Role of amygdala in the experience of fear

Role of amygdala in the experience of fear The amygdalae (from the Greek for almond) are two groups of almond-shaped nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans, (see Fig 1 below). Research has shown that the amygdalae perform a primary role in the processing and memory of emotional reactions, and are considered to be part of the limbic system. [pic] Fig 1: Location of Amygdala. (Image from: imemat.blogspot.com) The regions described as amygdalae are a combination of several nuclei with distinct functions. Among these nuclei are the basolateral complex, the cortical nucleus and the centromedial nucleus, (see Fig 2 below). The basolateral complex can be further subdivided into the lateral, the basal and the accessory basal nuclei. Anatomically, the amygdala and more particularly, its centromedial nucleus, may be considered as a part of the basal ganglia. The amygdala sends impulses to various parts of the brain, for example, to the hypothalamus to activate the symp athetic nervous system; to the thalamic reticular nucleus to increase reflex movement; and to the laterodorsal tegmental nucleus for the activation of various neurotransmitters such as dopamine, norepinephrine and epinephrine. The cortical nucleus is involved in the sense of smell and pheromone- processing. It receives input from the olfactory bulb and olfactory cortex. The lateral amygdalae, which send impulses to the rest of the basolateral complexes and to the centromedial nuclei, receive input from the sensory systems. The centromedial nuclei are the main outputs for the basolateral complexes, and are involved in emotional arousal in rats and cats. [pic] Fig 2: Nuclei of the rat amygdaloid complex. (ABmc = accessory basal magnocellular subdivision; ABpc = accessory basal parvicellular subdivision; Bpc = basal nucleus magnocellular subdivision; e.c. = external capsule; Ladl = lateral amygdala medial subdivision; Lam = lateral amygdala medial subdivision; Lavl = lateral amygdala v entrolateral subdivision; Mcd = medial amygdala dorsal subdivision; Mcv = medial amygdala ventral subdivision; Mr = medial amygdala rostral subdivision; Pir = piriform cortex; s.t. = stria terminalis). (Image from: Physiol Rev 83: 805) The amygdala filters sensory information and acts as a sort of interpretation channel. The basolateral amygdala receives sensory information from the thalamus and cortex and then forwards a signal to the appropriate target areas (see Figure 3 below). It is also known as the amygdala proper, and the several areas of the brain that it targets are part of a broader network that serves much more specialized functions. Because the basolateral amygdala is critical for emotion, a better understanding of the chemicals within these brain circuits should lead to improved pharmacological treatments for emotional dysfunction in psychiatric disorders. [pic] Fig 3: The basolateral amygdala. (Image from: Current Biology, Vol.10, (4)) Within most of these disorders i s a common symptom in that the patient often says I didnt think, I just reacted. Straker, D. (2006) believes they may be exactly right. All sensory data, with the exception of the sense of smell, is sent by the body first to the thalamus which then forwards it to both the relevant part of the cortex and to the amygdala. The information is sent out over two parallel pathways: the thalamo- amygdala pathway (the short route) and the thalamo-cortico-amygdala pathway (the long route). The short route transmits a quick estimated representation of the situation, in which no cognition is involved. This pathway activates the amygdala which, through its central nucleus, generates emotional responses before the mind can form a complete representation of the stimulus. The amygdala does a quick threat assessment by comparing the sensory data received with already stored fear responses. If any of these are triggered, then the amygdala floods the cortex with chemicals to stop it taking over. The r esult is action without conscious thought. (See Fig 4 below). Subsequently, the information that has travelled via the long route and been processed in the cortex reaches the amygdala and tells it whether or not the stimulus represents a real threat. Should a real threat be presented the amygdala will then activate the efferent structures responsible for physical manifestations of fear, such as increased heart rate and blood pressure, sweaty hands, dry mouth, and tense