Chapter 13 - Cognitive Neuroscience

Question 1

LATERALIZATION

Answer 1

The right and left hemispheres differ in function as well - the localization of a function in one hemisphere or the other is known as LATERALIZATION.

Generally speaking:

• the LEFT HEMISPHERE is specialised in language and logical processing.
• the RIGHT HEMISPHERE is specialised in prosody, musical abilities, spatial abilities, facial recognition, intuition and artistic skills.

Evidence for brain lateralization comes from:

1) SPLIT BRAIN OPERATIONS;
2) WADA TESTS;
3) DICHOTIC LISTENING TASKS.

Today, lateralisation can be observed using fMRI and DTI.

Question 2

SPLIT BRAIN OPERATIONS

Answer 2

In the SPLIT BRAIN OPERATION - used to reduce the severity of seizures - pathways connecting the right and left cerebral hemispheres are severed. Usually only the CORPUS CALLOSUM is removed, but sometimes also the MASSA INTERMEDIA, ANTERIOR COMMISSURE and HIPPOCAMPAL COMMISSURE are severed.

Question 3

SPLIT BRAIN TASKS

Answer 3

In a classic split brain task, a patient is asked to fixate their gaze on a dot in the centre of their visual field. Then, a word is briefly displayed on a screen, with the first half of the word to the left of the dot and the second half to the right.

When the participant is asked which word has been presented, she responds with the right half of the word - this is the half processed by the left hemisphere, which in most people processes language.

If the participant is asked to point with her left hand to the word she saw, she will point to the left half of the world - this is the half processed by the right hemisphere, which controls movement of the left hand.

Similarly, if a stimulus is displayed only on the left half of the screen, the participant claims not to know what the stimulus presented was, but still maintain the ability to draw it with their left hand.

Question 4

LATERALISATION of MOTOR and VISUAL SYSTEMS

Answer 4

Both the motor and the visual system show lateralisation:
1) in the VISUAL SYSTEM, input captured by NASAL HEMIRETINA goes to the opposite hemisphere, whereas input captured by the TEMPORAL HEMIRETINA stays in the same hemisphere. In other words, information from the right half of the visual field is transmitted to the left visual cortex, and vice versa.

2) in the MOTOR SYSTEM, movements of each half of the body are controlled by the opposite hemisphere.

Question 5

WADA TESTS

Answer 5

WADA TESTS were typically performed before surgery in order to determine which hemisphere is involved in a specific task. They consists of injection of a sedative in one hemisphere and subsequent observation of cognitive changes.

Question 6

DICHOTIC LISTENING TASKS

Answer 6

DICHOTIC LISTENING TASKS feature different sounds presented simultaneously to the left and right ears. If two different stimuli are presented simultaneously to both ears and participants are asked to report what they have heard, they mainly report info from the RIGHT EAR.

This phenomenon can be explained by the LATERALISATION of language processing; WERNICKE’S AREA, which is specialised in SPEECH COMPREHENSION, is found in the left temporal lobe. Although information from one ear is processed by both cerebral hemispheres, it is processed more rapidly by the CONTRALATERAL AUDITORY CORTEX.
This means that input from the left ear is first processed by the right auditory cortex and then sent to the left temporal lobe, whereas input from the right ear is directly sent to the left hemisphere - this difference in “distance travelled” favours input from the right ear, which reaches wernicke’s area in a shorter amount of time.

Question 7

HEMISPHERECTOMY

Answer 7

HEMISPHERECTOMY - a surgical procedure in which the cortex from one entire cerebral hemisphere is completely removed - provides insight on the power of NEURAL PLASTICITY during the developmental phase. Treated children - usually suffering from severe seizure attacks in only one hemisphere - do not show cognitive deficits, but only minor motor impairments.

Question 8

the EVOLUTION of LATERALIZATION

Answer 8

LATERALIZATION might have evolved in both vertebrates and invertebrates because it provides advantages:

• individual benefits include ENHANCED SKILL PERFORMANCE, FASTER REACTION TIME
• social benefits include COORDINATION: population lateralization is more common among social species, where it may coordinate responses to a predator.

