A theory of working memory without consciousness or sustained activity
Working memory and conscious perception are thought to share similar brain mechanisms, yet recent reports of non conscious working memory challenge this view. Combining visual masking with magnetoencephalography, we demonstrate the reality of non conscious working memory and dissect its neural mechanisms. In a spatial delayed response task, participants reported the location of a subjectively unseen target above chance level after a long delay. Conscious perception and conscious working memory were characterized by similar signatures: a sustained desynchronization in the alpha/beta band over frontal cortex, and a decodable representation of target location in posterior sensors. During non conscious working memory, such activity vanished. Our findings contradict models that identify working memory with sustained neural firing, but are compatible with recent proposals of 'activity silent' working memory. We present a theoretical framework and simulations showing how slowly decaying synaptic changes allow cell assemblies to go dormant during the delay, yet be retrieved above chance level after several seconds.