Maquire, Gadian, Johnsrude, Good,Ashburner, Frackowiak & Frith Navigation-Related Structural Changes in the Hippocampi of taxi-drivers Zachary Saadon Brian Prinzen Anteneh Kassa Emine Duygu Nangir

Outline Background 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 licensing Knowledge training increased the spatial memory of how routes and places relate to each other Test Subjects 16 right handed males years old (avg: 44) 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

Purpose This 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 Morphology Pixel Counting Anteneh Kassa

VBM Detects 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 Counting Computer 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 Method Matched 16 taxi drivers to 16 age-matched controls Tilted & divided images into mm slices and were categorized into 3 groups A = Anterior B = Body P = 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 Saadon

VBM Results a. Left – Sagittal cross-section Right – Coronal cross-section Red 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 Saadon

Pixel-Counting Results These results were consistent with VBM No significant difference in total hippocampal volume Regional differences Anterior:Greater volume in controls Right side greater than left Posterior:Greater volume in taxi drivers No significant difference in sides No significant difference in the body of the hippocampus Zachary Saadon

Pixel-Counting Results LH: Left Hemisphere RH: Right Hemisphere Anterior significantly larger in controls for both hemispheres Posterior significantly larger in taxi drivers for both hemispheres * indicates a statistical difference Zachary Saadon

Correctional analysis for Experimental Biases Correction 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 Summary Neuroanalysis TechniquesVBM Taxi driverControl Overall grey matter volumeDid not vary much Posterior HippocampusGreater - bilaterallySmaller Anterior HippocampusSmallerGreater - bilaterally Neuroanalysis TechniquesPixel-Counting Taxi driverControl Overall grey matter volume ---- Posterior Hippocampus Considerably larger than control group Smaller than taxi driver group Anterior HippocampusSmallerLarger 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

Conclusion The 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

Conclusion There 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

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