10 - Cognitive Functions Flashcards
Lateralisation of function
Human brain is asymmetrical: divided by the longitudinal fissure
Divided into left and right hemispheres
Each has different functions
Each controls the opposite side of the body, with some exceptions
Division of labour between the two hemispheres is known as lateralisation
The left and right hemispheres
Informations is exchanged across the longitudinal fissure via the:
Corpus callosum
Anterior commissure
Posterior commissure
Hippocampal/fornix commissure
Habenular commissure
Bundles of axons allow for the communication across hemispheres, the largest bundle is the corpus callosum
Visual connections to the hemispheres
Each hemisphere of the brain gets input from the opposite half of the visual field
Human vision
Light from the right half of the visual field shines into the left half of both retinas, projecting to the left hemisphere.
Light from the left half of the visual field shines onto the right half of both retinas, projecting to the right hemisphere.
After passing through optic chiasm, sorted into left and right hemispheres, not eyes
Auditory connections to the hemisphere
Each hemisphere pays more attention to the ear on the contralateral side
Each ear sends the information to both sides of the brain
For sound localisation, the brain must compare input from both ear
Dichotic listening task
Speech sound is presented to each ear simultaneously
Right ear dominance indicates lateralisation of function for language (typically report what was said in right ear over left ear)
Epilepsy
Neurological condition characterised by episodes of synchronised neural activity
Effective treatments are known: antiepileptic drugs, surgical removal of the focus.
Severing the corpus callosum has been shown to be effective in treatment resistant cases
Prevents neural exchange across hemispheres
Referred to as the split-brain operation of the corpus callosotomy
Split-brain operation (history)
First split-brain operations reported by Van Wagenen and Herren (1940)
Very few behavioural/cognitive abnormalities were initially observed
With more sophisticated assessment methods, some behavioural/cognitive abnormalities were later observed
Split-brain operations
Information is presented to the left or right visual field (left visual field projects to right hemisphere and vice versa)
Split-brain individuals are asked to verbally report what they saw
Information projected to the left hemisphere (right visual field) is verbally identified, information presented to right hemisphere (left visual field) cannot describe but can draw what they saw.
Indicates hemispheric lateralisation of brain function
Split hemispheres: competition and cooperation
Immediately after surgery, the brain hemispheres are often in conflict
The hemispheres show differences of opinion
Difficulty in everyday tasks because of hemispheric conflict
Left brain as the interpreter
Gazzaniga (2000) proposed the concept of the left brain as the interpreter
The interpreter theory: tendency to invent and defend explanations for actions
Split-brain individuals asked to verbally explain (left hemisphere) an action performed by the left hand (right hemisphere)
The right hemisphere
More adept at comprehending spatial relationships
Helps see “the big picture” - patterns, language comprehension, and emotion
Damage to the right hemisphere causes difficulty perceiving others’ emotions, failure to understand humour and sarcasm, and a monotone voice
Wada test
Typically performed prior to brain surgery Involves the injection of an anesthetiser into the carotid artery Induces temporary (<10 mins) inactivation of one hemisphere Used to indicate hemispheric lateralisation for vital cognitive functions
Anatomical differences between the hemispheres
The planun temporale
Auditory region of the temporal lobe
Shown to be larger in the left hemisphere in 65% of people
Also larger in infants, so born with it
Maturation of the corpus callosum
The corpus callosum gradually develops during childhood and adolescence
Results from process of axons myelination
Early difficulties in comparing actions and feelings from each hand are common
The brain generates more axons than it needs
Some shrinkage of the corpus callosum is observed during childhood and adolescence due to pruning
Precursors of language
Human language is likely a modification of a behaviour also found in other species
Chimpanzees use language but it differs from humans (sign language):
No creativity in the use of symbols
Use of symbols lacks productivity
Use of symbols is primarily used to request, not describe
Human language: phonological loop
The ability to hear something and remember it
Assessed through lists of digits (digit span) or repetition of non-words
