Abstract
This work examines how sounds are held in auditory working memory (AWM) in humans by examining oscillatory local field potentials (LFPs) in candidate brain regions. Previous fMRI studies by our group demonstrated blood oxygenation level-dependent (BOLD) response increases during maintenance in auditory cortex, inferior frontal cortex and the hippocampus using a paradigm with a delay period greater than 10s. The relationship between such BOLD changes and ensemble activity in different frequency bands is complex, and the long delay period raised the possibility that long-term memory mechanisms were engaged. Here we assessed LFPs in different frequency bands in six subjects with recordings from all candidate brain regions using a paradigm with a short delay period of 3 s. Sustained delay activity was demonstrated in all areas, with different patterns in the different areas. Enhancement in low frequency (delta) power and suppression across higher frequencies (beta/gamma) were demonstrated in primary auditory cortex in medial Heschl’s gyrus (HG) whilst non-primary cortex showed patterns of enhancement and suppression that altered at different levels of the auditory hierarchy from lateral HG to superior- and middle-temporal gyrus. Inferior frontal cortex showed increasing suppression with increasing frequency. The hippocampus and parahippocampal gyrus showed low frequency increases and high frequency decreases in oscillatory activity. This work demonstrates sustained activity patterns during AWM maintenance, with prominent low-frequency increases in medial temporal lobe regions.
Highlights
In this study we examine the process by which sounds are held in mind over seconds: auditory working memory (AWM)
The event-related spectral perturbations (ERSPs) for remaining subjects are included as supplementary figures (Supplementary Figures 1-5)
Delta power increases and suppression across higher frequencies were found in primary auditory cortex in medial Heschl’s gyrus (HG) whilst non-primary cortex showed patterns of activation and suppression that altered at different levels of the auditory hierarchy from lateral HG to superior and middle temporal gyrus
Summary
In this study we examine the process by which sounds are held in mind over seconds: auditory working memory (AWM). We use the term AWM to refer to the general process of keeping sound objects in mind as opposed to the specific process of phonological working memory to which it is sometimes applied. This general process is relevant to the analysis of auditory scenes in which auditory objects within the scene can remain constant, or come and go. Whilst a number of studies have demonstrated the involvement of early sensory areas in visual working memory That fMRI experiment used a long delay period to overcome the slow hemodynamic response (in order to demonstrate delay period activity ‘uncontaminated’ by encoding or retrieval activity) and may have engaged long-term memory mechanisms
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