Tilt responses were scored as the total sum of spikes during the first 2 s after onset of tilt.
The cross-correlation C ∆T) between the cells at time lag ∆T was the sum of the spike counts for all the i = 1, 2,..., M. The cross-correlation C ∆T) was normalized by the spike count that would be expected if the two spike trains were random Poisson events, which was m = M*N/B.
The question arises how the specific choice of the output, which is taken to be the sum of individual spike trains, affects the findings discussed above.
Additionally, for vanishing individual noise,, all output spike trains are identical and the information content of the population does not differ from the information content of the sum of identical spike trains.
The mutual information between the postsynaptic response and the sum of preceding spike ISIs is then I(mathcal{S} t_{k})=H mathcal{S} -H mathcal{S} H mathcal{S} -H mathcal{S}1,ldots, M. Figures 12 and 13 illustrate the results for both the control and the muscarine cases, at 5 and 50 Hz, respectively.
The output of the population is quantified by the sum of the individual spike trains.
Consequently, a population of AD neurons can be referred to as a broadband filter of information, because the sum of the output spike trains contains equal amounts of information about different frequency bands of the signal.
The spatial firing rate distributions ('place fields') for each cell were constructed in the standard manner by summing the total number of spikes that occurred in a given location bin (5 cm by 5 cm), dividing by the amount of time that the rat spent in that location, and smoothing with a Gaussian centered on each bin (Leutgeb et al., 2005).
Fig. 12 Mutual information between postsynaptic response and number of sum of preceding inter-spike intervals in the control and muscarine cases under 5 Hz Poisson stimulation Fig. 13 Information between postsynaptic response and number of sum of preceding inter-spike intervals in control and muscarine cases under 50 Hz Poisson stimulation.
However, as PSTHs are directly sums of neuronal spikes, this representational issue bears on the resulting histogram.
