Explicit memory is the conscious, intentional recollection of previous experiences and information. People use explicit memory throughout the day, such as remembering the time of an appointment or recollecting an event from years ago.
Explicit memory involves conscious recollection, compared with implicit memory which is an unconscious, unintentional form of memory. Remembering a specific driving lesson is an example of explicit memory, while improved driving skill as a result of the lesson is an example of implicit memory.
Episodic memory, a part of autobiographical memory, consists of the recollection of events in the life of a person. These can be memories that happened to the person directly or just memories of events that happened around them. Simply put, it is the memory of life experiences centered on oneself. Episodic memory is necessary for "time traveling": remembering your past. Episodic memory does not have any direct effect on how one imagines their future. It is considered a uniquely human quality that depends on maturation and therefore not to be found in babies and young children. For children, recollection of these memories can also be hindered by traumatic events that occur during childhood.
Semantic memory consists of all explicit memory that is not autobiographical. Examples of semantic memory is knowledge of historical events and figures; the ability to recognize friends and acquaintances; and information learned in school, such as specialized vocabularies and reading, writing and mathematics.
The neural basis of episodic and semantic memory is not yet known today. However, the scientists E. Tulving and R.F. Thompson suggest that episodic memory might be dependent on the right hemisphere, and semantic memory on the left hemisphere.
Encoding and retrieval
The encoding of explicit memory depends on conceptually driven, top-down processing, in which a subject reorganizes the data to store it. The subject makes associations with previously related stimuli or experiences. The later recall of information is thus greatly influenced by the way in which the information was originally processed. The depth-of-processing effect is the improvement in subsequent recall of an object about which a person has given thought to its meaning or shape. Simply put: To create explicit memories, you have to do something with your experiences: think about them, talk about them, write them down, study them, etc. The more you do, the better you will remember. Testing of information while learning has also shown to improve encoding in explicit memory. If a student reads a text book and then tests themselves afterward, their semantic memory of what was read is improved. This study – test method improves encoding of information. This Phenomenon is referred to as the Testing Effect.
Retrieval: Because a person has played an active role in processing explicit information, the internal cues that were used in processing it can also be used to initiate spontaneous recall. When someone talks about an experience, the words they use will help when they try to remember this experience at a later date. The conditions in which information is memorized can affect recall. If a person has the same surroundings or cues when the original information is presented, they are more likely to remember it. This is referred to as encoding specificity and it also applies to explicit memory. In a study where subjects were asked to perform a cued recall task participants with a high working memory did better than participants with a low working memory when the conditions where maintained. When the conditions where changed for recall both groups dropped. The subjects with higher working memory declined more. This is thought to happen because matching environments activates areas of the brain known as the left inferior frontal gyrus and the hippocampus.
Neural structures involved
Several neural structures are proposed to be involved in explicit memory. Most are in the temporal lobe or closely related to it, such as the amygdala, the hippocampus, the rhinal cortex in the temporal lobe, and the prefrontal cortex. Nuclei in the thalamus also are included, because many connections between the prefrontal cortex and temporal cortex are made through the thalamus. The regions that make up the explicit memory circuit receive input from the neocortex and from brainstem systems, including acetylcholine, serotonin, and noradrenaline systems.
Traumatic brain injury and explicit memory
While the human brain is certainly regarded for its plasticity, there is some evidence that shows traumatic brain injury (TBI) in young children can have negative effects on explicit memory. Researchers have looked at children with TBI in early childhood (i.e. infancy) and late childhood. Findings showed that children with severe TBI in late childhood experienced impaired explicit memory while still maintaining implicit memory formation. Researchers also found that children with severe TBI in early childhood had both increased chance of having both impaired explicit memory and implicit memory. While children with severe TBI are at risk for impaired explicit memory, the chances of impaired explicit memory in adults with severe TBI is much greater.
