Language and Laterization (class 10)

Left-Hemisphere Functions

• Words & letters

• Language sounds

• Complex movement & ipsilateral movement

• Verbal memory & finding meaning in memories

• *Language: speech, reading, writing, & arithmetic

Right-Hemisphere Functions

• Faces, geometric patterns, and emotional expressions

• Non-language sounds & music

• Touch: tactile pattern & braille

• Movement in spatial patterns

• Nonverbal memory & perceptual aspects of memories

• Emotional content of language

• *Spatial ability: mental rotation of shapes, geometry, direction, & distance

Cerebral Lateralization

The division of labor between the two cerebral hemispheres, where each hemisphere is specialized for particular types of processing. This specialization is statistical rather than absolute

Split Brain

Occurs when the corpus callosum, which transfers learned information between hemispheres, is surgically severed. This prevents direct communication between the hemispheres, causing them to function independently.

Split-Brain Studies

Have demonstrated hemispheric specialization for many processes. For example, the left hemisphere can verbally report words seen in the right visual field, while the right hemisphere cannot but can often identify the object with the left hand

Corpus Callosum

The largest cerebral commissure that transfers learned information from one hemisphere to the other. When it is cut, the two hemispheres function independently

Alien Hand Syndrome

A phenomenon where one hand acts as though it has a mind of its own, performing purposeful actions without the person's conscious control. It can occur after split-brain surgery

Cross-Cueing

A way the hemispheres of a split-brain patient can indirectly communicate. For example, the right hemisphere might produce a facial expression (facial feedback) when the left hemisphere gives an incorrect spoken answer

Helping-Hand Phenomenon

Occurs in split-brain patients when one hand, controlled by one hemisphere, corrects an action initiated by the other hand in response to different visual stimuli

Chimeric Figures Task

Demonstrates competition between hemispheres in split-brain patients. When presented with a composite of two different half-faces, they often only recognize the symmetrical version of the half-face presented to the right visual field (left hemisphere) as being less emotional

Z Lens

A contact lens opaque on one side, used to restrict visual input to only one hemisphere in split-brain patients. This allows researchers to assess each hemisphere’s understanding of spoken instructions

Recovery of Function

The restoration of behavioral capacity following brain damage from stroke or injury. It can involve mechanisms like collateral sprouting and the generation of new neurons

Constraint-Induced Movement Therapy

A rehabilitation technique where the unaffected limb is restrained to force the patient to repeatedly use the affected limb, helping to regain its function after a stroke

Language Lateralization & Handedness

Language is strongly lateralized to the left hemisphere. This is particularly true for right-handed individuals, where Broca’s and Wernicke’s areas are exclusively on the left. While the left hemisphere is also specialized for language in most left-handed people, right-hemisphere dominance for language is rarer but more likely in left-handers

Right Ear Advantage

In Dichotic presentation, right-handed people typically identify verbal stimuli delivered to the right ear more easily because it goes directly to the left (language-dominant) hemisphere

Up to 50% of left-handed individuals may show a left-ear advantage for verbal stimuli in dichotic presentation, or no ear advantage

Broca's Area

Located in the left inferior frontal region, is crucial for speech production. Damage leads to Broca’s aphasia (non-fluent aphasia), characterized by difficulties in producing speech, though comprehension remains relatively good

Hemiplegia

The paralysis of one side of the body (usually the right side), may occur in patients with Broca’s aphasia due to damage in the left inferior frontal region

Wernicke's Area

Located in the left posterior temporoparietal cortex, is key for language comprehension. Damage results in Wernicke’s aphasia (fluent aphasia), where speech is fluent but lacks meaning, and comprehension is poor

Symptoms of Wernicke’s Aphasia

• Paraphasias - language output error (substitution of a word by a sound, an incorrect word, or an unintended word)

• Neologisms – invented nonsense words

• Anomia- word deafness or word blindness

Planum Temporale

Located on the upper surface of the temporal lobe and involving part of Wernicke’s area, is larger in the left hemisphere, even in infants before language development. This supports the idea of an inborn neural mechanism for language

