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Neuropsychology 246 > Lecture 4 Laterality > Flashcards

Lecture 4 Laterality Flashcards

1
Q

Crude dichotomy is that _______H is rational, verbal, linear and analytic while ________H is emotional, spatial, holistic and intuitive.

A

Crude dichotomy is that LH is rational, verbal, linear and analytic while RH is emotional, spatial, holistic and intuitive.

Left-brainedpeoplewere said to be more:

  • analytical
  • logical
  • detail- and fact-oriented
  • numerical
  • likely to think in words

Right-brained people are said to be more:

  • creative
  • free-thinking
  • able to see the big picture
  • intuitive
  • likely to visualize more than think in words

Truth: Language is more localized to the left, attention more to the right, so one hemisphere may do more work, but this varies by system, rather than by person!

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2
Q

How many fibres in the corpus callosum

A

200 million

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3
Q

What roles does the Corpus Callosum play?

A

• Allocates different tasks to different hemispheres.

•

  • In children, plays a significant role in the development of lateralization of the brain, right from infancy.
  • Actively involved in the movement of eyes.

•

•Responsible for the spread of epilepsy seizure impulses from one hemisphere of the brain to the other.

•

•Possibly its most important role is to inhibit the other hemisphere from attending to a task.

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4
Q

What is the DSM-5 name for split personality/multiple personality disorder?

A

DMS-5- Dissociative Identity Disorder

  • At least two distinctive and relatively enduring mental states.
  • Inability to recall personal information.
  • Average number of identities = 16
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5
Q

Split brain is a lay term for ______

The surgical operation to produce this condition is called:

A
  • Split-brain is a lay term to describe the result when the corpus callosum connecting the two hemispheres of the brain is severed to some degree.
  • The surgical operation to produce this condition (corpus callosotomy) involves transection of the corpus callosum, and is usually a last resort to treat refractory epilepsy.
  • US: approx. 5000 per year.
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6
Q

What happens after the brain is split?

A

Eachhemisphere will have its own separate perception, concepts, and impulses to act

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7
Q

Talk about Kim Peek

A

KimPeek: Born with an absent corpus callosum and both the anterior and posterior commissures.

  • Was able to memorize over 9,000 books, and information from approximately 15 subject areas including world history, sports, movies, geography, actors and actresses, the Bible, literature, classical music, area codes/zip codes of the US, television stations serving these areas, and step by step directions within any major U.S. city.
  • Despite these abilities, he was unable to button his shirt, and had difficulties performing everyday tasks.
  • He also had developed language areas in both hemispheres, something very uncommon in split-brain patients.
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8
Q

•Michael Gazzaniga(godfather of modern split-brain science):

A

“You see a split-brain patient just doing a standard thing - you show him an image and he can’t say what it is. But he can pull that same object out of a grab-bag,” Gazzanigasays. “Your heart just races!”

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9
Q

4 Invasive methods of studying lateralization (splitting the brain) include:

A
  • Commissurotomy.
  • The Wada procedure.
  • Brain surgery.
  • Unilateral brain damage.
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10
Q

What is the WADA test?

A

Intracarotid Amobarbital Testing (WADA)

What is it?

  • Also known as WADA testing (named after the person who invented it).
  • A type of testing used to assess the laterality of language in people who will be undergoing brain surgery.

How is it done?

  • Sodium amobarbital(a short term anesthetic) is injected into right or left integral carotid artery.
  • This essentially puts the hemisphere on the same side as the artery to sleep, allowing the other hemisphere function to be assessed.
  • Patient usually has the contralateral arm in the air – when the injection is administered, the arm drops. The neuropsychologist then assesses the cognitive functions of the individual.
  • Hemisphere that is specialised for a particular function will perform better than the other hemisphere.
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11
Q

Results and limitations of WADA testing

A

Results:

•Has shown LH dominance for speech (although some people show bilateral or RH dominance for speech).

Limitations:

•Very intrusive procedure; therefore often done on brains that have experienced pathology, which may be different from neurologically normal brains.

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12
Q

Non-Invasive Methods: Dichotic Listening.

What is it?

What has it shown?

A

Dichotic listening: Presentingdifferent stimuli to each ear.

