chapter14 power point lecture

Chapter 14:Cognitive Functions

Lateralization of Function

• Lateralization of function refers to the idea that each hemisphere of the brain is specialized for different functions.

• Each hemispheres controls the contralateral (opposite) side of the body.– Example: skin receptors and muscles

mainly on the right side of the body.– Each hemisphere sees the opposite side of

the world.


• The left and right hemisphere exchange information primarily through a set of axons called the corpus callosum.

• Other areas that exchange information include:– The anterior commissure.– The hippocampal commissure.– A few other small commissures.

• Information crosses to the other hemisphere with only a brief delay.

Fig. 14-2, p. 418


• The two hemispheres are not mirror images of each other.

• Division of labor between the two hemispheres is known as lateralization.– In most humans the left side is specialized

for language.• The corpus callosum allows each hemisphere

of the brain access to information from both sides.


• Each hemisphere of the brain gets input from the opposite half of the visual world.

• The visual field is what is visible at any moment.

• Light from the right half of the visual field shines into the left half of both retinas.

• Light from the left visual field shines onto the right half of both retinas.


• The left half of each retina connects to the left hemisphere.

• The right half of each retina connects to the right hemisphere.

• Half of the axons from each eye cross to the opposite side of the brain at the optic chiasm.

• The auditory system is arranged differently in that each ear sends the information to both sides of the brain.

Fig. 14-3a, p. 419


• Damage to the corpus callosum interferes with the exchange of information between hemispheres.

• Epilepsy is a condition characterized by repeated episodes of excessive synchronized neural activity.– Mainly due to decreased release of the

inhibitory neurotransmitter GABA.• Physicians once cut the corpus callosum to

prevent the seizure from spreading to the opposite side of the body.


• People who have undergone surgery to the corpus callosum are referred to as split-brain people.

• Spit brain people maintain normal intellect and motivation but they tend to:– Use hands independently in a way others

cannot.– Respond differently to stimuli presented to

only one side of the body.

Fig. 14-4, p. 420


• Sperry (1974) revealed subtle behavioral differences for spilt brain people.

• Because the left side of the brain is dominant for language in most people, most split brain people:– Have difficulty naming objects briefly

viewed in the left visual field.• A small amount of information can still be

transferred via several smaller commissures.

Fig. 14-5, p. 422


• Immediately after surgery, each hemisphere can only quickly and accurately respond to information that reaches it directly. – Smaller commissures allow a slower

response.• The brain later learns use the smaller

connections:• Difficulty integrating information between both

remains.

Fig. 14-6, p. 423


• Right hemisphere is better at perceiving emotions.

• Damage to parts of the right hemisphere causes difficulty perceiving other’s emotions, failure to understand humor and sarcasm, and a monotone voice.

• Left hemisphere damage increases ability to accurately judge emotion.– Associated with decreased interference

from the left hemispheres.


• The right hemisphere is also better at comprehending spatial relationships.

• In general, the left hemisphere seems to focus more on visual details, and the right hemisphere focuses more on visual patterns.


• Some anatomical differences exist between the hemispheres of the brain.

• The planum temporale is an area of the temporal cortex that is larger in the left hemisphere in 65% of people.– Difference are slightly greater for people

who are strongly right handed.• MRI studies indicate that the a big difference

in the ratio of left to right planum temporale is related to increased language performance.

Fig. 14-9, p. 425


• Damage to left hemisphere often results in language deficiencies.

• Left side seems to be specialized for language from the very beginning in most people.

• The corpus callosum matures gradually through the first 5 to 10 years.– Thus, young children have difficulty

comparing information from the left and right hand.


• Being born with a condition where the corpus callosum does not completely develop results in extra development of the following:– Anterior commissure - connects the

anterior parts of the cerebral cortex.– Hippocampal commissure - connects the

left and right hippocampus.• Allows performance on some tasks that

differs from split-brain people.


• The left hemisphere is dominant for speech in 95% of right-handed people.

• Most left-handers have left-hemisphere or mixed-dominance for speech.– Few people have strong right hemisphere

dominance.


• Recovery of language after damage to the brain varies.

• Age affects extent of recovery.– Brain is more plastic at an early age.

• Right hemisphere reorganizes to serve some of the left-hemisphere function.


• Rasmussen’s encephalopathy is a rare condition in which the immune system initially attacks the glia and then the neurons of one hemispheres of the brain.– Usually begins in childhood or

adolescence.• Surgeons eventually remove or disconnect

the side of the damaged brain.• Language recovers slowly but substantially.

– Slow deterioration allows the other side of the brain to compensate and reorganize.


• Language recovery after brain damage is also influenced by how language was initially lateralized for the given person.

• Individuals with partial representation of language in both hemispheres recover better than those with language dominance in one hemisphere.

Evolution and Physiology of Language

• Human language is a complex form of communication.

• Compared to other species, human language has high productivity.– Productivity - the ability to produce new

signals to represent new ideas.


