Abstract
Hebb's idea of a cell assembly as the fundamental unit of neural information processing has dominated neuroscience like no other theoretical concept within the past 60 years. A range of different physiological phenomena, from precisely synchronized spiking to broadly simultaneous rate increases, has been subsumed under this term. Yet progress in this area is hampered by the lack of statistical tools that would enable to extract assemblies with arbitrary constellations of time lags, and at multiple temporal scales, partly due to the severe computational burden. Here we present such a unifying methodological and conceptual framework which detects assembly structure at many different time scales, levels of precision, and with arbitrary internal organization. Applying this methodology to multiple single unit recordings from various cortical areas, we find that there is no universal cortical coding scheme, but that assembly structure and precision significantly depends on the brain area recorded and ongoing task demands.
Highlights
Even more than six decades after its conception, Hebb’s (1949) fundamental idea of a cell assembly continues to play a key role in our understanding of how neural physiology may link up to cognitive function
For two independent units with stationary spike trains, the joint distribution of spike occurrences at a specified time lag l would factor into the single unit (‘marginal’) distributions, p(A,B)=p(A)p(B)
We examined assembly structure in different brain regions from which multiple single-unit recordings were obtained in previously published experiments, including the rat anterior cingulate cortex (ACC; (Hyman et al 2012; Hyman et al 2013)), hippocampal CA1 region, and entorhinal cortex (EC, (Mizuseki et al 2013; Pastalkova et al 2008; Mizuseki et al 2009))
Summary
Even more than six decades after its conception, Hebb’s (1949) fundamental idea of a cell assembly continues to play a key role in our understanding of how neural physiology may link up to cognitive function. At a coarser temporal scale, neurons could fire with a specific temporal patterning to which each neuron may contribute “bursts” of variable length (Figure 1A, IV) Such temporally ordered transitions among coherent firing rate patterns across sets of simultaneously recorded neurons have been described in different cognitive tasks and systems (Lapish et al 2008; Seidemann et al 1996; Jones et al 2007; Durstewitz et al 2010; Beggs & Plenz 2003). At a still broader temporal scale, sets of neurons jointly increasing their average rates for some period of time (Figure 1A, V), as during persistent activity in a working memory task, have been linked to the cell assembly idea (Durstewitz et al 2000)
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