17.13: Functional Brain Systems: Limbic System
The limbic system, often called the "emotional brain," is a complex set of structures located deep within the brain. The intricate network of the limbic system supports a wide range of psychological functions, from emotional regulation to memory formation and sensory processing. This functional brain region encompasses specific parts of the diencephalon and the cerebrum, integrating the higher mental functions of the cerebral cortex with the primitive emotional responses of the deep brain structures.
The Gyri
The limbic lobe includes three prominent gyri — the cingulate gyrus, the parahippocampal gyrus, and the subcallosal gyrus.
- • Cingulate Gyrus: The cingulate gyrus is located in the medial aspect of the cerebral hemisphere, positioned above the corpus callosum. It is involved in processing emotions and regulating behavior. It acts as a pathway connecting the amygdala and the hippocampus, which is crucial for emotional response and memory formation.
- • Parahippocampal Gyrus: This gyrus is situated in the inferior region of the temporal lobe next to the hippocampus, serving as an essential interface between the limbic system and sensory inputs. It comprises several subregions, notably the entorhinal, perirhinal, and postrhinal cortices, each contributing unique functions to memory processing and spatial navigation. Its extensive connections with the hippocampus establish the entorhinal-hippocampal circuit, a fundamental memory encoding and retrieval pathway. Through this intricate network, the parahippocampal gyrus facilitates the complex processes of spatial navigation and recognition memory.
- • Dentate Gyrus: The dentate gyrus is located between the parahippocampal gyrus and the hippocampus. It forms part of the hippocampal formation, primarily associated with memory formation and spatial navigation. It is characterized by its densely packed granule cells and generates new neurons throughout life via adult hippocampal neurogenesis. These newly formed neurons are believed to contribute to learning and memory processes, particularly pattern separation, which is the ability to distinguish between similar experiences or stimuli.
The Amygdala
Another vital component, the amygdala, is an almond-shaped nucleus within the temporal lobe known for its role in processing emotions, especially fear and anxiety. It is involved in detecting and evaluating threats in the environment, as well as in emotional learning and memory formation. The amygdala has extensive connections with other brain regions, including the prefrontal cortex, hippocampus, and hypothalamus. These connections allow the amygdala to integrate sensory information and emotional cues from the environment and coordinate appropriate behavioral and physiological responses. Its functions are critical for survival, as it generates emotional responses to threats and helps store memories of events that triggered strong emotions.
Additional Structures
In addition to these cortical areas, the limbic system includes several other structures contributing to its complex functionality. The mammillary bodies within the hypothalamus are integral for memory recall and spatial memory, indicating their importance in navigating and remembering spaces. Furthermore, the anterior and medial nuclei of the thalamus serve as vital relay stations, channeling information into the cerebral cortex and supporting emotional regulation and memory processes. The olfactory bulbs play a pivotal role in the sensory processing of smells, connecting specific scents to memories and emotions, thereby demonstrating the limbic system's significant involvement in our emotional responses to different odors.