•

Hasshown that:

•Dichotic listening technique of presenting different nonsense syllables showed that phonetic (speech) and auditory (nonspeech) perception are processed in different parts of the brain.

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13
Q

Non-Invasive Methods:

Tachistoscopic Presentations: what is it? What has it shown

A

Tachistoscopic Presentations:

•Rapid presentation of stimuli to either the RVF or LVF.

•

Has shown that:

•Visual info presented to right eye is interpreted by LH and vice versa.

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14
Q

Challenges in Studying Lateralization

A

•While one side of the brain might be dominant in function, both hemispheres have some degree of competency for most functions.

•

  • In reality normal neurological function relies on constant communication between hemispheres.
  • Invasive methods of localizing function means that that these samples are neurologically impaired.
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15
Q

Name 3 categories of Asymmetry between hemispheres

A
  • Structural
  • Functional
  • Neurochemical
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16
Q

What Structural Asymmetries are there between hemispheres?

A

Left hemisphere (LH) anatomy:

  • Gyri and sulci develop faster in the LH.
  • LH contains more grey matter relative to white matter.
  • LH contains greater cell packing density.
  • 65% of people have a longer planumtemporalein the LH – can even be ten times larger than in the RH.
  • One single Heschl’sgyrus.

Right hemisphere (RH) anatomy:

  • RH is larger and heavier than LH.
  • Two Heschl’sgyri.
17
Q

Functional Assymetries b/w Left and Right brain

A

Lefthemisphere (LH):

  • Specialized for language and control of right hand and fingers.
  • LH dominance for language but RH still has some involvement.
  • Processes the trees (local processing).

•

Right hemisphere (RH):

  • Specialized for music, emotion, and spatial abilities as well as control of left hand and fingers.
  • Processes the forest (global processing).
18
Q

Neurochemical Asymmetries between Left and Right

A

•Imbalances in specific asymmetries characterizesome brain disorders such as schizophrenia, depression, autismand Alzheimer’s disease.

•

•However, it is not clear whether these changes are a cause or a consequence of these disorders.

19
Q

Language dominance in LH brain

A

•Both invasive and non invasive studies of lateralization have shown LH dominance for speech and language.

•

•The best example of an established lateralization is that of Broca’s and Wernicke’s areas where both are often found exclusively on the left hemisphere.

20
Q

In what ways does language play a role in RH brain?

A

•RH – does have some part in language processing. For example, if the language task is automatic, there tends to be greater activation in the RH.

•

•RH also thought to play a role in the appreciation of metaphor; parts of the RH such as parts of PFC and middle temporal gyrus show increased activation in processing metaphors.

21
Q

Visuospatial Ability in L and R

A

•Visuospatial ability more reliant on RH than LH.

•

•Eg. Mental rotation task. Involves imagining the rotation of a series of stimuli.

•

•Mental rotation produces strong asymmetries especially in the right parietal cortex.

22
Q

Non-Verbal Stimuli (L, R dominance)

A

•RH also dominant for facial recognition – recognises faces more quickly than LH.

•

•Extends to other non-verbal stimuli eg. Differentiating ground from figure and localizing points in space.

23
Q

Music perception and dominance

A
  • RH usually dominant in processing musical chords and melodies, harmonies, pitch and timbre.
  • Right hand is better at tapping out a rhythm than left hand- true for both right and left handers. This shows difference to be due to hemispheric differences and not due to hand preference.
24
Q

Mathematical Ability and dominance

and two disorders/difficulties

A

LH- dominant in reading and writing numbers:

  • Difficulties in reading numbers = alexia.
  • Difficulties in writing numbers = agraphia.

RH- dominant in spatial processing of numbers:

  • Spatial acalulia= problems in representing numerical information spatially by misreading signs, omitting numbers or having problems with decimal places.
  • Possibly due to emphasis on visuospatial skills in calculation and arithmetical calculations.
25
Q

lateralization for handedness, speech dominance in each,

LH superior in____but inferior in______

A
  • We know that there is usually clear lateralization for handedness; RH controls left hand and LH controls RH.
  • Majority of right handers have LH speech.
  • Most left handers also have LH speech but some have right or bilateral represented language.
  • Left handers have been shown to be superior to right handers on test of verbal ability but are inferior to right handers on visuospatial ability.
26
Q

Name an anatomical theory of handedness

A

•Thomas Carlyle’s Sword and Shield Theory – states that handedness has its origins in early warfare; people held their sword in their right hand and shield in left were said to better protect their heart and therefore left handers had greater mortality in battle.

