Temporal processing, a preattentive process, may underlie deficits in higher-level cognitive processes, including attention, commonly observed in neurocognitive disorders. Using prepulse inhibition as an exemplar paradigm, we present a protocol for manipulating interstimulus interval (ISI) to establish the shape of the ISI function to provide an assessment of temporal processing.
Temporal processing deficits have been implicated as a potential elemental dimension of higher-level cognitive processes, commonly observed in neurocognitive disorders. Despite the popularization of prepulse inhibition (PPI) in recent years, many current protocols promote using a percent of control measure, thereby precluding the assessment of temporal processing. The present study used cross-modal PPI and gap prepulse inhibition (gap-PPI) to demonstrate the benefits of employing a range of interstimulus intervals (ISIs) to delineate effects of sensory modality, psychostimulant exposure, and age. Assessment of sensory modality, psychostimulant exposure, and age reveals the utility of an approach varying the interstimulus interval (ISI) to establish the shape of the ISI function, including increases (sharper curve inflections) or decreases (flattening of the response amplitude curve) in startle amplitude. Additionally, shifts in peak response inhibition, suggestive of a differential sensitivity to the manipulation of ISI, are often revealed. Thus, the systematic manipulation of ISI affords a critical opportunity to evaluate temporal processing, which may reveal the underlying neural mechanisms involved in neurocognitive disorders.
Temporal processing deficits have been implicated as a potential underlying neural mechanism for alterations in higher-level cognitive processes commonly observed in neurocognitive disorders. Prepulse inhibition (PPI) of the auditory startle response (ASR) is a translational experimental paradigm commonly used to examine temporal processing deficits, revealing profound alterations in neurocognitive disorders such as schizophrenia1, attention deficit hyperactivity disorder2 and HIV-1 associated neurocognitive disorders3,4. Specifically, assessments of temporal processing in preclinical models of HIV-1 have revealed the generality, relative permanence, and suggested the diagnostic utility of PPI across the majority of the animals' functional lifespan3,4,5,6.
Use of an approach varying interstimulus interval (ISI; i.e., the time between the prepulse and the startle stimulus) in the analysis of reflex modification dates back to Sechenov in 18637. The seminal studies of reflex modification, a measure of sensorimotor gating, employed an approach varying ISI to assess flexor response and audition in frogs7,8, as well as knee-jerk responses in humans9. The first clinical application of the reflex modification procedure assessed visual sensitivity in a man with hysterical blindness10. Over a century after the first reports of reflex modification, the approach of varying ISI was popularized across a series of seminal papers11,12,13. Despite the inherent differences in the seminal studies on reflex modification (i.e., species, experimental procedures, reflexes), they established a temporal relationship that was strikingly similar between species.
Assessment of prepulse inhibition using an approach varying ISI, as detailed in the present protocol, has multiple advantages over the popularized percent of control approach. First, the approach affords an opportunity to establish the shape of the ISI function, including increases (sharper curve inflections) or decreases (flattening of the response amplitude curve)3,15 in startle amplitude, as well as shifts in the peak point of response inhibition3,5. Additionally, when an approach varying ISI is employed, startle response is a relatively stable phenomenon1, suggesting the potential utility of the approach in longitudinal studies examining the progression of neurocognitive deficits5,15. Finally, PPI provides a critical opportunity to understand the underlying neural circuitry involved in neurocognitive disorders16.
In our study, we employed two experimental paradigms (Figure 1), including cross-modal PPI and gap prepulse inhibition (gap-PPI), to evaluate the utility of an approach varying ISI to delineate effects of sensory modality, psychostimulant exposure, and age. The cross-modal PPI experimental paradigm utilizes the presentation of an added stimulus (e.g., tone, light, air puff) as a discrete prestimulus prior to an acoustic startling stimulus. In sharp contrast, in the gap-PPI experimental paradigm, the absence of a background (e.g., removal of background noise, light, or air puff) serves as a discrete prestimulus. Here, we describe both experimental paradigms for the assessment of temporal processing, as well as statistical approaches for the analysis of PPI and gap-PPI. Within the discussion, we compared the conclusions one would draw from the variable ISI approach and the popularized percent of control approach.
The present protocol describes the power of varying ISI for the assessment of temporal processing for studies employing either cross-sectional or longitudinal experimental designs. Examining the effects of sensory modality, psychostimulant exposure, or age on the shape of the ISI function demonstrated its utility in revealing a differential sensitivity to the manipulation of ISI (i.e., shifts in the point of maximal inhibition) or a relative insensitivity to the manipulation of ISI (i.e., sharper inflec…
The authors have nothing to disclose.
This work was supported in part by grants from NIH (National Institute on Drug Abuse, DA013137; National Institute of Child Health and Human Development HD043680; National Institute of Mental Health, MH106392; National Institute of Neurological Diseases and Stroke, NS100624) and the interdisciplinary research training program supported by the University of South Carolina Behavioral-Biomedical Interface Program. Dr. Landhing Moran is currently a Scientific Officer at the NIDA Center for Clinical Trials Network.
SR-Lab Startle Response System | San Diego Instruments | ||
Isolation Cabinet | Industrial Acoustic Company | ||
SR-Lab Startle Calibration System | San Diego Instruments | ||
High-Frequency Loudspeaker | Radio Shack | model #40-1278B | |
Sound Level Meter | Bruel & Kjaer | model #2203 | |
Perspex Cylinder | San Diego Instruments | Included with the SR-Lab Startle Response System | |
SR-Lab Startle Response System Software | San Diego Instruments | Included with the SR-Lab Startle Response System | |
Light Meter | Sper Scientific, Ltd. | model #840006 | |
Airline Regulator | Craftsman | model #16023 | |
SPSS Statistics 24 | IBM | Used for Statistical Analyses (Optional) |