Role of the Hippocampus, Striatum, and Amygdala - Essay Example

Hippocampus Before probing into the issue of describing some distinguishing mnemonic functions of hippocampus, we must first get to know what hippocampus actually is. So starting with the term hippocampus, it is that structure of the brain that lies under medical temporal lobe whose positioning is one on either side of the brain. It is also considered as the main component of a brain. There are other structures in the brain with which hippocampus can be grouped that includes dentate gyrus. The grouping of hippocampus with other relative structures is known as hippocampal formation (Andersen, Morris, Amaral, Bliss, & O’Keefe, 2007). Hippocampus can be related to limbic system of the brain and it has a significant role in not only maintaining long term memory but also in spatial navigation. These roles of hippocampus make it a structure of critical importance for a brain. When we talk about hippocampus’s critical role in the brain, we should also mention its importance in the formation of factual and autobiographical memories in the brain of a human or a mammal. Hippocampus can also work as a gateway for the memory (Cohen & Eichenbaum, 1993). It is in a sense that all new memories pass through this gateway before getting into the permanent storage area of the brain. If we talk about the structure of hippocampus, we can call it a paired structure which is formed so that mirror image lies on both sides of the brain (Matthews, 2000). Damage to this critical structure of the brain can lead to a very detrimental disease which is anterograde amnesia. In anterograde amnesia, new memories can not be formed by the brain because it loses the ability of formation of any sort of new memories in the brain (Traub & Miles, 1991). In such case, older memories don’t get affected and they are kept safe in the brain. The affect is only on new memories. When a person gets damage to the hippocampus of the brain, he loses the ability to store new memories but all those memories which have a relation with his past, are kept safe in the brain. But it is not the case with skills and abilities of a person. Skills don’t get affected by the damage to hippocampus. Even new memories which are related to the skills and habits of a person can be formed without a proper functioning hippocampus in the brain (Buzsaki, 2006). There are various researches which are being made these days by the researchers in the medical field in order to determine those memories which don’t get affected due to improper functioning of hippocampus. These researches are also being made for the purpose of knowing how we can use these forms of memories for the process of rehabilitation. Hippocampus is extremely sensitive reductions in the oxygen level needed in the body of any human being (Domany, Hemmen & Schulten, 1994). Reduction of appropriate level of oxygen in the body leads to severe damage to the hippocampus of the brain. The reasons by which oxygen reduction may occur in the body of a human being are respiratory failure, near drowning, carbon monoxide poisoning and a heart attack. Mnemonic functions of hippocampus If we discuss functions of hippocampus in the brain of a human being, we should categorize its functioning in two major parts. First part is the role of hippocampus in the general memory of the human being and the second part is its role in the spatial memory and navigation of the brain. Let’s describe both of these functions of hippocampus in detail. Role of hippocampus in general memory It is generally considered in the fields of psychology and neurosciences that the precise role of hippocampus in the brain of any individual is a little controversial but it is agreed by both of the fields that appropriate working of hippocampus is very essential and critical in storing new memories in the brain. When the hippocampus of the brain will be in good condition, it will help the brain in storing those memories that an individual experiences in his daily life (Shaw, 2003). And when this structure of the brain will get damaged, it will have an adverse affect on the storing ability of the brain regarding new memories. Hippocampus is also considered as a part of medial temporal lobe memory system which is responsible for that sort of memory that can be verbalized explicitly (Levine, Brown & Shirey, 2000). These memories are also known as declarative memories like memories for facts which are in addition to episodic memory. We know from the evidences that declarative memories sometimes last a lifetime. But after a period of consolidation, hippocampus of the brain proves to be crucial and essential for the purpose of retention of those memories. Profound difficulties occur in the formation of new memories when damage to the hippocampus occurs (Maass & Bishop, 2001). This damage leads to the inability of the brain to store new memories. Damage to the hippocampus not only causes anterograde amnesia but also retrograde amnesia. In retrograde amnesia, some parts of the older memories also get affected. The memories which get affected due to retrograde amnesia are usually a few years back from the damage of the hippocampus (Hemmen, Cowan & Domany, 2002). But when we talk about the role of hippocampus in the general memory, we must mention that it has got critical importance in the preservation of new and old memories in the brain. Talking about effect of damage to hippocampus on the memories of the brain, all types of memories don’t get affected by the damage to hippocampus (Cacioppo, 2002). The memories which don’t get affected are newly learned skills and abilities of a person (Wermter, Austin & Willshaw, 2001). So we can say that the role of a well working hippocampus is crucial for the storage of memories in the brain. If the hippocampus is damaged, severe affects can be seen on the brain’s memory storing ability. Role of hippocampus in spatial memory The role of hippocampus is also very important in preservation of spatial information and memories in the brain. When the hippocampus of the brain will not be functioning efficiently, it will be very difficult or almost impossible for the brain to memorize the places where the person is at that time or those places where that person has to go. Another important role of hippocampus is to find out the new routes or the shortcuts for the places to be visited by any individual. While navigating, hippocampus plays an important role and those persons who have got the ability of memorizing places and navigating between those places efficiently, it is said that these persons have got relatively bigger hippocampi as compared to other persons. We can take an example of two cab drivers. Let’s say the hippocampus of first cab driver is perfectly working but the second driver’s hippocampus is damaged. Now out of these two cab drivers, the first driver whose hippocampus is perfect will be able to navigate between the places more efficiently rather than the other one whose hippocampus is not perfect. So, having discussed the role of hippocampus in the storage of general memory and in spatial memory, it can be concluded that hippocampus plays an effective and critical role in forming and preserving memories in the brain. Striatum Before we move on to discuss functions of striatum in the brain, we must first get to know the actual purpose of striatum in the brain of a human being. Striatum is a part of the basal ganglia and it is a very big collection of nerve cells. Striatum consists of caudate nucleus and the putamen whose purpose is to control the movements and balance of an individual. Basal ganglia are that part of the brain which is used for the purpose of voluntarily controlling the movements and also for the participation in motivational, emotional and cognitive aspects of the movements (Eeckman & Bower, 1993). Basal ganglia have not got any sort of direct connection with the spinal cord of an individual and belong to the extra pyramidal system (Bower, 1997). It not only controls voluntary eye movements but also controls the facial muscles. When we talk about striatum in terms of neurons, we can say that striatum is homogeneous and is composed of some neuronal cell types which are: Deiters’ neurons Spiny neurons, and Cholinergic interneuron When it comes to differentiation of striatum, it can be said that striatum is differentiated on the basis of immunochemical characteristics. The disease which results due to the loss of dopaminergic innervation to the striatum is Parkinson’s disease (Gerstner & Kistler, 2002). Another factor of striatum, atrophy, results in Huntington’s disease, dyskinesias and choreas. Functions of striatum If we talk about the functions of striatum, we can say that it plays a critical role in the value based decision making process. A large number of significant evidences show that the role of striatum is also in selection of any particular action. And also when it comes to evaluation of the actions, striatum’s role in that process can not be foregone (Feng, 2004). The role of the striatum is also in instrumental conditioning. Striatum plays a major role in mediating the response processing which is revealed by the focal excitotoxic lesions (Bear, Connors & Paradiso, 2007). If we talk about the role of discrete striatal areas, we come to know that though it is functionally disable but plays a major role in the organization of responding in the space. In order to get an insight on this specific matter related to striatum’s involvement in action selection and evaluation, let take an example of a rat in which we recorded the neuronal activity in the dorsal and the ventral striatum of the rat who was supposed to carry out a two armed bandit action. Not only that, we also examined and scrutinized the temporal profiles of those neural signals that were directly related to the rat’s choice, the outcomes or results of the neural signals and the action value. At the end of the test, we found that the signals that were related to the forthcoming choice of rat were considerably weaker and appeared only in the dorsal striatum earlier than the behavioral expression of the choice of the rat. But when the rat exposed its choice, not only those signals that were related to the choice but also the value began to increase quite sharply which continued until the results of the choice of the rat’s action