1887

n Suid-Afrikaanse Tydskrif vir Natuurwetenskap en Tegnologie - Hoekom skrik 'n mens vir koue pampoen? : research and review article

Volume 26, Issue 1
  • ISSN : 0254-3486
  • E-ISSN: 2222-4173

Abstract


The involuntary startle is part of the first rapid fear reactions an organism experiences in response to a sudden threatening stimulus. It is adaptive in the sense that it allows the organism to immediately withdraw from an object that might possibly be dangerous, while the higher centres of the brain are still busy processing whether the object is in fact dangerous. The involuntary startle reaction is colloquially described as "to jump with fright". This hair-trigger system is fine-tuned to protect organisms from danger and tends to err on the side of caution. Therefore, everyone has probably jumped with fright in response to an entirely harmless stimulus, for example mistaking a twig for a snake. This paper aims to explain why and how we jump with fright, even though we realise only milliseconds later that it was completely unnecessary to get a fright at all.
The fear centres of the brain are the amygdala, two small nuclei in the limbic system. Visual, auditory and olfactory input from the sensory organs is relayed to the amygdala via two different pathways. Like most types of sensory inputs to the brain the information that activates the fear response via the indirect route is routed via the thalamus to cortical areas where it is analysed in terms of previous experience quality and context. From here the analysed information reaches the amygdala - the cerebral structures generally associated with fear. Impulses from the amygdala will then stimulate the typical fear reactions. In contrast to the indirect route from thalamus to amygdala just described, a direct route is taken in the case of the startle reaction. Impulses from the thalamus are relayed directly to the amygdala and the person experiences the fear reaction and response before the information has been analysed by the cortical structures. This short-cut to the amygdala is a direct, fast and crude pathway from the senses through the relevant modalities to the thalamus to the central nucleus of the amygdala. In general its purpose is to prime the amygdala for detailed incoming information, but in conditions of sudden danger it provides for a rapid response to a potentially aversive situation. The advantage of the direct pathway is that it allows for a quicker reaction, almost half the time that it takes for the cortical input pathway to the amygdala. The startle reaction is essential when speed is more important than accuracy, for example, when a life may be at stake. The cortical pathway is indirect, slower and refined, which allows for cortical processing and thus a much more accurate presentation of the stimulus. This route can also inhibit an inappropriate fear response initiated through the direct route. In this paper the neuroanatomy, specifically explaining the direct and indirect (cortical) route by which perceptual information reaches the amygdala, is reviewed first. Then the physiology of the fear reaction is alluded to, after which we conclude with an integrating figure and state a few interesting implications.

Die onwillekeurige skrikreaksie vorm deel van die eerste vinnige vreesreaksies wat 'n organisme ervaar in respons tot 'n skielike bedreiging. Dit is voordelig in die sin dat dit 'n organisme toelaat om onmiddellik weg te beweeg van 'n voorwerp wat potensieel gevaarlik kan wees, terwyl die hoër breinsentra nog besig is om uit te werk of die voorwerp inderdaad gevaarlik is. Die skrikreaksie is daarop ingestel om die organisme te beskerm teen potensiële gevaar . Die onwillekeurige skrikreaksie onderlê wat in die omgangstaal bekend staan as "om te skrik vir koue pampoen", waar 'n individu skrik vir iets geheel en al onskadeliks, byvoorbeeld 'n tak wat aangesien word vir 'n slang - dus "eerder bang Jan as dooie Jan". Hierdie manuskrip poog om te verduidelik hoekom ons skrik, al besef ons 'n paar millisekondes later dat dit geheel en al onnodig was. Die onderliggende neuroanatomie, met verwysing na die direkte en indirekte (kortikale) bane waardeur sensoriese inligting die amigdala bereik, word hersien. Die fisiologie van die vreesreaksie word kortliks bespreek en die skrywe word afgesluit met 'n integrerende figuur en 'n paar interessante implikasies van die onwillekeurige vreesreaksie.

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/content/aknat/26/1/EJC20405
2007-03-01
2019-08-24

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