This article must include a clear description of the startle response. This concern has been noted on the talk page where whether or not to include such information may be discussed.(December 2013)

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 reflectory. The startle reflex is a brainstem reflectory reaction (reflex) that serves to protect the back of the neck (whole-body startle) or the eye (eyeblink) and facilitates escape from sudden stimuli. It is found across the lifespan and in many species. An individual's emotional state may lead to a variety of responses.[2]

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During neuromotor examination 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 response.[3]

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 imagining 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[clarification needed].

^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

^Grouen, Wouter. "Amygdala and Hippocampus Enlargement During Adolescence in Autism".Journal of the American Academy of Child & Adolescent Psychiatry,2010,p.552

^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

^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