- Implicit memory and explicit memory represent the distinct neural processes and the different states of awareness of our long-term memory.
- Explicit memory involves the recall of previously learned information that requires conscious effort to receive, while implicit memory is unconscious and effortless. Explicit memory fades in the absence of recall, while implicit memory is more robust and may last a lifetime, even in the absence of further practice.
- The discovery of implicit memory and explicit memory stemmed from the treatment of a patient suffering from amnesia. Typically, amnesic patients have great difficulty in retaining episodic and semantic information following the onset of amnesia.
- While implicit memory involves perceptional and emotional unconscious memories, explicit memory involves information and experiences we can consciously recall.
- Despite much research and many studies, the exact nature of the relationship between implicit memory and explicit memory is still ambiguous.
Our long-term memory can be fundamentally divided into two distinct types, namely implicit memory and explicit memory (Squire, 2004).
It should be noted that the formation of explicit memories requires several rounds of stimulation, significant effort and considerable time. Alternatively, the learning and retention of implicit memories may be triggered by a single stimulus.
Moreover, while implicit memory relies on specified areas of the brain, explicit memory depends upon multicomponent brain links involving the brain’s cortical and temporal regions.
In This Article
Origin and Development
The discovery of implicit memory and explicit memory stemmed from the treatment of the neuroscience patient, Henry Gustav Molaison (Squire, 2009).
An attempt to cure his epilepsy via a bilateral medial temporal lobotomy destroyed parts of Molaison’s brain. Consequently, he suffered from amnesia. Although following the surgery, Molaison was able to form short-term memories, his long-term memory was impaired.
Molaison was able to quickly learn skills such as hand-to-eye coordination. However, he could not recall events from his former days prior to the surgery.
Memory for events and knowledge acquired before the onset of amnesia tend to remain intact, but amnesiacs can’t store new episodic or semantic memories.
In other words, it appears that their ability to retain declarative information is impaired.
However, their procedural memory appears to be largely unaffected. They can recall skills they have already learned (e.g. riding a bike) and acquire new skills (e.g. learning to drive).
The nature of Molaison’s amnesia provided scientists insight into the workings of different memory systems as well as the brain structures governing their functioning.
In addition to Molaison’s case, the study of patients suffering from various forms of neurodegeneration and trauma too, has developed our understanding of implicit and explicit memory (Squire, 2015).
For instance, examining how the damaged hippocampus of patients with Alzheimer’s disease impacts their ability to create and retain explicit memories has generated important discussion.
What is Implicit Memory?
Implicit memory, also known as unconscious memory or automatic memory, refers to perceptional and emotional unconscious memories which influence our behavior (Dew & Cabeza, 2011).
The impact which implicit memory has on our current behavior occurs without our conscious retrieval of memories.
Hence, implicit memory enables our prior experiences to improve our performance of various tasks without our conscious and explicit awareness of such experiences.
Types of Implicit Memory
- Procedural memory is part of implicit memory that is responsible for knowing how to perform a particular type of action, such as reading, tying shoes, and riding a bike.
- Procedural memories are automatically retrieved for the execution of procedures involved in both cognitive and motor skills. This enables task performance without the need for conscious control or attention.
- The association of procedural learning with muscle memory can make certain actions second nature (Bullemer, Nissen, & Willingham, 1989).
- Priming is a non conscious form of human implicit memory concerned with perceptual identification of words and objects. Priming can be associative, negative, positive, affective, conceptual, perceptual, repetitive, or semantic.
- The subtle effects which this complex psychological phenomenon encompasses can be employed to manipulate individual behavior.
- Category learning involves the attainment of a concept in order to clarify and categorize various entities via grouping (Ell, Shawn; Zilioli, & Monica, 2012). Category learning allows for comparisons and indicates subjective divisions for better comprehension.
- Perceptual learning constitutes the foundation for cognitive processes, and cooperates with the neural basis to produce the prime effect. Perceptual learning also improves perception by enabling the distinguishing of similar things from each other.
