Long-Term Activity Dynamics of Single Neurons and Networks
The firing rate of neuronal spiking in vitro and in vivo significantly varies over extended timescales, characterized by long-memory processes and complex statistics, and appears in spontaneous as well as evoked activity upon repeated stimulus presentation. These variations in response features and their statistics, in face of repeated instances of a given physical input, are ubiquitous in all levels of brain-behavior organization. They are expressed in single neuron and network response variability but even appear in variations of subjective percepts or psychophysical choices and have been described as stemming from history-dependent, stochastic, or rate-determined processes.
But what are the sources underlying these temporally rich variations in firing rate? Are they determined by interactions of the nervous system as a whole, or do isolated, single neurons or neuronal networks already express these fluctuations independent of higher levels? These questions motivated the application of a method that allows for controlled and specific long-term activation of a single neuron or neuronal network, isolated from higher levels of cortical organization.
This chapter highlights the research done in cultured cortical networks to study (1) the inherent non-stationarity of neuronal network activity, (2) single neuron response fluctuations and underlying processes, and (3) the interface layer between network and single cell, the non-stationary efficacy of the ensemble of synapses impinging onto the observed neuron.
KeywordsResponse fluctuations Long-memory processes Self-organized criticality Single neuron Direct response Synaptic dynamics
Memories of ongoing discussions in the lab of Shimon Marom with Avner Wallach, Asaf Gal, Hanna Keren, Netta Haroush, and Dani Dagan helped assembling this overview. I further thank Iacopo Hachen, Artoghrul Alishbayli, and Luciano Paz for help in reviewing and discussing the manuscript. The financial support of the Human Frontier Science Program (http://www.hfsp.org; project RGP0015/2013) and the European Research Council advanced grant CONCEPT (http://erc.europa.eu; project 294498) is kindly acknowledged.
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