The Case of HM

The Case of HM

1. H.M. had bilateral resection of part of temporal lobes

   • Post-operatively he could not recall events from about 3 years before operation to present ,i.e., retrograde amnesia
     • However, he could recall events before that time, including childhood
       • He could not consolidate new factual (declarative) memories, i.e., anterograde amnesia
         • However, memory for learned skills was intact

2. Conclusion from the case of HM

   • Confirmed the existence of different processes of memory such Encoding vs. consolidation and different kinds of memory such as Implicit (procedural) versus explicit (declarative)
     • Also suggested that the hippocampus is not the location for long term memory, not necessary to retrieve long-term memory and not the location of immediate short-term memory
       • But is involved in converting short-term to long-term memories (that reside in the cerebral cortex).

3. CA3 size predicts precision of memory recall (Chadwick, Bonnici and Maguire, 2013)

   • People vary in ability to differentiate when retrieving past events (i.e., pattern separation). Variation in size of hippocampal subfield CA3 predicts: The amount of retrieval confusion between past memories. The amount of neural interference between episodic memories within CA3

4. The hippocampus and cortex are both involved in encoding and retrieval, they both interact with each other

5. Two views of long term memory (Nadel)

   • 1. Standard model of memory consolidation. Memory storage initially requires a link between the hippocampus and various neocortical storage sites, but over time the hippocampal component is rendered unnecessary.
     • 2. “Multiple memory trace" theory. Hippocampal ensembles are always involved in storage and retrieval of episodic memories. Neuroimaging studies show that retrieval of remote (25-year-old) memories elicits as much activation in hippocampus as retrieval of quite recent memories