Initial purpose/function was unclear
Now seen as important for learning of new words in childhood
Provides a mechanism for the temporary storage of new words
Human language - gestures
Language may have evolved from communication by gestures
Gestures are a central component of human communication
Adding sound to mouth gestures may have been a precursor to human speech
Theories of brain evolution for language
By-product of overall brain development
Evolved as a specialisation
Language as a by-product: arguments
People with a full-sized brain and normal overall intelligence can show severe language deficits - argues against this theory
People with impaired intelligence can have normal language skills (argument for):
Eg. People affected by Williams syndrome have significantly reduced IQ by have relatively normal language capacity
Language as a specialisation
Specialised brain adaptation occurred to allow for language
Language acquisition device (Chomsky) proposes that language capacity is innate
Genetic basis for language:
FOXP2 gene codes for a protein that influences genetic expression
Brain damage and language
Localised brain damage often results in aphasia (language impairment)
Extensive damage to the left hemisphere may result in complete loss of language ability, even loss of inner voice (global aphasia)
Distinct types of aphasia can result from damage to specific regions of the left hemisphere:
Broca’s aphasia
Wernicke’s aphasia
Broca’s aphasia
Impairment in speech production
Referred to as non-fluent aphasia
Speech is laboured and hesitant, but is still meaningful
Writing is also impaired
Although production is impaired, language comprehension is relatively unaffected
Does not require damage only to Broca’s area
Wernicke’s aphasia
Characterised by:
Paraphrasia: sound or word substitution
Anomia: difficulty in naming
Syntactic structure is maintained despite these impairments
Speech remains fluent
Same pauses in speech due to anomia
Language comprehension is impaired but fluency is not
Language system - connectionist model
Connectionist model suggests a network of brain regions involved in language
Speaking a heard word:
Sound is transduced and transmitted from the auditory cortex to Wernicke’s area
Wernicke’s area determines what word was said (comprehension)
Arcuate fasciculus (bridge between Broca’s and Wernicke’s) projects from Wernicke’s area to Broca’s area which forms a motor plan for work expression
Broca’s area projects to the motor cortex to produce speech
Dyslexia
Impairment in reading accuracy or comprehension
Independent of sensory, motivational and cognitive capacity
Difficulty in temporal ordering (replaces words and moves letters around)
Types of dyslexia
Acquired dyslexia: occurs after brain damage
Development dyslexia: post-mortem research shows abnormal arrangement of neurons of the cortex
Genetic abnormalities
Consciousness - dualism
Belief that mind and body (brain) are different substances that exists independently
Consciousness - monism
Belief that the universe consists of only one kind of substance
Materialism (everything is physical)
Mentalism (everything is a mental illusion)
Identity position (both the brain and the mind exists, ‘mind’ is brain activity, they’re the same thing)
Consciousness
Consciousness is a difficult concept to define, no comprehensive definition exists
Search is underway for the neural correlates of consciousness
The minimal neuronal mechanisms that are jointly sufficient for any one specific conscious percept (what is the minimal brain activity for consciousness)
Assessing consciousness
Operational definition:
If a cooperative person reports awareness of one stimulus and not another, than he or she was conscious of the first and not the second
A stimulus is presented in two conditions (conscious and unconscious)
Comparison is made between neural activity in the conscious and unconscious condition
Masking protocols
Some experiments with consciousness use masking
Reduced conscious awareness of a target image when another image (mask) is presented immediately before and after
Using this protocol, neural correlates of consciousness have been considered:
Stronger activation of the primary visual cortex in conscious condition
Consciousness of a stimulus depends on the amount and spread of brain activity
Threshold of consciousness
Consciousness is seen by some as a continuum of brain activity and perception:
Cortical activity is gradually increased in response to a visual stimulus as recognition increased
Others suggest that consciousness is an all-or-none phenomenon:
Conscious awareness relies on a stimulus producing activation beyond a threshold
Exceeding the consciousness threshold produces automatic amplification
