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Clinical and Cognitive Neuropsychology > Lecture 10: Hemispheric Lateralisation insights from the split brain > Flashcards

Lecture 10: Hemispheric Lateralisation insights from the split brain Flashcards

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1
Q

What is Lateralization?

A

The specialisation of certain brain functions or cognitive processes to one side of the brain (left or right)

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2
Q

What are cerebral commissures?

A

Nerve fibres that connect the two halves of the brain

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3
Q

What are split brain patients?

A

Patients who have a severed or absent corpus callosum, therefore eliminating the main connection between the two hemispheres of the brain

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4
Q

Why does lateralization happen?

A

One theory suggests that having one hemisphere specialise in certain tasks increase brain efficiency.

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5
Q

How does lateralization increase brain efficiency?

A

It prevents the duplication of functions across both hemispheres allowing for better coordination and processing speed

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6
Q

How does lateralization affect dogs?

A

They have lateralized responses to acoustic stimuli, that is to say, certain sounds activate one side of the brain more

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7
Q

How does lateralization affect songbirds?

A

The left hemisphere controls song production similar to how humans use the left hemisphere to control speech

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8
Q

How does lateralization affect Parrots?

A

Parrots have symmetrical control over their vocalisations, meaning that both hemispheres contribute equally

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9
Q

How does lateralization affect chicks?

A

They prefer to use their right foot to scratch the ground, showing lateralized motor control

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10
Q

How does lateralization affect primates?

A

They perform certain tasks in a way similar to humans, suggesting some levels of lateralization.

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11
Q

What are some neuroanatomical asymmetries

A
  • Primary auditory cortex
  • Hemispheric weight difference
  • Left vs right occipital lobe
  • Sylvian Fissure
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12
Q

What is asymmetrical about the primary auditory cortex?

A

The right hemisphere only has two “Heschl’s Gyri” whilst the left hemisphere only has one

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13
Q

What is Heschl’s Gyri?

A

Gyri that are responsible for processing sound, which might explain some differences between hemispheres when processing sound

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14
Q

What are the hemispheric weight differences?

A

The right hemisphere is heavier than the left, suggesting that it may contain more neural connections and a higher density of neurons

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15
Q

What is the difference between the left and right occipital lobe?

A

Left occipital lobe is larger than the right. This may relate to the visual processing differences between the two, like the right hemisphere’s specialisation in spatial awareness

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16
Q

What is the Sylvian Fissure?

A

A deep groove that separates parts of your brain

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17
Q

How is the sylvian fissure asymmetrical in the two hemispheres?

A

It is larger on the left, which is significant because language-related structures are located near the sylvian fissure in the left hemisphere, meaning that the asymmetry might be linked to the left hemisphere’s dominance in language processing.

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18
Q

What is the functionality of asymmetry in lateralization?

A

It leads to:
- More efficient processing
- Reduction in Redundancy
- Better Multitasking
It allows for improvement in specialisation in cognitive tasks and efficiency

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19
Q

What is Aphasia?

A

A deficit in language comprehension or production due to brain damage

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20
Q

Where does usual damage occur for it to lead to Aphasia?

A

Broca’s area

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21
Q

What is Apraxia?

A

A difficulty in performing movements when asked to do so out of context, also a consequence of damage to the left hemisphere

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22
Q

What do Aphasia and Apraxia have in common?

A

They are both associated with damage to the left hemisphere

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23
Q

What are the two main tests that determine which of the two hemispheres is dominant?

A
  • Sodium Amytal test
  • Functional Brain Imaging
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24
Q

What is the Sodium Amytal Test?

