PSYC 301 - Readings M2

2 obstacles to developing evidence based therapis for recovery of function after cerebral injury 

• no generally accepted definition of what constitutes “recovery”

• organisation of the brain is not static and the brain has the capacity to alter its structure and functions in reaction of environmental diversity

no generally accepted definition of what constitutes “recovery”

the word can be used to imply a complete return of function, a marked improvement in function or any degree of improvement

organisation of the brain is not static and the brain has the capacity to alter its structure and functions in reaction of environmental diversity

relationship between brain plasticity and behaviour is correlational 

3 general principles of plasticity in the normal brain 

• plastic changes are age dependent 

• experience dependent changes interact 

• the brain is altered by a surprisingly wide variety of experiences throughout the lifespan 

plastic changes are age dependent (3)

• generally presumed that developing will be more responsive to experiences than the adult brain

• increase in spine density only shown in adult rats where placed in a complex environment

• decrease in spine density shown in juvelines rates

experience dependent changes interact (3)

• if animals are exposed to psychomotor stimulants either as juveniles or in adulthood, later experience have a much reduced effect

• when rats are given methylphenidate as juveniles or amphetamine as adults and then placed in complex environments, the later experience dependent changes are blocked 

• although these drugs dont show any obvious direct effects, prior exposure prevents the expected changed in these regions 

the brain is altered by a surprisingly wide variety of experiences throughout the lifespan

• many of these experiences are obvious such as sensorimotor training

• many are less intuitive

• e..g social play, task learning

surgical procedure that result in split brain deficits

severing of the corpus callosum, the super highway of neurons connecting the halves of the brain

abilities of split brain patients in terms of vision and speech (4)

• visual information no longer moved between the two hemisphere

• the right brain saw the image and could mobilise a non verbal response by drawing with left hand but couldn’t talk about it

• the left brain is dominant for language and speech

• the right brain excels at visual motor tasks

bow- arrow task

• one hemisphere of a patient was flashed a card with the word “bow

• the other hemisphere saw “Arrow”

split brain patients performance on bow-arrow task (4)

• patient drew a bow and arrow - assumed that two hemisphere were still able to communicate

• then flashed “sky” and “scraper” but the image produced was not synthesising the information

  • one hemisphere drew what it had seen, the other drew its word

• clear that each hemisphere was capable of synthesis

implications of split brain patient research on our understanding of false memory (2)

• the left hemisphere creates coherent stories to explain actions or experiences, even without full information revealing its tendency to confabulate and construct meaning.

• suggest false memories stem from the left hemisphere’s reconstructive and schema-building processes, which fill in missing details to make past events feel consistent and logical, even when inaccurate.

primary visual pathway

from the retina to the primary visual cortex

effects of lesions on the primary visual pathway (3)

• total blindness of the left eye resulting from a complete lesion of the optic nerve

• bitemporal hemianopia resulting from a lesion of the optic chiasm

• right homonymous hemianopia resulting from a lesion of the primary visual cortex in the left hemisphere

phenomenon of blindsight

in which patients respond to visual stimuli that they cannot see

two explanations for blindsight 

• alternative visual pathways hypothesis

• spared islands of cortical tissue hypothesis 

alternative visual pathways hypothesis (3)

• visual pathways projecting from the retina to the superiror colliculus remain functional

• these pathways allow for unconscious visual processing enabling patients to detect and respond to visual stimuli without conscious awareness

• while conscious vision is lost, visual information still reaches parts of the brain

spared islands of cortical tissue hypothesis (2)

• intact patches of V1 within the damaged area continue to function

• these islands may provide limited visual input that supports the patient’s residual abilities

which explanations best fit with evidence 

• most support alternative visual pathways hypothesis 

bootstrapping

conscious visual ability is manipulated in order to reveal the processing of visual input of which the patient remains quite unaware

patient SF

had severe visual agnosia and could nto identity simple visual forms but have no difficulty naming colors or discriminaitng between different shades of colour

what did Aglioti et al investigate (2)

• whether or not SF’s spared colour perception could be used to improve his ability to discrimination form 

• used a variant of the Stroop test

experiment

• asked SF to identify the letters “R” and “V” the initial letters of the italian colours “rosso” and “verde”

• given stroop test

performance (4)

• could not discriminate between single letters

• but in stroop test, he was more accurate and faster at reading V and R when those letters were printed in the congruent colours, the letter R in red and the letter V in green

• claimed to be unaware of the forms of the two letters

• claimed that he had a feeling that he was performing above chance level

what did Aglioti argue

that SF’s normal colour perception which allowed him to accurately identity the colour of the letters automatically activated his stored memories of the colour names which in turn produced some sort of internal image of the colour words