Declarative memory

The declarative memory is part of long-term memory. This is the knowledge memory, which consists of semantic memory contents about the world and episodic memory contents about one's own life. Depending on the localization, amnesias can only be limited to semantic or episodic content.

What is declarative memory?

In addition to short-term memory, every person has a long-term memory. This permanent storage system is not a uniform structure, 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, a distinction is made between two forms of long-term memory that store different information. The procedural memory stores behavioral information, such as courses of action or learned forms of movement such as cycling.

There is also a declarative memory, which is also known as the knowledge memory. Facts or events are stored in declarative memory that a person consciously perceives and can just as consciously reproduce.

Declarative memory consists of two areas. In addition to the semantic memory for world knowledge, it contains the 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 & task

Long-term memory depends on the interaction of the cortex and subcortical areas of the brain. The entire neocortex is involved in declarative memory and thus knowledge memory. The episodic memory is based in particular on the participation of the right frontal and temporal cortex. The semantic memory is mainly located in the temporal lobe.

Many subcortical areas of the brain are involved in processes of declarative memory. This applies in particular to the process of storage, which takes place with the participation of the limbic system, the medial temporal lobe system, the hippocampus and the adjacent areas. The structures involved are summarized in the Papez neuron circle.

The storage is essentially based on neural plasticity. Memory contents are stored in the connections of nerve cells and as such are stored in the memory. A memory content of the declarative memory thus essentially corresponds to the synaptic efficiency of certain neuron networks.

The declarative memory is not only responsible for storing knowledge, but also for encoding and retrieving knowledge. The semantic memory takes care of these tasks in connection with factual information about the world. The episodic memory, on the other hand, is entrusted with specific episodes and chains of events from one's own life.

Declarative memory contents are encoded in both semantic and episodic memory in a context-bound manner and accessed in the same way. The episodic memory contents use the semantic memory contents of the declarative memory, but go beyond this 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 to a large extent of sensory perceptions and emotions that a person has collected at a certain moment in his life. In the semantic memory, however, the objective knowledge about the world is stored.

Some scientists suspect that the episodic part of declarative memory in this form is exclusively human.

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Illnesses & ailments

In connection with memory, amnesia is the most important pathological phenomenon. Amnesia can take various forms and depends on the respective damaged brain regions. In the case of semantic memory disorders of this type, long-term stored memory contents of the semantically declarative memory are affected. In individual cases, this includes, for example, professional expertise, the storage of word meanings or the conceptual association.

Since different regions of the brain are responsible for the semantic and episodic memory contents, a patient with semantic amnesia can have an intact episodic or autobiographical memory. In such a case of amnesia, there are usually lesions of the temporal lobe, so that only partial sections of the semantic memory are affected by the disorders.

In addition to trauma, degenerative organic brain diseases such as Alzheimer's dementia can impair semantic memory. Even more often than semantic memory disorders, organic brain damage leads to an anterograde memory disorder. Patients with this amnesia have difficulty remembering current events, personal names, and new knowledge.

Anterograde amnesia occurs primarily in the context of cerebral, neurological or psychiatric diseases. In addition to trauma, circulatory disorders of the brain, strokes, hypoxia or inflammatory brain diseases can be the cause. Usually the primary cause lies in local lesions of the hippocampal system, which result in reduced long-term potentiation by the functionally disturbed hippocampus or inadequate linking of new knowledge and existing memory contents.

Dissociative memory disorder is to be distinguished from these forms of amnesia, which is purely psychological and in most cases mainly affects personal information, especially information about psychologically stressful events. In this form of amnesia, the memory gaps are not constant, but depend on the day. In part, the dissociative memory disorder manifests itself in the form of a complete loss of identity.

A frequently cited case of illness in connection with amnesia of declarative memory is the case of patient HM. To treat severe epilepsy, both sides of his hippocampus were removed. The operation cured his epilepsy. After the operation, however, he showed a severe form of anterograde amnesia and could no longer incorporate any new knowledge into his declarative memory. However, previously acquired memory contents remained intact.