Such analyses, however, are very sensitive to the averaging window (several hundreds of milliseconds), and do not capture fine temporal spiking patterns on the order of a few spikes, which, if they exist, would have significant consequences for our understanding of neural information processing. To circumvent these difficulties, spike patterns have been viewed as patterns of firing rates ( Zipser et al., 1993), rather than patterns of spike times. Finding different patterns in real data has been difficult because neurons typically may jump from one pattern to another at times that cannot be predicted and because single patterns are themselves difficult to identify in the presence of neuronal noise. In the noiseless case, whether the spikes occur on the odd or even cycles of the sine wave is determined solely by the initial conditions ( Tiesinga, 2002) and depends on the prestimulus history of the neuron. When various types of perturbations were made to the injected current in both in vitro neurons and computational models, the neural responses relaxed to the original spike pattern within a few tens of milliseconds ( Tiesinga, 2002 Tiesinga et al., 2002).ĭifferent spike patterns can occur in vitro, for example, when a neuron is reliably entrained in the 1:2 regimen by an injected current sine wave of sufficiently high frequency to generate one spike every two cycles. The spike pattern depends on stimulus features such as frequency and amplitude ( Hunter et al., 1998 Fellous et al., 2001 Hunter and Milton, 2003) and on the intrinsic properties of the neuron, such as its refractory period ( Berry and Meister, 1998 Reich et al., 1998 Kara et al., 2000), intrinsic channel noise ( White et al., 2000), and overall level of excitability ( Schreiber et al., 2004). Similar observations have been made in vivo using visual stimuli in the retina, lateral geniculate nucleus (LGN), and visual cortices ( Berry et al., 1997 Gur et al., 1997 Buracas et al., 1998 Kara et al., 2000 Reinagel and Reid, 2000, 2002) and in invertebrate preparations ( Bryant and Segundo, 1976 Wehr and Laurent, 1996 de Ruyter van Steveninck et al., 1997 Warzecha et al., 2000). Repeated injection of a fluctuating current into the soma of a cortical neuron in vitro yields similar spike patterns, precise to within a few milliseconds ( Mainen and Sejnowski, 1995).
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