Memory loss and explicit memory
Current research is also being done to show that patients with severe neural degeneration can still be classically conditioned and learn new tasks without consciously recalling that they have ever learned them. This can prove to be helpful in the future with treatments of brain trauma and other neurodegenerative conditions.Alzheimer’s disease has a profound effect on explicit memory. Mild cognitive impairment is an early sign of Alzheimer’s disease. People with memory conditions often receive cognitive training. When an fMRI was used to view brain activity after training, it found increased activation in various neural systems that are involved with explicit memory. People with Alzheimer’s have problems learning new tasks. However, if the task is presented repeatedly they can learn and retain some new knowledge of the task. This effect is more apparent if the information is familiar. The person with Alzheimer’s must also be guided through the task and prevented from making errors. Alzheimer’s also has an effect on explicit spatial memory. This means that people with Alzheimer’s have difficulty remembering where items are placed in unfamiliar environments. The hippocampus has been shown to become active in semantic and episodic memory. The effects of Alzheimer’s disease are seen in the episodic part of explicit memory. This can lead to problems with communication. A study was conducted where Alzheimer’s patients were asked to name a variety of objects from different periods. The results shown that their ability to name the object depended on frequency of use of the item and when the item was first acquired. This effect on semantic memory also has an effect on music and tones. Alzheimer’s patients have difficulty distinguishing between different melodies they have never heard before. People with Alzheimer’s also have issues with picturing future events. This is due to a deficit in episodic future thinking.
- E. Tulving: Episodic memory: from mind to brain. In: Annual review of psychology 53:1-25, 2002.
- Kolb & Whishaw: Fundamentals of Human Neuropsychology (2003), page 454-455.
- Einstein, G. O., Mullet, H. G., & Harrison, T. L. (2012). The testing effect: Illustrating a fundamental concept and changing study strategies. Teaching Of Psychology, 39(3), 190-193. doi:10.1177/0098628312450432
- Unsworth, N., Brewer, G. A., & Spillers, G. J. (2011). Variation in working memory capacity and episodic memory: Examining the importance of encoding specificity. Psychonomic Bulletin & Review, 18(6), 1113-1118. doi:10.3758/s13423-011-0165-y
- Staresina, B. P., Gray, J. C., & Davachi, L. (2009). Event congruency enhances episodic memory encoding through semantic elaboration and relational binding. Cerebral Cortex, 19(5), 1198-1207. doi:10.1093/cercor/bhn165
- H.L. Petri and M. Mishkin: Behaviorism, cognitivism, and the neuropsychology of memory, in: American scientist, 82:30-37, 1994
- Lah, S., Epps, A., Levick, W., & Parry, L. (2011). Implicit and explicit memory outcome in children who have sustained severe traumatic brain injury: Impact of age at injury (preliminary findings). Brain Injury, 25(1), 44-52. doi:10.3109/02699052.2010.531693
- Hampstead, B. M., Stringer, A. Y., Stilla, R. F., Deshpande, G., Hu, X., Moore, A., & Sathian, K. K. (2011). Activation and effective connectivity changes following explicit-memory training for face–name pairs in patients with mild cognitive impairment: A pilot study. Neurorehabilitation And Neural Repair, 25(3), 210-222. doi:10.1177/1545968310382424
- Metzler-Baddeley, C., & Snowden, J. S. (2005). Brief report: Errorless versus errorful learning as a memory rehabilitation approach in Alzheimer's disease. Journal Of Clinical And Experimental Neuropsychology, 27(8), 1070-1079. doi:10.1080/13803390490919164
- Kessels, R. C., Feijen, J. J., & Postma, A. A. (2005). Implicit and Explicit Memory for Spatial Information in Alzheimer's Disease. Dementia And Geriatric Cognitive Disorders, 20(2-3), 184-191. doi:10.1159/000087233
- Hoscheidt, S. M., Nadel, L., Payne, J., & Ryan, L. (2010). Hippocampal activation during retrieval of spatial context from episodic and semantic memory. Behavioural Brain Research, 212(2), 121-132. doi:10.1016/j.bbr.2010.04.010
- Small, J. A., & Sandhu, N. (2008). Episodic and semantic memory influences on picture naming in Alzheimer's disease. Brain And Language, 104(1), 1-9. doi:10.1016/j.bandl.2006.12.002
- Irish, M., Addis, D., Hodges, J. R., & Piguet, O. (2012). Considering the role of semantic memory in episodic future thinking: Evidence from semantic dementia. Brain: A Journal Of Neurology, 135(7), 2178-2191. doi:10.1093/brain/aws119