Declarative memory is a part of long-term memory. It is the knowledge memory that consists of semantic memory contents about the world and episodic memory contents about one’s own life. Amnesias may be limited to semantic or episodic content only, depending on the localization.
What is declarative memory?
Declarative memory is a part of long-term memory. It is the knowledge memory. In addition to short-term memory, every person has long-term memory. This permanent memory system is not a unified entity, but corresponds to several storage capacities for different types of information. So far, nothing is known about a limitation of the capacity of the long-term memory. Basically, two forms of long-term memory are distinguished, which store different information. The procedural memory stores behavioral information, for example sequences of actions or learned forms of movement such as riding a bike. In addition, there is a declarative memory, which is also known as knowledge memory. In declarative memory, facts or events are stored that a person consciously perceives and can also consciously reproduce. Declarative memory consists of two areas. In addition to semantic memory for world knowledge, it contains episodic memory for facts related to one’s own life. The different forms of information are independent of each other and are stored in different brain areas.
Function and task
Long-term memory relies on an interaction of cortex and subcortical areas of the brain. Involved in declarative memory and thus knowledge memory is the entire neocortex. Episodic memory is based in particular on the involvement of the right frontal and temporal cortex. Semantic memory is primarily located in the temporal lobe. Many subcortical areas of the brain are involved in processes of declarative memory. This is especially true for the process of storage, which involves the limbic system, the medial temporal lobe system, the hippocampus, and adjacent areas. The structures involved are grouped in the Papez neuron circuit. Memory is essentially based on neuronal plasticity. Memory contents are deposited to the connections of neurons and as such are stored in memory. Thus, a memory content of declarative memory essentially corresponds to the synaptic efficiency of specific neuron networks. Declarative memory is responsible not only for storing knowledge, but also for encoding and retrieving it. Semantic memory performs these tasks in relation to factual information about the world. Episodic memory, on the other hand, is entrusted with specific episodes and chains of events from one’s own life. Declarative memory content is encoded in context in both semantic and episodic memory and retrieved in the same way. The episodic memory contents thereby use the semantic memory contents of declarative memory, but go beyond them due to the personal references. The neural components in episodic memory therefore correspond to a widely ramified network of cortical and subcortical brain areas that crosses the networks of semantic memory. In contrast to semantic memory, episodic memory does not contain “hard facts” but consists largely of sensory perceptions and emotions that a person has collected at a particular moment in his or her life. Semantic memory, on the other hand, stores objective knowledge about the world. Some scientists suggest that the episodic part of declarative memory is exclusive to humans in this form.
Diseases and ailments
In connection with memory, the main pathological phenomenon to be emphasized is amnesia. Amnesia can be of various forms and depends on the brain regions damaged in each case. In semantic memory disorders of this kind, long-term stored memory contents of the semantic declarative memory are affected. In individual cases, this includes, for example, professional knowledge, the storage of word meanings or the conceptual association relationship.Since different regions of the brain are responsible for semantic and episodic memory contents, a patient with semantic amnesia may have an intact episodic or autobiographical memory. In such a case of amnesia, lesions of the temporal lobe are usually present, so that only partial sections of semantic memory are affected by the disorders. In addition to trauma, degenerative brain-organic diseases such as Alzheimer’s dementia can affect semantic memory. Even more frequently than semantic memory impairment, brain-organic damage leads to anterograde memory impairment. Patients with this amnesia have difficulty remembering daily events, personal names, and new factual knowledge. Anterograde amnesia occurs primarily in the context of cerebral neurological or psychiatric disorders. In addition to trauma, circulatory disturbances of the brain, strokes, hypoxia, or inflammatory brain diseases may be the cause. In most cases, the primary cause is local lesions of the hippocampal system, which result in decreased long-term potentiation by the functionally impaired hippocampus or cause inadequate linkage of new knowledge and existing memory content. Dissociative memory disorder is to be distinguished from these forms of amnesia, which is purely psychological and in most cases affects mainly personal information, especially that about psychologically stressful events. The memory gaps are not constant in this form of amnesia, but depend on the day. In some cases, dissociative memory disorder manifests itself inform a complete loss of identity. A frequently cited case of illness in connection with amnesia of declarative memory is the case of patient HM. He underwent bilateral hippocampus removal for therapy of severe epilepsy. His epilepsy was cured by the operation. However, after the operation he showed a severe form of anterograde amnesia and could no longer incorporate new knowledge into his declarative memory. However, previously acquired memory contents remained intact.
