Prepulse inhibition of change-related P50m no correlation with P50m gating

Abstract

Both prepulse inhibition (PPI) of the startle response and P50 sensory gating are important tools to investigate the inhibitory mechanisms of sensory processing. However, previous studies found no or a weak association between these two measures, which may have been due to the different indexes used. We examined the relationship between P50 sensory gating and P50 PPI. P50m sensory gating and PPI of Change-related P50m were assessed in 14 subjects using magnetoencephalography. Concerning P50m sensory gating, the amplitudes of the response to the second click relative to that to the first one were reduced by 43 and 47% for the left and right hemisphere, respectively. Change-related P50m was evoked by an abrupt sound pressure increase by 10 dB in a continuous click train of 70 dB. When this test stimulus was preceded by a click (prepulse) with a weaker sound pressure increase (5 dB) at a prepulse-test interval of 30, 60, or 90 ms, Change-P50m was suppressed by 33 ~ 65% while the prepulse itself elicited no or very weak P50m responses. Although the amplitude of the P50m response to the first click and the amplitude of the Change-P50m test alone response were positively correlated (r = 0.6), the degree of the inhibition of the two measures was not (r = -0.06 ~ 0.14). The neural origin was estimated to be located in the supratemporal plane around the superior temporal gyrus or Heschl's gyrus and did not differ between P50m and Change-P50m. The present results suggest that P50m and Change-P50m are generated by a similar group of neurons in the auditory cortex, while the mechanisms of P50m sensory gating and Change-P50m PPI are different.

Keywords: Auditory evoked magnetic fields; Prepulse inhibition; Sensory gating.

Figure 1

Auditory stimuli for prepulse inhibition. A), a single sine wave 1 ms in duration was repeatedly presented at 100 Hz. B), the standard or background stimulus was a train of click sounds 70 dB SPL in sound pressure and 600 ms in duration. The test stimulus to evoke change-related cortical responses consisted of a similar train of clicks of 70 dB for 400 ms followed by 80 dB clicks for 200 ms. One click of 75 dB was inserted before the test stimulus as a prepulse.

Figure 2

Magnetic responses to the stimuli. Superimposed waveforms of all 204 sensors recorded from one representative subject. Aa, responses to the Standard, Test alone, Prepulse (30 ms) + Test, and Prepulse alone stimuli. Ab, subtracted waveforms. Red and pink arrowheads indicate the onset of the Test and Prepulse, respectively. B), magnetic responses under the P50m sensory gating paradigm.

Figure 3

Grand-averaged source strength waveforms. Grand-averaged waveforms of Change-P50m (A) and P50m (B). The mean peak latencies are indicated by arrows. Upward and downward deflections indicate the source strength of the current directing anterosuperior and posteroinferior, respectively. C), the mean location of the estimated dipole for Change-P50m and P50m superimposed on standard MR images.

Figure 4

Correlation of the baseline amplitude between Change-P50m and P50m. Plots show the relationship between the amplitude of P50m for the first click (x axis) and that of Change-P50m for the Test alone response (y axis).

Figure 5

Correlation between PPI and P50m sensory gating. Data for the 60-ms Prepulse PPI are shown.