Question 9

the DEVELOPMENT of LATERALIZATION

Answer 9

Two hypotheses of LATERALIZATION DEVELOPMENT have been advanced:

1) the first hypothesis suggested that PRENATAL ANDROGENS play key roles in the lateral­ization of language and visuospatial skills and that high levels of androgens promote left-handedness.
2) the second hypothesis maintains that structural and functional lateralization originates in different GENES involved in the development of the right and the left hemisphere - genes involved in the development of axons and dendrites are expressed differently in the right and left hemispheres between 3 and 5 months of life.

Not only exposure to androgens and genes seem involved in this development, but also exposure to LIGHT affects lateralisation - chicks incubated in dark environments show poor lateralisation compared to chick incubated in the presence of light.

Question 10

the LATERALIZATION of EMOTION and MUSICAL ABILITIES

Answer 10

EMOTION and MUSICAL ABILITIES show lateralisation.

1) The RIGHT HEMISPHERE plays a larger role in expression of EMOTION and the perception of emotion in others’ faces.
On the other hand,PROSODY, or the ability to produce and detect emotional tone in language, appears to involve.

2) Different aspects of MUSIC appear to produce more activity in one hemisphere or the other.
In DICHOTIC LISTENING TASKS with musical stimuli, NON-MUSICIANS typically remember more notes from LEFT ear (input processed by the right hemisphere), whereas MUSICIANS typically remember more notes from RIGHT ear (input processed by the left hemisphere). This could be explained by the fact that musical training leads musicians to process music with similar brain areas involved in verbal language. Furthermore, musicians show neural STRUCTURAL DIFFERENCES: the PLANUM TEMPORALE - parto of the auditory cortex - is usually larger in the left hemi­sphere than in the right. However, the difference between the left and right planum temporale is about twice as large in musicians with perfect pitch as in non-musicians.

Question 11

IDIOTS SAVANTS

Answer 11

IDIOTS SAVANTS are individuals with mild mental retardation who show exceptional skills and talents in specific tasks, usually in the arts. Some research maintains that these skills could be due to abnormalities in the left hemisphere, which, in typical individuals, overshadows such artistic abilities of the right hemisphere.

Question 12

HANDNESS, LANGUAGE and LATERALIZATION

Answer 12

One of the strongest correlations regarding lateralization is the association between handedness and the localization of language - of the 90 percent who are right-handed, 96 percent localize language to the left hemisphere. Among the 10 percent who are left-handed, only 70 percent local­ize language to the left hemisphere, with the remaining 30 percent localising language in the right or both hemispheres.

LEFT-HANDNESS is an advantage in forward­ facing sports, such as fencing, tennis, and base­ball, but not in non-interactive sports. This is because left-handedness provides an advantage in physical confrontation, since the majority of the population is right-handed - in support of this theory, it has been found that left-handedness becomes more frequent in societ­ies engaged in sustained wars.

Question 13

LANGUAGE

Answer 13

LANGUAGE is defined as a system for communicating thoughts and feelings using arbi­trary signals, such as sounds, gestures, or written signals. Several criteria have been identified to discern language from simple communication:

1) SEMANTICITY, or the use of symbols to refer to objects and actions;
2) ARBITRARINESS, or the absence of a connection between a symbol and what it refers to;
3) SPONTANEOUS USAGE;
4) DUALITY, or use of different sounds or different orders of sounds;
5) DISPLACEMENT, or the ability to communicate about objects and events that are distant in time and place;
6) STRUCTURE-DEPENDENCE, or the use of grammar;
7) CREATIVITY, or the ability to create novel utterances;
8) TURN-TAKING, the existence of social communicative rules.