muscles. The parallel operation of our explicit (hippocampal) and implicit (amygdalic) memory systems explains why we do not remember traumas experienced very early in our lives. At that age, the hippocampus is still immature, while the amygdala is already able to record unconscious memories. Early childhood traumas can disturb the mental and behavioural functions of adults by mechanisms that they cannot access consciously. In complex vertebrates, including humans, the amygdalae perform primary roles in the formation and storage of memories associated with emotional events. Amunts et al (2005) indicate that, during fear conditioning, sensory stimuli reach the basolateral complexes of the amygdalae, particularly the lateral nuclei, where they form associations with memories of that particular stimuli. These associations between stimuli and the aversion may be mediated by long-term potentiation, a lingering potential for affected synapses to react more readily. Memories of emotional experiences that become imprinted in the reactions of synapses in the lateral nuclei produce fear behaviour through their connections with both the amygdalaes central nucleus and the bed nuclei of stria terminalis (BNST). These central nuclei are involved in the production of many typical fear responses, including freezing (immobility), tachycardia (rapid heartbeat), increased respiration, and stress-hormone release. Damage to the amygdalae impairs both the attainment and the expression of Pavlovian fear conditioning, which is a form of classical conditioning of emotional responses.    [pic]Fig 4: The Amygdala Bypass System. (Image from: www.changingminds.org) Advances in neuroimaging technology such as fMRI, have allowed neuroscientists to show just how much of a role the amygdala plays in many psychological disorders. Donegan et al. (2003) studied patients with Borderline personality disorder who showed significantly greater left amygdala activity than the normal control subjects. Some of these borderline patients even had difficulties classifying neutral faces or classed them as being threatening. In support of these findings, in 2006, researchers at Monash University, Australia, observed increased levels of activity in the amygdala when patients with social phobia were shown images of threatening faces or when they were confronted with frightening situations. These activity levels in the amygdala were in direct correlation with the severity levels of the social phobia. Similarly, depressed patients showed more activity in the left amygdala when interpretin g emotions for all faces, and especially for fearful faces, although this hyperactivity was normalized when patients were prescribed antidepressants. Cultural studies such as Williams et al (2006) showed that normal subjects exposed to images of frightened faces or faces of people from another race will show increased activity of the amygdala, even if that exposure is subliminal. However, according to Tsuchiya et al (2009), the amygdala is not necessary for the processing of fear-related stimuli, since people with bilateral damage show rapid reactions to fearful faces. Early research on primates has also provided explanations for the functions of the amygdala in relation to emotional disorders. An early study by Brown Shafer (1888) observed rhesus monkeys with a lesioned temporal cortex (including the amygdala) and found that they suffered from significant social and emotional deficits. Kluver Bucy (1939) later expanded upon this observation by showing that large lesions to the an terior temporal lobe produced not only fearlessness, but also severe emotional disturbances including increased sexual behaviour and a propensity to place objects in their mouths. Some monkeys also displayed an inability to recognize familiar objects and would approach both animate and inanimate objects indiscriminately, while also exhibiting fearlessness towards the researchers. This behavioural disorder was later named Klà ¼ver-Bucy syndrome. However, their study can be criticised in that these lesions were so large and crude when compared to todays techniques, that researchers werent exactly sure of the structures responsible for these significant changes in behaviour. Improved techniques, such as using the neurotoxin ibotenic acid to make more precise lesions are partly responsible for the more detailed understanding of the amygdale today. | | | |[pic] |   | Fig 5: Sensory data routes, the fear response and