In this article from our Johns Hopkins Memory Bulletin, Dr. Peter V. Rabins and colleagues explain how the brain's memory systems are affected in Alzheimer's and other memory-stealing conditions.
The human brain contains an estimated 100 billion nerve cells (neurons). Chemical and electrical activity allows these neurons to perform their tasks and to communicate with one another. This elaborate communication system controls vital body functions and enables us to think, see, move, talk, remember, and experience emotions.
Normal aging leads to changes in the brain, especially in areas involved in learning and memory. Some neurons shrink; others are disabled by damaging molecules called free radicals. Daily "insults," such as high blood pressure or elevated low-density lipoprotein (LDL) cholesterol, also take their toll.
Over time, these changes can make it more difficult for an older person to learn new tasks or to retrieve information from memory, such as someone's name. With Alzheimer's disease, the damage is more severe and ultimately affects larger regions of the brain.
The different memory systems -- episodic, semantic, procedural, and working -- involve multiple areas of the brain.
Episodic Memory. The temporal lobe, which contains the hippocampus, and the prefrontal cortex are important to episodic memory, which enables us to learn new information and remember recent events. The hippocampus is one of the first brain structures damaged in Alzheimer's disease and accounts for one hallmark of early Alzheimer's: difficulty remembering recent events, without any trouble remembering events from long ago.
Semantic Memory. Semantic memory governs general knowledge and facts, including the ability to recognize, name, and categorize objects. This system also involves the temporal lobes and, researchers suspect, multiple areas within the cortex. People with Alzheimer's disease may be unable to name a common object or to list objects in a category, such as farm animals or types of birds.
Procedural Memory. The cerebellum is one of the structures involved in procedural memory. Procedural memory is what enables people to learn skills that will then become automatic (unconscious), such as typing or skiing. This memory system typically is not damaged in Alzheimer's disease or is one of the last cognitive domains to deteriorate.
Working Memory. Working memory involves primarily the prefrontal cortex. This memory system governs attention, concentration, and the short-term retention of needed information, such as a street address or phone number. Problems with working memory can impair a person's ability to pay attention or to accomplish multi-step tasks. Numerous cognitive disorders, such as Alzheimer's, Parkinson's, and Huntington's disease as well as dementia with Lewy bodies, can affect working memory.
