1

Maguire E., Frackowiak R., Frith C. (1997)

Recalling Routes around London: Activation of the Right

Hippocampus in Taxi DriversJournal of Neuroscience, 17, 7103-7110

Where is spatial memory?

2

here?

here?

here?

here? here

?

here?

here?

here

?

here?

3

Core studies (Banyard, p152-3)

• PET – positron emission tomography

4

Core studies

• MEG – magneto-encephalography

5

Core studies

• MRI – magnetic resonance imaging• Slice / box technique

6

Core studies

• fMRI – functional magnetic resonance imaging

7

Evaluation of PET scans

• With colour and shading it all looks pretty wonderful, but…

• PET (&fMRI) don’t show neural activity as such, rather blood flow or glucose metabolism indicative of neural activity

• Excitatory ‘hotspot switches’ on and off look the same to the scan

• With practice, brain activity on task decreases

8

Evaluation of PET scans

• Sensitive machine; must inject enough radioactive material – dangerous?

• ‘Noise’ from surrounding brain areas (e.g. out of 17 studies, 84 areas were indicated as being involved in object recognition)

• PET scanners are large and expensive

9

• Nevertheless, brain scans do tell some interesting stories…

• e.g. Maguire et al 1997

(Optional research assignment)

• What are some similarities & differences between the types of scans?

• Think about:– How they work– The data they provide

10

11

Maguire et al (1997)

• Aim:• Investigate the neural basis for spatial

memory

• Method:• Using PET, measure neural activity during

topographical (=space/location) semantic (=facts/language) memory tasks

12

Maguire et al (1997)

• Participants:

• 11• London black-cab taxi drivers• Av. age 45

• Av. experience 14.5 years

• Informed written consent

• Local hospital ethics committee approved the study

Procedure

• Factorial design, 2 factors of interest:• Topographical and sequencing memory

• Why? To distinguish brain activity during route planning, i.e. places in order (topo. & seq.), from brain activity during other types of memory task

• How?13

Procedure

• Tasks: describe…

• routes (shortest legal) → T+ S+

• landmarks (not in London) → T+ S-

• film plots (famous) → T- S+

• film frames (stills) → T- S-• 4-digit numbers (baseline comparison task)

14

15

Procedure

T+ T-S+

Routes Film plots

S-Landmarks Film

frames

Controls

• repeat 4-digit numbers as baseline comparison task

• participants blindfolded throughout

• speech output digitally recorded

• identical procedure for each participant

16

PET scans

• Data is gathered over 90 seconds following the radioactive injection

• During each scan one item is presented (i.e. one route / plot / landmark / frame)

17

18

Results

• Comparing the two factors…– memory type: topographical vs. non-topographical– sequencing: with vs. without

• …with the baseline condition…– number repetition

• …gives a picture of the neural systems supporting each task

19

Results / Understanding

• Simple main effects• Routes recall:

– increased activation of the medial parietal lobe, posterior cingulate cortex,

parahippocampal gyrus and the R hippocampus

• Landmarks recall:– increased activation of the medial parietal lobe, posterior cingulate cortex,

parahippocampal gyrus, oocipitotemporal regions but not the R hippocampus

• Film plots vs. frames, no sig. diff. in rCBF– (=Regional cerebral blood flow)

20

Results / Understanding

• So…?

• the evidence supports:

• semantic topographical memory retrieval is associated with the R hippocampus

21

Results / Understanding

• Compound main effects – 1/2• Routes & landmarks (topographical)• vs.• Film tasks (non-topographical)

• Increased activation of bilateral medial parietal regions, posterior cingulate

cortices, fusiform gyri, parahippocampal gyri (i.e. a number of) brain areas during topo. tasks

22

Results / Understanding

• Compound main effects – 2/2• Routes & plots (sequencing)• vs.• Landmarks & frames (non-sequencing)

• Some small differences in brain area activity

Results / Understanding

• So…?

• the evidence supports:

• ‘entirely different’ brain regions are activated during topo. and non-topo. memory retrieval

23

Understanding

• This study indicates:

• the role of the R hippocampus (and some specific other brain regions) in processing spatial layouts over long time periods

24

But…• Another study (Aguirre 1996) found no

hippocampal activation in topographical memory tasks

• Who’s right?

• Aguirre used a computer-simulated environment

• Higher ecological validity Maguire 1997• Real world task

25

Understanding

• both topographical tasks (routes and landmarks) activated many of the same brain areas

• main difference: activation of R hippocampus in routes task, not in landmarks task

• route planning (=navigation) appears to be located there

26

27

Application

• Is this research useful?• Why? Why not? Does it matter?• Topographical disorientation after brain lesions

• Humans and many animals can navigate in large-scale space. Many species with far smaller brains can navigate successfully.

• Navigation is a phylogenically old ability – located in the ‘primitive’ hippocampus, not in frontal cerebral regions.

28

Analysis & Evaluation

• Small sample?

• No research on

• … but brain scans are a relatively new research technique – each new study adds to our body of knowledge

Analysis & Evaluation

• Nature• Are London taxi drivers born with

unusual brains?

• Nurture• Do London taxi drivers develop unusual

brains? (see Maguire et al 2000, in Banyard p158)

29

30

Can you evaluate this study?

• in terms of…

• experimental validity (control of variables)• ecological validity (realistic task)• external validity (generalisation)• ethical validity• reliability (replication, objectivity)

Review

• Where was/were the– experimental design– IV– DV– Factors of interest– Method/procedure– Main results/findings

31

Further reading

• Maguire et al.’s article: Journal of Neuroscience • At the bottom of that page, you can find more on:

– The hippocampus– Spatial memory & wayfinding e.g. in blind people – MRI and brain development

• The Wellcome Trust • UCL

32