Memories affect people’s actions and behavioral algorithms. They could make people to be strong and confident or take wrong decisions. Significant memory elements are integrated and stored in the temporal lobes and are impacted by the hippocampus. In this connection, the paper is aimed at revealing peculiarities connected to memory and learning activities focusing on several types of memory including episodic, semantic, and procedural memories.
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The hippocampus is a brain region in the form of a horseshoe that plays an essential role in the transformation of information from the short-term memory to the long-term memory. It is a part of the limbic system associated with emotions. The hippocampus is engaged in such complex processes as the formation, organization, and storage of memories. As both sides of the brain are symmetrical, the hippocampus could be found in both hemispheres.
The hippocampus is essential for the memory and its structure. According to Wicking, Nees, and Steiger, “hippocampus memory tests are used to assess functions related to the process of declarative memory involving episodic memory semantic memory, and procedural memory” (61). However, it is known that the long-term storage of memories involves the frontal cortex as well and the memory increasingly depends on the frontal cortex and less from the hippocampus with time.
There are several types of the long-term memory, and each of them depends on the particular set of storage and retrieval of memories. Declarative memory is the memory concerning facts and knowledge. It allows a person to keep in mind that London if the capital of Great Britain or that about seven billion people live in the world, for example. There are three types of the declarative memory:
- Episodic memory is the memory concerning events. It allows humans remembering events of childhood, or what they ate for breakfast. It is associated with the hippocampus.
- Procedural memory is engaged with experience and skills. For example, it is responsible for the memory of how to ride a bicycle, drive a car, or play a musical instrument. Initially learning these skills requires plenty of efforts, but then they become automatic.
- Semantic memory is the memory concerning meanings and concepts. It is necessary to read and uses the ability to memorize meanings of words.
Complete removal of the hippocampus makes it impossible to form new memories. The case with the patient H.M. is a convincing argument that proves the above statement. Henry Gustav Molaison has suffered from epilepsy since childhood. After the application of conventional methods, his doctor understood their uselessness and suggested to carry out a complicated operation by removing the temporal lobe and the hippocampus part (Cacioppo and Freberg 332). After surgery, epileptic seizures did not recur, but another much more serious problem appeared.
As a matter of fact, Molison ceased to learn new facts. Only old information remained in his head as he remembered events happened 10-20 years ago. However, it is especially important to point out that in a case like this one, he was able to learn to play a musical instrument and computer games. Nevertheless, he did not remember when and how he learned it. Molison suffered from severe anterograde amnesia, although his procedural memory was not impaired, he could no longer remember events of the short-term memory. Despite this, he could, for example, learn new motility skills though he could not later recall how he learned them.
Moreover, disturbances in the hippocampus could lead to Korsakoff syndrome, which is also expressed in the inability to capture current events while preserving the old memory. All of this assures that the hippocampus plays a key role in the mechanism of memory.
It is also should be noted that fMRI and EEG examine the episodic memory formation. It was stated by scientists that brain activity during encoding phase could forecast if the issue would be remembered or not in the test phase. For example, men and women have different emotional memory. Scientists from Stanford University scanned brains of 12 men and 12 women, and they were shown a series of 96 images, some of which were neutral, boring, and other emotionally-charged, or alarming (Murty et al. 3461).
Three weeks later, participants were shown the same images plus 48 new and proposed to recall any of the 144 images they are already familiar with. As a result, men and women remembered boring pictures to the same extent while women remembered emotionally charged scenes 10-15 percent better. Besides, during the scanning of emotionally charged images, different parts of the brain of men and women became more active.
The left side of the brain of women shone brighter than the right one, men’s brains scanning represented the opposite situation. Since the left side of the brain is associated with speech, researchers suggested that viewing emotional scenes evoked in women internal dialogue that contributed to a better memorization of these pictures. Therefore, the scanning forecasted that emotional pictures would be better remembered by women rather that by men.
