Influence of acoustic masking noise in fMRI of the auditory cortex during phonetic discrimination

The effect of sequence repeat time on auditory cortex stimulation during phonetic discrimination

Acoustic noise generated by the MR scanner gradient system during fMRI studies of auditory function is a very significant potential confound. Despite these deleterious effects, fMRI of the auditory cortex has been successful and numerous practitioners have circumvented the problem of acoustic masking noise. In the context of auditory cortex fMRI, the sequence repeat time (TR) has the effect of altering the length of time during which the scanner is quiet. Indeed, the move to whole-brain fMRI makes the problem of acoustic noise more acute and points to the need to examine the role of TR and its influence on the BOLD signal. The aim of this study was to examine the effect of varying the TR time on activation of auditory cortex during presentation and performance of a phonetic discrimination task. The results presented here demonstrate that the influence of sequence repeat time is considerable. For a short repeat time it is likely that the noise from the scanner is a significant mask and hinders accurate task performance. At the other extreme, a repeat time of 9 s is also suboptimal, probably due to attentional effects and lack of concentration and not least because of the longer overall measurement times. The results of this study point to a complicated interplay between psychophysical factors as well as physical parameters; attention, acoustic noise, total duration of the experiment, consideration of the volume of acquisition, and overall difficulty of the task have to be assessed and balanced. For the paradigm used here, the results suggest an optimal TR of around 6 s for a 16-slice acquisition.

Recognition of emotional prosody and verbal components of spoken language: an fMRI study

This study examined the neural areas involved in the recognition of both emotional prosody and phonemic components of words expressed in spoken language using echo-planar, functional magnetic resonance imaging (fMRI). Ten right-handed males were asked to discriminate words based on either expressed emotional tone (angry, happy, sad, or neutral) or phonemic characteristics, specifically, initial consonant sound (bower, dower, power, or tower). Significant bilateral activity was observed in the detection of both emotional and verbal aspects of language when compared to baseline activity. We found that the detection of emotion compared with verbal detection resulted in significant activity in the right inferior frontal lobe. Conversely, the detection of verbal stimuli compared with the detection of emotion activated left inferior frontal lobe regions most significantly. Specific analysis of the anterior auditory cortex revealed increased right hemisphere activity during the detection of emotion compared to activity during verbal detection. These findings illustrate bilateral involvement in the detection of emotion in language while concomitantly showing significantly lateralized activity in both emotional and verbal detection, in both the temporal and frontal lobes.

Attention modulates activity in the primary and the secondary auditory cortex: a functional magnetic resonance imaging study in human subjects

Using functional magnetic resonance imaging, ten healthy subjects were scanned whilst listening to consonant-vowel syllables under three different conditions: (i) a 'no-attention' condition required subjects to ignore the stimuli; (ii) an 'attend' condition requiring attentive listening to stimuli; (iii) a 'detect' condition requiring detection of a specific target syllable. Hemodynamic responses were measured in the primary and secondary auditory cortex. These three conditions were associated with significantly different activations in the primary and secondary auditory cortex. The strongest activations were found for the 'detect' condition, followed by the 'attend' condition. The weakest activation was evident during the 'no-attention' condition. There were also stronger activations in the left hemisphere and within the primary auditory cortex. These results suggest that the primary and secondary auditory cortex play a main role in the selective attention.