Prepulse Modulation of Auditory Startle Reflex with Different Stimulus Onset Asynchronies CC13-CC16
Dr. Richa Gupta,
Associate Professor, Department of Physiology, Mahatma Gandhi Medical College and Research Institute,
Introduction: Startle reflex is measured by delivering a sensory stimulus and measuring eyelid closure in human beings to investigate the neurophysiology of information processing. However, the characteristics of startle reflex can be modified by weaker prepulse. Since this modification is increasingly being associated with various psychiatric disorders, it is worth exploring the prepulse modification of startle reflex.
Aim: The aim of the present study was to explore the differential modulatory effect of auditory stimulus onset asynchronies on startle response magnitude as well as latency.
Materials and Methods: The study was conducted on 30 healthy right handed male subjects aged 18-40 years. Auditory prepulse was delivered binaurally which was followed by startle stimuli. The startle reflex was recorded from orbicularis oculi muscle by electromyography. Inter stimulus interval was varied in different trials from 30 ms to 1000 ms. The startle reflex from different trials were later analysed for response latency and magnitude.
Results: The results of the present study show that latency of the response was not different with different Stimulus Onset Synchronies (SOAâ€™s). However, the magnitude of the response was inhibited with SOAs 60 ms, 120 ms and 250 ms while facilitated with SOA 1000 ms when compared to baseline. SOAs 30 ms and 500 ms had no effect on the response.
Conclusion: Differential response to different prepulse to pulse inter stimulus interval implies that temporal presentation of stimuli is very important for priority coding. Very small SOAâ€™s are important for priority coding of the stimulus. However, with much larger SOAâ€™s, the first stimulus serves as an orienting response for the next stimulus.