Arcuate Fasciculus

A neural pathway that connects Wernicke’s and Broca’s areas. Lesions can cause Conduction aphasia, where patients have difficulty repeating spoken words but may retain comprehension and spontaneous speech

Conduct Aphasia

A language disorder characterized by difficulty repeating words or phrases, although the individual can generally understand and produce fluent, grammatical speech. It's often caused by damage to the arcuate fasciculus

Astereognosis

The inability to recognize objects by touch, despite being able to feel them. It can be caused by damage to the anterior parietal lobe (primary somatosensory cortex) and the fusiform gyrus

Prosopagnosia

Also known as face blindness, is the inability to recognize faces, including one's own. It can be caused by damage to the fusiform gyrus, and bilateral damage can cause complete facial blindness

Global Aphasia

A total loss of the ability to understand or produce language. It results from widespread left hemisphere lesions affecting all speech zones, and the prognosis for language recovery is poor

Angular Gyrus

Located posterior to Wernicke’s area, is involved in decoding visual information to recognize words and associate visual forms with spoken forms. Lesions can cause difficulty saying words that have been seen but not heard

Other Aphasias

Agraphia: an impairment in writing that often accompanies aphasia

Alexia: an impairment in reading that often accompanies aphasia

Apraxia: a motor impairment characterized by difficulty in making sequences of movements, and it can occur with aphasia

Tachistoscope Tests

Involving brief presentation of visual stimuli to one visual field, confirm the verbal-spatial division of labor. Verbal stimuli in the right visual field (left hemisphere) are better recognized, while non-verbal stimuli in the left visual field (right hemisphere) are better recognized

Contralateral Processing

Sensory information received on one side of the body is usually processed by the opposite hemisphere. For example, the right visual field is processed by the left hemisphere

Verbal-Spatial Division of Labor

The specialization between the hemispheres where the left hemisphere is dominant for verbal stimuli, and the right hemisphere is better at processing non-verbal, spatial stimuli. This is confirmed by tachistoscopic studies

Motor Theory of Language

Proposes that anterior and posterior left-hemisphere language zones are motor control systems involved in both the production and perception of complex motions that produce speech. TMS studies provide support for this theory

Transcranial Magnetic Stimulation (TMS)

A technique that can be used to simulate a lesion by disrupting neural activity for up to an hour, allowing researchers to evaluate specialized areas within the brain, including language-related regions

Sign Language and Aphasia

Users of sign language employ the same neural mechanisms that speakers do, and comparable brain injury leads to the same aphasias

Caveats of Aphasia and Brain Lesions

It's important to note that in reality, no aphasic patients have damage restricted solely to Broca’s or Wernicke’s areas, and they almost always have damage to subcortical white matter. Large anterior lesions tend to produce expressive symptoms, while large posterior lesions are more likely to cause receptive symptoms

Damasio’s PET Study

Study showed that left temporal lobe areas activated by naming varied with the category of the item being named (faces, animals, tools), and activity extended beyond Wernicke’s area

The Connectionist Model of Language (Speaking a Heard Word)

Step 1: Information about the sound is analyzed by the Primary Auditory Cortex

Step 2: Wernicke’s area analyzes the sound information to determine the word that was said

Step 3: This information is then transmitted via the Arcuate Fasciculus

Step 4: Broca’s area forms a motor plan to repeat the word

Step 5: The Motor Cortex implements the plan, manipulating the larynx and related structures to say the word

The Connectionist Model of Language (Speaking a Written Word)

Step 1: The Visual Cortex analyzes the image of the written word

Step 2: The Angular Gyrus decodes the visual information to recognize the word and associate this visual form with its spoken form in Wernicke’s area

Step 3: Information about the word is then transmitted via the Arcuate Fasciculus

Step 4: Broca’s area formulates a motor plan to say the appropriate word

Step 5: The Motor Cortex implements the plan, manipulating the larynx and related structures to say the word

Communication

The transmission of information between individuals that occurs in many species.

