For decades, scientists have disagreed about the way the brain gathers memories, developing two apparently contradictory concepts. But newly published research by a team of scientists at Rutgers-Newark’s Center for Molecular and Behavioral Neuroscience (CMBN) indicates that both models of memory may be partially correct – and that resolving this conflict could lead to new approaches for the treatment of memory disorders such as Alzheimer’s disease.
The dispute has centered on how the hippocampus – a structure deep inside the brain – processes new information from the senses and stores it. Some researchers – such as Mark Gluck and Catherine Myers, co-directors of the Memory Disorders Project at the CMBN – have been proponents of “incremental memory,” viewing the acquisition of memory as a learning process that occurs over time.
“If you see thunder and lightning occur together once, that may be seen as a coincidence,” Myers observed. “But the more often you see them happen at the same time, the more likely you are to remember them as related parts of one event.”
Other researchers, such as Martijn Meeter, also with the CMBN, have focused on “episodic memory,” which is more like memorization. This model argues that “an event only has to occur once and you’ll remember it,” Myers said. “If someone tells you a name, you may not remember it for a long time, but you will remember it initially at least.” More dramatic events tend to be stored in long-term memory most easily. But Gluck, Myers and Meeter are developing a computer model that suggests the two methods of storing memory work together, and present their novel ideas in a paper published in the June issue of the journal Trends in Cognitive Science. Research using new classes of drugs that affect specific portions of a laboratory rat’s hippocampus and the region around it with greater accuracy has led the Rutgers-Newark team to propose a new interpretation of how the brain organizes all the sensory input that becomes memories.
That input goes through a kind of assembly line as the brain gathers it and directs it to the hippocampus, Myers said. Before reaching the hippocampus itself, the information all passes through a structure adjacent to the hippocampus called the entorhinal cortex for processing. The two parts of the brain lie side by side, resembling two halves of a hotdog bun. The new paper by the Rutgers-Newark investigative team floats the possibility that the entorhinal cortex – part of the “hippocampal region” but not part of the hippocampus itself – handles incremental learning. The main task of the hippocampus may be storing episodic memory.
“Understanding how the entorhinal cortex differs in function from the hippocampus is a hugely important and timely problem in the neurobiology of memory,” Gluck said. “The entorhinal cortex is among the very first brain regions that are damaged in the earliest stages of Alzheimer’s Disease, so understanding it is crucial to measuring the effectiveness of novel drugs to fight AD.”
Until very recently, write the researchers, only broad generalizations could be made about how memory was processed in the general hippocampal region. When humans suffer brain injuries, note the Rutgers-Newark scientists in their paper, “the damage is seldom limited to a single brain structure.” As a result, some memory functions long assumed to take place in the hippocampus alone may occur in surrounding parts of the brain, such as the entorhinal cortex.
A coordinated effort between different portions of the brain, taken as a whole, may contribute to what we think of as memory, Myers observed. “It’s a team, and everyone is doing a specialized job,” she said. She likened much previous research to the poem The Blind Men and the Elephant, wherein each of six men is right about the portion of the elephant that he is touching but is unable to form a comprehensive understanding of the animal as a whole.
“Everyone has been so caught up in his or her own world that everyone has been right on one component, but has not been able to take in the larger picture,” Myers said.