Week 9: Multiple Memory Systems
Declarative Memory Systems
Declarative memory, also known as explicit memory, is conscious memory. It is
knowledge of facts and events that includes both episodic (time-related data of past
experiences) and semantic (fact-related) data. Declarative memory stores information
about facts and the relationship between them i.e. who, what, when, where.
The Amnesiac Patient H.M.
Dr. William Beecher Scoville was a neurosurgeon at Hartford Hospital. Scoville
established the Department of Neurosurgery at Connecticut's Hartford Hospital in
1939. He performed surgery on Henry Gustav Molaison (H.M) in 1953 to relieve
epilepsy that led to damage of H.M.'s hippocampus. The hippocampal damage left him
with a memory disorder.
Dr. Brenda Milner is a Canadian neuropsychologist who has contributed extensively
to the research literature on various topics in the field of clinical neuropsychology.
Milner worked with patient H.M. and through her encounters with him, established
her reputation as one of the most important neuroscientists of the twentieth century.
Henry Gustav Molaison (H.M) suffered from epilepsy, a disorder characterized by
recurrent seizures. In order to treat his epilepsy, Dr. Scoville performed a bilateral
medial temporal lobe resection. The cause of epilepsy is in the tip of the temporal lobe
and because this cause was so severe, both temporal lobes were removed (he was,
Removal of both temporal lobes
resulted in the loss of H.M.’s
hippocampus, the cortex surrounding it
(parahippocampal gyrus) and the
Seizure activity was greatly reduced
but he developed a major loss of
H.M. was widely studied from late 1957
until his death. His case played a very
important role in the development of
theories that explain the link between
brain function and memory, and in the
development of cognitive
neuropsychology. H.M. memory disorder was selective in five important ways:
1. Higher-order perceptual, motor, and cognitive functions not affected (above
average IQ, recognizes and names common objects, normal language)
2. Loss the capacity for new learning (anterograde amnesia)
3. The span of short-term memory was normal, but devastated by delays.
4. Spared remote memory
5. Spared other domains of learning and memory capacity
Anterograde amnesia is the loss of the ability to create new memories after the
traumatic event. It leads to a partial or complete inability to recall the recent past,
while long-term memories from before the event remain intact. For example, H.M.
scored zero on tests that assess the persistence of his memory for stories, lists of
words and numbers, pictures, or any of a large range of other material.
Although H.M.’s old memories were fairly unaffected, he was unable to create new
memories. He could, however, do a variety of interesting tasks including sensory-
motor learning tasks (i.e. drawing of a star in a mirror). He improved each day at
this task, showing that he was able to learn new things even though he could not
remember learning it.
Similarly, he could perform percep