A

When the scientists anesthetise one hemisphere and check for language function

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25
What is functional brain imaging
fMRI or PET scan is used to see which half is active when performing a language test
26
Is there a sex difference in brain lateralisation?
Women tend to use both hemispheres more often for language tasks than men do. They tend to be less lateralised than men
27
What is the Corpus Callosum?
The largest cerebral commissure that connects the two hemispheres. It transfers learned information from one hemisphere to the other. When cut, both hemisphere functions independently
28
What is the Optic Chiasm?
The area of the brain where the two optic nerves cross and split and visual information is sent from one part of the brain to the other
29
What did Myers and Sperry want to see in 1959-1968?
What would happen if both the corpus callosum and optic chiasm were severed
30
What did Myers and Sperry do at the beginning of their operations?
They cut the corpus callosum and the optic chiasm, preventing direct communication between the two hemispheres and made sure that each eye's visual information remained confined to one hemisphere respectively.
31
What was the training phase in Myers and Sperry's experiment?
The cats were trained to perform a task whilst one of their eyes where covered. As the optic chiasm and corpus collosum were cut, the eye receiving information could not relay the information to the second eye (covered)
32
What did Myer and Sperry find?
That cat's with split brain: - Learned the task normally with one eye - But when the patch was switched to the other eye, it was as if the task had never been learnt before, and therefore had to be relearnt - They also found that the control cats (nothing cut) and the single cut cats (Only one structure cut) could still transfer the information from one side of the brain to the other
33
Why is Myers and Sperry's experiment important to humans?
It provided strong evidence for hemispheric Specialisation
34
What is hemispheric specialisation?
The idea that the left and right prats of the brain can have distinct cognitive functions
35
What is a Commissurotomy?
Cutting through a band of muscle/nerve fibres in the body
36
Why is the corpus callosum cut in severe epileptic patients
Because the seizures are spread to both hemispheres of the brain and is therefore uncontrollable even with medication. By cutting the corpus callosum, the seizures are confined to just one hemisphere and is controllable.
37
What is the left hemisphere typically dominant for?
Language - Speech production and comprehension - Analytical thinking and logical reasoning - Reading and writing - Sequential processing
38
What is the right hemisphere typically dominant for?
Non verbal actions but it is still capable of processing sensory information and responding in other ways - Spatial Ability - Emotions - Musical Ability - Some memory Tasks
39
Why is the left hemisphere often called the interpreter?
Because it is dominant in language and logical reasoning. Research on split-brain patients showed that the left hemisphere often tries to make sense of events, even when it lacks full information
40
How is Vision lateralized?
LH = Words and letters RH = Faces, geometric patterns and emotional expressions
41
How is audition lateralized
LH = Language sounds RH = Nonlanguage sounds and music
42
How is touch lateralized?
LH = Nothing, the left hemisphere doesn't interact with touch RH = tactile patterns and braille
43
How is movement lateralized?
LH = Complex movement and ipsilateral movement RH = Movement in spatial patterns
44
How is memory lateralized?
LH = Verbal memory and finding meaning in memories RH = non-verbal memory and perceptual aspects of memories
45
How is language lateralized?
LH = Speech, reading, writing, arithmetic RH = Nothing, the right hemisphere doesn't interact with language
46
How is spatial ability lateralized?
LH = Nothing RH = Mental rotation of shapes, geometry, direction and distance
47
What is a more accurate way to think of lateralizations?
Rather than broad clusters of abilities it is better to think of individual sub-processes within abilities being handled by different hemispheres
48
What are the three main theories of the evolution of cerebral asymmetry?
- Analytic-Synthetic Theory - Motor Theory - Linguistic Theory
49
What is the Analytic-Synthetic theory?
A theory that suggests that the two hemispheres process information in fundamentally different ways, leading to greater efficiency in cognition
50
According to the Analytic-Synthetic theory, what does the Left Hemisphere specialise in?
Analytic thinking (examining information, data, or problems systematically to understand their components, identify relationships, and develop logical conclusions or solutions)
51
According to the Analytic-Synthetic theory, what does the Right hemisphere specialise in?
Synthetic thinking (Combining different ideas, information, or concepts to create a new, more complex understanding or solution)
52
On an evolutionary scale, what does the Analytic-Synthetic theory argue why specialisation evolved?
Better survival skills and efficiency. It also improves energy conservation
53
What are the strengths of the Analytic-Synthetic theory?
- Explains why hemispheres function differently - It accounts for complex human cognition
54
What are the weaknesses of the analytic-synthetic theory?
- Too simplistic - Doesn't explain why lateralization varies across individuals
55
What is the Motor theory?
