Two Key Studies using Post-Mortem Analysis: The case of HM (Corkin 1997) & The Case of Tan (Broca 1861) (SL IB Psychology)

Aim:  To investigate memory loss in a brain-damaged patient known as HM via examination of his brain post-mortem

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 and mood tests, depression questionnaires, and 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) 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

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
  • Being able to study HM’s brain post-mortem allowed the researchers to validate the theory that the hippocampus is strongly implicated 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

Aim: To investigate speech impairment in one patient.  

Participant: The patient known as ‘Tan’ was being cared for by a French doctor, Paul Broca. The patient was given the name of ‘Tan’ as this was the only word that he could say even though his mouth, tongue and vocal cords were normal. He could understand what was said to him, but he could not reply in any way that was articulate.

Procedure: Broca made observations of Tan’s behaviour and speech over a long period of time. After Tan’s death, Broca conducted a post-mortem analysis of his brain.

Results: Broca found that Tan had a catastrophic lesion in his left frontal lobe.

Conclusion: Language – specifically speech production - can be localised to the left frontal lobe in a region now known as Broca’s area. If damage occurs in this area it results in Broca’s aphasia i.e. the inability to produce coherent speech.

Evaluation of Broca (1861)

   Strengths

• • The longitudinal nature of this study (and similarly in the case of HM) means that a full, in-depth investigation into the individual and their condition was possible
  • Tan’s case highlighted important new insight into the brain and its link to language and speech production

   Limitations

• • This is extremely dated research; a modern researcher would be able to use a range of brain-imaging techniques to isolate the brain region involved in the condition
  • There may have been other explanations for Tan’s speech impairment which were not explored at the time