Elsevier

NeuroImage

Volume 86, 1 February 2014, Pages 131-137
NeuroImage

Change-related auditory P50: A MEG study

https://doi.org/10.1016/j.neuroimage.2013.07.082Get rights and content

Highlights

  • Environmental change-detecting system is very important for survival.

  • We demonstrated the presence of an auditory change-related P50m response.

  • The amplitude and latency depended on the magnitude of the sound change.

  • It reflects endogenous brain activity earlier than change-related N1m.

Abstract

Changes in continuous sounds elicit a preattentive component that peaks at around 100 ms (Change-N1m) on electroencephalograms or magnetoencephalograms (MEG). Change-N1m is thought to reflect brain activity relating to the automatic detection of changes, which facilitate processes for the execution of appropriate behavior in response to new environmental events. The aim of the present MEG study was to elucidate whether a component relating to auditory changes existed earlier than N1m. Change-related cortical responses were evoked by abrupt sound movement in a train of clicks at 100 Hz. Sound movement was created by inserting an interaural time delay (ITD) of 0.15, 0.25, 0.35, and 0.45 ms into the right ear. Ten out of 12 participants exhibited clear change-related cortical responses earlier than Change-N1m at around 60 ms (Change-P50m). The results of source analysis showed that Change-P50m originated from the superior temporal gyrus of both hemispheres and that its location did not differ significantly from dipoles for the response to the sound onset. The magnitude of Change-P50m increased and the peak latency shortened with an increase in the ITD, similar to those of Change-N1m. These results suggest that change-related cortical activity is present as early as its onset latency at around 50 ms.

Introduction

The quick detection of abrupt changes in the sensory environment is one of the most important factors for survival. Sensory changes should be detected involuntarily and processed in a specific brain network for this purpose. Previous studies using electroencephalograms (EEG), magnetoencephalograms (MEG), and functional magnetic resonance imaging (fMRI) demonstrated a preattentive brain system sensitive to sudden sensory changes (change-related responses) in the auditory (Akiyama et al., 2011, Inui et al., 2010a, Inui et al., 2010b, Jones, 1991, Nishihara et al., 2011, Ohoyama et al., 2012, Otsuru et al., 2012, Yamashiro et al., 2011), visual (Urakawa et al., 2010), somatosensory (Kodaira et al., 2013, Otsuru et al., 2011), and multisensory (Downar et al., 2000, Tanaka et al., 2009) cortical areas. Change-related responses are considered to be based on sensory memory and comparisons of new sensory events with the preceding status.

Change-N1(m) of auditory evoked potentials (AEPs) or evoked fields (AEFs) is a very clear component peaking at around 100–130 ms after the change onset elicited by any abrupt auditory change (Inui et al., 2010a) and exhibits good test–retest reliability (Inui et al., 2012, Otsuru et al., 2012). The characteristics of Change-N1(m) are as follows. (1) It is elicited by any auditory change including the onset of a sound (Nishihara et al., 2011), offset of a sound (Yamashiro et al., 2009), and changes in sound pressure, frequency, or location (Inui et al., 2010a). (2) The amplitude is affected by the length of the preceding control sound to be compared (Akiyama et al., 2011, Inui et al., 2010a, Yamashiro et al., 2011), or the probability of the control and change sounds (Inui et al., 2010b, Ohoyama et al., 2012). (3) Its amplitude and latency depend on the magnitude of the auditory change (Inui et al., 2010a, Inui et al., 2010b, Nishihara et al., 2011, Yamashiro et al., 2011). (4) It arises in the superior temporal gyrus (STG) and the location does not differ among auditory changes in source estimation studies (Inui et al., 2012, Nishihara et al., 2011, Otsuru et al., 2012, Yamashiro et al., 2009).

However, no detailed studies have been performed on change-related cortical activity before Change-N1(m). AEP studies showed that the earliest component from the auditory cortex appeared as a small vertex-negativity peaking at around 20 ms. This was followed by positive deflections at 30 ms and 50 ms, which have been referred to as the middle-latency responses, P30 (Pa) and P50 (P1). Although P50(m) has been investigated in detail in both basic and clinical studies (for review, see Potter et al., 2006, Ross et al., 2010), parametric studies using middle latency components are generally rare. Furthermore, no study has examined change-related activity at the P50(m) latency in detail. The purpose of this study was to investigate whether change-related components preceded Change-N1m and how, if present, the magnitude of the change affected it using MEG.

Previous studies on change-related auditory responses have used abrupt changes in sound features in a continuous pure tone, and earlier components are typically not detected under these paradigms. Sharp transient stimuli, such as clicks characterized by steep rises in sound energy, have been used to investigate P50(m) and the earlier components (Orekhova et al., 2013, Potter et al., 2006, Ross et al., 2010), therefore, we considered that we would be able to identify early change-related responses clearer using clicks. Hence, we used an abrupt change in a continuous click train to investigate change-related early components in the present study.

Section snippets

Participants

Twelve healthy volunteers (ten males and two females), aged 23–51 (mean 35.4) years old, participated in this study. This study was approved in advance by the Ethics Committee of the National Institute for Physiological Sciences, Okazaki, Japan, and written consent was obtained from all participants.

MEG recording

The experiment was carried out in a magnetically shielded room. Participants were instructed to watch a silent movie without attending to the sound stimuli. Magnetic signals were recorded using a

Sound location change-evoked magnetic responses

In all participants, the sound onset evoked clear magnetic responses in the bilateral temporal areas (Fig. 2A). The first clear magnetic component elicited by the stimulus onset appeared at around 50 ms (On-P50m, Fig. 2Aa), which was followed by a larger one at around 100 ms (On-N1m, Fig. 2Ab). Similar components were elicited at slightly later latencies for the ITD sounds. The first component peaked at around 60 ms (Fig. 2Ac) and the second one at around 110 ms (Fig. 2Ad) after the onset of the

Discussion

In the present MEG study, we recorded cortical responses to an abrupt auditory change in sound location using clicks, and investigated change-related responses earlier than Change-N1m. The results showed that (1) change-related responses were elicited at around 60 ms (Change-P50m), (2) the amplitude increased and latency shortened with an increase in the sound location change, and (3) source location was estimated in bilateral STG. All these results were consistent with previous findings on

Conclusion

The present study demonstrated that an abrupt change in sound location in a continuous click train elicited change-related cortical responses at around 60 ms following the onset of the change. To support that this P50m response was an endogenous component relating to the change, its amplitude and latency varied according to the degree of the change in a manner similar to Change-N1m. Therefore, the present results suggest that Change-P50m reflects endogenous brain activity driven by environmental

Acknowledgments

This work was supported by JSPS KAKENHI Grant Number 25351001.

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