The startle response is a sudden, reflex-like response to an unexpected stimulus, such as a loud noise or bright light. It is an unlearned and largely unconscious defense mechanism shared by animals and humans. The startle response occurs when stimuli startle someone or something.
The startle response consists of a sequence of skeletomuscular contractions typically measured by eyeblinks in humans. In rodents, full or partial muscle contractions are displayed through head, neck, back, paw, or tail movements and can be seen in the face as an expression of fear.1 The facial and skeletal muscles react within a few milliseconds during a startle response.
Habituation is a non-associative learning process in which an innate response is weakened after an organism is frequently exposed to a particular stimulus. This occurs as the organism becomes accustomed to the stimulus and knows it is non-threatening.
Animals and humans exhibit startle response and habituation. This process allows organisms to conserve energy by not responding unnecessarily to nonthreatening stimuli.
Startle response habituation, sometimes called sensory filtering, occurs when an organism responds less to a stimulus with repeated exposure. This post provides an overview of startle response habituation and its significance.
Image Credit: Kateryna Kon/Shutterstock.com
How startle response works
The startle response involves neural pathways handling the body’s reaction to loud auditory stimuli. Sensory receptors, such as the ears or eyes, observe information and then pass it through the sensory neurons to the brain’s inferior colliculus.
Once there, the information is communicated to the amygdala, where emotional responses are processed, before a signal is sent to the hypothalamus, activating the sympathetic nervous system to trigger a startle response.
The body’s automatic “fight or flight” reflexes include common startle responses such as increased heart rate, muscle tension, rapid breathing, and twitches. In addition to movement responses, a startle response can invoke anxiety or fear and boost an organism’s alertness.
Startle response habituation
Ongoing exposure to safe stimuli enables an organism to learn that it is free from threat. This startle response habituation occurs when the brain learns which stimuli are safe, and the body’s startle reflex to that stimulus decreases. This process is key in decreasing stress and anxiety.
As organisms begin to distinguish between what is threatening and what is not, their bodies react accordingly. When non-threatening stimuli emerge, the brain recognizes that the organism is safe and does not initiate a fight-or-flight response, reducing anxiety, stress, and physical responses to a minimum.
Understanding how startle response habituation works is important for many therapeutic practices, including exposure therapy and cognitive-behavioral therapy, which help individuals overcome conditions such as anxiety disorders, phobias, and schizophrenia,2 as well as stress and fear when met with non-threatening stimuli.
Startle response and startle response habituation are essential for emotional regulation and organism behaviors.
Measuring startle response
San Diego Instruments has developed a startle response system to precisely record rodent subjects’ motor responses. The SR-LAB startle response system is the most widely used research instrument worldwide for analyzing startle habituation, pre-pulse inhibition, and fear-potentiated startle.
This system is appropriate for various startle applications thanks to its combined hardware and software package, which can control a combination of bursts of air puffs, background noise, light and noise, and more.
References and further reading:
- Brown, J.S., Kalish, H.I. and Farber, I.E. (1951). Conditioned fear as revealed by magnitude of startle response to an auditory stimulus. Journal of Experimental Psychology, 41(5), pp.317–328. https://doi.org/10.1037/h0060166.
- SR-LAB SR-LAB Startle Response System. https://sandiegoinstruments.com/wp-content/uploads/2018/08/SR-Lab.pdf.
- Halberstadt, A.L. and Geyer, M.A. (2009). Habituation and sensitization of acoustic startle: Opposite influences of dopamine D1 and D2-family receptors. Neurobiology of Learning and Memory, 92(2), pp.243–248. https://doi.org/10.1016/j.nlm.2008.05.015.
About San Diego Instruments, Inc.
For more than 30 years, San Diego Instruments has served the scientific community as a comprehensive resource for the design, manufacture and distribution of behavioral neuroscience research instruments used in human and animal studies. Utilized in laboratories and cited in research papers worldwide, SDI systems have come to represent the industry standard for quality and longevity. Our premier SR-LAB™ is the world’s most widely used startle response system. At SDI, our commitment to developing quality products that stand the test of time is matched only our dedication to excellent customer service. We take pride in our ever-growing core of loyal clientele.
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