Abstract
Working memory is of great interest because of its importance in cognitive function, its relation to consciousness, and impairments in disease, but the cellular mechanisms remain elusive and controversial. A recent article by Barbosa and colleagues overturns the conclusions of an influential study by Wolff and colleagues, which concluded that working memory can be maintained in a hidden state by transient plasticity of synaptic connections that form dynamic ensembles of neurons encoding information temporarily. A reanalysis of the data reveals that there is a persistent electrically active signature in the EEG recordings that is sustained for the duration of the working memory. This reanalysis adds to a large body of evidence indicating that working memory is encoded by sustained action potential firing. However, several studies show that unconscious (unattended) working memories can be recalled even in the absence of measurable neural activity, suggesting that electrically silent mechanisms may be involved. Testing that hypothesis is problematic, given that it posits no neuronal firing that could be easily measured.