the amygdala. (Image from: http://thebrain.mcgill.ca/flash/index_a.ht ml) Previous studies have examined activation of the amygdala in response to emotional facial stimuli, but these have been carried out in either the U.S. or Western Europe, although none of these explored cross-cultural differences. Although culture shapes several aspects of human emotional and social experience, including how fear is perceived and expressed to others, very little is known about how culture influences neural responses to fear stimuli. In response to this gap in the research, a study by Chiao et al (2008) found that the bilateral amygdalas response to fear faces is, in fact, modulated by culture. Using fMRI, they measured the amygdalas response to fear and non-fear faces in two distinct cultures, Native Japanese in Japan and Caucasians in the United States. Both culture groups showed greater activation in the amygdala to fear expressed by members of their own culture, (their in-group), than in any of the other emotional measures such as anger, happiness or neutrality . (See Fig 6 below). [pic] Fig 6: The amygdalas response to fearful facial expressions is culture- specific. (Image from: Chiao et al 2008). As mentioned earlier, sensory data, apart from the sense of smell, is sent by the body to the thalamus and then forwarded to both the cortex and the amygdala. In relation to this sense of smell, when faced with a threatening situation, many organisms, including insects, fish and mammals, release volatile pheromones, signalling the danger to other members of the same species. Nearly 70 years ago, Karl von Frisch (1941), described the alarm response in a species of small freshwater fish called the European minnow (Phoxinus phoxinus). Frisch, who was one of the founders of the scientific study of animal behaviour, demonstrated that when a minnow was eaten by a predator, a chemical released from its damaged skin would be reacted to by other minnows that were close by. They would at first dart about randomly, form a tight school and then retreat fro m the source of the chemical. Frisch called this substance schreckstoff, meaning scary stuff, and we now know that similar chemicals are used throughout the animal and plant kingdoms. A team of researchers from the University of Lausanne in Switzerland (Brechbuhl et al, 2008) have shown that mice detect alarm pheromones by means of a recently identified sensory system in the nose by examining a structure called the Grueneberg ganglion (GG), which in mammals is located on both sides in the tip of the nose, close to the openings of the nostrils. When the GG was first discovered by Hans Grueneberg in 1973, its anatomy was not known in such detail and so it was thought to be a non-sensory structure. It is only very recently that the olfactory system has come to be viewed as containing 3 distinct channels, each with a unique structure and function. The main channel is involved in detecting aromatic molecules; the second channel is called the vomeronasal system, and is an accessory olfact ory system which is now known to be involved in the detection of pheromones; the GG constitutes a third component of the olfactory pathway, one that was thought to be involved in mother-pup recognition and suckling behaviour, because it is present at the time of birth. The researchers sought to investigate the role of the GG in behaviour. Because of its location, the GG is easily accessible, so they were able to cut the axons of GG neurons in live mice (axotomy), thus preventing any signals from reaching the brain. But after numerous tests for nipple finding and other possible functions, the team actually found that the ganglion played a role in danger communication. [pic] Fig 7: Scanning electron microscope images of the mouse Grueneberg ganglion. Left: a cluster of neurons (GC) in a meshwork of fibroblasts (Fb) Right: and a higher magnification of a single GG neuron (green), with its axon (red) and thin ciliary process (blue). Scale bars: 20 microns (L) and 5 microns (R). (Image f rom: Brechbuhl et al, (2008)). 