Navigation-related structural change in the hippocampi of taxi drivers

1. Navigation-related structural change in the hippocampi of taxi drivers 3FA3- Module 4 Group A5 Swiya Nath Preeyam Randeria Catherine Leslie Tapiwa Musewe Nicholas Hawkes

2. Table of Contents • Target Article • Background Information • Critique Subject Selection • Sex Bias • Critique Methods • Alternative Results • Conclusion

3. Swiya Nath Target Article Aim : Test adult plasticity Method: Compare taxi driver’s brains to control subjects’ Conclusion: Adult hippocampus is plastic

4. Table of Contents • Target Article • Background Information • Critique Subject Selection • Sex Bias • Critique Methods • Alternative Results • Conclusion

5. Swiya Nath Hippocampal size related to foraging behavior Food storing species Bird species that store food have higher relative hippocampus size

6. Swiya Nath Hippocampal plasticity related to season of foraging Retrieval Storing Number of large cells in anterior hippocampus increase during August Number of large cells in hippocampus increase during October

7. Table of Contents • Target Article • Background Information • Critique Subject Selection • Sex Bias • Critique Methods • Alternative Results • Conclusion

8. Preeyam Randeria Age Variance • Average age = 44 years • Range = 32-62 years • Not an accurate representation of the wide age group

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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

16. Catherine Leslie 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

17. Table of Contents • Target Article • Background Information • Critique Subject Selection • Sex Bias • Critique Methods • Alternative Results • Conclusion

18. Catherine Leslie 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

19. 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

20. Catherine Leslie Brain Anatomy Sex differences in brain anatomy may be able to explain differences in behaviour.

21. Table of Contents • Target Article • Background Information • Critique Subject Selection • Sex Bias • Critique Methods • Alternative Results • Conclusion

22. Tapiwa Musewe Inter-rater Reliability Would strengthen results if corresponding measurements were found by multiple experts.

23. 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

24. Tapiwa Musewe Test – Retest Reliability Used 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

25. Table of Contents • Target Article • Background Information • Critique Subject Selection • Sex Bias • Critique Methods • Alternative Results • Conclusion

26. Swiya Nath Results 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

27. HIPER Model Swiya Nath Do taxi drivers have more experience with spatial memory, or simply retrieval as the HIPER model suggests?

28. Taxi Driver with Bilateral Hippocampal Damage Swiya Nath BUT lesion not isolated to posterior hippocampus

29. Conclusion Selection bias = Randomized selection Sex bias = Lacks generalizability Test retest reliability HIPER model = Other memory test