were exposed. Some neurons that were present in the structures conveyed signals which were related to the choice, results and the value of the action that was chosen by the animal. So, all those components were found in the striatum that were essential for the updating process of the value of the chosen action. So, the outcomes of the experiment showed that striatum corresponded to those values which were linked with the potential choices earlier than the rat’s choice of action. It also updated the value of the action that was chosen when the result of the action was revealed. Amygdale Having discussed hippocampus and striatum, let’s now put our focus on amygdale. It is named because of its resemblance with the shape of almonds. It is that set of the nuclei in the brain that is located very closely to each other and for this reason they are grouped under the same name. Amygdale is collection of those nuclei which are present in the anterior portions of the temporal lobes in the primates’ brain (O’Reilly & Munakata, 2000). If we talk about the most prominent and visible amygdales, these are: The Centro medial nucleus The bastolateral complex, and The cortical nucleus Amygdale is said to be a part of the limbic system and its purpose is to regulate the emotions. The basic purpose and responsibility of the amygdale is the regulation of the emotions which are generated by any individual (Parks, Levine & Long, 1998). The most common emotions with which the amygdale is associated are fear, anxiety and nervousness. These are the emotions with which amygdale is closely associated and work under the regulations set by amygdale in the limbic system of the brain. The size of amygdale is directly related to the level of aggression and violence in any specific individual (Rugg, 1997). There are two amygdales present in the limbic system of the brain. Both of the amygdales are arranged symmetrically near the center of the brain of a human being and are located above the thalamus (Rapp, 2001). The length of both of the amygdales is approximately one inch. Several researches are being made on amygdale as it is one of the latest fields to be researched on. Talking about the researches, we are able to discuss some important functions of amygdale which are revealed due o the current researches in this specific field. Functions of amygdale Amygdale plays a critical role in the general purpose defense response control network. Amygdale plays an important role in the activation of several emotions. Some of these emotions are avoidance, anger, evasion and defensiveness. Another major function of the amygdale is that it activates the ancestral signs of distress and defensive postures. Amygdale not only activates the emotions of fear in an individual but also it is able to judge these emotions in other persons (Gazzaniga, 2000). Now if we talk about effects of a damaged amygdale in an individual, we can say that a damaged amygdale creates and develops autism and social blindness in an individual. Evidences have proved that amygdale activates the emotions of an individual so when it gets damaged, activation of emotions becomes unable and a person gets in the disease of social blindness. Amygdale suppresses the periaqueductal gray which is known as another major structure used for the purpose of interpretation of the emotion of fear (Kosslyn & Andersen, 1995). Amygdale has got direct implications on anxiety and fear stages. Not only amygdale but also its central nucleus interacts with various regions of the brain that includes autonomic response, breathing control, release of hormones, motor functions and processing of information. Amygdale plays a significant role in not only forming but also storing the memories that are linked with the emotional events (Farah & Feinberg, 1997). Amygdale also performs a critical role in formation ad storage of memories. These memories are linked with the emotional events and are saved in the memory of any individual. Evidences have shown that in the condition of fear, sensory stimuli arrive at the basolateral complex of amygdale in order to form the links between the memory and the stimuli. Amygdale plays an important role in modulation of memory consolidation and appetitive conditioning (Parkin, 1996). Another role of amygdale is that it mediates the effects of emotional arousal on the potency of the memory of any specific event which is another very important and a significant function regarding amygdale. References Andersen, P., & Morris, R., Amaral, D., Bliss, T., & O’Keefe, J. (2007). The hippocampus book. New York, NY: Oxford University Press. Cohen, N., & Eichenbaum, H. (1993). Memory, Amnesia, and the Hippocampal system. U.S.A: The MIT Press. Traub, R., & Miles, R. (1991). Neuronal networks of the hippocampus. New York, NY: Cambridge University Press. Buzsaki, G. (2006). Rhythms of the brain. New York, NY: Oxford University Press. Shaw, J. (2003). The brain’s alpha rhythms and the mind. Amsterdam: Elsevier Science. Levine, D., Brown, V., & Shirey, V. (2000). Oscillations in neural systems. New Jersey: Lawrence Erlbaum Associates. Maass, W., & Bishop, C. (2001). 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