30 days after the axotomy, the researchers then compared how mice with and without their Grueneberg ganglia responded to alarm pheromones. According to Broillet, the contrast was very striking. Normal mice with the ganglia showed fear immediately by freezing while mice without the ganglia seemed to be unaffected and they carried on as before, apparently unaware of the danger signals that affected the normal mice. Although their sense of smell did not seem to be affected as they were able to sniff out cookies hidden in their cages as well as the normal mice. This study clearly shows that in mice the GG is involved in detecting alarm pheromones, rather than in mother-pup interactions, as was previously thought. It is able to perform this primitive function thanks to a specialized yet very basic structure as the GG consists simply of a small group of cells separated from the external environment by a water-permeable sheet of epithelial cells. Its location , far away from the main olfactory system, enables rapid detection of alarm pheromones. Such a mechanism is crucial an organisms survival rate, and the GG is found in every mammalian species examined so far, including humans. However, whether or not alarm pheromones affect, or even exist in humans, has been a subject for debate in the scientific community. Since pheromones are not detectable by the human sense of smell, scientists believe that pheromones are sensed by the vomeronasal organ (VNO), part of the olfactory system and located inside the mouth or nose. For many years, the existence of the VNO produced much speculation because it had only been found occasionally in adult humans, and when it was found, it was believed to be vestigial. However, Johnston et al, (1985) conducted a study in which the noses of 100 human adults were examined post-mortem and the VNO was found in the septums of 70% of those examined. Since then, much evidence has been gathered to support these findi ngs of a presence of the VNO in most adult humans, but many scientists still believe it to be a functionless organ that was inherited from some ancestor of humans. However, recent genetic research has shown the possibility of a receptor in the nose that could sense pheromones. When searching the human genome for genes that had similar sequences to those of rodent pheromone receptors, a team of researchers from The Rockefeller University in New York and the Yale University School of Medicine identified for the first time a candidate pheromone receptor gene in humans. The findings, reported in Nature Genetics, may shed new light on the molecular basis of social communication between humans, including the fear response. In conclusion, despite the saying, have no fear, to live without the ability to experience and recognise fear is to be deprived of a vital neural mechanism that enables appropriate social behaviour, and possibly even survival.

How to Prevent Obesity Essay

We must stay active. This is an important step in preventing obesity. Join a gym or yoga class to stay slim and trim. Take the stairs or walk to do your chores. Simple steps like these can go a long way in preventing overweight and obesity. Joining a gym or yoga class will help you mingle with like-minded people who can give you valuable tips on how to prevent obesity. We must eat healthy foods.The Food and Drug Administration advises that one must consume about 2,000 calories each day. Ensure that you include legumes, vegetables, fruits, whole grain breads, meats and dairy items. To avoid obesity, your daily calorie intake must not exceed the number of calories expended. So, if you are not an active person, reduce your calorie intake to ensure your weight does not balloon up. We have to Drink Plenty of Water. Many people mistake thirst for hunger and start gorging. Drink plenty of water every day to flush out toxins and impurities from your system. Most health experts advise drinking eight to 10 glasses of water every day. Whenever you feel hungry, first try drinking water and see if that satiates you. Water is thus a great way to combat hunger pangs and ensure you do not overeat. We must eat only when you feel hungry. Research reveals that naturally thin people eat only when they feel hungry. If you do not feel hungry at regular meal time, then cut down your portion size and eat just enough food to keep you satiated and energetic for your daily tasks. Thus to prevent obesity, ensure you start eating only when you feel hungry. Do not store Junk food and soda. Do not keep any stock of junk food in your home. Stocking junk food will always tempt you to take a bite now and then. This can be harmful in the long run. So, be smart and avoid buying junk food in the first place. Similarly, avoid storing soda and sweet fizzy drinks in your fridge. These harmful beverages can also add on the flab and therefore should be avoided at all costs.