• Human language is most likely a modification of a behavior also found in other species.

• Chimpanzees use language but it differs from humans:– Seldom use symbols in new original

combinations.– Use of symbols lacks productivity.– Use of symbols is primarily used to request

and not describe.– Production of requests is better than

understanding other’s requests.


• Bonobos or pygmy chimpanzees show an increased comprehension of human language:– Understand more than they can produce.– Use symbols and names to describe

objects.– Request items not seen.– Use symbols to describe past events.– Make original, creative requests.


• Non-primates also display some aspects of spoken language.

• Elephants imitate sounds they hear, including the vocalizations of other elephants.

• Dolphins respond to gestures and sounds.• The African gray parrot show a great ability

for imitating sounds and also using sounds meaningfully.– Example: Alex the gray parrot.


Studies of nonhuman language abilities:• Give insights to how best to teach language

to those who do not learn it easily.– Examples: Brain damaged people or

children with autism.• Illustrate the ambiguity of our concept of

language.– Allows for more precise definition.


• Two categories of theories attempt to explain the human ability to learn language more easily than other species.

1. “Language evolved as a by-product of overall brain development.”

2. “Language evolved as an extra part of the brain.”


• Problems associated with the “language as a by-product of increased intelligence” theory:

1. People with a full-size brain and normal overall intelligence can show severe language deficits.

2. People with impaired intelligence can have normal language skills.• Williams syndrome characterized by

metal retardation but skillful use of language.

Fig. 14-14, p. 433


• Evidence suggesting language evolved as an extra brain module specialization includes:– Language acquisition device is a built in

mechanism for acquiring language.• Evidence comes from the ease at which

most children develop language.– Chomsky (1980) further suggests the

poverty of stimulus argument: children do not hear many examples of some of the grammatical structures they acquire.


• Most researchers agree that humans have a specially evolved “something” that enables them to learn language easily.– Certain brain areas are indeed necessary

for language.– But same areas are also necessary for

other tasks (memory and music perception).

• Exactly how humans evolved language is unknown but is perhaps due to the pressure for social interaction.


• Research suggests a critical period exists for the learning of language.

• Learning of a second language differs as a function of age:– Children are better at learning

pronunciation and unfamiliar aspects of grammar.

• No sharp cutoff exist for second language learning.– Adults learn a second-language vocabulary

better.


• Rare cases of children not exposed to language indicates limited ability to learn language later.

• Deaf children unable to learn spoken language and not given the opportunity to learn sign language while young reveals:– Little development of skill at any language

later.– Early exposure to some language

increases ability to learn another language later.


• Most knowledge of brain mechanisms of language come from the study of people with brain damage:– Broca’s area is a part of the frontal lobe of

the left cerebral cortex near the motor cortex.• Damage results in some language

disability.– Aphasia refers to a condition in which there

is severe language impairment.


• Broca’s aphasia/nonfluent aphasia refers to serious impairment in language production, usually due to brain damage.

• Omission of most pronouns, prepositions, conjunctions, auxiliary verbs, tense and number endings during speech production.

• People with Broca's aphasia have trouble understanding the same kinds of words they omit (prepositions and conjunctions).


• Broca’s aphasia is usually accompanied by comprehension deficits when: – The sentence meaning depends on

prepositions, word endings or unusual word order.

– Sentence structure is complicated.• Broca’s area thus seems to be critical for the

understanding of some, but not all, aspects of grammar.

Fig. 14-15, p. 435

Fig. 14-16, p. 436


• Wernicke’s area is an area of the brain located near the auditory part of the cerebral cortex.

• Wernicke’s aphasia is characterized by the impaired ability to remember the names of objects and also impaired language comprehension.– Sometimes called “fluent aphasia” because

the person can still speak smoothly.• Recognition of items is often not impaired;

ability to find word is impaired.


• Typical characteristics of Wernicke’s aphasia include:

1. Articulate speech / fluent speech except with pauses to find the right word.

2. Difficulty finding the right word - anomia refers to the difficulty recalling the name of objects.

3. Poor language comprehension - difficulty understanding spoken and written speech (especially nouns and verbs).

Table 14-1, p. 438


• Dyslexia is a specific impairment of reading in a person with adequate vision and adequate skills in other academic areas.– More common in boys.– Research suggests a genetic influence.


• In some cases, dyslexia is associated with mild abnormality in the structures of various brain areas.– More likely to have a bilateral symmetrical

cerebral cortex.– Language–related areas in the right

hemisphere are larger in some.– Weak connections exist among other

areas.


• Different kinds of dyslexics have different reading problems.

• “Dysphonic dyslexics” have trouble sounding out words.– Attempt to remember them as a whole.

• “Dyseidetic dyslexics” fail to recognize a word as a whole.– Read slowly and have particular trouble

with irregularly spelled words.


• Most severe cases of “dyseidetic dyslexia” result from brain damage that restricts the field of vision.

• Characterized by the following:– only seeing one letter a time.– short eye movements.– very slow reading.– difficulty with long words.


