Maquire, Gadian, Johnsrude, Good,Ashburner, Frackowiak & Frith

Navigation-Related Structural Changes in the Hippocampi of

taxi-drivers

Zachary SaadonBrian PrinzenAnteneh KassaEmine Duygu Nangir

OutlineBackground

Hippocampus Case Study of HM

Introduction Spatial Memory

Methods Why London Taxi Drivers? VBM & Pixel Counting

Results

Conclusion

Brian Prinzen

Background: HIPPOCAMPUS

Consolidates information into long term memory

Formation of new semantic and episodic memory

Case Study: HM

Lesions of the hippocampus effect spatial memory

Brian Prinzen

Introduction: SPATIAL MEMORY

What is food storing?

Observed increased brain to body ratio in animals that store food

Hippocampus enlarges during seasons of food storing

Brian Prinzen

Research Subjects: LONDON TAXI DRIVERS

Extensive training required before licensingKnowledge training increased the spatial memory of how

routes and places relate to each other

Test Subjects16 right handed males32-62 years old (avg: 44)1.5-42 years of experience (avg: 14.3)10 months to 3.5 years study time (avg: 2)Specific test group used to limit amount of variability

between subjects and increase validity of results

Brian Prinzen

PurposeThis study aims to observe whether plasticity

of the brain could be detected with extensive spatial knowledge and experience.

Hypothesis:The hippocampus will be the structure showing plastic change

Brian Prinzen

Methods

Voxel-Based MorphologyPixel Counting

Anteneh Kassa

Anteneh Kassa

VBMDetects differences in regional Grey Matter

volume

VBM is not biased

Generates a map of voxel intensities

Perform t-test on the voxel intensities

Generates Statistical Parametric Map

Anteneh Kassa

Pixel CountingComputer software counts how many pixels

are present in a given region of an MRI scan

Uses this information to calculate the volume. 

Statistics used to compare it across groups ANOVA Correlations

Anteneh Kassa

Pixel Counting MethodMatched 16 taxi drivers

to 16 age-matched controls

Tilted & divided images into 26 1.5mm slices and were categorized into 3 groups

A = AnteriorB = BodyP = Posterior

Values were averaged using ANOVA & correlation p<0.05

Anteneh Kassa

Results

Zachary Saadon

VBM Results

Overall grey matter volume did not vary

Taxi drivers – grey matter volume increase in posterior hippocampus bilaterally

Control – grey matter volume increase in anterior hippocampus bilaterally

No other changes noticed

Zachary SaadonZachary Saadon

VBM Resultsa. Left – Sagittal cross-section

Right – Coronal cross-sectionRed box – Hippocampus

b. Images show the taxi group results superimposed on a random control individual

Yellow represents increased grey matter

The y value represents successive coronal slice positions

c. Red indicates increased grey matter

Zachary SaadonZachary Saadon

Pixel-Counting Results

These results were consistent with VBMNo significant difference in total hippocampal

volumeRegional differences

Anterior: Greater volume in controlsRight side greater than left

Posterior: Greater volume in taxi driversNo significant difference in sides

No significant difference in the body of the hippocampus

Zachary SaadonZachary Saadon

Pixel-Counting Results

LH: Left HemisphereRH: Right HemisphereAnterior significantly

larger in controls for both hemispheres

Posterior significantly larger in taxi drivers for both hemispheres

* indicates a statistical difference

Zachary SaadonZachary Saadon

Zachary Saadon

Correctional analysis for Experimental BiasesCorrection to age made to exclude bias for pre-existing disparity

a. Posterior hippocampus - area of greatest increase in taxi drivers

b. Positive correlation between the right posterior hippocampus and time spent as a taxi driver (r = +0.5)

c. Negative correlation between the right anterior hippocampus and time spent as a taxi driver (r = – 0.6)

Zachary Saadon

Conclusion

Duygu Nangir

Results SummaryNeuroanalysis Techniques

VBM

Taxi driver ControlOverall grey matter volume

Did not vary much Did not vary much

Posterior Hippocampus Greater - bilaterally SmallerAnterior Hippocampus Smaller Greater - bilaterally

Neuroanalysis Techniques

Pixel-Counting

Taxi driver ControlOverall grey matter volume

---- ----

Posterior Hippocampus Considerably larger than control group

Smaller than taxi driver group

Anterior Hippocampus Smaller Larger than taxi driver group (right > left)*the data corrected to age also showed similar

relationships

Duygu Nangir

Results Summary Converging results from both of the

independent analytical techniques:

Positive correlation between time spent as taxi driver in posterior hippocampus;

While negative correlation for the anterior hippocampus

There is a professional dependence on the navigational skills in licensed London taxi drivers – related with the reorganization of hippocampal grey matter

Duygu Nangir

ConclusionThe results go along with the fact that posterior

Hippocampi store a spatial map of the surrounding environment Also show a major dependence on navigational skills

There is room for plasticity in the adult human brain as exposure to environmental stimuli increase

Due to occupational dependence on spatial navigation, the volume of the posterior hippocampus increases

Duygu Nangir

ConclusionThere is functional division of tasks in the

hippocampus:

Posterior hippocampus is involved in using previously learned spatial information

Anterior hippocampus is involved (in combination with posterior hippocampus) in encoding new environmental maps

Challenges the conventional view of hippocampus as a temporary function in memory

Duygu Nangir

References (2007). Brain specimens - hippocampus. Retrieved October

12, 2008, from Morphonix LLC Web site: http://morphonix.com/software/education/science/brain/game/specimens/hippocampus.html

E. (2007, June 10). UK taxi drivers to face eco-safe tests. Retrieved October 12, 2008, from Keetsa Web site: http://keetsa.com/blog/green/green-transportation/uk-taxi-drivers-to-face-eco-safe-tests/

(2005). Mind trip: journey into the brain. Retrieved October 12, 2008, from Wired to Win Web site: http://www.wiredtowinthemovie.com/mindtrip_xml.html

Maguire, E. A., Gadian, D. G., Johnsrude, I. S., Good, C. D., Ashburner, J., Frackowiak, R. S. et. Al. (2000). Navigation-related structural change in the hippocampi of taxi drivers. Proc Natl Acad Sci U S A, 97, 4398-4403.