The Power of Interstimulus Interval for the Assessment of Temporal Processing in Rodents

This method can help answer key questions in the field of neuroscience by characterizing neurocognitive disorders and their progression across the lifespan via cross-sectional and longitudinal assessments. The main advantage of this technique is that it utilizes the systematic manipulation of ISI to afford a critical opportunity for the evaluation of a temporal processing. The implications of this technique extend for the assessment of neurocircuitry alterations in neurocognitive disorders, because the serial neural circuit mediating PPI has been well-established.

To begin this procedure, open the Startle Response system software, define a pulse-only ASR trial by selecting Definitions, then Define Trial. Type a trial name, hit enter, and Record Data. Set the Analog Level to 720.

Define the Wait Length as 20 milliseconds, and introduce Background. End the trial and hit Accept to save it. To create a 30-milliseconds trial definition for acoustic PPI, select Definitions, then Define Trial.

Type a trial name and hit enter. Set the Analog Level to 600 at zero millisecond to introduce the pre-stimulus. Assign the Wait Length to 20 milliseconds to specify the length of the pre-stimulus.

Then, set the Analog Level to 440 at 20 milliseconds to remove the pre-stimulus. Define the Wait Length dependent upon ISI, and specify Record Data. Set the Analog Level to 720 and assign the Wait Length to 20 milliseconds.

Next, introduce Background, then end the trial and hit Accept to save the trial. Afterward, create a 30-milliseconds definition for acoustic gap PPI. Selection Definitions, one, Define Trial.

Type a trial name and hit enter. Set the Analog Level to zero at zero millisecond to introduce the pre-stimulus. Assign the Wait Length to 20 milliseconds to specify the length of the pre-stimulus.

Then, set the Analog Level to 440 at 20 milliseconds to remove the pre-stimulus. Subsequently, define the Wait Length dependent upon ISI, then specify Record Data. Set the Analog Level to 720.

Assign the Wait Length to 20 milliseconds, and introduce Background. End the trial, hit Accept to save the trial. To create a habituation session, select Definitions and Define Session.

Set the number of Record Samples to 200, the Samples per Second to 2, 000, the Background analog level to 440, the Acclimation Period to 5 minutes, and the sequence Repetitions to 36. Type 10 into the ITI List box. Next, click Add, and select the Pulse Only ASR trial.

Click Save to save the Habituation session. Subsequently, define the session for cross-modal PPI by selecting Definitions and Define Session. Set the number of Record Samples to 200, the Samples per Second to 2, 000, the Acclimation Period to five minutes, the Background analog level to 440, and the sequence Repetitions to one.

Then, define the ITI list by typing 10 into the first five ITI List boxes. Type the ITI values into the next 72 ITI list boxes, representing trials with a pre-stimulus. Afterward, click Add, select the Pulse Only ASR trial, and load it six times for trials one to six.

Load the six-trial blocks in an A-B-B-A counterbalanced order of presentation for a cross-modal PPI. Then, click Save to save the session. Next, define the session for gap PPI by selecting Definitions and Define Session.

Set the number of Record Samples to 200, the Samples per Second to 2, 000, the Acclimation Period to five minutes, the Background analog level to 440, and the sequence Repetitions to one. To define the ITI list, type 10 into the first five ITI List boxes. Type the ITI values into the next 72 ITI List boxes, representing trials with a pre-stimulus.

Then, select the Pulse Only ASR trial and add it six times for trials one to six. Create six trial blocks for each pre-stimulus modality using a Latin square design and save the session. In this procedure, handle the animals to allow for acclimation across a series of days prior to beginning experimentation.

Open the Startle Response system software. Click Run and select the session of interest. Then, input an Output File Name and click OK.Enter Subject, Group, and ID information and click Continue.

Place the animal into the startle apparatus, using an animal enclosure that is most appropriate for the size of the animal. Click OK to begin the session. When it is done, export data for analysis by clicking Reports, then, Concatenate Data.

Load the data file and click Add. Then, click ASCII to save the data output. The utility of an approach varying the ISI to delineate effects of sensory modality and cross-modal PPI are illustrated here.

A prominent shift in the point of maximal inhibition is dependent upon sensory modality, suggesting a differential sensitivity to the manipulation of ISI. Specifically, maximal inhibition is observed at the 30-milliseconds ISI following the presentation of a discrete acoustic pre-stimulus at the 50-milliseconds ISI following the presentation of a discrete visual pre-stimulus and at the 200-milliseconds ISI following the presentation of a discrete tactile pre-stimulus. Following an animal’s experience with each pre-stimulus in cross-modal PPI, the generalizability of sensory modality effects was assessed in gap PPI.

This figure demonstrates the generalizability of varying the ISI to delineate effects of sensory modality. A prominent shift in the point of maximal inhibition suggesting a differential sensitivity to the manipulation of ISI was observed in tactile gap PPI relative to acoustic gap PPI and visual gap PPI. The utility of an approach varying the ISI to delineate effects of psychostimulant in cross-modal PPI are illustrated here.

At the post-test assessment, most notably, a relative flattening of the ISI function is observed, suggesting a relative insensitivity to the manipulation of ISI relative to the pre-test assessment. Additionally, a prominent shift in the point of maximal inhibition is also revealed, supporting a differential sensitivity to the manipulation of ISI. Specifically, maximal inhibition is observed at the 30-millisecond ISI during the pre-test assessment and at the 100-millisecond ISI during the post-test assessment.

Subsequently, the generalizability of the varying ISI approach to delineate effects of psychostimulant exposure was assessed in auditory gap PPI. A significantly flatter ISI function was observed at the post-test assessment relative to the pre-test assessment, suggesting a relative insensitivity to the manipulation of ISI. The development of temporal processing can be assessed using a longitudinal experimental design.

The development of temporal processing in visual PPI is illustrated here. The point of maximal inhibition at all ages is at the 50-millisecond ISI, however, a sharper inflection of the ISI function is observed across age, suggesting a perceptual sharpening which occurs with development. Subsequently, the generalizability of the varying ISI approach to examine the development of temporal processing was assessed in auditory gap PPI.

At post-natal day 30, an insensitivity to the manipulation of ISI was observed, evidenced by a flatter ISI function relative to PD90 or PD150. While attempting this procedure, it’s important to implement critical experimental design considerations, including a Latin square experimental design for the presentation of ISIs, two control trials including the zero and 4, 000-millisecond ISI and a variable ITI. Following this procedure, other neurocognitive assessments including a signal-detection operant task and neuroanatomical assessments can be performed to further assess temporal processing deficits and their underlying neural mechanisms.