Dynamical Systems in Neuroscience:

248 Excitability(g)9 ms(f)(e)(d)(c)(b)(a)membranepotential (mV) spike rasterinjectedcurrent (pA)7 ms6 ms4 msno burstinput200-20-40-602000frozen noiseburst input2 mV6.7 ms50 100 150 200 250 300 350 400 450 500time (ms)Figure 7.24: Frozen-noise experiments demonstrate frequency preference and resonanceto embedded bursts. (a) A random signal (frozen noise) is injected into a neuron invitro to simulate the in vivo conditions (b). The neuron responds with some spiketimingvariability depicted in (c). (d-g) Burst input is added to the frozen noise. Noticethat the neuron is most sensitive to the input having the resonant period 7 ms, whichis near the period of subthreshold oscillation (6.7 ms). Shown are in vitro responses ofmesencephalic V neuron of rats brainstem recorded by the author, Niraj S. Desai, andBetsy C. Walcott. The order of stimulation was first line of c,d,e,f,g, then second lineof c,d,e,f,g, then third line, etc., to avoid slow artifacts.(frozen noise in Fig. 7.24a) and saved it into the memory of the program that injectscurrent into a neuron. Then we injected the stored signal into the neuron 50 times tosee how reliable its spike response is. Despite the in vivo-like activity in Fig. 7.24b,the spike raster in Fig. 7.24c shows vertical clusters indicating that the neuron prefersto fire at certain “scheduled” moments of time corresponding to certain features of thefrozen-noise input.In Fig. 7.24d-g, we added bursts of 3 spikes to the frozen noise. The amplitudesof the bursts were constant (less than 10% of the frozen noise amplitude), but theinterspike periods were different. The idea is to see whether the response of the neuronwould be any different when the burst period is near the neuronal intrinsic period of 6.7ms (see the inset in Fig. 7.24b). As one expects, the non-resonant bursts with 4 ms and9 ms periods remained undetected by the neuron, since the spike rasters in Fig. 7.24d