•

Problems with this theory:

  • Right handedness was the norm long before the Bronze Age.
  • This would indicate that men are more likely than women to be right handed.
27
Q

second anatomical theory of handedness: Salk

A

•Salk’s parent holding baby theory: says that babies are more easily comforted when held in left arm, due to being close to parent’s heartbeat, leaving right hand of the parent free to do things.

•

Problems with this:

•It is assumed that this baby holding arrangement would have more influence on the parents handedness than the baby’s; when in fact it would leave the baby’s left hand free which you would think more likely to influence the baby’s handedness.

•

28
Q

What is the crowding hypothesis of handedness?

A

•Left handers have superior verbal ability because they have more variable language representation and have a greater neural mass devoted to language.

•

•However, because RH is undertaking part of a function (language) supposed to be dealt with in LH, it has less neural mass to devote to its own specialization, visuospatial ability. This however has only been demonstrated in a small study.

•

29
Q

2 environmental/psychosocial theories of handedness;

A

•Jackson’s parental pressure theory:argues that all children can be either right or left handed and they simply follow the handedness of their parents.

•

•Blau’sPsychodynamic theory: left handedness claimed to be the result of emotional negativism.

•

30
Q

Genetic Theories of handedness:

A

•Adoption studies indicate that handedness is genetic.

•

•Most genetic studies propose handedness to be a recessive trait (following laws of mendeliangenetics).

31
Q

what are the problems with genetic theories for handedness?

A

Problems with genetic theories:

  • The pattern of inheritance for handedness seems too complex for the laws of mendeliangenetics, and the proportion of left handed children born of two left handed parents is too low to support such a simple model.
  • Many genetic theories therefore postulate an element of chance within the genetic model.
  • Apart from adoption studies it is very difficult to separate environments from genetics.
  • Genes code for the production of proteins, not behaviours. Although genes could be the mechanism of lateralization, genes do not provide information regarding why lateralization provides a adaptive advantage.
32
Q

What is a developmental theory of handedness? And its limitations..

A

Geschwind and Galaburda model:

•Based on the argument that increased fetal testosterone levels modify neural development, immune development, and neural crest development.

•

•According to the theory, male brains mature later than females, and the left hemisphere matures later than the right.

LIMITATIONS:

  • Largely discredited by several other studies in the 1990s.
  • Criticized for having been misguided in its representation of the cerebral basis of handedness, and of the links between testosterone and immune function.
  • Far from proven that left-handers are more susceptible to immune disorders.
  • Does not explain twins who exhibit different handedness.
  • It does not explain how testosterone can affect the brain hemispheres differently anyway, nor why, if testosterone is the major cause, the male-female gender gap in left-handedness (about 13% of males compared to 11% of females in the developed West) is not more pronounced than it actually is.
33
Q

What is the Pathological Left-Handedness Theory ?

A
  • Most extreme claim: right handedness is the norm and left handedness is always the result of some sort of brain injury.
  • Medium extreme claim: sometimes left handedness is normal and sometimes it is pathological.
  • More chill claim: left handedness itself is not pathological but serves as a marker for other pathologies.

•

Supporting evidence:

  • Higher prevalence of left handedness in infants who appear to have been exposed to stressors.
  • Higher prevalence of left handedness among people with a number of pathological conditions.

•

34
Q

Problems with the pathological left-handedness model

A

Problems with model:

  • Left handedness has not decreased in prevalence over time despite improvements in medical science and birth.
  • Presence of direct birth stressors have not been linked to left handedness.
  • Let handedness has often been linked with various professional groups and groups of the intellectually gifted.
  • The birthing process varies a lot betweencultures.

•

35
Q

Distributive processing: Two sided advantage in chicks

A

Neuropsychology 246 (22 decks)

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