Speaking of the semantic memory, the experiment of Huth et al. should be mentioned. Scientists decided to investigate humans’ brain activity during the natural movie. They used fMRI scanning to determine the arrangement of items in the human brain. All in all, Huth et al. stated that “across the cortex, semantic representation is organized along smooth gradients that seem to be distributed systematically” (1219). It shows that every concept does not place in a particular brain region, but concepts distributed in the brain. In addition, the hippocampus participates in other forms of learning as well, for example, in spatial learning like in the case of taxi drivers who increase the volume of their hippocampus due to their professional experience.
A human’s ability to remember comprises different activities of the brain. The brain sends special sample signals in accordance with the event occurred and creates neuronal connections called synapses. After that, one might note the consolidation of the memory when the event transforms from the short-term memory into the long-term memory so that people could remember it later. Usually, the above process occurs during sleep when the brain reproduces the same events which have arisen before to strengthen synapses. In this connection, it seems necessary to consider the short-term memory along with the working memory, too.
The short-term memory and the working memory consist of visuospatial sketchpad (visual semantics), episodic buffer (episodic LTM), and phonological loop (language) according to the model of Baddeley and Hitch (Hulme and Mackenzie 22). It is important to mention that different components of working memory occur in different parts of the brain.
According to the model, the working memory is a part of the long-term memory, and includes the short-term memory. The working memory contains only the information from the non-volatile memory in the active processing. Utilities supply the information to relevant fields of the brain including the implicit knowledge about language and visual-spatial world making easier to remember combinations of letters such as words and patterns.
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Speaking of the cellular level, it should be mentioned that synapses are one of the most vulnerable neurons and plastic components. It occurs due to the fact that interneuron contacts ripen unevenly, and it forms the basis for plasticity changes as a result of the learning process. There are short and long-term synaptic plasticities as well as potentiation and depression in the hippocampus.
The Frequency Dependency of NMDA Receptor-dependent Synaptic Plasticity in the Hippocampal CA1 Region of Freely Behaving Mice research based on stimulation revealed that the high-frequency tetanic electrode stimulation mimics the stimulation induced by learning increasing the plasticity. At the same time, the low-frequency stimulation decreases the synaptic strength. Scientists conclude that “plasticity responses are NMDAR dependent, suggesting that these phenomena are relevant for hippocampus-dependant learning” (Buschler, Jinzhong, and Manahan-Vaughan 2245). Therefore, brain synaptic plasticity and direct synaptic connections are crucial for learning and memory.
In conclusion, it should be stressed that hippocampus plays an integral part of learning and memorization processes. The surgical removal of parts of the hippocampus for the treatment of epilepsy leads to disability to acquire new information. However, such people could satisfactorily remember almost all the previously acquired information. Available evidence suggests that the hippocampus is used for storing and processing spatial information. Moreover, it affects learning processes and emotional memory. Also, the hippocampus is involved in the transformation of the short-term memory into the long-term memory. In addition, there is an obvious connection between the hippocampus and the synaptic strength.
Buschler, Arne, Jinzhong Jeremy Goh, and Denise Manahan-Vaughan. “Frequency Dependency of NMDA Receptor-dependent Synaptic Plasticity in the Hippocampal CA1 Region of Freely Behaving Mice.” Hippocampus 22.12 (2012): 2238-2248. Print.
Cacioppo, John T., and Laura Freberg. Discovering Psychology: The Science of Mind, Belmont, CA: Cengage Wadsworth, 2013. Print.
Hulme, Charles, and Susie Mackenzie. Working Memory and Severe Learning Difficulties, New York, NY: Psychology, 2014. Print.
Huth, Alexander G., Shinji Nishimoto, An T. Vu, and Jack L. Gallant. “A Continuous Semantic Space Describes the Representation of Thousands of Object and Action Categories across the Human Brain.” Neuron 76.6 (2012): 1210-1224. Print.
Murty, Vishnu P., Maureen Ritchey, R. Alison Adcock, and Kevin S. Labar. “FMRI Studies of Successful Emotional Memory Encoding: A Quantitative Meta-analysis.” Neuropsychologia 48.12 (2010): 3459-3469. Print.
Wicking, Manon, Frauke Nees, and Frauke Steiger. “Neuropsychological Measures of Hippocampal Function.” Frontiers of Neurology and Neuroscience 34.2 (2014): 60-70. Print.