A theory that suggests that the left hemisphere is specialised not speech specifically but rather for fine motor control, including speech movement
56
What is the core idea of the Motor theory?
That the left hemisphere's role in speech is not because it evolved specifically for language. Instead it evolved for precise motor control, which later became crucial for speech production. Speech is just one example of fine motor coordination requiring precise control of the tongue, lips and vocal cords.
57
What is some evidence supporting the Motor theory
LH lesions affect both speech and motor function
58
Why did motor function become lateralized?
- Increased Efficiency - Tool use and Gesturing - Energy conservation
59
What are the strengths of the motor theory?
- It explains the link between motor control and speech - It is supported by neurological evidence (LH damage affecting motor skills and speech)
60
What are the weaknesses of the Motor Theory
- It doesn't fully explain why some speech-related functions still involve the right hemisphere - Other cognitive abilities, like language comprehension, do not rely on motor skills
61
What is the Linguistic theory?
A theory that proposes that the left hemisphere's primary specialisation is in language rather than motor control or analytic processing
62
What is the core idea of the linguistic theory?
Argues that language itself is the primary specialisation of the LH. That the LH evolved solely for language processing, rather than for general problem-solving or motor control.
63
What evidence supports the linguistic theory?
- Aphasia studies - Comparative studies in non-human primates
64
What is the strengths of the linguistic theory?
- It best explains why LH damage affects both spoken and sign language - It accounts for why language is so dominant in the LH compared to other functions
65
What are the weaknesses of the linguistic theory?
- Does not explain why the RH still plays a role in language - Lacks a strong evolutionary explanation for how language emerged in humans
66
What is the Language instinct?
Put forward by Steven Pinker, it is the theory that humans are born with an innate ability to learn language
67
What evidence is there for the language instinct?
- Universal Grammar Theory (Noam Chomsky): Argued that all human languages share underlying grammatical structures, hinting at a build in brain mechanism for language acquisition. - Critical period Hypothesis: If a child is not exposed to language early in life, they may struggle to learn it later, supporting the idea of a biological basis for language
68
What are the key stages of infant language development?
- Babbling = 4-6months - One word stage = >12 months - Two word stage = >18-24 months - Rapid vocab growth = > 2 + years
69
What is the Wernicke-Geschwind model?
A predominant theory of how language functions are organised in the brain. It identifies specific regions within the left hemisphere responsible for different aspects of language processing
70
What did Norman Geschwinf integrate to make into a complete model of language processing?
- Broca's theory - Wernicke's theory
71
What did Norman Geschwind's theory involve?
- Language Localization - Key brain Areas
72
What are the Key brain areas for the Wernicke-Geschwind model
- Primary visual Cortex - Broca's Area - Wernicke's Area - Arcuate Fasciculus - Primary Auditory cortex - Left Angular Gyrus - Primary Motor Cortex
73
Whhat does the Primary visual cortex (occipital lobe) process?
- Written words before sending them to the Angular Gyrus for interpretation
74
What does Broca's Area process?
- Responsible for Speech articulation and grammatical processing
75
What does Wernicke's Area process?
- Spoken and written language meaning
76
What does damage to Broca's area lead to?
- Broca's Aphasia = Difficulty forming speech but intact comprehension
77
What does damage to Wernicke's Area lead to?
Wernicke's Aphasia = Fluent but meaningless speech and poor comprehension
78
What is the Arcuate Fasciculus
The connection of nerves between Wernicke's and Broca's areas
79
What can damage to the Arcuate Fasciculus lead to?
Conduction Aphasia = An inability to repeat words despite understanding them
80
What does the primary Auditory cortex process?
- Sounds including speech - It sends auditory information to Wernicke's Area for meaning interpretation
81
What does the Left Angular Gyrus interpret
- Reading and Writing - It converts visual input into language
82
What does damage to the Left Angular Gyrus cause?
Alexia (reading impairment) and Agraphia (writing impairment)
83
What does the primary motor cortex control?
- Muscles involved in speech production (tongues, lips, vocal cords)
84
What evidence supports the Wernicke-Geschwind Model?
- Clinical observations of Aphasia - Stroke, tumour and injury studies
85
What clinical observations of Aphasia were made in support of the Wernicke-Geschwind model?
- Patients with Broca's aphasia had damage to Broca's area - Patients with Wernicke's aphasia had damage to Wernicke's area - These findings led to the localizationist view
86
What stroke, tumour and injury studies supported the Wernicke-Geschwind model?
- Early researchers linked damage to different language areas with specific deficits in speech production and comprehension
87
What are some problems with the Wernicke-Geschwind model?
- Diffuse brain damage complicates the studies - Lack of expected effects from damage to Specific areas - Surgical evidence contradicts the model

Clinical and Cognitive Neuropsychology (9 decks)

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