Question 14

The ORIGINS of LANGUAGE

Answer 14

CLICK LANGUAGES might represent the earliest form of human language - studies of genetic relatedness among African groups using click languages show that the origin of click languages occurred long before human beings settled down to begin agriculture.

Several lines of reasoning point to a BIOLOGICAL ORIGIN or human language:

• no human culture on earth exists without language;
• no specific instruction is needed to learn spoken language;
• language learning does not always correlate with intelligence - there might be an independent “language module” in the brain.

One GENE associated with speech and language disorders is the forkhead box P2 gene (FOXP2), located on chromosome 7 - mutations of this gene lead to severe difficulties in speech production. This gene could be responsible for transferring the control of vocalization from the subcortical level - as it is for primates - to the cortical level in hominis.

Question 15

COMMUNICATION in nonhuman ANIMALS

Answer 15

Many animals communicate with one another - communication, however, is not the same as language. If we are to find an animal precursor to human language capability, the most logi­cal place to start is with our nearest relatives, the great APES. The most important question researchers asked themselves was whether the reason why animals do not produce language was a CENTRAL ISSUE - a lack of cognitive skills - or a PERIPHERAL ISSUE - a lack of anatomical structures to support extensive vocalisation.

Researchers have attempted to teach human-like languages to apes with ambiguous results: while some chimpanzees were able to learn and recognize a few words, the results were scarce and the learning process very laborious. Attempts to teach chimps SIGN LANGUAGE have been somewhat successful.

1) GUA - a baby CHIMPANZEE - did not show significant results in learning human speech;
2) WASHOE - a CHIMPANZEE - successfully learned 132 signs of ASL;
3) KANZI - a BONOBO CHIMPANZEE - learned to associate geometric symbols with words;
4) PANBANISHA - a BONOBO CHIMPANZEE - learned to use a keyboard to produce grammatical sentences.

Question 16

MULTILINGUALISM

Answer 16

MULTILINGUALISM refers to proficiency in more than one language.
Research into the effects of brain damage in multilin­gual patients provides fascinating insights into the way the brain manages multiple languages and suggests that multiple languages use some of the same areas of the brain but that the degree of overlap is not 100 percent.

Although different languages share the same brain areas, we are able to keep them separate - according to the “LANGUAGE SWITCH” hypothesis, switching languages involves an executive function of the DORSOLATERAL PREFRONTAL CORTEX - thus, it would be more costly to switch language than not.

Gray-matter density in the LEFT INFERIOR PARIETAL REGION - involved in attentional processes related to language - is (1) positively correlated with proficiency in a second language and (2) negatively correlated to the age of acquisition of such language.

Question 17

SIGN LANGUAGE

Answer 17

SIGN LANGUAGE is a language not of sounds but of sight and movement.
In spite of the spatial nature of sign language - for which it would be better processed by the right hemisphere - the LEFT HEMISPHERE is the likely place for sign language to be processed. In fMRI studies, the same areas of the brain are activated during language tasks regardless of whether the person uses spoken English or sign language.

Question 18

COMMUNICATION DISORDERS

Answer 18

COMMUNICATION DISORDERS include:

1) APHASIAS;
2) disorders of READING and WRITING;
3) STUTTERING.

Question 19

APHASIAS

Answer 19

APHASIAS are neurological disorders that result in total or partial loss of the ability to either produce or comprehend spoken language.
There are FIVE types of aphasia:
1) BROCA's APHASIA;
2) WERNICKE's APHASIA;
3) CONDUCTION APHASIA;
4) GLOBAL APHASIA;
5) TRANSCORTICAL APHASIAS.

Question 20

BROCA’S APHASIA

Answer 20

PAUL BROCA made some of the earliest observations of the localiza­tion of language in the brain. He studied the case of a patient known as TAN who showed severe impairment in SPEECH PRODUCTION, but retained the ability to understand most of what was said to him. Broca found signifi­cant damage to the patient’s left inferior frontal region, now referred to as Broca’s area.

