Left temporal alpha band activity increases during working memory retention of pitches

The functional role and regional specificity of approximately 10 Hz alpha band activity remains of debate. Alpha band activity is strongly modulated in visual working memory tasks and it has been proposed to subserve resource allocation by disengaging task-irrelevant regions. It remains unknown if alpha band activity plays a similar role during auditory working memory processing. In this study we applied whole-head magnetoencephalography to investigate brain activity in a delayed-match-to-sample task including pure tones, non-harmonic complex tones and harmonic tones. The paradigm included a control condition in which no active auditory maintenance was required. We observed a bilateral increase in 5-12 Hz power during the perception of harmonic and non-harmonic complex tones compared with the control tone. During the maintenance period a left-lateralized increase in 5-12 Hz was found for all stimuli compared with the control condition. Using a beam-forming approach we identified the sources in left temporal regions. Given that functional magnetic resonance imaging, positron emission tomography and lesion studies have identified right hemisphere regions to be engaged in memory of pitch, we propose that the 5-12 Hz activity serves to functionally disengage left temporal regions. Our findings support the notion that alpha activity is a general mechanism for disengaging task-irrelevant regions.