As it turns out, different types of memories are stored in distinct regions of our brains. Long-term memory is divided into two types: declarative and procedural.
There are two types of declarative memory: Recollections of experiences such as the day we started school and our first kiss are called episodic memory. This type of recall is our interpretation of an episode or event that occurred. Factual knowledge, on the other hand, such as the capital of France, is part of semantic memory. These two types of declarative memory content have one thing in common—you are aware of the knowledge and can communicate the memories to others. [...]
One of the most famous studies showing the separate memory systems was that of an epileptic named Henry Gustav Molaison (aka H. M.). In the 1950s he underwent the removal of portions of his brain, including large parts of his hippocampus. After the operation doctors found that although the number of seizures had decreased, H. M. was unable to form new memories. Many of his memories of the time before the operation were also erased. [...]
Even with traumatic brain injury the procedural memory system is hardly ever compromised. That’s because the basal ganglia, structures responsible for processing nondeclarative memory, are relatively protected in the brain’s center, below the cerebral cortex. However, it’s not clear, beyond brain damage, why procedural memory contents are not as easily forgotten as declarative ones are. According to one idea, in the regions where movement patterns are anchored fewer new nerve cells may be formed in adults. Without this neurogenesis, or continuous remodeling in those regions, it’s less likely for those memories to get erased.
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