Two Key Studies of Localisation of Brain Function: Maguire (2000) & HM (Corkin 1997) (DP IB Psychology)

Key Study 1: Maguire (2000)

Aim: To investigate localisation of function linked to spatial navigation experience  in London black cab taxi drivers

Participants: 16 healthy, right-handed male London black cab taxi drivers who had passed ‘The Knowledge’, a test of spatial navigation, aged 32-62 years with a mean age of 44 years. They had all been taxi drivers for at least 18 months, with the highest number of years as a taxi driver at 42 years

Procedure: The participants were placed in an MRI scanner and their brains were scanned. The MRI measured the volume of grey matter in the hippocampus of each participant, and this was then compared to pre-existing scans of 50 healthy, right-handed males (the control group). Grey matter was measured using voxel-based morphemetry (VBM) which focuses on the density of grey matter and pixel counting

Results: The posterior hippocampi of the taxi drivers showed a greater volume of grey matter than that of the controls, who had increased grey matter in their anterior hippocampi compared to the taxi drivers. Maguire also carried out a correlational analysis which showed a positive correlation between volume of posterior hippocampal grey matter and length of time spent as a taxi driver

Conclusion: The posterior hippocampus may be linked to spatial navigation skills

Evaluation of Maguire (2000)

Strengths

• The use of MRI technology means that the researchers were able to pinpoint the key area of the brain localised to spatial navigation

• The correlational analysis of time spent as a taxi driver linked to increased volume of hippocampal grey matter lends validity to the idea of neuroplasticity due to learning and experience

Limitations

• A correlation cannot show cause-and-effect so it is impossible to know whether the taxi drivers already had naturally high levels of hippocampal grey matter

• MRI technology is not 100% reliable: it is vulnerable to noise, temperature and operator-error

Key terms:

• Spatial navigation

• Anterior hippocampus

• Pixel-counting 

Key Study 2: The case of HM (Milner 1968, Corkin 1997)

Aim: To investigate memory loss in a brain-damaged patient known as HM and to investigate the areas of the brain implicated in his amnesia

Participant: The patient known as ‘HM, (Henry Molaison) had been run over by a bicycle at the age of nine which resulted in him experiencing epileptic fits. These became so severe that at the age of 27 he underwent a bilateral medial temporal lobe re-section which involved the removal of about two thirds of his hippocampus. HM’s epilepsy improved but he began to suffer extreme anterograde amnesia and partial retrograde amnesia:  he completely lost the ability to form new memories while long-term memories from the past remained fairly intact

Procedure: HM was initially studied by Brenda Milner, a doctoral student who visited HM frequently, administering a range of tests and measures including psychiatric tests such as personality, mood and depression questionnaires as well as interviews with psychiatrists. His scores did not indicate depression, anxiety or psychosis and he communicated a good awareness of his condition (i.e. he did not ‘forget’ that he was suffering from anterograde amnesia). He completed a standard IQ test on which his score was normal, however his scores on the Wechsler Memory Scale test demonstrated his severe memory impairment. Milner noted that HM frequently forgot what had happened that day, thought he was younger than his actual age, forgot the names of people he had just met and commented that every day felt as if he was just waking up from a dream. Milner studied him (and later, Corkin, who used MRI to scan HM’s brain) for over 50 years until his death at the age of 82

Results: The key finding from the study of HM is that memory is not simply part and parcel of a collection of cognitive functions which reside in the cortex, rather it is a distinct function which is localised to the temporal lobe, specifically the hippocampus. Post-mortem analysis of HM’s brain helped to confirm these findings. The MRI scans agreed with the post-mortem analysis

Conclusion: Hippocampal damage may be linked to long-term anterograde amnesia

Evaluation of the case of HM (Milner 1958, Corkin 1997)

Strengths

• This case study employed both qualitative and quantitative methods, generating both reliable and rich data

• HM’s case highlighted important new insight into the brain and its link to memory function, specifically the role of the hippocampus in memory formation

Limitations

• One possible confounding variable could be that HM’s brain was already damaged due to his epilepsy which would decrease the validity of the findings

• Working closely with one participant for decades could mean that researcher bias may have interfered with Milner’s objectivity