Navigation-related structural change in the

hippocampi of taxi drivers

3FA3- Module 4 Group A5Swiya NathPreeyam RanderiaCatherine LeslieTapiwa Musewe Nicholas Hawkes

Table of Contents

•Target Article•Background Information•Critique Subject Selection

▫Sex Bias•Critique Methods•Alternative Results •Conclusion

Target Article

Aim : Test adult plasticity

Method: Compare taxi driver’s brains to control subjects’

Conclusion: Adult hippocampus is plastic

Swiya Nath

Table of Contents

•Target Article•Background Information•Critique Subject Selection

▫Sex Bias•Critique Methods•Alternative Results •Conclusion

Hippocampal size related to foraging behavior

Food storing species

Bird species that store food have higher relative hippocampus size

Swiya Nath

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

Table of Contents

•Target Article•Background Information•Critique Subject Selection

▫Sex Bias•Critique Methods•Alternative Results •Conclusion

Age Variance

• Average age = 44 years

• Range = 32-62 years

• Not an accurate representation of the wide age group

Preeyam Randeria

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

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

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

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

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

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

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

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

Table of Contents

•Target Article•Background Information•Critique Subject Selection

▫Sex Bias•Critique Methods•Alternative Results •Conclusion

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

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

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

Table of Contents

•Target Article•Background Information•Critique Subject Selection

▫Sex Bias•Critique Methods•Alternative Results •Conclusion

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

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

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

Table of Contents

•Target Article•Background Information•Critique Subject Selection

▫Sex Bias•Critique Methods•Alternative Results •Conclusion

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

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

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

ConclusionSelection bias = Randomized selectionSex bias = Lacks generalizabilityTest retest reliabilityHIPER model = Other memory test