New paradigm for auditory paired pulse suppression

Abstract

Sensory gating is a mechanism of sensory processing used to prevent an overflow of irrelevant information, with some indexes, such as prepulse inhibition (PPI) and P50 suppression, often utilized for its evaluation. In addition, those are clinically important for diseases such as schizophrenia. In the present study, we investigated long-latency paired-pulse suppression of change-related cortical responses using magnetoencephalography. The test change-related response was evoked by an abrupt increase in sound pressure by 15 dB in a continuous sound composed of a train of 25-ms pure tones at 65 dB. By inserting a leading change stimulus (prepulse), we observed suppression of the test response. In Experiment 1, we examined the effects of conditioning-test intervals (CTI) using a 25-ms pure tone at 80 dB as both the test and prepulse. Our results showed clear suppression of the test response peaking at a CTI of 600 ms, while maximum inhibition was approximately 30%. In Experiment 2, the effects of sound pressure on prepulse were examined by inserting prepulses 600 ms prior to the test stimulus. We found that a paired-pulse suppression greater than 25% was obtained by prepulses larger than 77 dB, i.e., 12 dB louder than the background, suggesting that long latency suppression requires a relatively strong prepulse to obtain adequate suppression, different than short-latency paired-pulse suppression reported in previous studies. In Experiment 3, we confirmed similar levels of suppression using electroencephalography. These results suggested that two identical change stimuli spaced by 600 ms were appropriate for observing the long-latency inhibition. The present method requires only a short inspection time and is non-invasive.

Fig 1. Paired stimulation paradigm using auditory change-related cortical responses.

A. The sound stimuli consisted of 86 repeats of a 25-ms pure tone at 65 dB SPL. For the Test stimulus, a 25-ms sound at 80 dB was inserted at 1800 ms. The conditioning stimulus was also a 25-ms pure tone at 80 dB presented at 300–800 ms before the Test stimulus. B. Grand-averaged waveforms for the subjects. C. Mean P50m-N100m and N100m-P200m amplitudes for each condition.

Fig 2. Rate of inhibition against conditioning-test intervals.

For both measurements, the inhibition rate peaked at the 600-ms interval.

Fig 3. Correlation of inhibition rate between two calculations, Test alone response-based and Conditioning response-based.

Plots show the relationship of inhibition rate between the test response / conditioning-evoked response (y axis) and test response / test alone-evoked response (x axis).

Fig 4. Effects of sound pressure on inhibition.

A. Stimulation paradigm used in Experiment 2. The sound stimuli consisted of 86 repeats of the 25-ms tone at 65 dB. The Test sound of 80 dB was inserted at 1800 ms. The conditioning stimulus was 65–80 dB of sound pressure and presented at 600 ms before the test stimulus. B. Grand-averaged waveforms. C. Mean amplitude for each condition.

Fig 5. Rate of inhibition against sound pressure level of Prepulse.

Inhibition rate results obtained in Experiment 2.

Fig 6. Recordings obtained with EEG.

A. Evoked potentials were recorded using Fz referred to linked mastoids. B. Mean amplitude for each condition. Black and white bars show P50-N100 and N100-P200 amplitude, respectively.