Prose Commentary, Pat Barker Essay

The title of the book from which this excerpt is taken, â€Å"Regeneration,† highlights what I see as the main theme in this thought provoking prose piece. This piece of prose raises images for me of the moist dampness, humid soil, death and the prospect of life arising from the continuation of the cycle of life and death. These Images are shown in phrases such as the final sentence, which says, â€Å"Now they could dissolve into the earth as they were meant to.† This sentence is the one which stuck out most to me in the whole excerpt; I found it very powerful in that it brings out the theme of â€Å"regeneration† to the reader and it is a sentence which sticks in your mind. I can see this as an overall whole picture, where â€Å"Burns,† who I view as a returning soldier, perhaps from the Gulf War given the date, experiences, and successfully faces one of his terrible fears, picked up from the war, of bloody, dead â€Å"corpses,† and through this finds the prospect of soul peace before him. I also see that nature and the cycle of life as a big theme in this excerpt as it shows up in nearly every line. Words such as, â€Å"rain,† â€Å"mud,† â€Å"trees† and â€Å"wind† support this. The narrative structure of this excerpt is also important, because it is as if the story of â€Å"Burns† is being told by someone else and so it is likely not subject to the bias of the actual person’s account. In the first three paragraphs, rain and the wetness of the land is a large part of describing, setting the scene and the tone of the rest of the excerpt. The author creates a feeling about â€Å"Burns†, that he is somewhat stranded, for the writing states, â€Å"He didn’t know what to do† and â€Å"so long since he’d been anywhere alone.† As well as creating a â€Å"lost† feeling this sentence confirms the thoughts, though not directly, that â€Å"Burns† is a returning soldier. The use of the words, â€Å"Raindrops dripped† with the repeated â€Å"d† sound, creates the patter of large raindrops. â€Å"Persistent† and â€Å"monotonous† link up with each other to remind the reader of the continuity of the wetness. When â€Å"Burns† reaches a fence, he sees that, â€Å"A tuft of grey wool had caught on one of the barbs.† Perhaps an animal had once quite recently struggled to free itself from this discontinuity in nature as â€Å"Burns† does when he too gets caught on a barb just like an animal. The repetition of the â€Å"b† sound in â€Å"Burns blinked,† carries on the theme of the persistence of the rain. Throughout the whole of the third paragraph there is another repetition of the â€Å"b† sound, this time though it is used to bring out the sound of the thud and plodding of â€Å"Burns† in â€Å"his mud encumbered boots†. There is also a repetition of the â€Å"s† sound in words such as â€Å"slipping and stumbling† for exactly that, to create the sound of someone slipping in the wet mud. The writer also uses words such as â€Å"cold†, â€Å"khaki† and â€Å"tight cloth† to create a chilling stiff sou nd to make the reader feel the cold that â€Å"Burns† is experiencing. In the next two paragraphs, the author makes the wind and its severity, an impacting factor on â€Å"Burns'† progress toward the safety that he seeks. The wetness of the setting which surrounds â€Å"Burns† is also again a major influence in his quest. The tone of these two paragraphs is much more severe than the first three. The author says that the wind tries to â€Å"scrape† â€Å"Burns† â€Å"off its side.† suggesting that the situation has become more intense. That line is very effective literally because the word â€Å"scrape† is an onomatopoeic word and when joined together with â€Å"side† it creates an alliterating â€Å"s† sound. The fact that he has to keep his â€Å"head bent† and the â€Å"Rain beat onto his head† both confirm the increased severity of the weather. When the weather is so bad that the distance vanishes in a â€Å"veil of rain†, the alliterating â€Å"v† sound bringing out the hum of the constant rain, â€Å"Burns'† survival instinct kicks in and he decides to take shelter, running â€Å"clumsily† toward a clump of trees. But again he is slowed to a walk because of the dragging mud. The words â€Å"mud dragged † are effective here, for even to say them together takes effort and your reading is slowed by them, amplifying their effect. The â€Å"sucking† of your reading is again shown in the words â€Å"mud-clogged boots†, the â€Å"d†, â€Å"g† and â€Å"b† sounds all together make the reader have to pronounce each syllable in a drawn out way. Where the author talks about, â€Å"the whine of shells† he is referring to the sound that you hear when you put a shell to your ear and compares it to the noise of the wind through the trees. In paragraph five the author shows the exhausted â€Å"Burns† so tired he cannot even be bothered to â€Å"wipe away† the rain drenching his face. In the next three paragraphs, the tone