In general terms, the main role of the medial temporal lobe is to store and categorize declarative memory. This includes factual knowledge and personal memories, and it acts as an essential intermediate step before memories are transferred to our long-term memory.
If you have a talent for storytelling and can remember memories from years ago, or if you’re always the first to recall that obscure actor from a little-known movie, then you can thank your medial temporal lobe (MTL). This part of the brain, with its intricate and interconnected structures, is what allows us to remember things for longer than a few moments. However, the complexity of the human brain cannot be overstated, so there is much more to the MTL than just memory storage.
Components of the Medial Temporal Lobe
In general terms, the primary function of the medial temporal lobe is to store and categorize declarative memory, including factual knowledge and personal memories, and act as a crucial intermediate step before transferring memories to our long-term memory, which is managed by the neocortex. However, there are several individual structures within and related to the medial temporal lobe that ensure these delicate and vital processes occur smoothly and accurately. These key components and their specific functions will be explained in more detail below.
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The medial temporal lobe is physically located within the temporal lobe, near the front base of the brain. It consists of a relatively small series of cortexes that are closely connected to the olfactory cortex, as well as the ventral and dorsal streams, and therefore the occipital and parietal lobes.
Hippocampal Region
The hippocampal region of the medial temporal lobe is a curved tube-like structure, often compared to the shape of a seahorse. It is divided into two parts in each hemisphere of the brain and cannot be seen unless through dissections, as it is located beneath the parahippocampal gyrus in primates and humans. The hippocampus is closely associated with the limbic system and is crucial for converting short-term memory into long-term memory. It also plays a role in spatial memory, enabling the creation of mental maps and aiding in navigation.
Extensive research has been conducted on the hippocampus, and it has been found to play a key role in the retrieval and maintenance processes of declarative memory stored in the neocortex. Given its placement in both hemispheres of the brain and its early connection to Alzheimer’s disease, the hippocampus is believed to have a particularly important role in the limbic system. It is one of the first areas to show damage and is often referred to in early diagnoses of this disease.
Perirhinal Cortex
In humans and primates, the perirhinal cortex is a cortical region consisting of two areas, Brodmann areas 35 and 36. It is highly connected to all sensory inputs to the brain, particularly associated with the processing of visual information and its relation to memory formation. Specifically, it works to classify and record environmental stimuli from a visual perspective, helping the brain encode familiarity and the recent appearance of items.
The entorhinal cortex, a part of the medial temporal lobe, plays a crucial role in the retrieval and storage of declarative memory. Damage to this region can result in difficulties in associating meaning to objects, making it harder to distinguish between items with similar physical characteristics, such as an unopened umbrella and a cane.
Another important component of the medial temporal lobe is the entorhinal cortex, which is responsible for our perception of space and time. It receives sensory information from external stimuli and helps us associate what we see and hear. Additionally, the entorhinal cortex aids in mental mapping by processing aural and visual stimuli and helping us orient ourselves in space. Studies on rats have revealed the presence of “grid cells” in this cortex, which are directly linked to exploring and learning new environments.
The parahippocampal cortex, also known as the parahippocampal gyrus, is closely connected to memory encoding and retrieval. It is a crucial part of the limbic system and contributes to our perception and understanding of the world. This gyrus helps identify and code landscapes, city skylines, natural scenes, and visual tableaus into memory. It may also play a role in recognizing social context, enhancing our memory of physical landscapes and scenes.
The amygdala, although not always associated with the medial temporal lobe, is found in both hemispheres of the brain. It is located deep within the temporal lobe, just in front of the hippocampus. The amygdala is primarily linked to emotional responses and the relevant memories that inform those responses. It receives inputs from various parts of the brain and contributes to decision-making, attention, and emotional responses. Recent research has shown that the amygdala is not only involved in fear-based responses but also in reward-based or positive associations.
Overall, the medial temporal lobe, including the entorhinal cortex, parahippocampal cortex, and amygdala, plays a crucial role in memory, perception, emotional responses, and decision-making.
A Final Message
Even though it may not have the same level of fame as the medulla oblongata or the cerebellum, the medial temporal lobe plays a vital role in our perception of the world. Its various regions impact our ability to understand and recall spatial information, personal memories, and factual knowledge. Additionally, certain areas within the lobe serve as convergence points for different sensory inputs, allowing for their processing and integration. This unique combination of space, perception, time, and memory is essential for our cognition, making the preservation of this brain region crucial!