Limbic System Flashcards

Question

Hippocampal damage just read

Answer 1

Damage relayed to the hippocampal region of the brain has reported vast effects on overall cognitive functioning, particularly memory such as spatial memory. As previously mentioned, spatial memory is a cognitive function greatly intertwined with the hippocampus. While damage to the hippocampus may be a result of a brain injury or other injuries of that sort, researchers particularly investigated the effects that high emotional arousal and certain types of drugs had on the recall ability in this specific memory type. In particular, in a study performed by Parkard, rats were given the task of correctly making their way through a maze. In the first condition, rats were stressed by shock or restraint which caused a high emotional arousal. When completing the maze task, these rats had an impaired effect on their hippocampal-dependent memory when compared to the control group,. Then, in a second condition, a group of rats were injected with anxiogenic drugs. Like the former these results reported similar outcomes, in that hippocampal-memory was also impaired. Studies such as these reinforce the impact that the hippocampus has on memory processing, in particular the recall function of spatial memory. Furthermore, impairment to the hippocampus can occur from prolonged exposure to stress hormones such as Glucocorticoids (GCs), which target the hippocampus and cause disruption in explicit memory.

Answer 2

The amygdala, another integrative part of the limbic system, is also involved in many cognitive processes. Just as in the hippocampus, memory seems to be impacted by processes in the amygdale; however, it is not spatial memory as in the hippocampus, but episodic-autobiographical memory (EAM) networks. The amygdala, as researched by Markowitsch,[16] was found to be responsible for the encoding, storage, and retrieval of these types of memories. To delve deeper into these types of processes by the amygdala, Markowitsch[16] and his team provided extensive evidence through investigations that the “amygdala’s main function is to charge cues so that mnemonic events of a specific emotional significance can be successfully searched within the appropriate neural nets and re-activated.” These cues for emotional events created by the amygdala encompass the EAM networks previously mentioned.

Answer 3

Besides memory, the amygdala also seems to be an important brain region involved in attentional and emotional processes. First, to define attention in cognitive terms, attention is the ability to home in on some stimuli while ignoring others. Thus, the amygdala seems to be an important structure in this ability. Foremost, however, this structure was historically thought to be linked to fear, allowing the individual to take action to rid that fear in some sort. However, as time has gone by, researchers such as Pessoa,[17] generalized this concept with help from evidence of EEG recordings, and concluded that the amygdala helps an organism to define a stimulus and therefore respond accordingly. However, when the amygdala was initially thought to be linked to fear, this gave way for research in the amygdala for emotional processes. Kheirbek[10] demonstrated research that the amygdala is involved in emotional processes, in particular the ventral hippocampus. He described the ventral hippocampus as having a role in neurogenesis and the creation of adult-born granule cells (GC). These cells not only were a crucial part of neurogenesis and the strengthening of spatial memory and learning in the hippocampus but also appear to be an essential component in the amygdala. A deficit of these cells, as Pessoa (2009) predicted in his studies, would result in low emotional functioning, leading to high retention rate of mental diseases, such as anxiety disorders.

Answer 4

Social processing is an area of cognition specific to the amygdala. To be specific, the evaluation of faces in social processing is of particular importance. In a study done by Todorov,[18] fMRI tasks were performed with participants to evaluate whether the amygdala was involved in the general evaluation of faces. After the study, Todorov concluded from his fMRI results that the amygdala did indeed play a key role in the general evaluation of faces. However, in a study performed by researchers Koscik[19] and his team, the trait of truthworthiness was particularly examined in the evaluation of faces. They investigated how brain damage to the amygdala played a role in truthworthiness, and found that individuals that suffered damage tended to confuse trust and betrayal, and thus placed trust in those having done them wrong. So Koscik demonstrated that the amygdala was involved in evaluating the truthworthiness of an individual. Yet, a man named Rule,[20] along with his colleagues, expanded on the idea of the amygdala in its critique of truthworthiness in others and performed a study in 2009 in which he examined the amygdala in its role of evaluating general first impressions and relating them to real-world outcomes with his study involving first impressions of CEOs. Rule demonstrated that while the amygdala did play a role in the evaluation of truthworthiness, as observed by Koscik in his own research two years later in 2011, the amygdala played a generalized role in the overall evaluation of first impression of faces. This latter conclusion, along with Todorov’s study on the amygdala’s role in general evaluations of faces and Koscik’s research on truthworthiness and the amygdala, further solidified evidence that the amygdala plays a role in overall social processing.