of the extract becomes quieter; there is neither mention of the intense rain nor the sound of it. The tone of the setting becomes almost sinister amongst the trees. â€Å"Burns† now in what he thinks is the safety of the trees continues to stumble and the writer again uses the repeated â€Å"b† sounds in the words, â€Å"began†, â€Å"stumbling†, â€Å"blindly† and â€Å"between† to show us that â€Å"Burns† has still not quite got his bearings right yet. The author uses the repeated â€Å"c† sounds in the words â€Å"catching†, â€Å"clumps† and â€Å"bracken† to the same effect. Because he is â€Å"stumbling† â€Å"blindly†, something â€Å"brushed† â€Å"Burns'† cheek and when he tried to push it away, his hand touched what he first thought to be slime. On turning to see what it was, â€Å"Burns† discovered that there was a â€Å"d ead mole, suspended, apparently, in air†. The use of commas in those few words are effective because they make the reader pause and thus put emphasis on a very important part of the extract, it begins the change in plot of the whole extract. â€Å"Its small pink hands folded on its chest.† suggests the authors’ feeling that the mole was innocent, but was still killed. The author provokingly compares the dead animals â€Å"Burns† sees to a â€Å"fruit† tree bearing, what the author makes you think are heavy fruit by using the word â€Å"laden†. Heavy fruit because they are generally more likely to smell of decay, which is what the dead animals are, decaying. The author quite interestingly uses animals from each part of the earth; the â€Å"magpies† from the sky; the â€Å"fox† from the ground and the â€Å"moles† from under the ground, this I see as a continuation of the regeneration theme carried on throughout the whole excerpt. I think that the fox scared â€Å"Burns† so much because it reminded of something that he saw in the war. Again in paragraph eight the trees are â€Å"against† â€Å"Burns†. The author uses the alliteration of the words â€Å"twigs tore† through the â€Å"t† sound to remind the reader of the snapping sound of twigs and the force that â€Å"Burns† was putting into getting away was enough to snap the twigs on his skin. It brings out how frightened he really was. The writer’s reference to â€Å"dead leaves† also fits in with the theme of â€Å"Regeneration† for dead leaves must â€Å"dissolve into the earth† to create nutrients for the trees from which they fell and thus continue the circle of life. In the short paragraph nine, the setting changes briefly once more because â€Å"Burns† goes out into the field once more. He splashes effectively through the alliterated â€Å"flooded furrows†, the â€Å"f† making the sound of the swishing water. â€Å"Burns† then hears a voice, probably the voice of a fellow soldier from the war. It is said to be the voice of a person named â€Å"Rivers†. I did find it quite ironic that the author of the book from which this excerpt is taken, would use the name â€Å"Rivers† for the voice which â€Å"Burns† hears because in Scotland a small river is called a burn. This brings out to me that the author is making the aspect of water very important to this particular scenario. I feel that the use of water here is important to the overall theme of regeneration because water is a key part in the cycle of life, it is the source of all life and so I think that this is why the author emphasises this point. The voice that â€Å"Burns† hears tells him that, â€Å"If you run now, you’ll never stop.† basically telling him to face his fear. This may be because perhaps â€Å"Burns† ran away from something before and did not face his fear. The last two paragraphs of the excerpt talk of â€Å"Burns† facing his fear, finding a peace amongst his dead â€Å"companions† and his finding a control which he did not have at the beginning of the excerpt. â€Å"Burns† turns back therefore facing his fears. The fact that the author talks about what the â€Å"real Rivers† might have said confirms that â€Å"Rivers† is a real person and he is probably still alive. When â€Å"Burns† lets down the dead animals he is allowing for the natural cycle of â€Å"Regeneration† to be complete. This seems to make him feel better for he sits down inside the circle of his â€Å"companions† who he no longer views as scary and is happy because, â€Å"Now they could dissolve into the earth as they were meant to do.† By facing his fear, â€Å"Burns† was regenerated in himself, this also made him content. The last line is the most important in the whole text; it sums up and puts into context the entire idea of Regeneration. In conclusion I would say that there is one main theme in this excerpt; it being the ongoing recurrence of the idea of â€Å"Regeneration† through the means of nature, water, the cycle of life and death and the facing of fear. It is also important to say that in order for regeneration to happen, something has to die.

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