Researchers at the School of Medicine have discovered that short-term memory remains even after brain damage occurs at the area responsible for forming memories.
“The severity of the damage depends on how it’s damaged and how much it’s damaged,” psychiatry and neurosciences professor Larry R. Squire said.
The participants in Squire’s study included four patients with damage to their medial temporal lobe, or the area responsible for forming long-term memories. The subjects — who were aged 49 to 71 — included volunteers, patients at the UCSD Medical Center and the VA system.
The experiment was held at Squire’s Memory Research Laboratory, which studies the structures and functions of mammalian memory.
“This study was based on an experiment in 1966 where patients were asked to repeat back a string of numbers,” Squire said. “Patients with MTL damage could recall up to six digits, but with numbers larger than seven digits, severe discontinuity became apparent. We used the logic of the experiment to form our study.”
The four brain-damaged subjects were told to briefly study an array of small toys, such as small cars and tops, on a table. They then were asked to recreate the object’s relative positions to each other and their results were compared to a control group of nine individuals without brain damage. The task was self-paced.
Patients with MTL damage were able to easily replicate the position of three objects or less by using short-term memory. But when asked to remember four or more objects, their performance decreased because they had to start using long-term memory
This showed that, despite brain damage, patients can still maintain working, or short-term, memory. Short-term memory is the mental ability to remember things for a few seconds immediately after experiencing (viewing, hearing, feeling) them.
This is because long-term memory involves the hippocampus, while short-term memories rely on supporting brain structures.
“There has been major confusion about distinction about short-term memory and long-term memory,” Squire said. “We chose to do this research to clear up this misconception. MTL patients are impaired even when delays are very short, and most cognitive tasks in experiments only last one second. Short-term memory is not about time as much as it is about memory capacity — short term does not mean short time.”
Short-term memory is dependent on the medial temporal lobe.
However, these patients only displayed impairment because their memory capacity had been exceeded, not because they lacked working memory.
The results were the same for all patients, and there were no discrepancies between men and women.
“This study illuminates how the brain accomplishes learning and memory by affirming the fundamental distinction between short-term memory and long-term memory [and] the specific importance of particular brain regions for the formation of long-term memory,” Squire said.