Answer 5

Paul D. MacLean, as part of his triune brain theory, hypothesized that the limbic system is older than other parts of the fore-brain, and that it developed to manage fight or flight circuitry, which is an evolutionary necessity for reptiles as well as humans. MacLean postulated that the human brain has evolved three components, that evolved successively, with more recent components developing at the top/front. These components are, respectively: 1 - The archipallium or primitive ("reptilian") brain, comprising the structures of the brain stem - medulla, pons, cerebellum, mesencephalon, the oldest basal nuclei - the globus pallidus and the olfactory bulbs. 2 - The paleopallium or intermediate ("old mammalian") brain, comprising the structures of the limbic system. 3 - The neopallium, also known as the superior or rational ("new mammalian") brain, comprises almost the whole of the hemispheres (made up of a more recent type of cortex, called neocortex) and some subcortical neuronal groups. It corresponds to the brain of the superior mammals, thus including the primates and, as a consequence, the human species. According to Maclean, each of the components, although connected with the others, retained "their peculiar types of intelligence, subjectivity, sense of time and space, memory, mobility and other less specific functions". However, while the categorizaton into structures is reasonable, the recent studies of the limbic system of tetrapods, both living and extinct, have challenged several aspects of this hypothesis, notably the accuracy of the terms "reptilian" and "old mammalian". The common ancestors of reptiles and mammals had a well-developed limbic system in which the basic subdivisions and connections of the amygdalar nuclei were established.[21] further, birds, which evolved from the dinosaurs, which in turn involved separately but around the same time as the mammals, have a well-developed limbic system. While the anatomic structures of the limbic system are different in birds than in mammals, there are functional equivalents.

Answer 6

Damage to the structures of limbic system results in conditions like Alzheimer's disease, anterograde amnesia, retrograde amnesia, and Kluver-Bucy syndrome.

Answer 7

The French physician Paul Broca first called this part of the brain le grand lobe limbique in 1878.[22] He examined the differentiation between deeply recessed cortical tissue and underlying, subcortical nuclei.[23] However, most of its putative role in emotion was developed only in 1937 when the American physician James Papez described his anatomical model of emotion, the Papez circuit.[24] Paul D. MacLean expanded these ideas to include additional structures in a more dispersed "limbic system," more on the lines of the system described above.[25] The term was formally introduced by Paul D. MacLean in 1952. Paul D. MacLean developed the intriguing theory of the “triune brain” to explain its evolution and to try to reconcile rational human behavior with its more primal and violent side. He became interested in the brain’s control of emotion and behavior. After initial studies of brain activity in epileptic patients, he turned to cats, monkeys, and other models, using electrodes to stimulate different parts of the brain in conscious animals.[26] Furthermore, He then recorded the animals’ responses and, in the 1950s, he began to trace individual behaviors like aggression and sexual arousal to their physiological sources. He analyzed the brain’s center of emotions, the limbic system, and described an area that includes structures called the hippocampus and amygdala. Developing observations made by Dr. James W. Papez, he determined that the limbic system had evolved in early mammals to control fight-or-flight responses and react to both emotionally pleasurable and painful sensations. The concept is now broadly accepted in neuroscience.[27] Additionally, Dr. MacLean said that the idea of the limbic system leads to a recognition that its presence “represents the history of the evolution of mammals and their distinctive family way of life.”In the 1960s, Dr. MacLean enlarged his theory to address the human brain’s overall structure and divided its evolution into three parts, an idea that he termed the triune brain. In addition to identifying the limbic system, he pointed to a more primitive brain called the R-complex, related to reptiles, which controls basic functions like muscle movement and breathing. The third part, the neocortex, controls speech and reasoning and is the most recent evolutionary arrival.[28] The concept of the limbic system has since been further expanded and developed by Walle Nauta, Lennart Heimer and others.

Answer 8

There is recent controversy over the use of the term limbic system, with scientists such ss Ledoux arguing that the term be considered obsolete and abandoned.[4] Originally, the limbic system was believed to be the emotional center of the brain, with cognition being the business of the neocortex. However, cognition depends on acquisition and retention of memories, in which the hippocampus, a primary limbic structure, is involved: hippocampus damage causes severe cognitive (memory) deficits. More important, the "boundaries" of the limbic system have been repeatedly reedfined because of advances in neuroscience. Therefore, while it is true that limbic structures are more closely related to emotion, one must think of the brain as an integrated whole.