DYNAMICS UNDERLYING AUDITORY WORKING MEMORY

We aim to understand the dynamics underlying auditory working memory for maintaining 'simple' tones. We recorded MEG in 17 subjects while they maintained one of the two presented tones (or ignore both as control condition). After 12s, subjects compared the pitch of a test tone with the maintained tone.
Analysis of evoked responses showed persistent activity throughout maintenance compared to the pre-stimulus silent baseline but only at the start of maintenance when compared to the control condition. The evoked response during maintenance was source localized against baseline to bilateral auditory cortex. Analysis of induced responses showed suppressed alpha in the left auditory cortex, enhanced theta in medial prefrontal cortex, and enhanced beta in cerebellum.
In a second experiment, 19 new subjects were presented with a tone and a Gabor patch to maintain either for 12s. Analysis of the induced responses in auditory condition yielded similar results.
Connectivity analysis showed that the theta activity in medial prefrontal was phase-locked to left hippocampus and left auditory cortex. The beta activity in cerebellum’s phase-locking to left IF) was correlated to subject’s task accuracy.
Using MVPA, a LDA classifier was trained to decode the contents of AWM (discriminate low vs high pitch) using beta PLV with right cerebellum as its features. A channel searchlight analysis showed that decoder performance at right Anterior Cingulate Gyrus (56.17% acc.) was above chance. Further, the decoder performance at Right STG was correlated to subject’s task accuracy, showing a correspondence between encoding distance and behavioural performance.