Aki Tsuruhara

Prepulse inhibition of auditory change-related cortical responses

BackgroundPrepulse inhibition (PPI) of the startle response is an important tool to investigate the biology of schizophrenia. PPI is usually observed by use of a startle reflex such as blinking following an intense sound. A similar phenomenon has not been reported for cortical responses.ResultsIn 12 healthy subjects, change-related cortical activity in response to an abrupt increase of sound pressure by 5 dB above the background of 65 dB SPL (test stimulus) was measured using magnetoencephalography. The test stimulus evoked a clear cortical response peaking at around 130 ms (Change-N1m). In Experiment 1, effects of the intensity of a prepulse (0.5 ~ 5 dB) on the test response were examined using a paired stimulation paradigm. In Experiment 2, effects of the interval between the prepulse and test stimulus were examined using interstimulus intervals (ISIs) of 50 ~ 350 ms. When the test stimulus was preceded by the prepulse, the Change-N1m was more strongly inhibited by a stronger prepulse (Experiment 1) and a shorter ISI prepulse (Experiment 2). In addition, the amplitude of the test Change-N1m correlated positively with both the amplitude of the prepulse-evoked response and the degree of inhibition, suggesting that subjects who are more sensitive to the auditory change are more strongly inhibited by the prepulse.ConclusionsSince Change-N1m is easy to measure and control, it would be a valuable tool to investigate mechanisms of sensory gating or the biology of certain mental diseases such as schizophrenia.

Effects of acute nicotine on prepulse inhibition of auditory change-related cortical responses

Prepulse inhibition (PPI) of startle is a measure of inhibitory function in which a weak leading stimulus suppresses the startle response to an intense stimulus. Usually, startle blink reflexes to an intense sound are used for measuring PPI. A recent magnetoencephalographic study showed that a similar phenomenon is observed for auditory change-related cortical response (Change-N1m) to an abrupt change in sound features. It has been well established that nicotine enhances PPI of startle. Therefore, in the present magnetoencephalographic study, the effects of acute nicotine on PPI of the Change-N1m were studied in 12 healthy subjects (two females and 10 males) under a repeated measures and placebo-controlled design. Nicotine (4 mg) was given as nicotine gum. The test Change-N1m response was elicited with an abrupt increase in sound pressure by 6 dB in a continuous background sound of 65 dB. PPI was produced by an insertion of a prepulse with a 3-dB-louder or 6-dB-weaker sound pressure than the background 75 ms before the test stimulus. Results show that nicotine tended to enhance the test Change-N1m response and significantly enhanced PPI for both prepulses. Therefore, nicotines enhancing effect on PPI of the Change-N1m was similar to that on PPI of the startle. The present results suggest that the two measures share at least some mechanisms.

Steady-state visual-evoked response to upright and inverted geometrical faces: a magnetoencephalography study.

The face is one of the most important visual stimuli in human life, and inverted faces are known to elicit different brain responses than upright faces. This study analyzed steady-state visual-evoked magnetic fields (SSVEFs) in eleven healthy participants when they viewed upright and inverted geometrical faces presented at 6Hz. Steady-state visual-evoked responses are useful measurements and have the advantages of robustness and a high signal-to-noise ratio. Spectrum analysis revealed clear responses to both upright and inverted faces at the fundamental stimulation frequency (6 Hz) and harmonics, i.e. SSVEFs. No significant difference was observed in the SSVEF amplitude at 6 Hz between upright and inverted faces, which was different from the transient visual-evoked response, N170. On the other hand, SSVEFs were delayed with the inverted face in the right temporal area, which was similar to N170 and the results of previous steady-state visual-evoked potentials studies. These results suggest that different mechanisms underlie the larger amplitude and delayed latency observed with face inversion, though further studies are needed to fully elucidate these mechanisms. Our study revealed that SSVEFs, which have practical advantages for measurements, could provide novel findings in human face processing.