The Limbic System
The limbic system refers to a collection of subcortical structures in the brain that surround the thalamus. Among other structures, this area consists of the amygdala, olfactory cortex, hippocampus and parahippocampal gyrus in the medial temporal lobe. Individuals with medial temporal lobe amnesia have shown impairment for learning as well as retrograde amnesia for recent events, but no such deficit for remembering remote events (Bayley, Hopkins, & Squire, 2003; Reed & Squire, 1998).
The Limbic Function in Olfaction
Odourants bind to the olfactory receptors in the back of the nasal cavity, sending sensory information to the glomeruli in the olfactory bulb. This signal is relayed through the olfactory nerve to the primary olfactory cortex (piriform) in the medial temporal lobe, classically considered to be part of the limbic system. This is a primitive area of the brain associated with the processing of emotion and memory (Shipley and Ennis 1996; Haberly and Price 1977; Carmichael et al. 1994). Olfactory information is also processed in the orbito-frontal cortex (OFC) in the forebrain where odours are consciously identified. For both of these modalities however, no evidence was found of thalamic relay to both the primary olfactory cortex and the OFC. This is in contrast with other sensory systems in the brain, normally relaying information through the thalamus in the midbrain before being processed in the cortex. Olfaction is the only mode of sensation that completely bypasses this area of the brain (Sullivan & Mouly 2010). As a result, olfaction is inferred to be more directly related to other limbic processes involving emotions and memory (Sullivan, Wilson & Mouly, 2015).
There has been substantial evidence to support this claim, fMRI studies have found piriform, amygdalar and hippocampal activation to be evident with olfactory stimulation (Herz et al., 2004; Poellinger et al., 2001). A study by Herz & Cupchik (1995) found that odour-evoked autobiographical memories of paintings with emotionally positive and negative valence were enhanced when the odour and valence of the paintings were hedonically congruent. Activation was also found in the hippocampus and parahippocampal area. However,
Smell, on the other hand, is the sense that comes from odor molecules attaching to the olfactory nerve. Air carries the odor into the nose. Then odor contacts the olfactory nerves at the top of the nasal passages. The the olfactory nerves send a signal to the olfactory bulb of the brain, and the nerve sends a signal to the front of the brain. The forebrain translates the signals of the odor into a specific smell (Swindle, Mark).
Some researchers hypothesize that the hippocampus is involved in some types of memory processes but not others. This particular study measured brain activity using fMRI during two types of memory tasks: remember (episodic memory) and know (familiarity). A memory was considered “episodic” if the person could recall the moment it was learned and “familiar” if they felt they recognized the word but could not retrieve the specidic moment it was learned. The a priori (pre-selected) region of interest( ROI) in the hippocampus
Decreased interest in olfaction may be related to early work which contrasted varying levels of olfactory abilities among animals, highlighting primates as deficient in this sense. In Turner’s 1891 paper The Convolutions of the Brain, he proposed a classification of Mammalia into three groups 1) Anasmotics, where the organs of smell are absent and included dolphins and whales, 2) Macrosmatics, defined by animals with a highly developed sense of smell and included ungulates, carnivores and most mammals, and 3) Microsmatics where the sense of smell is “feeble” as in pinnipeds, some whales, and apes and man. This idea of apes and humans, indeed, primates in general having a poor sense of smell was corroborated by Negus in 1958 and Le
Research has shown that there is “greater activation in the left inferior frontal and medial temporal lobes” (Stanford, 2006, p. 208) during the encoding of words which were later remembered as compared to those which were forgotten. The sensations perceived by sensory nerves are decoded in the hippocampus of the brain into a single experience (Mastin, 2010). The hippocampus analyses new information and compares and asssociates it with previously stored memory (Mastin, 2010). Human memory is associative in that new information can be remembered better if it can be associated to previously acquired, firmly consolidated information (Mastin, 2010). The various pieces of information are then stored in different parts of the brain (Mastin, 2010). Though the exact method by which this information is later identified and recalled has yet to be discovered, it is understood that ultra-short term sensory memory is converted into short term memory which can then later be consolidated into long term memory (Mastin, 2010).
Emotion and memory are actually very closely related. Thus, it is not surprising that the hippocampus is located in the limbic system, which is the emotion system portion of the brain. The limbic system is mainly associated with memory, motivation, and emotions (Memory). The hippocampus itself is located within the temporal lobes, right next to the amygdala. The structure is a horseshoe shaped paired brain structure, where one half of it is located in the left brain hemisphere, while the other half is in the right brain hemisphere (Robson).
What is the hippocampus? The hippocampus is the formation of memories and a part of the cerebrum.Some people say if you damage the hippocampus you develop a disease called Antevograde amnesia which is the unibaily to form new memories.It also said there are regions that regulates the emotions.
