Task- and performance-related modulation of domain-specific auditory short-term memory representations in the gamma-band.

The short-term retention of information has been related to oscillatory activity in the gamma-band. In recent auditory spatial short-term memory studies we have found stimulus-specific components of parieto-occipital gamma-band activity (GBA) which might reflect the activation of local networks tuned to task-relevant stimulus features. The present magnetoencephalography study (N=22) tested this interpretation by assessing whether the topography of stimulus-specific GBA depends on task demands. Sample sounds were characterized by both a variable interaural time delay and a variable central frequency. In separate task blocks, either the lateralization or the frequency of the same stimuli had to be maintained. Statistical probability mapping of differences in oscillatory responses to the retention of sample sounds replicated the contralateral posterior topography for GBA components distinguishing between medial and lateral sounds in the spatial memory task. In contrast, lower- and higher-frequency stimuli were accompanied by frontal GBA components in the frequency task. Memory for lateralization versus frequency selectively enhanced oscillatory activity for these posterior versus frontal components, directly demonstrating their modulation by task demands. Incorrect "non-match" responses were negatively correlated with delay-phase GBA to the relevant feature, whereas incorrect "match" responses correlated positively with GBA to the irrelevant feature. In summary, the topography of stimulus-specific GBA to identical stimuli reflected the selective representation of task-relevant features. Task performance was predicted by both enhanced stimulus-specific GBA for the task-relevant stimulus attribute and reduced gamma-band representations of the task-irrelevant stimulus feature. Stimulus-specific GBA may reflect the memory representation that is used in subsequent recognition.