Maguire et al. (2000) Navigation-related structural changes in the hippocampi of taxi drivers.

What is the hippocampus? Research into the role of the hippocampus has shown its importance in memory, specifically spatial memory. comes from the Venetian anatomist Julius Caesar Aranzi (1587), who likened it to a seahorse (Latin: hippocampus from Greek: ἵππος, "horse" and κάμπος, "sea monster").

London taxi drivers undergo extensive training, known as ‘The Knowledge’. London taxi drivers make an ideal group of participants to study when examining the role of the hippocampus in helping them to navigate their way around the city.

Aim: To examine whether structural changes could be detected in the brain of people with extensive experience of spatial navigation (this will show the extent of brain plasticity) To see if there is a correlation between length of taxi-driving experience and measure of grey matter volume

Sample: 16 male London taxi drivers (1.5+ years experience) All right handed Aged between 32 and 62 (mean = 44) Healthy medical, neurological and psychiatric profiles

Comparison group 50 healthy right-handed males who do not drive taxis for comparison Aged between 32 and 62. (Mean age similar to taxi drivers)

Method and Design QUASI EXPERIMENT What is this? QUASI EXPERIMENT IV = taxi drivers & non taxi drivers DV = volume of hippocampus Involves correlational analysis Independent measures design Why?

Procedure Structural MRI scan - Involves using a computer software programme to produce a 3D image of the brain.

Procedure Analysing MRI Scans Step 1: 1st Technique – Voxel-Based Morphometry. Identifies differences in the density of grey matter in different parts of the brain. Grey matter has dense neural connections and is associated with higher order thinking.

Procedure Analysing MRI Scans Step 2: Pixel 2nd technique counting A pixel is a single point on a graphic image. In order to calculate hippocampal volume, pixels were counted on photographic ‘slices’ made through the brain using an MRI scan

NOTE The person counting the pixels was ‘blind’ to whether the brain belonged to a taxi driver or control participant

Results: Taxi drivers have greater grey matter volume in their posterior right hippocampus. Controls have greater volume in their anterior hippocampus. These results are significant at p <0.05

Were the aims met? To examine whether structural changes could be detected in the brain of people with extensive experience of spatial navigation

Correlational Analysis A comparison of length of driving experience with the measure of grey matter volume of the taxi drivers showed a significant positive correlation for the right posterior hippocampus. r=0.6, p<0.05 This means the more experienced the driver is, the greater the grey matter volume is in their right posterior hippocampus.

Were the aims met? To see if there is a correlation between length of taxi-driving experience and measure of grey matter volume

Conclusions The difference in taxi drivers’ hippocampi may have led them to do a job which requires navigational skills as they are good with that OR The taxi drivers’ hippocampi may have changed as a result of studying for the ‘knowledge’ thus showing plasticity of the brain.

The results of the correlational analysis would support the second idea – because the longer they had been a cab driver, the greater the volume of their right posterior hippocampus.

Biological approach work packs Complete pages 14-19

In pairs… I am not providing you with an ‘answer sheet’. This means the person answering and the person asking must know the answers!

Stretcher activity: Maguire fill in the blanks

You must come up with two points (PEEL) to present to the class Half of the class will look at the strengths of the study, the other half; the weaknesses You must come up with two points (PEEL) to present to the class Split class into two

Evaluation checklist… Ethical considerations Validity Reliability Sampling bias Ethnocentricism

Pages 23-24 (methodological issues and evaluation) Provide evaluation handout

What would you change? Complete pages 20-24

Starter: Maguire crossword

When our brain is damaged… The effects can be life changing… The extent to which it affects an individual depends on many factors including: The extent of the trauma The subsequent care

What is functional recovery? A partial or complete return to the normal or proper physiologic activity of an organ or part following disease or trauma

Almost all individuals who suffer brain injury can make some recovery New dendrites need to grow within neurons but in some instances, the brain adapts to the trauma and finds another way to complete a function Recovery is not always complete and depends on the level, and type of damage

Functional recovery Rewire and reorganise itself by forming new synaptic connections close to the area of damage (like the taxi drivers)

Plasticity Plasticity (in terms of functional recovery) is the ability to replace the function lost through damage A cell body can never be replaced But axons (in some cases) can

There are three main anatomical ways that a body can replace axon function in brain after trauma

1. Increased brain stimulation As neurons are damaged, this influences neighbouring neurons as they longer have input This can happen with brain hemispheres Although damage may be on one side only, the other hemisphere functions can decline due to reduce input  Takatsure et al (2009) demonstrated that if the undamaged hemisphere is stimulated, recover from a stroke can be improved

2. Axon sprouting When an axon is damaged its connection with neighbouring neuron is lost In some cases, other axons that already context with that neuron will sprout extra connections, replacing the ones which have been lost It is compensating for the loss of a neighbour This occurs in the 2 weeks after damage happens

2. Axon sprouting This helps replace function But only if the damaged axon and the compensatory axons do similar jobs If not… problems can occur with function

3. Denervation supersensitivity This occurs when axons that do similar jobs become aroused at a higher level to compensate for the ones that are lost However it can have the unfortunate consequence of over- sensitivity to messages such as pain This will increase ones level of pain

Functional recovery of the brain after trauma Much recovery after trauma is due to anatomical compensation, brought about by intensive rehabilitation The brain learns to compensate for function The brain can be taught to learn how to use the working facilitates and function to compensate for the ones that are lost

Research into functional recovery Tajiri et al (2013)

Research into functional recovery Tajiri et al (2013) provided evidence for the role of stem cells in recovery from brain injury. They randomly assigned rats with traumatic brain injury to one of 2 groups. One group received transplants of stem cells into the region of the brain affected by traumatic injury. The control group received a solution infused into the brain containing no stem cells. Three months after the brain injury, the brains of stem cell rats showed clear development of neuron-like cells in the area of injury. This was accompanied by a solid stream of stem cells migrating to the brain’s site of injury. This was not the case with the control group.  

Animal study so hard to generalise to humans Animal studies enable us to monitor the function of the brain before and after trauma because we cause it. Ethically we couldn’t do this in humans and it’s unlikely that we would have measured their function before a natural event (because we didn’t know it was going to happen).

Factors affecting recovery of the brain after trauma Perseverance Physical exhaustion, stress and alcohol consumption Age Gender