The Role of the Amygdala in Fear Processing - Report Example

In terms of fear and its causes the search for an exact definition entails a level of uncertainty amongst neuroscience researchers. Much more is understood in regards to the physiological and metabolic effects of fear than a mechanistic determination of the precise brain chemistry involved in the process of fear and/or fear conditioning. Although there are certain studies that provide evidence of a localization of the fear response within the brains temporal lobe, as has been revealed through epilepsy studies. (LeDoux et al. 1995) The most functional justifications for the fear/panic response is an evolutionary self-preservation mechanism with the obvious intent of preserving the organisms safety in situations of predation or other forms of physical danger. (Holt, 2008) the essentials of the mechanism that initiates the fear/panic response appears to be rooted in a signaling process directed towards the amygdala. This region upon receiving the signal appears to demonstrate a priority stimulus, by which the relative importance of a particular external phenomena is impressed into a neural cellular pattern that can trigger emotion – based responses. This would include the fight or flight mechanism, common to virtually all chordates, including humans. (Blanchard, 2008) as well as other emotional states that are responsible for the regulation of the appropriate endocrine functions that would permit the appropriate response, such as increased output in the adrenal glands for instance. Researchers have found over the years that while a particular unpleasant stimulus can trigger the fear response in the amygdala of humans and other mammals, there is also the possibility of a fear stimulus based simply on the threat of an event; through the mechanism of fear conditioning. The fear response has been studied in regards to the contributions of the human amygdala; which demonstrates involvement at all stages of fear/panic conditioning or phobia acquisition. (Delgado et al. 2006) Classical studies have warned human subjects that a particular color presentation will presage a mild electric shock to the wrist, and the reactions garnered from the subjects prove that in humans physiological conditioning to fear can be easily achieved, in a process called instruction acquisition. (Hugdahl & Ohman, 1977) Activity in the left amygdala could be measured using functional magnetic resonance imaging even though during the course of the study, none of the subjects actually received the mild electric shock to the wrist that they were initially promised. (Phelps et al. 2001) The amygdala itself is described by Holt (2008) as an almond shaped organ where memories, especially those relating to intense emotions are stored. Its role in memory and attention is also verified by Phelps. (Phelps, 2004) As with many cellular and neurological structures, animal studies provide evidence of this role through the typical experimental method of damaging/disabling the organ or structure, and then documenting the resulting pathologies. The strategies for elucidating the role of the amygdala might include surgical excision as a possibility, (in animal studies) (LeDoux, 1995) but studies have demonstrated that less invasive sonic stimuli can produce an effective, unconditioned fear stimulus – apparently disconnected to a specifically identifiable experiential trauma. (LaBar, 1996), unfocused White noise is effective as a fear stimulus as well. (Helmstetter & Bellgowan) Early studies demonstrate the importance of high-decibel sound as a tool for avoidance conditioning in animal models. Among primates, the amygdala is located within the anterior region of the temporal lobe. But it also serves as a central nexus of coordination for several other important functions of the limbic system, including the frontal cortex, and the olfactory system. (Isaacson, 1984), (Holt, 2008) the amygdala later works to communicate with the prefrontal lobe, or the hippocampus as well as the hypothalamus. Conditioning, in terms of fear specifically involves the basolateral complex. (Campeau, 1995) In some cases the amygdala also has an effect on the core of the medulla oblongata – otherwise known as the brain stem. (Holt, 2008) In this case it is important to distinguish categories of brain activity in the interest of greater specificity, the writings of Holt (Holt, 2008) attempt to distinguish between an emotion and what is termed in the popular parlance a feeling. An emotion can be understood as a definable pattern of neural activity that can be tracked by objective instrumentation, such as an electroencephalograph. A feeling on the other hand, is a label given to psychological phenomenon that may be rooted in past emotions, but are essentially functions of the conscious mind. The impressions formed from real experience can inform emotions, but their characteristics demonstrate consistency between the brains of different individuals as dependent upon conserved similarities in human neuroanatomy. Current studies of the fear process centered on the amygdala represent a departure from the ideas that informed more traditional methods. Phelps describes approaches involving the quantification of cognition from the perspective of information processing. This method tended to downplay the importance of emotion in terms of active comprehension and to the extent that our emotions are intertwined with memory. But the role of the amygdala and studies thereof allow researchers to explore the connection between emotion and cognition. Indeed, the information processing function of the brain is incompletely understood as long as we ignore the functions of emotional learning, as well the ways our emotions influence the functions of attention and attentiveness. (Phelps, 2006) work from animal models has proven important for highlighting the interconnection between emotion and cognition in the human brain. (LeDoux, 1996) While the amygdala has an important role in emotion processing, it is interconnected with other parts of the brain, such as the visual cortex where a system of reciprocating connections can stimulate activity concerning emotional significance before conscious awareness or recognition occurs. (Moris et al. 1998), (Whalen et al. 1998) highlighting the importance of emotional memory, there is evidence that the amygdalas function of enhancing attention and awareness to a possible threat may be transient. (Morris et al. 