• Honeybees- communicate through dances; indicate where the pollen is (round dance, waggle dance)

• Chimpanzees- touch each other’s hands to greet each other

Communication vs. Language

First is the transmission of information between individuals, while the other is a highly specialized communication based on arbitrary symbols and rules to convey a vast range of concepts, and a grammatical code (what makes humans UNIQUE)

Features of Human Language

• Abstract: talk about things in the past, present, and future

• Arbitrary: able to pick any sound or sign we like to refer to things

• Rule-governed (syntax): specific rules guide the way we put these words together to make sense of them

• Generative: can be combined in countless ways

Phonemes

The basic speech sounds of a language. Babies are born knowing all but learn to parse out those used around them. (i.e. the words "cat" and "bat" are distinguished by the /c/ and /b/ phonemes)

Morphemes

The simple units of meaning that are assembled into words with meanings; semantics (i.e. ‘ing’, ‘ed’, ‘un’ or ‘s’ for plural)

Critical Period

A period in development when exposure or practice must occur for skills to develop

• e.g. visual processing – the brain's plasticity will reconnect a baby’s neurons from a blocked eye; thus, the eye must be corrected quickly, or normal sight will never be regained.

Sensitive Period

A period in development when exposure or practice will most facilitate the development of skills

• e.g. social behavior – an individual who experiences extreme stress as a child may show social deficits/abnormalities, but these abnormalities can be overcome (sometimes)

FOXP2

A hereditary specific gene that has been shown to be relevant to language development. Mutations in this gene are associated with language abnormalities. It also plays a role in vocalizations in other species. Neanthertals had this, but chimpanzees do not

Sensitive Period for Language

Appears to be from early childhood to late adolescence, with the most crucial time being before around 7 years old. Adults typically have a harder time learning languages and may use different brain regions

Acquired Dyslexia (Alexia)

The sudden dyslexia after brain damage, usually to the left hemisphere. There are different types:

• Deep dyslexia is characterized by semantic errors when reading, difficulty reading abstract words aloud, and trouble sounding out nonsense words

• Surface dyslexia involves difficulties restricted to the regular sound rules of letters and trouble sounding out exception words

Developmental Dyslexia

A difficulty unique to written language, not a general cognitive deficit, affecting around 5% of children. It may involve neurological abnormalities in the frontal and temporal lobes

The "Interpreter" Role

The left hemisphere has been described as this, suggesting its role in making sense of information and generating explanations. Also better in in controlling ipsilateral movement

Split-Brain Cats

Myers and Sperry’s studies on split-brain cats showed that each hemisphere could learn independently, and learning did not transfer between hemispheres when the optic chiasm and corpus callosum were transected and visual input was restricted to one hemisphere at a time

Commissurotomy

The surgical cutting of the corpus callosum, is sometimes performed in humans as a last-ditch effort to control severe epilepsy

Human and Animal Split Brains Differences

Unlike split-brain animals, the two hemispheres in split-brain humans have very different abilities, with the left hemisphere typically capable of speech while the right hemisphere is not

Factors Affecting Brain Injury Recovery

Recovery from brain injury depends on factors such as the passage of time, the age of the patient (better recovery when younger), and the types of rehabilitation therapies received. Recovery tends to be better from a concussion than a stroke

Recovery vs. Compensation

Restoration of function is different from compensation. While compensatory behaviors can reduce the impact of an injury, stroke victims can sometimes regain use of affected limbs if forced to use them repeatedly, as in constraint-induced movement therapy

Types of Brain Injuries

Concussion: a closed-head brain injury caused by a jarring blow to the head.

Chronic traumatic encephalopathy (CTE) is dementia that results from too many blows to the head and is characterized by excess tau protein within neurons, which interferes with their function.

Doing Two Things at Once

Each hemisphere of a split-brain patient can learn independently and simultaneously

• Helping-hand phenomenon – presented with two different visual stimuli, the hand that “knows” may correct the other

• Dual foci of attention – split-brain hemispheres can search for the target item in an array faster

• Chimeric figures task– only the symmetrical version of the right half of the faces was recognized (indicates competition between hemispheres)