BROCA’S APHASIA - or production aphasia - is the result of damage to BROCA’S AREA (brodmann 44) in the FRONTAL LOBE.
Main symptoms of the disorder are:
- difficulty in producing speech, which is very slow and has a telegraphic quality;
- difficulty in writing;
- ANOMIA, or difficulty in retrieving the words for the ideas one wishes to express;
- comprehension is slightly affected as well.

Broca’s patients seem to be able to fluently sing song they know very well - this, in addition to the fact that their writing shows the same limits of their speech, provides evidence that Broca’s aphasia is not only a motor impairment.

Question 21

WERNICKE’S APHASIA

Answer 21

WERNICKE’S APHASIA affects an area of the brain known as WERNICKE’S AREA (brodmann 22) , located on the superior surface of the temporal lobe, adjacent to the primary auditory cortex. Main symptoms of the disorder are:

• difficulty in speech comprehension, usually for both written and spoken language;
• fluent but virtually meaningless speech production;
• difficulty in repeating sentences;
• no apparent distress and unawareness of the disorder.

Question 22

CONDUCTION APHASIA

Answer 22

CONDUCTION APHASIA results from damage to the ARCUATE FASCICULUS, a band of fibers connecting Broca’s and Wernicke’s areas. The main symptom of this disorder is a major impairment in the REPETITION of words, reflecting the damage in the connection between the two areas - or the connection between comprehension and production.
These patients are less impaired in language function than patients with either Wernicke’s or Broca’s aphasia - speech remains fluent, and comprehension is fairly good.

Question 23

GLOBAL APHASIA

Answer 23

GLOBAL APHASIA combines all of the deficits of Broca’s, Wernicke’s, and conduction aphasia. It is the result of substantial cortex damage involving at least BROCA’s AREA, WERNICKE’s AREA and the ARCUATE FASCICULUS. Most cases of global aphasia are caused by damage to the MIDDLE CEREBRAL ARTERY, which serves the language centers of the left hemisphere.
Individuals with global aphasia lose all language functions - abilities to speak, comprehend, read and write.

Question 24

TRANSCORTICAL APHASIAS

Answer 24

TRANSCORTICAL APHASIAS is caused by damage to connections between the major language centers, which results in isolation of these areas from other parts of the brain. There are two type of transcortical aphasia:

1) TRANSCORTICAL MOTOR APHASIA results from damage of the DORSOLATERAL PREFRONTAL CORTEX or of the supplementary motor area (adjacent to the primary motor area). These areas are involved in the executive control and initiation of speech.
Patients show symptoms similar to those of Broca’s aphasia (production aphasia), yet they are can accurately repeat even complex sentences.

2) TRANSCORTICAL SENSORY APHASIA results from damage to areas at the intersection of the temporal, occipital and parietal lobes. These areas connect the language centers to brain areas responsible for word meaning.
Patients show symptoms similar to those of Wernicke’s aphasia (comprehension aphasia), yet they are can accurately repeat even complex sentences.

Question 25

the WERNICKE-GESCHWIND LANGUAGE MODEL

Answer 25

WERNICKE and GESCHWIND developed a language model that could explain language pathways and be consistent with the neurological disorders - such as aphasias - that they observed.
According to this model, written and spoken language are processed differently.

WRITTEN LANGUAGE:

1) input is captured by the visual system and transmitted to the PRIMARY VISUAL CORTEX, located in the occipital lobe;
2) ANGULAR GYRUS, specialised in visual processing of written language;
3) WERNICKE’S AREA, specialised in comprehension.

SPOKEN LANGUAGE:

1) auditory information is process in the PRIMARY AUDITORY CORTEX, located in the temporal lobe;
2) information is transmitted to WERNICKE’S AREA, specialised in comprehension.

From wernicke’s area, both type information follow the same pathway if the individual responds to the input:

1) info travels through the ARCUATE FASCICULUS;
2) info reaches BROCA’S AREA, specialised in speech production;
3) info is sent to the PRIMARY MOTOR CORTEX, which produces movement of the mouth and lips. The primary motor cortex is located in the frontal cortex, and the areas associated to lips and mouth are especially close to Broca’s area.

