Although the physical location of memory remains relatively unknown, it is thought to be distributed in neural networks throughout the brain.
Many areas of the brain have been associated with the processes of memory storage. Lesion studies and case studies of individuals with brain injuries have allowed scientists to determine which areas of the brain are most associated with which kinds of memory. However, the actual physical location of memories remains relatively unknown. It is theorized that memories are stored in neural networks in various parts of the brain associated with different types of memory, including short-term memory, sensory memory, and long-term memory. Keep in mind, however, that it is not sufficient to describe memory as solely dependent on specific brain regions, although there are areas and pathways that have been shown to be related to certain functions.
Memory traces, or engrams , are the physical neural changes associated with memory storage. The big question of how information and mental experiences are coded and represented in the brain remains unanswered. However, scientists have gained much knowledge about neuronal codes from studies on neuroplasticity, the brain’s capacity to change its neural connections.
Most of this research has been focused on simple learning and does not clearly describe changes involved in more complex examples of memory.
Encoding of working memory involves the activation of individual neurons induced by sensory input. These electric spikes continue even after the sensation stops. Encoding of episodic memory (i.e., memories of experiences) involves lasting changes in molecular structures that alter communication between neurons. Recent functional-magnetic-resonance-imaging (fMRI) studies detected working memory signals in the medial temporal lobe and the prefrontal cortex. These areas are also associated with long-term memory, suggesting a strong relationship between working memory and long-term memory.
Imaging research and lesion studies have led scientists to conclude that certain areas of the brain may be more specialized for collecting, processing, and encoding specific types of memories. Activity in different lobes of the cerebral cortex have been linked to the formation of memories.
The temporal and occipital lobes are associated with sensation and are thus involved in sensory memory. Sensory memory is the briefest form of memory, with no storage capability. Instead, it is a temporary “holding cell” for sensory information, capable of holding information for
seconds at most before either passing it to short-term memory or letting it disappear.
Short-term memory is supported by brief patterns of neural communication that are dependent on regions of the prefrontal cortex, frontal lobe, and parietal lobe. The hippocampus is essential for the consolidation of information from short-term to long-term memory; however, it does not seem to store information itself, adding mystery to the question of where memories are stored. The hippocampus receives input from different parts of the cortex and sends output to various areas of the brain. The hippocampus may be involved in changing neural connections for at least three months after information is initially processed. This area is believed to be important for spatial and declarative (i.e., fact-based) memory as well.
Long-term memory is maintained by stable and permanent changes in neural connections spread throughout the brain. The processes of consolidating and storing long-term memories have been particularly associated with the prefrontal cortex, cerebrum, frontal lobe, and medial temporal lobe. However, the permanent storage of long-term memories after consolidation and encoding appears to depend upon the connections between neurons, with more deeply processed memories having stronger connections.
Psychologists distinguish between three necessary stages in the learning and memory process: encoding , storage , and retrieval ( Melton, 1963 ). Encoding is defined as the initial learning of information; storage refers to maintaining information over time; retrieval is the ability to access information when you need it. If you meet someone for the first time at a party, you need to encode her name (Lyn Goff) while you associate her name with her face. Then you need to maintain the information over time. If you see her a week later, you need to recognize her face and have it serve as a cue to retrieve her name. Any successful act of remembering requires that all three stages be intact. However, two types of errors can also
occur. Forgetting is one type: you see the person you met at the party and you cannot recall her name. The other error is misremembering (false recall or false recognition): you see someone who looks like Lyn Goff and call the person by that name (false recognition of the face). Or, you might see the real Lyn Goff, recognize her face, but then call her by the name of another woman you met at the party (misrecall of her name).
Whenever forgetting or misremembering occurs, we can ask, at which stage in the learning/memory process was there a failure?—though it is often difficult to answer this question with precision. One reason for this inaccuracy is that the three stages are not as discrete as our description implies. Rather, all three stages depend on one another. How we encode information determines how it will be stored and what cues will be effective when we try to retrieve it. And too, the act of retrieval itself also changes the way information is subsequently remembered, usually aiding later recall of the retrieved information. The central point for now is that the three stages—encoding, storage, and retrieval—affect one another,and are inextricably bound together.