Effects of acoustic gradient noise from functional magnetic resonance imaging on auditory processing as reflected by event-related brain potentials

The processing of sound changes and involuntary attention to them has been widely studied with event-related brain potentials (ERPs). Recently, functi onal magnetic resonance imaging (fMRI) has been applied to determine the ne ural mechanisms of involuntary attention and the sources of the correspondi ng ERP components. The gradient-coil switching noise from the MRI scanner, however, is a challenge to any experimental design using auditory stimuli. In the present study, the effects of MRI noise on: ERPs associated with pre attentive processing of sound changes and involuntary switching of attentio n to them were investigated. Auditory stimuli consisted of frequently prese nted "standard" sounds, infrequent, slightly higher "deviant" sounds,: and infrequent natural "novel" sounds. The standard and deviant sounds were eit her sinusoidal tones or musical chords, in separate stimulus sequences. The mismatch negativity (MMN) ERP associated with preattentive sound change de tection was elicited by the deviant and novel sounds and was-not affected b y the prerecorded background MRI noise tin comparison with the condition wi th no background noise). The succeeding positive P3a ERP responses associat ed with involuntary attention switching elicited by novel sounds were also not affected by the MRI noise. However, in ERPs to standard tones and chord s, the P1, N1, and P2 peak latencies-were significantly prolonged by the MR I noise. Moreover, the amplitude of the subsequent "exogenous" N2 to the st andard sounds was significantly attenuated by the presence of MRI noise, In conclusion, the present results suggest that in fMRI the background noise does not interfere with the imaging of auditory processing related to invol untary attention. (C) 2001 Academic Press.