Learning Activity 7.10: Review Questions

Chapter 7: Reliability of memory

Learning activity 7.10: Review questions

Suggested answers

1. Who was Henry Molaison and why is he well known to memory researchers?

• Henry Molaison (known as H.M. until his death to protect his privacy) was a 27-year-old male who underwent brain surgery to treat the severe, debilitating epileptic seizures suffered since childhood.

• The surgery involved removal of the medial temporal lobe from both hemispheres, including about two-thirds of each hippocampus, most of each amygdala, and adjacent cerebral cortex from around the hippocampus and amygdala.

• Publication of his case study in 1957 documented serious memory problems attributed to the surgery and provided evidence of the role of the hippocampus in memory formation and for different types of memories (e.g. procedural and episodic), memory systems (e.g. LTM and STM) and processes (e.g. formation and storage).

• He subsequently participated in hundreds of research studies on memory for over 50 years until his death in 2008, and the original case study is still considered relevant and widely cited e.g. distinguishing between explicit and implicit memories.

2. List the STM and LTM memory impairments experienced by H.M. after his surgery and what these indicate about the roles played and not played by the hippocampus in explicit and implicit memories.

• STM impairments:

 storage capacity and duration normal but retention of information in STM is dependent on continual attention, with immediate and permanent loss when distracted, even for a moment — hippocampus unlikely to be involved in STM functioning (or ‘working memory’) per se (other than possibly the transfer of information about facts and events from STM to LTM); provides evidence that STM is different from LTM

• LTM impairments include:

 memory loss was virtually ‘total’ for about 2 years pre-surgery and ‘partial’ back to about 10 years pre surgery (i.e. retrograde amnesia) — suggests a role of the hippocampus in retrieval of LTMs; had retained a good deal of previously stored long-term memories suggesting that the hippocampus is not entirely responsible for their retrieval

 could not remember things that happened in the period leading up to his operation — suggests a role of the hippocampus in consolidation i.e. surgery disrupted the process

 could not remember any personal event that happened at a specific time and place but he had retained the gist of personal experiences e.g. could describe in a general way events experienced until his operation but could not report specific details — suggests episodic memories are relatively intact and that date and time stamping of these explicit memories may involve a discrete process

 anterograde amnesia as incapable of forming new explicit memories (episodic or semantic) post-surgery but could learn and retain new motor skills (mirror drawing) so formation of implicit procedural memories was relatively normal and hippocampus may not be involved with procedural memory, either formation or retrieval.

3. What does the H.M. case study suggest about where LTMs are stored in the brain? Explain with reference to the case study.

• Implications include:

 hippocampus is unlikely to store explicit memories given episodic and semantic memories that could be retrieved

 explicit memories are stored in brain regions outside those that were surgically removed, most likely within the cerebral cortex

 hippocampus is unlikely to store procedural memories given these could be retrieved, especially mirror drawing motor skills that improved with practice on different occasions.