The startle response is a sudden, reflex-like response to something unexpected or sudden, such as a bright light or loud noise. It is an unlearned and mainly unconscious defense mechanism that animals and humans have, occurring when a stimulus startles someone or something. Startle response is a series of skeletomuscular contractions commonly measured by eyeblinks in humans and full or partial muscle contractions in rodents, displayed through head, neck, back, paw, or tail movements, but it can also be viewed in the face as a look of fear1. In a startle response, the facial and skeletal muscles react within a few milliseconds.
Habituation is a non-associative learning process where an innate response is weakened when an organism is repeatedly exposed to a specific stimulus. This happens because the organism becomes used to the trigger and can understand that it is not a threat. As mentioned, a startle response is present in both animals and humans and so is habituation. The process enables organisms to conserve energy by not responding unnecessarily to unthreatening stimuli.
Startle response habituation is sometimes called sensory filtering because an organism responds less to a stimulus over time. This blog post has been written to provide an overview of startle response habituation and why it is important.
How Startle Response Works
Startle response involves neural pathways that manage how the body responds to a loud auditory stimulus. The brain’s sensory receptors, such as the eyes or ears, detect information and then pass it through the sensory neurons to the inferior colliculus in the brain. Once in the inferior colliculus, the information is transmitted to the amygdala, where emotional responses are processed. Finally, a signal is sent to the hypothalamus, and the sympathetic nervous system activates a startle response.
Common startle responses are a body’s automatic ‘fight or flight’ reflexes, including an increased heart rate, rapid breathing, muscle tension, or twitches. Apart from movement responses, a startle response can also trigger fear or anxiety and increase alertness in an organism.
Startle Response Habituation
The more an organism is exposed to a safe stimulus, the more they learn that is not a threat to them. What happens as the brain learns what stimuli are safe is known as startle response habituation, where the body’s startle reflex to that stimulus diminishes. This process is crucial in reducing anxiety and stress. As organisms learn to understand what is threatening and what isn’t, their body responds accordingly. When non-threatening stimuli appear, the brain registers that its organism is safe and does not trigger a fight or flight response, keeping anxiety, stress, and physical responses to a minimum.
Understanding how startle response habituation works is vital for many therapeutic processes, such as cognitive-behavioral therapy and exposure therapy. It is used to support people in overcoming schizophrenia2, anxiety disorders, and phobias, as well as fear or stress in response to non-threatening stimuli. However, startle response and startle response habituation are both crucial for emotional regulation and organism behaviors.
San Diego Instruments and Measuring Startle Response
San Diego Instruments have designed and manufactured a startle response system to accurately record the motor responses of your rodent subjects. Our SR-LAB startle response system is the world’s most widely used research instrument for measuring startle habituation, pre-pulse inhibition (PPI), and Fear Potentiated Startle (FPS). It is suitable for a range of startle applications due to its complete hardware and software package, with the ability to control a combination of bursts of light and noise, background noise, air puffs, and more.
To learn more about startle response habituation or our startle response testing systems, please contact a member of San Diego Instruments today.