1998) This may be the result of a network between different brain regions assigning emotional significance towards a particular stimulus. The amygdala can evaluate the importance of visual stimuli before conscious awareness, and it is probable that the amygdala interacts with sensory cortical regions of the brain to a varying degree in response to the priority of a certain stimulus. Thus, there is a subjectivity in the early responsiveness of the amygdala which appears to be dependent upon the initial priority designation of that event, in terms of its potential danger or relevance to the individual. This evaluation appears to be essential to the enhancement of attention. (Davis & Whalen, 2001), (Costafreda et al. 2008) We have all experienced incidents in which a profound memory, with accompanying emotional and/or fear-based involvement can place the mind back into the same emotional state as that which triggered the formation of the memory, the emotions are a part of the process. Fear in particular, can be conditioned, enhanced, or rendered extinct through an emotional memory process. (Schafe, 2004) This function occurs in the amygdala. Numerous studies involving cognitive neuroscience have demonstrated the function of emotional arousal in the retention of episodic memories, in association with amygdala activity. (Berlyne, 1969), (Heuer & Reisberg, 1992) the degree of activation of the amygdala can predict the later ability to recall and retain emotional stimuli. Brain imaging studies have documented that the initial prioritizing should the amygdala receives in response to a particular phenomenon relegates that phenomenon towards a certain degree of priority. The memory of emotionally charged episodes is dependent upon this initial encoding process within the amygdala, (Dolcos et al. 2004) and also in association with the anterior hippocampus. (Stefanacci et al. 1996) The elucidation of these functions yields obvious applications for the understanding of fear; or fear-based conditioning. Adding to our understanding of the role the amygdala can play in terms of threat perception and conditioning, researchers have also investigated the possibility of a broader role in the identification of complex social cues and various behavioral signals within social settings. But the social consciousness common among higher mammals as well as within ourselves gives us a penchant for ascribing social signals even where the other agency does not genuinely express them; there exists a sensitivity for non-social stimuli to serve as a source of social signals. This is commonly seen in the context of anthropomorphism. (The dog is not really smiling when he pants, but we have an awareness of such displays that the idea nonetheless occurs to us.) Studies of this sort aid our understanding of facial threat cues, based in the amygdala. (Armony & LeDoux, 2000) Classical experiments have been conducted with the intent of confirming the role of the amygdala in terms of anthropomorphic tendencies, as well as for the purposes of fully categorizing the organs function through the disabling of the physical structure. The role of the amygdala in social awareness and conditioning was demonstrated in a study that displayed to subjects of film of various geometric shapes moving around the confines of a box. The shapes were simplistic, but their motions were energetic enough that normal subjects were able to describe the geometric forms as agencies possessing motivation interacting with one another in a social environment. (Heider & Simmel, 1944) However, patients suffering amygdala damage, when viewing these exact same shapes and motions were only able to describe them in terms of their literal movements, with no implications for underlying emotional projection. (Heberlein & Adolphs, 2004) It is apparent that out understanding of the cognitive neurology of the amygdala, pertaining to strong emotional conditioning (such as fear) is a field for which continuous research is needed. The functions of emotion itself demonstrate an architecture equal in complexity to the concepts of reason or memory. (Russel & Barrett, 1999) The division of human cognitive function into strictly rational and emotional spheres is not as clear-cut as early investigators believed. REFERENCES Armony & Le Doux. 2000. How danger is encoded. In M. S. Gazzaniga (ed) The New Cognitive Neurosciences. Cambridge: MIT Press Blanchard, R. J et al. (2008). Handbook of Anxiety and Fear, vol 17 Campeau, S., & Davis, M. (1995). Involvement of the central nucleus and basolateral complex of the amygdala in fear conditioning. The journal of Neuroscience, 15(3):2301-2311. Costafreda, S. G., et al. (2008). Predictors of amygdale activation during the processing of emotional stimuli: a meta-analysis of 385 PET and fMRI studies. Brain Reserch reviews, 58, 57-70. Davis M, Whalen PJ. 2001. The amygdala: vigilance and emotion. Mol. Psychiatry 6:13–34 Delgado, M.R. Olsson, A. Phelps, E.A. (2006). Extending animal models of fear conditioning to humans. Biological Psychology. 73: 39–48. Dolcos F, LaBar KS, Cabeza R. 2004. Interaction between the amygdala and the medial temporal lobe memory system predicts better memory for emotional events. Neuron 42:855–63 Heider F, Simmel M. 1944. An experimental study of apparent behavior. Am. J. Psychol. 57:243–59 Helmstetter FJ., Bellgowan PS. (1994). Hypoalgesia in response to sensitization during acute noise stress. Behavioral Neuroscience, 108, 177-185. Holt D, 2008. The Role of the Amygdala in Fear and Panic. SerendipUpdate on Tue, 01/08/2008 - 11:16am Biology 202. http://serendip.brynmawr.edu/exchange/node/1749. Accessed 3/7/2012. Hugdahl K, Ohman A. 1977. Effects of instruction acquisition and extinction of electrodermal responses to fear-relevant stimuli. Her J. Exp. Psychol. Hum. Learn. Mem. 3:608– Isaacson R. 1982. The Limbic System. Plenum Press, New York, NY, 1982 LaBar KS, LeDoux JE, 1996. Partial disruption of fear conditioning in rats with unilateral amygdala damage: correspondence with unilateral temporal lobe activity in humans. 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Organization of connections between the amygdaloid complex and the perirhinal and parahippocampal cortices in macaque monkeys. J. Comp. Neurol. 375(4):552–82 Whalen PJ, Rauch SL, Etcoff NL, McInerney SC, Lee MB, Jenike MA. 1998. Masked presentations of emotional facial expressions modulate amygdala activity without explicit knowledge. J. Neurosci. 18:411–18 Read More