The Miller Lab

Our new paper describing a new model of working memory.  Actually, not so much a new model as an update to the classic model. The classic model posited that we hold thoughts “in mind” (i.e., in working memory) via the persistent spiking of neurons.  That is not wrong.  It is right to a certain level of approximation. There is little doubt that spikes help maintain working memories. However, a closer examination revealed that there is much more going on than persistent spiking.

It is important to keep in mind (pun intended) that virtually all evidence for persistent spiking comes from experiments that averaged neural activity across trials.  The assumption was that averaging boosts signal and decreases noise (“noise” meaning changes in activity from trial to trial). But what if that noise was not noise but real neural dynamics?  We don’t always think about the same thing in the same way.  Averaging assumes we do.

With this in mind, we and others have been leveraging multiple-electrode recording to examine neural activity in “real time” (on individual trials).  This has revealed that working memory-related spiking occurs in sparse, coordinated bursts of activity.  It also revealed oscillatory dynamics between brain waves in two frequency bands, beta and gamma.  Gamma seems to act as a carrier wave that maintains the contents of working memory. Beta seems carry the top-down control signals that allow us to exert volitional control over working memory.

Miller, E.K., Lundqvist, M., and Bastos, A.M. Working Memory 2.0 Neuron  DOI:https://doi.org/10.1016/j.neuron.2018.09.023  (Download a *free* copy for the next 50 days)

Here’s the abstract:
Working memory is the fundamental function by which we break free from reflexive input-output reactions to gain control over our own thoughts. It has two types of mechanisms: online maintenance of information and its volitional or executive control. Classic models proposed persistent spiking for maintenance but have not explicitly addressed executive control. We review recent theoretical and empirical studies that suggest updates and additions to the classic model. Synaptic weight changes between sparse bursts of spiking strengthen working memory maintenance. Executive control acts via interplay between network oscillations in gamma (30–100 Hz) in superficial cortical layers (layers 2 and 3) and alpha and beta (10–30 Hz) in deep cortical layers (layers 5 and 6). Deep-layer alpha and beta are associated with top-down information and inhibition. It regulates the flow of bottom-up sensory information associated with superficial layer gamma. We propose that interactions between different rhythms in distinct cortical layers underlie working memory maintenance and its volitional control.