The Effect of Brain Damage on Memory (DP IB Psychology): Revision Note

The effect of brain damage on memory

• The brain is divided into two hemispheres, left and right and is covered by a thin layer known as the cerebral cortex

• The brain has four main lobes, each of which regulates and controls specific functions:

  • The frontal lobe

  • The parietal lobe

  • The occipital lobe

  • The temporal lobe

• Each lobe is divided between the two hemispheres

  • There is symmetry in the brain, with each lobe mirroring itself on the right/left hemisphere

• As each hemisphere is responsible for different functions then each lobe is also responsible for different functions too 

Cognitive neuroscience

• Cognitive neuroscience is the scientific study of brain structure and function and how these relate to behaviour

  • E.g., movement, impulse control, memory, perception

• Cognitive neuroscience is relevant to the localisation of brain function as it seeks to ‘map out’ the brain in terms of which structures and functions can be linked to specific behaviours

• If the brain is damaged then the functions which are associated with specific structures may subsequently become impaired

  • E.g., damage to the region in the left hemisphere known as Broca's area would result in someone having difficulty producing fluent speech

  • damage to the pre-frontal cortex would result in someone exhibiting a changed personality, possibly becoming more aggressive or impulsive

Research support for the effect of brain damage on memory

Milner (1958); Scoville (1997)

Aim:  

• To investigate memory loss in a brain-damaged patient known as HM via examination of his brain post-mortem and via MRI.

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 seizures

• At the age of 27 he underwent a bilateral medial temporal lobe resection, 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 reasonably intact

Procedure:

• HM was initially studied by Brenda Milner, 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 knew 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:

  • he frequently forgot what had happened that day

  • he thought he was younger than his actual age

  • he forgot the names of people he had just met

  • he commented that every day felt as if he was just waking up from a dream

• MRI scans on HM's brain conducted in 1992-1993 confirmed that HM's medial temporal lobe had been particularly affected by the surgery

• Milner and Corkin studied him 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

  • It is a distinct function which is localised to the temporal lobe, specifically the hippocampus

Conclusion:

• Hippocampal damage may be linked to long-term anterograde amnesia

• The findings support localisation of brain function, as the formation of new memories is linked to the hippocampus

Evaluation of the effect of brain damage on memory

   Strengths

• The case study of HM employed both qualitative and quantitative methods, generating both reliable and explanatory data

• The case of HM was groundbreaking in providing huge insight into localised regions of the brain

    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

• Not enough is known about the brain for researchers to form iron-clad conclusions as to exactly which functions are impacted by brain damage

Link to concepts

Bias

• Case studies usually involve one or more researchers working closely with a single participant, which runs the risk of researcher bias affecting the researcher's objectivity and impartiality

• Becoming too close to the participant means that the researcher may over-report some findings and under-report others (possibly because of a sense of duty towards the participant, i.e., not wanting to show them in a negative light)

• Researchers must practise reflexivity throughout the research process so as to ensure that the results are credible

Responsibility

• When investigating topics such as the effect of brain damage on memory, it is vital that researchers are mindful of the potential for harm that they may (unwittingly) inflict on the participant

• With the case of HM the researchers were dealing with a vulnerable person who had no recollection of recent events (not even recognising the researchers themselves) and who had to live under supervision due to his catastrophic memory loss

• One ethical consideration that is problematic is that of informed consent

  • How could HM consent to something that he would instantly forget?

  • M's mother initially gave consent (known as consent by proxy) for the research to take place, followed by a court-appointed conservator, after his mother's death

  • HM's family, however, contested this and argued that he never willingly gave consent to be studied, which illustrates the sensitive nature of this type of research