The subiculum is a subarea in the brain. It is located in the inrolled cortical structure at the end of the hippocampus. In the learning process, it performs an important task.
What is the subiculum?
The subiculum is a part of the limbic system and thus the central nervous system. This is responsible for tasks such as emotions. The hippocampus is located in the limbic system. This is important for learning as well as memory formation in addition to the formation of emotions. The hippocampus is mostly located in the inner edge of the temporal lobe. This is also called the temporal lobe. The subiculum is located in the inner structure of the hippocampus. This connects the hippocampus to the parahippocampal gyrus. The subiculum has an essential role in the learning process and the storage of information in memory. It is considered the final instance of information processing of the hippocampus. This provides the basis for forming long-term memories. The hippocampus contains a three-layered archicortex. This area is also known as the hippocampal formation. The three layers include the dentate gyrus, the Ammon’s horn, and the subiculum. In the ammonic horn, for example, prerequisites for operant conditioning are created. The dentate gyrus is considered the most important afferent system in the hippocampus. The bulk of the efferent system is formed by the subiculum.
Anatomy and structure
The hippocampus is located on the inner surface of the temporal lobes. Visually, it has the shape of a seahorse, excluding the area of the head. A frontal section of the lower part of the hippocampus results in visibility of the three layers lying within it. Like the tail of a seahorse, this area is curled up. The structure of the tissue there is called the curled cortical structure because of its special characteristics. Along this area of tissue, the microscopic archicortex structure becomes visible. From a developmental point of view, the archicortex is the oldest part of the cortex cerebri. The three layers in the inrolled area of the hippocampus are the dentate gyrus, the Ammon’s horn, and the subiculum. The subiculum is considered the transitional area between the hippocampus and the entorhinal cortex. This is the cerebral lobe that is a transitional zone between the archicortex and the neocortex. Most of the efferent fibers of the hippocampus arise from the subiculum. From there, they travel in the fornix to the mammillary body. The fornix is a fiber pathway that connects the hippocampus to the forebrain. The mammillary body is a paired cusp and part of the hypothalamus.
Function and tasks
The subiculum has an essential role in the consolidation of memory content. This is understood to mean the entire learning process with its individual processes. Information must be transferred from short-term memory to long-term memory so that it is permanently available. This process takes several days to months until the memories are firmly anchored in the brain. If it is interrupted, the learned information reaches the long-term memory incompletely. Thus, the main task of the subiculum is long-term potentiation. This forms the basis of all learning and memory processes. Primarily, this applies to long-term memories. They include the formation of knowledge in the declarative memory. This stores the factual knowledge and all information around experienced events. Spatial orientation is just as much a part of this as learned content. In addition, the prerequisites for consolidating implicit memory content are also created here. This includes habits, automatic action sequences, motor and emotional learning. Since the subiculum forms the bulk of the efferent system, most information in the hippocampus flows through the dentate gyrus as well as the subiculum. This region of the hippocampus is considered the last before the transition to the enthorial cortex. Thus, it represents the crucial hierarchical level in hippocampal information processing. The preparations for storing a long-term memory were made in the other regions of the hippocampus. Now it is decided in the subiculum whether it will really remain permanently in the memory or whether it will be dropped again. Factors such as the speed of information transfer between neurons and synapses are just as important as processes of effective learning.
Diseases
Lesions of the subiculum cause immense disruptions within the exchange of information between neurons as well as between regions in the brain. Memory consolidation builds on a strand of information and cannot function adequately if any part of the system fails or is impaired. This leads to disturbances in long-term potentiation. As a result, memory loss occurs. This is usually accompanied by decreased intelligence. A disturbance of the memory is called amnesia in medicine. Two forms of amnesia can be distinguished. They are the anterograde and the retrograde amnesia. In anterograde amnesia, no new memory formation is possible. The memories that have already been made are completely preserved, but new ones cannot be formed. Access to already formed memory contents is no longer possible in retrograde amnesia. Everything that was learned before brain damage must be relearned, since these memories are no longer available completely or to a large extent. The three layers in the hippocampus play an essential role in the formation of memory content. If one of the layers is impaired, this leads to memory loss as well as problems with long-term memory formation. Since the subiculum is the last instance in long-term potentiation, this is where it is ultimately decided whether a memory will be permanently present in memory.
