Navigation-related structural change in the hippocampi of taxi drivers
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Navigation-related structural change in the
hippocampi of taxi drivers
3FA3- Module 4 Group A5Swiya NathPreeyam RanderiaCatherine LeslieTapiwa Musewe Nicholas Hawkes
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Table of Contents
•Target Article•Background Information•Critique Subject Selection
▫Sex Bias•Critique Methods•Alternative Results •Conclusion
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Target Article
Aim : Test adult plasticity
Method: Compare taxi driver’s brains to control subjects’
Conclusion: Adult hippocampus is plastic
Swiya Nath
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Table of Contents
•Target Article•Background Information•Critique Subject Selection
▫Sex Bias•Critique Methods•Alternative Results •Conclusion
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Hippocampal size related to foraging behavior
Food storing species
Bird species that store food have higher relative hippocampus size
Swiya Nath
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Hippocampal plasticity related to season of foraging
Storing Retrieval
Number of large cells in anterior hippocampus
increase during August
Number of large cells in hippocampus increase during
October
Swiya Nath
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Table of Contents
•Target Article•Background Information•Critique Subject Selection
▫Sex Bias•Critique Methods•Alternative Results •Conclusion
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Age Variance
• Average age = 44 years
• Range = 32-62 years
• Not an accurate representation of the wide age group
Preeyam Randeria
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Training Variance
• Licensing training lasted = 10 months to 3.5 years
• Average time spent before passing the licensing test = 2 years
• Amount of time spent on training can affect spatial development
Preeyam Randeria
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Experience Variance
• Years of experience ranged = 1.5 years to 42 years
• Average years of experience = 14.3 years
• Too large a range, leads to inconsistency
Divide the years of experience into two ranges
Preeyam Randeria
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Control Group’s Experience
• Driving experience of the control group was not calculated
• More driving experience would result in a larger spatial capacity
Preeyam Randeria
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Selection Bias• MRI scans from control group was used to
compare hippocampus sizes
• Record scans were used thus MRI scans were conducted for some deficit or problem
• Not representing the general population
Preeyam Randeria
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Socio-Economic Status (SES)
• SES was not identified for drivers or the control group
• Control Group: lower SES might take public transportation more often and do not drive
• Drivers: different SES might depend on the type of area one works in
Preeyam Randeria
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Cause and Effect
• Did not measure or have records of the hippocampus size before the licensing training
• These individuals became taxi drivers because they were naturally better at spatial memory or vice versa?
• There is evidence for a correlation but not for a causal relationship
Preeyam Randeria
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Uncontrolled Variables
•Education Level▫Based on education pursued, the taxi driver
might already be used to memorizing•Similar limitation with control group and
between the control group and taxi drivers
Preeyam Randeria
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Control Subjects
•16 control subjects taken from a group of 50
•Group of 50 came from MRI scan Database
•Not a random group of people
Catherine Leslie
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Table of Contents
•Target Article•Background Information•Critique Subject Selection
▫Sex Bias•Critique Methods•Alternative Results •Conclusion
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Sex Differences
Study cannot be generalized.It has been proven that men and women
are different in terms of spatial ability
•Differences in spatial functioning
•Differences in brain anatomy
Catherine Leslie
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Spatial Functioning
Components of Spatial Function•Spatial Visualization –Mental rotation•Spatial Perception – Water level task•Spatial Memory – Visual features vs.
location•Spatial Orientation – Difference in used
cues
Catherine Leslie
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Brain Anatomy
Men Women•Higher % of Working memory and cerebral spinal fluid•Higher Amount of grey matter in left hemisphere•Asymmetries
•Higher % of grey matter• No asymmetries
Sex differences in brain anatomy may be able to explain differences in behaviour.
Catherine Leslie
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Table of Contents
•Target Article•Background Information•Critique Subject Selection
▫Sex Bias•Critique Methods•Alternative Results •Conclusion
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Inter-rater Reliability
Would strengthen results if corresponding measurements were found by multiple experts.
Pros Cons• Eliminates rater - rater ambiguity
•Only measured by one expert•Human errors•Precision•24 X 32 Measurements
Tapiwa Musewe
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Restrictive Selection
•All participants were right-handed•Prevented age-scale cluster•Eliminated individual anatomical
differences by creating one template•Participants were all male
Tapiwa Musewe
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Test – Retest ReliabilityUsed three different approaches to analyse volumetric
changes in grey matter
• Magnetic Resonance Imaging (MRI) ▫ Provides detailed images of soft tissues in the brain
• Voxel-Based Morphology (VBM)▫ Useful for determining neuroanatomical differences
between individuals▫ Allows anatomical differences of focal regions of the
brain to be analysed rather than volumes of the whole brain
• Pixel counting▫ Volume of hippocampus calculated by logical
calculations
Tapiwa Musewe
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Table of Contents
•Target Article•Background Information•Critique Subject Selection
▫Sex Bias•Critique Methods•Alternative Results •Conclusion
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Results
Swiya Nath
•Posterior hippocampus larger for taxi drivers than control subjects
•Anterior hippocampus larger for control subjects than taxi drivers
•Results more drastic in left hemisphere
•Adults show plasticity
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HIPER Model
Anterior Hippocampus
Posterior Hippocampus
Smaller for taxi drivers than control subjects
Larger for taxi drivers than control subjects
Encoding Retrieval
Do taxi drivers have more experience with spatial memory, or simply retrieval as the HIPER model suggests?
Swiya Nath
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Taxi Driver with Bilateral Hippocampal Damage
BUT lesion not isolated to posterior hippocampus
Retrieval EncodingWell on spatial information (landmarks)
Poor in actively navigating novel neighbourhoods
Well on main roads Poor on detours
Swiya Nath
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ConclusionSelection bias = Randomized selectionSex bias = Lacks generalizabilityTest retest reliabilityHIPER model = Other memory test