Startle response

The startle response is a defensive response to sudden or threatening stimuli, and is associated with negative affect.[1] Usually the onset of the startle response is a reflex reaction. The startle reflex is a brainstem reflectory reaction (reflex) that serves to protect the back of the neck (whole-body startle) and the eyes (eyeblink) and facilitates escape from sudden stimuli. It is found across the lifespan of many species. An individual's emotional state may lead to a variety of responses.[2]

Neuromotor examination

During neuromotor examinations of newborns, it is noted that, for a number of techniques, the patterns of the startle reaction and the Moro reflex may significantly overlap, the notable distinction being the absence of arm abduction (spreading) during startle responses.[3]

Acoustic startle reflex

The acoustic startle reflex is thought to be caused by an auditory stimulus greater than 80 decibels.[4] The reflex is typically measured by electromyography, brain imaging or sometimes positron electron tomography [5][6] There are many brain structures and pathways thought to be involved in the reflex. The amygdala, hippocampus, bed nucleus of the stria terminalis (BNST) and anterior cingulate cortex are all thought to play a role in modulating the reflex.[7][8] The anterior cingulate cortex in the brain is largely thought to be the main area associated with emotional response and awareness, which can contribute to the way an individual reacts to a startle inducing stimuli.[9] Along with the anterior cingulate cortex, the amygdala and the hippocampus are known to have implications in this reflex. The amygdala is known to have a role in the “fight or flight” response, and the hippocampus functions to form memories of the stimulus and the emotions associated with it.[10] The role of the BNST in the acoustic startle reflex may be attributed to specific areas within the nucleus responsible for stress and anxiety responses.[11] Activation of the BNST by certain hormones is thought to promote a startle response [12] The auditory pathway for this response was largely elucidated in rats in the 1980s.[13] The basic pathway follows the auditory pathway from the ear up to the nucleus of the lateral lemniscus (LLN) from where it activates a motor centre in the reticular formation. This centre sends descending projections to lower motor neurones of the limbs.

In slightly more detail this corresponds to ear (cochlea) -> cranial nerve VIII (auditory) -> cochlear nucleus (ventral/inferior) -> LLN -> caudal pontine reticular nucleus (PnC). The whole process has a less than 10ms latency. There is no involvement of the superior/rostral or inferior/caudal colliculus in the reaction that "twitches" the hindlimbs, but these may be important for adjustment of pinnae, gaze towards the direction of the sound or the associated blink.[14]

See also

References

  1. ↑ Rammirez-Moreno,David."A computational model for the modulation of the prepulse inhibition of the acoustic startle reflex". Biological Cybernetics,2012,p.169
  2. ↑ "Peter J. Lang, Margaret M. Bradley, Bruce M Cuthbert. "Emotion, attention, and the startle reflex" 1990". Mendeley.com. Retrieved 2011-10-01.
  3. ↑ http://books.google.com/books?id=2chdTE4SHE8C&pg=PA472
  4. ↑ Rammirez-Moreno,David."A computational model for the modulation of the prepulse inhibition of the acoustic startle reflex". Biological Cybernetics,2012,p.169
  5. ↑ Pissiota,Anna. "Amygdala and Anterior Cingulate Cortex Activation During Affective Startle Modulation:a PET Study of Fear". The European Journal of Neuroscience,2003,p 1325
  6. ↑ Phillips, R.G. "Differential Contribution of Amygdala and Hippocampus to Cued and Contextual Fear Conditioning". Behavioral Neuroscience,1992,p.274
  7. ↑ Medford, Nick. "Conjoint Activity of Anterior Insular and Anterior Cingulate Cortex:Awareness and Response". Brain Structure and Function,2010,p.535
  8. ↑ Lee, Younglim. "Role of the Hippocampus, the Bed Nucleus of the Stria Terminalis, and the Amygdala in the Excitatory Effect of Corticotropin-Releasing Hormone on the Acoustic Startle Reflex". The Journal of Neuroscience,1997,p.6434
  9. ↑ Medford, Nick. "Conjoint Activity of Anterior Insular and Anterior Cingulate Cortex:Awareness and Response". Brain Structure and Function,2010,p.535
  10. ↑ Grouen, Wouter. "Amygdala and Hippocampus Enlargement During Adolescence in Autism".Journal of the American Academy of Child & Adolescent Psychiatry,2010,p.552
  11. ↑ Lee, Younglim. "Role of the Hippocampus, the Bed Nucleus of the Stria Terminalis, and the Amygdala in the Excitatory Effect of Corticotropin-Releasing Hormone on the Acoustic Startle Reflex". The Journal of Neuroscience,1997,p.6434
  12. ↑ Lee, Younglim. "Role of the Hippocampus, the Bed Nucleus of the Stria Terminalis, and the Amygdala in the Excitatory Effect of Corticotropin-Releasing Hormone on the Acoustic Startle Reflex". The Journal of Neuroscience,1997,p.6434
  13. ↑ Davis, M; Gendelman, Ds; Tischler, Md; Gendelman, Pm (Jun 1982). "A primary acoustic startle circuit: lesion and stimulation studies" (Free full text). Journal of Neuroscience 2 (6): 791–805. ISSN 0270-6474. PMID 7086484.
  14. ↑ Castellote, Jm; Kumru, H; Queralt, A; Valls-Solé, J (Feb 2007). "A startle speeds up the execution of externally guided saccades". Experimental brain research. Experimentelle Hirnforschung. Experimentation cerebrale 177 (1): 129–36. doi:10.1007/s00221-006-0659-4. ISSN 0014-4819. PMID 16944110.
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