonemes from every human language.
• During early babbling, infants produce a wide range of phonemes, including ones not used in their native language.
• Language Pattern Sensitivity by 7 Months:
• At around 7 months, infants pay more attention to unfamiliar sentence structures—even in sign language, suggesting sensitivity to linguistic patterns, not just sounds.
• Sensitive Period for Language Acquisition:
• There is a critical (sensitive) period from early childhood to puberty when the brain is especially receptive to language input.
• Language development is considered experience-expectant, meaning it requires exposure to language during this time to fully develop.
• Estimated Number of Languages: • Roughly 7,000 spoken languages exist across the world today. • Evolutionary Linguistic Biology: • Some researchers propose that all modern languages may have originated from ~7 major ancestral language groups. • These hypothetical language families are based on similarities in phonetics, structure, and geography. • While still debated, this suggests a shared evolutionary root for human language.
Key Takeaway:
• Babies show innate sensitivity to language from birth, supporting the idea that humans are biologically prepared for language. Evolutionary theories suggest today’s 7,000+ languages may have emerged from a small number of ancestral families.
What evidence supports an ancestral link between speech and gestures in language evolution?
Key Findings:
• Theory:
• Language likely evolved from earlier systems used for gestures and facial expressions.
• Behavioral Evidence:
• When people are prevented from gesturing, they show more speech errors and pauses, suggesting that gestures support fluent speech.
• Neural Evidence:
• Deaf signers activate the same language areas (e.g., Broca’s, Wernicke’s) as spoken language users.
• Damage to these areas causes similar language production deficits, regardless of modality.
• Developmental Evidence:
• Deaf children without formal sign exposure invent their own gesture-based systems, which show structural features similar to natural languages.
• Conclusion:
• These findings support the idea that core components of language are heritable and not dependent on speech alone.
Key Takeaway:
• Spoken language likely evolved from gesture-based systems, and the shared brain circuits and spontaneous language creation in deaf children suggest that language is biologically rooted and inheritable.
What are dyslexia, deep dyslexia, and acquired dyslexia, and how do they differ?
Key Findings:
• Dyslexia (Developmental Dyslexia):
• A lifelong reading disorder present from childhood, not caused by brain injury.
• Involves difficulty mapping letters to sounds (phonological processing).
• Often associated with reduced activity in the left temporoparietal cortex.
• Deep Dyslexia:
• A severe form of acquired dyslexia, usually following brain injury such as a stroke.
• Features include:
• Semantic reading errors (e.g., reading “apple” as “fruit”)
• Inability to sound out unfamiliar or nonsense words
• Reliance on whole-word recognition
• Reflects disruption in both phonological and semantic pathways.
• Acquired Dyslexia (General):
• A reading disorder that develops after brain damage, in contrast to developmental dyslexia.
• Includes deep dyslexia and other types like surface dyslexia (difficulty recognizing whole words) and phonological dyslexia (difficulty sounding out words).
Key Takeaway:
• Developmental dyslexia is a phonological-based reading disorder from childhood, while acquired dyslexia (including deep dyslexia) results from brain injury and may involve broader language processing deficits.
What is surface dyslexia, and what neural abnormalities are seen in developmental dyslexia?
Surface Dyslexia:
• A form of acquired dyslexia where individuals struggle to recognize whole words, especially those with irregular spelling (e.g., “sew” or “yacht”).
• Reading relies on sounding out words, leading to mispronunciations of irregular words.
• Typically caused by damage to the left lateral temporal regions involved in visual word recognition.
• Developmental Dyslexia – Neural Abnormalities:
• Appears in childhood and is not due to brain injury.
• Associated with structural differences in the brain, including:
• Micropolygyria:
• Abnormal condition where the cortical surface has too many small folds, leading to disorganized cortical layering and possibly impaired connectivity.
• Ectopias:
• Clusters of misplaced neurons that fail to migrate to the proper cortical layer during development.
• These are often found in language-related areas, especially in the left hemisphere.
Key Takeaway:
• Surface dyslexia affects recognition of irregular words due to damage in whole-word reading areas, while developmental dyslexia involves abnormal brain structures like micropolygyria and ectopias, which may disrupt phonological processing from early development.
How is fMRI used to study dyslexia, and what has it revealed?
Key Findings:
• fMRI (Functional Magnetic Resonance Imaging) allows researchers to observe real-time brain activity during language and reading tasks.
• Findings in Individuals with Dyslexia:
• Show reduced activation in left hemisphere language areas, particularly:
• Left temporoparietal cortex (involved in phonological processing)
• Left inferior frontal gyrus (Broca’s area)
• Left occipitotemporal region (visual word form area)
• Increased Activation in Right Hemisphere:
• Some individuals with dyslexia show greater right hemisphere activity, which may reflect compensatory processing.
• Applications:
• Helps identify neural signatures of dyslexia.
• Can be used to evaluate the effectiveness of reading interventions by tracking changes in brain activation.
Key Takeaway:
• fMRI studies reveal that dyslexia is linked to underactivation in left hemisphere reading circuits, and increased right hemisphere activation may represent compensation or rerouting of language processing.
How do brains process reading, and what does this reveal about dyslexia?
Key Findings:
• Two Language Systems for Reading:
• Phonological System → Focuses on sounds of letters (phonemes).
• Semantic System → Focuses on meanings of whole words.
• Dyslexia and Connectivity Issues:
• People with dyslexia often have weaker connections between these two systems, making it harder to link sounds to meanings.
• The brain scans in the image highlight areas of decreased activity in dyslexic individuals during a phonological reading task (judging rhyming words).
• fMRI Findings:
• The image shows regions in the left hemisphere with reduced activation in dyslexic individuals.
• These include areas in the temporal and frontal lobes, which are key for processing phonological and semantic aspects of reading.
Key Takeaway:
• Reading relies on both phonological (sound-based) and semantic (meaning-based) processing systems, and dyslexia is associated with weaker connectivity between them, leading to difficulties in reading fluently.
What is the heritable component of dyslexia, and what does current research suggest?
Key Findings:
• Heritability of Dyslexia:
• Dyslexia has a strong genetic component, often running in families.
• Twin studies suggest hereditary factors account for 40–60% of dyslexia risk.
• Key Genes Associated with Dyslexia:
• DYX1C1 → Involved in neuronal migration during brain development.
• ROBO1 → Plays a role in axon guidance and hemispheric connectivity.
• KIAA0319 → Implicated in cortical development, particularly in regions linked to phonological processing.
• Developing Research:
• Studies suggest that these genes may contribute to abnormal brain structures, such as ectopias and micropolygyria, which disrupt language processing networks.
• Researchers are investigating how gene-environment interactions (e.g., early language exposure, reading interventions) influence dyslexia severity.
• Neuroimaging studies continue to explore how these genetic factors correlate with differences in brain activation patterns in dyslexic individuals.
Key Takeaway:
• Dyslexia has a strong genetic basis, with genes like DYX1C1, ROBO1, and KIAA0319 linked to disrupted brain development and phonological processing. Ongoing research is exploring how these genetic influences interact with environmental factors to shape reading abilities.
