Your third approach to study is the Biological Approach. You will need to bring your notes and answers to class to be assessed on your understanding of the study.
2000 was a year for good brains and bad brains. Good brains belonged to Pope John Paul II, who apologised for all the wrongs committed by the Catholic Church throughout the ages, and the boffins at the Human Genome Project who published their completed draft of human DNA. Bad brains must go to the boffins at Microsoft and the voters of the USA: between them they gave us Windows ME and George W Bush for President. What were they thinking?
Eleanor Maguire and colleagues at University College London put their brains to good use by looking at the brains of taxi drivers. Maguire was inspired by her work with patients suffering brain damage and wanted to identify the structures in the brain that hold our memories and power of navigation. This was a natural (or quasi-) experiment and a correlational study. Maguire was trying to find out if our brain structure is fixed or if it changes in response to our environment. First she compared taxi drivers with non taxi drivers, then she correlated the amount of time spent as a taxi driver with the size of the changes.
Look at Holah's study guide - which contains links and a test-yourself quiz.
Download the original study in pdf format.
Find out about "the Knowledge" and try a mock test online here
|Find out more about these changes in the brain by reading about the Double-Edged Sword of the Cabbies' Hippocampi on PsychBLOG.||Not sure about correlations? Read Holah's clear explanation of correlational analysis.||Hungry for more brains? Visit the Brain Zone and take a virtual tour through the brain.|
Scientists have been interested in the different parts of the brain for centuries, but in the past research could only be done on dead bodies or occasional victims of brain damage. The case of H.M. suggests that the hippocampus is the part of the brain responsible for memory - H.M. was a young man who suffered from epileptic seizures and in the early '50s he was operated on by the famous surgeon William Scoville, who removed part of the hippocampus from H.M.'s brain. H.M.'s epilepsy was reduced, but the young man lost most of his memory. Not only did he have amnesia about the ten years before the operation, but he could no longer make new memories. H.M. probably never understood what had happened to him: he had the memories of his teenage life and forgot everything else that happened within a few minutes.
Modern brain scanning techniques have increased our ability to study the brain. For example, CAT scans involve taking X-rays of the brain, 180 degrees round the head. Eleanor Maguire used Magnetic Resonance Imaging (MRI) to find out more about the behaviour of the hippocampus in ordinary people.
Maguire et al. wanted to answer some questions left unanswered by previous research into the hippocampus.
Are brain differences pre-determined at birth or does the brain change in response to your environment - in other words, is the brain a product of nature or nurture?
Previous research shows that the hippocampus plays an important part in spatial memory - rembering locations, directions and routes. Maguire wanted to find out more about what precisely the hippocampus does.
Other animals that depend on spatial memory (for example, birds who fly or animals who migrate) have much larger hippocampi, as a proportion of their brain size. Will the brains of human beings who use spatial memory a lot have large hippocampi too?
Maguire selected a group of London taxi drivers. Because these taxi drivers have to pass a very difficult exam (called "the Knowledge"), it is assumed they must have excellent spatial memory and use their spatial awareness regularly. Maguire recruited 16 taxi drivers. All were males between 32 and 62 who had been taxi drivers for over a year. She made sure they were all right-handed and had healthy medical and psychiatric profiles. For a control group, Maguire used 16 men who were NOT taxi drivers but who matched her experimental group of age.
All the participants received brain scans using Magnetic Resonance Imaging (MRI). This brain scan involves lying down in a tubular machine that surrounds your head with a strong magnetic field. This makes the atoms in the brain change their spin, sending out tiny radio sugnals. A detector picks up these signals and a computer creates an image of the structure of the brain from them.
The IV in this experiment is whether or not the participant was a taxi driver. This is a naturally occurring variable, making this a natural (or quasi-) experiment. Maguire couldn't create taxi drivers, she had to find people who already happened to be taxi drivers. This type of experiment has certain problems, because we cannot be sure the participants in the two conditions are identical in every other respect.
The DV is the result of the MRI brain scan. This data was analysed using two techniques.
VBM stands for 'voxel-based morphometry'. It is time consuming but lets us measure the volume of large parts of the brain and how dense it is. Because the hippocampus is made of denser "grey" matter, it will stand out when studied using VBM.
Pixel-counting involves counting the "dots" in the computer-generated images of the brain. As a control, the person counting the dots did not know whether he was analysing a taxi driver's brain or an ordinary person's brain - this is known as a blind technique. The dots were taken from "slices" from the 3D computer image of the brain, 6 slices from the anterior (front) hippocampus, 12 slices from the main body of the hippocampus and 6 from the posterior (back) hippocampus.
Using VBM, the two groups had similar brains except for the hippocampi, where the taxi drivers had more grey matter. Specifically, the taxi drivers had more grey matter in the posterior (rear) hippocampi, but slightly less grey matter in the anterior (frontal) hippocampi, compared to the control group.
Pixel-counting showed similar variations. The taxi drivers had larger posterior hippocampi than the controls. The controls had larger hippocampi in the anterior and main body areas, particularly on the right side of the brain.
When she found a difference between the two groups of men, Maguire wanted to know if these differences were down to nature or nurture. Basically, did the taxi drivers end up with their jobs because they'd started out with enlarged posterior hippocampi... or had their hippocampi altered shape because of the time they spend learning routes around London...
Just using the taxi drivers, Maguire carried out a test for correlation between two variables: (1) the volume of the posterior hippocampus and (2) the amount of time they'd spent as a taxi driver.
The amount of time the men had been taxi drivers correlated POSITIVELY with the volume of the right posterior hippocampus. In other words, the longer they'd been working in taxis, the larger that part of the hippocampus had grown.
The amount of time the men had been taxi drivers correlated NEGATIVELY with the volume of the anterior hippocampus. In other words, the longer they'd been working in taxis, the smaller that part of the hippocampus had shrunk.
There is a relationship between using navigational skills and the distribution of grey matter in the hippocampus.
The results of the correlations suggest there is "local plasticity in the structure of the healthy human brain as a function of exposure to environmental stimuli". In plain English, your brain changes shape depending on how it's being used.
The posterior hippocampus seems to be used for PREVIOUSLY LEARNED spatial memory. In other words, the taxi drivers carry around a mental map of London and this increases the volume of their posterior hippocampus. This seems to be particularly true of the right hippocampus but there was no real correlation with the left hippocampus. Perhaps the left hippocampus stores other types of memories, like people or events associated with driving.
This study is very interesting for treating people with brain damage. It looks as if, when extra demands are put on the brain, it can "borrow" cells from less-used areas to "build up" the much-needed areas.