What was the significance of HM's case in relation to working memory?

• A. HM's long-term memory remained completely intact.
• B. HM's long-term memory impairment did not affect short-term memory.
• C. HM's short-term memory could hold information, indicating working memory was undamaged.
• D. HM's sensory memory was enhanced.

Answer: (C)

Working memory is the system that holds and manipulates information in consciousness for a short time. In HM’s case, removing the hippocampus and surrounding medial temporal structures caused a severe difficulty in forming new long-term memories, but his ability to retain and work with information over brief periods remained intact. He could perform short-term tasks, like repeating a sequence of numbers or keeping a few items in mind for seconds, which shows the mental workspace of working memory was preserved. This clear separation between the ability to maintain information momentarily (working memory) and the ability to form lasting memories (long-term memory) explains why his short-term memory could hold information even though his long-term memory was impaired.