- Emotional learning which involves autobiographical memories entangled with emotions, refers to the impact of emotions upon an individual.
Examples of Implicit Memory
Some examples of implicit memory include knowing how to play the piano, ride a bike; tie your shoes and other motor skills. These skills involve procedural knowledge which involves “knowing how” to do things.
Other examples of implicit memory may include:
- Knowing how to make breakfast.
- Knowing how to play a musical instrument.
- Navigating a familiar area such as your house or neighborhood.
Skills using implicit memory do not involve conscious thought (i.e. they are unconscious and automatic). For example, we brush our teeth with little or no awareness of the skills involved.
Related Brain Structures
The functioning of implicit memory is thought to involve the cerebellum and the basal ganglia (Dew & Cabeza, 2011). The cerebellum which is essential for procedural memories is located at the base of the brain.
Although it does not initiate actions, the cerebellum receives and coordinates signals from the spinal cord, the brain and sensory systems to carry out motor movements. & Cabeza, 2011). The cerebellum which is essential for procedural memories is located at the base of the brain.
The cerebellum which forms the hindbrain is primarily responsible for skill development as well as a few cognitive tasks such as attention and language (13.2 The Central Nervous System – Anatomy and Physiology, 2013). & Cabeza, 2011). The cerebellum which is essential for procedural memories is located at the base of the brain.
The basal ganglia, on the other hand, which engage in action selection, are essential for the smooth controlling of sequential movements (Ullman, 2004).
Responsible for processes such as habit formation and the regulation of emotions, the basal ganglia consist of a pair of structures deep inside the brain. & Cabeza, 2011). The cerebellum, which is essential for procedural memories, is located at the base of the brain.
The basal ganglia’s constitution explains why implicit memory involves subconsciously driven sensorimotor behavior which we typically remain unaware of.
What is Explicit Memory?
Explicit memory, also known as declarative memory, refers to memories involving personal experiences as well as factual information which we can consciously retrieve and intentionally articulate (Dew & Cabeza, 2011).
Recalling information from explicit memory involves some degree of conscious effort – information is consciously brought to mind and “declared”.
For example, declarative knowledge involves “knowing that” London is the capital of England, zebras are animals, and the date of your mom’s birthday etc (Cohen & Squire, 1980).
Types of Explicit Memory
- Semantic memory is a part of the long-term memory responsible for storing information about the world. This includes knowledge about the meaning of words, as well as general knowledge.
- For example, London is the capital of England. It involves conscious thought and is declarative.
- Autobiographical memory involves various episodes from the past gathered from our personal history based on a certain time, space, object, or person. Autobiographical memories often combine episodic and semantic memories.
- Episodic memory is a type of long-term memory responsible for storing information about events (i.e. episodes) that we have experienced in our lives.
- Episodic memories involve conscious thought and can be declared explicitly. An example would be a memory of our 1st day at school.
- Spatial memory is crucial for the formation of cognitive maps. It involves the recording of facts concerning an individual’s spatial arrangement. Spatial memory accounts for our readily finding our way through familiar towns.
Examples of Explicit Memory
The knowledge that we hold in semantic and episodic memories focuses on “knowing that” something is the case (i.e. declarative). For example, we might have a semantic memory for knowing that Paris is the capital of France, and we might have an episodic memory for knowing that we caught the bus to college today.
Other examples of explicit memory may include:
- Recollecting the items on a to-do list.
- Remembering the dates of various events for a history exam.
- Remembering the time for a doctor’s appointment.
Related Brain Structures
Explicit memory is governed by communications between the prefrontal cortex, the amygdala and the hippocampus (Dew & Cabeza, 2011).
The prefrontal cortex is thought to be necessary to store and retrieve long-term memories involving information and facts (13.2 The Central Nervous System – Anatomy and Physiology, 2013).
