Neuroscientists at New York University (NYU) and Harvard have identified how the brain’s hippocampus helps people to learn and remember the sights, sounds and smells that make up long-term memory for the facts and events, termed declarative memory. By studying the activity of neurons of the hippocampus, the scientists have illuminated how the brain signals the formation of new associative memories, a form of declarative memory. These results provide some of the strongest direct evidence to date for learning-related plasticity in the hippocampus.
The research findings are reported in the June 6 issue of the publication Science in a paper entitled “Single Neurons in the Monkey Hippocampus and the Learning of New Associations.”
Since the 1950s, scientists have been aware of the link between the hippocampus and memory, but knew little of how this association manifested itself in neural activity. The NYU research team, led by NYU post-doctoral fellow Sylvia Wirth, NYU professor Wendy Suzuki and graduate student Marianna Yanike, examined the neural correlates of associative memory formation by using electrodes to monitor the electrical activity of individual neurons in the brains of monkeys performing an associative learning task. The neural and behavioral data was analyzed using dynamic estimation algorithms developed by post-doctoral fellows Loren Frank, Anne Smith and professor Emery Brown at Harvard University.
Each day, the monkeys were shown complex images superimposed with four identical targets. As the monkeys learned through trial and error which target location was associated with reward, the scientists observed dramatic changes in the activity of some hippocampal neurons. They called these cells “changing cells”. The changes in neural activity paralleled the animal’s behavioral learning curve indicating that these neurons are involved in the initial formation of new associative memories.
”Because the activity in many changing cells continued after the animal learned the association, this suggest that these cells may participate in the eventual storage of the associations in long-term memory.” said Suzuki.
The team’s research signifies a major breakthrough in understanding the brain basis of memory. Understanding the memory functions of the normal brain is a critical first step in intervening in situations where memory function is impaired such as in Alzheimer’s Disease.