Question 26

DISORDERS of READING and WRITING

Answer 26

DISORDERS of READING and WRITING include:

1) ALEXIA;
2) AGRAPHIA;
3) DYSLEXIA.

Question 27

ALEXIA

Answer 27

ALEXIA is a READING DISORDER that produces total inability to read while sparing comprehension and production skills. Alexia appears to be the result of damage of pathways that connect an area responsible of the visual recognition of letters - found at the junction of the left occipital lobe and the temporal lobe - to language areas of the insula.

Question 28

DYSLEXIA

Answer 28

DYSLEXIA is the most common form of learning disability - it refers to unexpected reading difficulties in spite of normal intelligence and exposure to normal teaching methods. It results from overactivation of ANTERIOR language areas, including Broca’s area, coupled with a LACK of activation of POSTERIOR language areas, including Wernicke’s area and the angular gyrus. In typical reades, the opposite occurs.

Dyslexia has a strong genetic origin and heritability. Anatomical features of dyslexia include hemisphere SYMMETRY: in typical readers the LEFT PLANUM TEMPORALE is significantly larger than its right counterpart, whereas individuals with dyslexia do not show strong asymmetry.

Question 29

AGRAPHIA

Answer 29

AGRAPHIA is a WRITING DISORDER that produces inability to write while sparing comprehension and production skills. It appears to be the result of damage to the motor areas responsible for making skilled movement, especially the SUPPLEMENTARY MOTOR AREA.

Question 30

STUTTERING

Answer 30

STUTTERING is a problem in speech fluency which typically results in repetition or prolongation of sounds. Although nearly all children struggle with fluency, stuttering children begin to stutter between the ages of 2 and 7 years, with a peak onset at about 5 years of age.

Stuttering can be the result of:

1) ABNORMAL LATERALISATION - individuals who stutter process some part of language in the RIGHT hemisphere. As a result, both hemispheres try to control the vocal apparatus simultaneously, leading to conflict. This conflict is resolved to some extent when the stuttering person SINGS because singing activates right-hemisphere areas that are not otherwise involved in speech.
2) abnormally high activity in the motor structures of the BASAL GANGLIA and MIDBRAIN.

Question 31

INTELLIGENCE

Answer 31

INTELLIGENCE is defined as an individual’s ability to engage in goal-directed adaptive behavior. Assessing intelligence has been a controversial issue, for some scholars argue that all intelligent behaviour arises from a single trait, whereas others make an argument for multiple types of intelligent.

Today’s IQ tests support the former viewpoint, and are structured in such a way that the results fall along a statistically normal curve. The average IQ score is 100, with a standard deviation of 15. Normal distributions follow a 68-95-99.7 (68% falls within a standard deviation, 5% within 2, 0.3% within 3).

Gardner, supporter of the latter view point, proposed 7 dimensions of intelligence:

1) LINGUISTIC intelligence;
2) LOGICAL or MATHEMATICAL intelligence;
3) SPATIAL intelligence;
4) KINESTHETIC - or motor - intelligence;
5) MUSICAL intelligence;
6) INTERPERSONAL - or social - intelligence;
7) INTRAPERSONAL intelligence;

Question 32

INTELLIGENCE, GENETICS and STRUCTURAL CORRELATES

Answer 32

The heritability of adult intelligence as measured by IQ tests is reported to be .75 - this means that about 75 percent of the variation in intelligence among humans can be attributed to genetic factors.

Insight on the role of genes in intelligence is also provided by comparison studies between identical and fraternal twins. Monozygotic twins display a .95 correlation in GRAY-MATTER VOLUME. In turn, gray matter volume and frontal cortical thickness are espe­cially highly correlated with INTELLIGENCE.

In the animal kingdom, measures of intelligence correlate positively with overall brain vol­ume, adjusted for body size.