Dynamics of auditory working memory

Abstract

Working memory denotes the ability to retain stimuli in mind that are no longer physically present and to perform mental operations on them. Electro- and magnetoencephalography allow investigating the short-term maintenance of acoustic stimuli at a high temporal resolution. Studies investigating working memory for non-spatial and spatial auditory information have suggested differential roles of regions along the putative auditory ventral and dorsal streams, respectively, in the processing of the different sound properties. Analyses of event-related potentials have shown sustained, memory load-dependent deflections over the retention periods. The topography of these waves suggested an involvement of modality-specific sensory storage regions. Spectral analysis has yielded information about the temporal dynamics of auditory working memory processing of individual stimuli, showing activation peaks during the delay phase whose timing was related to task performance. Coherence at different frequencies was enhanced between frontal and sensory cortex. In summary, auditory working memory seems to rely on the dynamic interplay between frontal executive systems and sensory representation regions.

Keywords: coupling; event-related potentials; gamma; non-spatial processing; review; spatial processing; spectral activity.

FIGURE 1

Stimulus-specific gamma activity to sounds of different lateralization angle in a spatial AWM task. The graph on the left shows grand-average time courses of a gamma activity differentiation score reflecting the degree to which oscillatory signals differentiate between the two sample stimuli. Positive values indicate a “consistent” differentiation with larger amplitudes to the preferred stimulus, while negative values stand for an “inconsistent” differentiation with larger amplitudes to the non-preferred sound. The amplitude of this difference score was tested against zero to obtain a statistical (p-value) time course. Curves were overlaid for both delay durations and aligned for the time point of S2. The red curve (referring to the time axis at the top) shows the short, the green curve (referring to the time axis at the bottom) the long delay period. The map on the right shows the sensor positions showing stimulus-specific effects for the lateral (l) and medial (m) sample sounds during the short (red circles) and the long (green circles) delay durations. Adapted from Kaiser et al. (2009b), copyright 2009 with permission from Elsevier.

FIGURE 2

Time courses of the differentiation score (see legend to Figure 1) for good and bad performers (in blue and red, respectively) for the short delay duration (A) and the long duration (B) in the study by Kaiser et al. (2009b).