1. The Content of Memory: Memory Systems and the Hippocampus

2. The Content of Experience Matters to the Brain: Example 2: Personal Facts and Skills
The many hours of practice required to play a musical instrument or a sport leave an enduring impression on your brain that now supports the skill.
In addition to acquiring a skill, however, you will also remember much about the practice sessions—where they occurred, who your instructors were, and how difficult it was initially to perform.
Nevertheless, these aspects of your memory have absolutely nothing to do with your ability to perform the skill.
We know this because people who are amnesic in the sense of having no recollection of the training episodes can still perform.
The inescapable conclusion is that the memory system that supports skillful behaviors is outside of the region of the brain that supports our ability to recollect the training episodes.

3. The Content of Experience Matters to the Brain: Multiple Memory Systems
Memory researchers believe
A complete understanding of memory can only be achieved by recognizing that the content of experience is important.
Memories are segregated into different brain regions according to their content.
These ideas are the central premises of what is called the multiple memory system perspective.

4. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M. Contribution to Memory Research
FIGURE 12.1 A hippocampus dissected from a human brain (left) and the tropical fish hippocampus or seahorse (right). The striking similarity in shape is undoubtedly why the Bolognese anatomist Giulio Cesare Aranzi named this brain region the hippocampus (Andersen et al., 2007). (Photo courtesy of Professor Laszio Seress, University of Pécs, Hungary.)
The multiple memory systems view and the significance of the hippocampus begins with Brenda Milner’s analysis of patient H.M.

5. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research
Henry Gustav Molaison (H.M.) is the most famous patient in the history of memory research. He suffered profound epilepsy. To alleviate this problem, a region of the brain called the medial temporal lobe was bilaterally removed. This region included the hippocampus, amygdala, and surrounding cortex. As a consequence, H.M. became severely amnestic.

6. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research
Surgery
Retrograde amnesia
Anterograde amnesia
H.M.’s retrograde amnesia (memory for events that occurred before surgery) extended back to childhood. His anterograde amnesia (memory for events that occurred after surgery) was permanent.
H.M. lost all contact with the past. He could not recognize people he saw every day nor himself.

7. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research: Not All Memory Functions Were Lost
H.M.’s short-term memory remained intact but he could not convert a short-term memory into a long-term declarative memory.
He could acquire new skills such as mirror tracing.
Even though his performance improved, H.M. could not remember participating in the tasks.
FIGURE 15.2 (A) The mirror-tracing task. (B) H.M.’s performance improved with training.

8. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research
“Right now, I’m wondering. Have I done or said anything amiss. You see at this moment everything looks clear to me, but what happened just before? That’s what worries me. It’s like waking from a dream; I just don’t remember.”
—H.M., quoted by Brenda Milner.

9. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research
He had a conscience. For example, when explaining why he could not fulfill his dream of being a neurosurgeon, he cited the fact that he wore glasses, and that blood might spurt up onto his glasses, creating an obstacle to his vision and causing him to miss his target in the patient's brain, thereby causing the patient harm.
In addition, he had good insight into his memory disorder. When I asked him, "What do you do to try to remember?" he replied, "Well, that I don't know 'cause I don't remember (laugh) what I tried." He had a sense of humor, and often made jokes.

10. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research
H.M. was not the first patient to display amnesia for certain types of information. What was unique was that the location of his brain damage was known.
This meant that specific regions of the brain may be critical to memory and, for the first time, researchers had a testable hypothesis about just what regions were critical.
That his intellectual capacities were intact also meant that memory functions could be separated from other cognitive abilities.
That H.M.’s anterograde and retrograde amnesia was restricted to certain kinds of content is also part of the foundation for the multiple memory systems view.

11. The Hippocampus and Episodic Memory: H. M
The Hippocampus and Episodic Memory: H.M.’s Contribution to Memory Research
Today many researchers believe that the removal of HM’s medial temporal lobes disrupted what is called the episodic memory system.
This memory system extracts and stores the content of our personal experiences in a manner that allows them to be consciously retrieved.

12. The Hippocampus and Episodic Memory: The Extent of H.M.’s Brain Lesion
William Scoville
FIGURE 15.3 The tissue removed from H.M.’s brain. (A) This sagittal view of the brain shows that most of the amygdala and hippocampus were removed. (B) This view shows the extent to which underlying cortical tissue was removed. (After Scoville and Milner, 1957.) (C) This coronal section illustrates the combined loss of the cortical regions and hippocampus. (D) Another coronal view shows the cortical regions (entorhinal cortex, perirhinal cortex, parahippocampal cortex) and hippocampus in more detail.

13. The Hippocampus and Episodic Memory: Animal Models of H.M.’s Amnesia
Given the extent of H.M.’s brain damage, it was difficult to know if any particular region was more critical to his amnesia than another. Thus, researchers turned to animal models to determine what regions of the brain were critical to H.M.’s amnesia.
The research strategy:
Devise a memory task that could be used with primates to study episodic memory.
Surgically remove various regions of the brain that were removed from H.M. and test animals on this task.

14. The Hippocampus and Episodic Memory: The Delayed Nonmatching-to-Sample Task Developed by Mishkin
FIGURE 15.4 The delayed nonmatching-to-sample task was invented to study episodic memory in monkeys. The animal’s task is to remember the object it sampled and to choose the novel object on the choice trial.

15. The Hippocampus and Episodic Memory: Mishkin’s Experiments
% Correct
Delay Interval (sec) H A AH

16. The Hippocampus and Episodic Memory: Damage to the Rhinal Cortices Impairs Performance on the DNMS Task
FIGURE 15.5 (A) A sagittal view of the human brain. (B) The performance on the delayed nonmatching-to-sample task. Primates with damage to both the amygdala and hippocampus (AH) performed normally. However, removal of the rhinal cortical regions profoundly disrupted performance. (After Meunier et al., 1993; Murray and Mishkin, 1998.)
Larry Squire suggested that it is the cortices surrounding the hippocampus that support DNMS performance. Primates in this experiment had selective damage to the hippocampus and amygdala or to the underlying perirhinal cortex. Note that only damage to the rhinal cortex impaired performance.

17. The DNMS Paradox Resolved
Dual Process Theories of Recognition Memory: The DNMS task does not depend only on the episodic memory system. It has two solutions—one that depends on the hippocampus and one that does not. According to this analysis, monkeys without a hippocampus can still perform correctly on the DNMS task because they still have the neural system (perirhinal cortex) needed to make familiarity-based judgments.

18. The Hippocampus and Episodic Memory: Patients with Selective Damage to the Hippocampus
Other patients who have much more focal damage to the hippocampus, such as patient R.B., also show a similar pattern of spared and impaired memories. However, R.B’s impairments were not as severe as H.M.’s.
Damage to the hippocampus of patient R.B. was restricted to a massive loss of neurons in the CA1 field, outlined in white in the figure, thereby disrupting the sequence of information flow through the hippocampus.