• One hypothesis to explain dyslexia emphasizes a hearing impairment rather than visual impairment.– Less than normal response to speech

sounds in the brain.– Lack of ability to pay close attention to

sounds.


• Another hypothesis to explain dyslexia is connecting vision to sound.

• Brain scans indicate that reading strongly activates areas of the left temporal and parietal cortex for most people.– Areas are associated with connecting

visual and auditory information.• Only weakly activated for people with

dyslexia.


• A final hypothesis relates dyslexia to differences in attention.

• Reading requires the shifting of attention.• People with dyslexia do not shift their

attention in the same way.• Effective treatment may be for dyslexics to

focus on one word at a time.

Fig. 14-17, p. 440

Attention

• Attention is a multi-dimensional process and related to consciousness.

• Attention relates to increased brain activity in the areas responsive to a stimulus.

• Stimuli destined to become conscious or unconscious produce about the same brain activity in the first 200-250 milliseconds.

• In the next few milliseconds, the brain enhances activity for stimuli that become conscious.

Attention

• Enhancement of activity can be due to intensity of the stimulus, similarity to past important stimuli, or other features of the stimulus itself.

• Enhancement of activity can also be due to shifting of attention.

• Research suggests that attention pertains more to the enhancing of relevant activity than inhibiting irrelevant activity.

Attention

• “Inattention” or “neglect” is the opposite of attention.

• Spatial neglect is a tendency to ignore the left side of the body and its surroundings or the left side of objects.– Often associated with damage to the right

hemisphere of the brain.

Attention

• Exact location of the damage to the right hemisphere can affect the details of what the person neglects.– Damage to the inferior part of the right

parietal cortex leads to the neglect of everything to the left of their own body.

– Damage to the superior temporal cortex neglect the left side of objects, regardless of location.

Fig. 14-19, p. 444

Attention

• Problems of neglect are associated with attention and not sensation.

• Someone with neglect can see an entire letter enough to say what it is.

• The same person ignores the left half when asked to cross out all the letters that compose a word.

Attention

• Several procedures can increase attention to the neglected side:– telling the person to pay attention to the left

side.– telling the person to look left while feeling

an object with the left hand or hearing a sound from the left side.

• A touch stimulus briefly increases attention to one side of the body or the other.

• Crossing of the hands in front of the body also decreases neglect to the left side.

Fig. 14-20, p. 444

Attention

• Many patients with spatial neglect also have deficits with spatial working memory and with shifting attention, even when location is irrelevant.

• Thus, problems associated with neglect extend to many aspect of attention rather than simply the left-right dimension.

Attention

• Attention-Deficit Hyperactivity Disorder (ADHD) is characterized by the following:– Attention deficits (distractibility).– Hyperactivity (fidgetiness).– Impulsiveness.– Mood swings.– Short temper.– High sensitivity to stress.– Impaired ability to make and follow plans.

Attention

• ADHD affects social behavior and school performance.

• Some have occupational problems and antisocial behaviors in adulthood.

• Estimates range from 3%-10% of children• Twice or three times as likely in males.• Research is complicated by the ability to

make reliable diagnoses.

Attention

• Three example of tasks which people with ADHD differ:

1. “The choice delay task” - more likely than others to choose a smaller but quicker reward (impulsiveness).

2. “The stop signal task” - difficulty inhibiting behaviors.

3. “The attentional blink task” - indicates trouble controlling attention and difficulty shifting it when needed.

Attention

• Twin studies suggest fairly high heritability (Thapar et al., 2003).– Several genes have been identified which

influence performance on tests of attention.• ADHD probably depends on multiple genes

as well as environmental influences.• Probability of ADHD is elevated among

children of women who smoked cigarettes during pregnancy.

Attention

• Structural brain differences include a smaller than average prefrontal cortex and cerebellum.– Cerebellar dysfunction is known to be

associated with difficulty switching attention.

• Structural differences in the brain are small and inconsistent between cases.– Brain scans do not provide reliable results

for diagnoses.

Attention

• The most common treatment for ADHD is stimulant drugs or amphetamines.– Example: methylphenidate/Ritalin.

• Stimulant drugs increase attentiveness, improve school performance and social relationships, and decrease impulsiveness.

• Also improve scores on laboratory tests, such as the “stop signal task”.

• Justifying the benefits derived from taking the drugs is a complex and controversial issue.

Attention

• Amphetamines and methylphenidate increase the availability of dopamine to the postsynaptic receptors.

• Maximum benefit occurs 1 hour after ingestion and benefits last for a few hours.

• Several studies have found that stimulant drugs enhance certain aspects of learning and attention for all people, not just those with ADHD.

Attention

• Behavioral techniques are available as supplements or substitutes for stimulant drugs:– Reduce distractions.– Use lists, calendars, and other

organizational techniques.– Practice strategies to pace yourself.– Learn to relax; tension and stress can

magnify attention deficits.

chapter14 power point lecture

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