Located deep within the brain’s temporal lobe, the hippocampus is essential for spatial awareness and navigation as well as the consolidation of information from a short-term to a long-term memory (Squire, 2015).
The hippocampus does not involve implicit memory. The amygdala which engages in emotional learning is located near the hippocampus.
While the retention and the recalling of events rely on the function of the hippocampus, the declarative inside the brain’s medial temporal lobe is consolidated into the temporal cortex (Squire, 2009).
The Relationship between the Two Memory Systems
While recent evidence suggests a significant impact of implicit memory’s priming on explicit memory’s fact recalling, the two memory systems are thought to work independently with fundamentally distinct rules of operation (Squire, 2004).
The study of amnesic patients implies a separation of implicit and explicit memory. For instance, on one occasion, some amnesic patients with severely impaired long-term verbal memories demonstrated no difficulty in mastering a certain puzzle even though they could not recall having seen the same puzzle before (Brooks & Baddeley, 1976).
While damage to the hippocampus may explain the loss of explicit memory, the loss of their ability for conscious remembering seems to have still left intact various residual learning abilities.
Despite this apparent separation, implicit memory and explicit memory seem to work in parallel to shape our behavior (Squire, 2015).
The relationship between the two memory systems may also be influenced by chronic drug use, aging and stress. In spite of manifold studies and much research however, the exact nature of this relationship is still ambiguous (Dew & Cabeza, 2011).
Consequently, whether the two memory systems are cooperating with, or competing against each other is yet to be discovered.
13.2 The Central Nervous System – Anatomy and Physiology. (2013, March 6). Opentextbc.Ca. https://opentextbc.ca/anatomyandphysiology/chapter/13-2-the-central-nervous-system/
Brooks, D.N.; Baddeley, A.D. (1976). What can amnesic patients learn. Neuropsychologia, 14 (1), 111–129. doi:10.1016/0028-3932(76)90012-9
Bullemer, P.; Nissen, MJ.; Willingham, D.B. (1989). On the Development of Procedural Knowledge. Journal of Experimental Psychology: Learning, Memory, and Cognition. 15 (6): 1047–1060. doi:10.1037/0278-73220.127.116.117.
Cohen, N. J., & Squire, L. R. (1980). Preserved learning and retention of pattern analyzing skill in amnesia: Dissociation of knowing how and knowing that. Science, 210, 207–209.
Dew, I. T. Z., & Cabeza, R. (2011). The porous boundaries between explicit and implicit memory: behavioral and neural evidence. Annals of the New York Academy of Sciences, 1224(1), 174–190. https://doi.org/10.1111/j.1749-6632.2010.05946.x
Ell, Shawn; Zilioli, Monica (2012), Categorical Learning, in Seel, Norbert M. (ed.), Encyclopedia of the Sciences of Learning, Springer US, pp. 509–512, doi:10.1007/978-1-4419-1428-6_98, ISBN 978-1-4419-1428-6
Squire, L.R. (2004). Memory systems of the brain: A brief history and current perspective. Neurobiology of Learning and Memory. 82(3), 171–177. CiteSeerX 10.1.1.319.8326. doi:10.1016/j.nlm.2004.06.005. PMID 15464402.
Squire, L. R. (2009). The Legacy of Patient H.M. for Neuroscience. Neuron, 61, 6–9. https://doi.org/10.1016/j.neuron.2008.12.023
Squire, L. R., & Dede, A. J. O. (2015). Conscious and unconscious memory systems. Cold Spring Harbor Perspectives in Medicine, 5 (1). https://doi.org/10.1101/cshperspect.a021667
Tulving, E. (1972). Episodic and semantic memory. In E. Tulving & W. Donaldson (Eds.), Organization of Memory, (pp. 381–403). New York: Academic Press.
Ullman, MT (2004). Contributions of memory circuits to language: the declarative/procedural model. Cognition, 92 (1–2), 231–70. doi:10.1016/j.cognition.2003.10.008. PMID 15037131. S2CID 14611894.