Abstract
Neuronal action potentials or spikes provide a long-range, noise-resistant means of communication between neurons. As point processes single spikes contain little information in themselves, i.e., outside the context of spikes from other neurons. Moreover, they may fail to cross a synapse. A burst, which consists of a short, high frequency train of spikes, will more reliably cross a synapse, increasing the likelihood of eliciting a postsynaptic spike, depending on the specific short-term plasticity at that synapse. Both the number and the temporal pattern of spikes in a burst provide a coding space that lies within the temporal integration realm of single neurons. Bursts have been observed in many species, including the non-mammalian, and in brain regions that range from subcortical to cortical. Despite their widespread presence and potential relevance, the uncertainties of how to classify bursts seems to have limited the research into the coding possibilities for bursts. The present series of research articles provides new insights into the relevance and interpretation of bursts across different neural circuits, and new methods for their analysis. Here, we provide a succinct introduction to the history of burst coding and an overview of recent work on this topic.
Highlights
Neurons communicate with other neurons in the form of all-or-none action potentials
Bursting is observed in many different species and systems (Figure 1), including the CA3 of the rodent hippocampus (Traub and Wong, 1981; Miles and Wong, 1986; Traub et al, 1989), the electrosensory system of the weakly electric fish (Gabbiani et al, 1996), mammalian midbrain dopaminergic neurons (Wang, 1981; Grace and Bunney, 1984; Grace and Onn, 1989; Tepper et al, 1995; Hyland et al, 2002) thalamocortical relay (TCR) neurons in the mammalian thalamus (Jahnsen and Llinás, 1984; Williams et al, 1997)
Recent experimental evidence obtained by optogenetic interference suggests an important role for sharpwave-ripples in the hippocampus in renormalizing synaptic weights during sleep (Norimoto et al, 2018)
Summary
Neurons communicate with other neurons in the form of all-or-none action potentials (spikes). These spikes are the brain’s language for encoding information, both extracted from external stimuli and sent by internal sources. There is a long-lasting and ongoing debate about how much information is transferred in the precise timing of individual spikes, the time-scale of the neural code and the role of noise and trial-to-trial variability (Bair et al, 1994; London et al, 2010), i.e., the debate about whether the brain uses a ‘‘timing’’ or a ‘‘rate’’ code (ill-defined as these terms may be). A salient spike pattern that has been widely observed is the burst: a group of action potentials generated in rapid succession, followed by a period of relative quiescence. Bursts add an extra dimension to the coding debate: are bursts just generated to increase the reliability using unreliable synapses, or is there information in the number (Eyherabide et al, 2009) or firing rate (Izhikevich et al, 2003) of spikes within a burst? Does the precise pattern of spikes within a burst carry information, or is it just the binary information that there was a burst-event (Miles and Wong, 1986)?
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