The hippocampus collects different bits of information that affect the senses and puts all of it into an event of a memory. In the Working Memory, it quotes, “The hippocampus is where the vast amount of knowledge you have acquired over your lifetime is housed for long-term storage.” Page 6. When the hippocampus collects different information and holds it for use at any time later in life. Said in the Working Memory…, “The PFC is the home of working memory. Located in the front of the brain, the PFC coordinates with other areas of the brain through electrical signals and receives information from those regions so your working memory can make use of it.” Page 6. Partial Frontal lobe is controlled other parts of the brain and sends signals and take in information, so it gets saved in your memory. This is important for long-term memory is used in further or moderately in life. “The amygdala is the brain’s emotional center. When you are experiencing a strong emotion, like fear, your amygdala is activated.” Quoted by the Working Memory…, page
The temporal lobe consists of the hippocampal region as well as the the entorhinal, perirhinal and parahippocampal cortices which are important for long-term memory. The hippocampal region consists of the hippocampus proper, the dentate gyrus and the subicular complex. The entorhinal cortex receives most of its input from the perirhinal and parahippocampal cortices as well as inputs from the olfactory bulb, orbital frontal cortex, insular cortex, cingulate cortex and superior temporal gyrus (Squire & Zola,
Under the mentorship of Dr. William Fifer, an expert in conducting high density, high impedance EEG to study learning and memory in human subjects, I will learn how to apply a combination of EEG analytic techniques and ANS function assessment to define and characterize odor-related oscillatory and dynamic electrophysiological patterns in the medial temporal lobe, where the primary olfactory neural system and entorhinal-hippocampal memory system are located. Under the mentorship of Dr. D.P Devanand, an expert of conducting clinical trials in Alzheimer’s disease, I will learn how to translate the findings from EEG and autonomic reactivity into high specificity
These findings suggest that areas specific for semantic memory play a significant role in the retrieval of distant memories, whereas midline posterior parietal structures may be primarily involved with more current events. Regardless of time frame, ABM retrieval appears to be significantly associated with the integrity of the hippocampus, agreeing with current theories highlighting a time-invariant role for the medial temporal lobes in recovering events from the past (Irish et al.,
Hippocampus is a small, curved region, which exists in both hemispheres of the brain and plays a vital role in emotions, learning and acquisition of new information. It also contributes majorly to long term memory, which is permanent information stored in the brain. Although long term memory is the last information that can be forgotten, its impairment has become very common nowadays. The dysfunction is exemplified by many neurological disorders such as amnesia. There are two types of amnesia, anterograde and retrograde. Anterograde amnesia is inability in forming new information, while retrograde refers to the loss of the past memory. As suggested by Cipolotti and Bird (2006), hippocampus’s lesions are
Anterograde amnesia, as described earlier, is an inability to form lasting memories after some disturbance to the brain, such as a brain injury or degenerative brain disease. The revelation of the H.M. case was the identification of the medial temporal lobes as memory consolidation and storage centers. Within the medial temporal lobes, the hippocampus has been identified specifically as a brain area involved in learning new information (Gluck, 2014). To put it another way, people with damage to the hippocampus will have difficulty forming new memories because they won’t be able to learn new things. The hippocampus helps to integrate objects in a spatial and temporal context. Episodic and semantic memory forming is impaired, otherwise known as declarative memory, though the person can remember declarative memory from the past. The process of encoding, storage consolidation, and retrieval seems to go through the medial temporal lobe with the hippocampus playing a key role. In anterograde amnesia, the consolidation process is damaged. Thus, in the short term new information can be learned, but since it is not consolidated, it can’t be retrieved, so it is forgotten (Webbe slides). Additionally, damage to the basal forebrain can cause anterograde amnesia. This is because the basal forebrain sends neurotransmitters to the hippocampus to tell it whether and when to process and store information (Gluck, 2014). In this way, the hippocampus is the main brain structure involved so
Limbic system is involved in many emotions essential for survival such as fear, anger and felling of pleasure. The hippocampus is the limbic system structure that plays the role in memory forming storing and retrieval. It is involved in connecting emotions and senses to memories. . The hippocampus sends the memories to the cerebral hemisphere for long term storage and also has a role in retrieval of memories when needed.. Patients with damaged hippocampus might lose the ability to form new memories.
The brain is dividing into several sections, including the cerebellum, the frontal lobe, and the temporal lobe, among others. The temporal lobe exists in two parts, one on each side of the brain close to the ears. It is largely responsible for the memory system (2). On the medial surface of the temporal lobe there are three important structure that are essential for human functioning. These structures are named, in order from rostral to caudal, the olfactory cortex, the amygdala, and the hippocampus. Together these three structures are referred to as the "limbic system" (1). Their functions became understood after studying how the brain functions upon loss of each structure. For example, in 1953, a patient suffering from epilepsy underwent surgery which removed most of his medial temporal lobe (1). After the surgery, the patient was able to remember who he was and was able to carry out coherent, intelligent conversations. However, if the person with whom he was talking left the room, he would have no
Case 1 tells the story of Henry Molaison (HM), a man with no memory. He lost his memory due to the operation of suctioned out the hippocampus to treat his epileptic seizures. At that time, it was not known yet that the hippocampus was essential for making memories. After operation, his seizures were significantly reduced, but Henry suffered a global amnesia. Owen et al. (2007) describes patients with global amnesia as perceptive and attentive but with a total loss of short-term memory and some trouble accessing memories of the recent past. Henry could not learn new things as he quickly forgot everything that he had learned. He could learn at a subconscious level only.