% ----------- [BI,Ib,It,Sb,St] = burstindex(varargin) -----------------
%
% Calculates the burst index of a rebound-bursting neuron from a CCIV ranging from
% negative to postivie currents. Assumes that the CCIV protocol sweeps
% through a large enough range of currents to elicit rebound bursts and
% tonic firing.
%
% Burst index is defined as follows:
%
% BI = 1 - (B / (B+T))
% where
% B = abs(Ib)/sqrt(Sb)
% T = abs(It)/sqrt(St)
% and
% Ib = threshold current for eliciting rebound burst
% It = threshold current for eliciting tonic spikes
% Sb = (# spikes in rebound) / (stim length in seconds)
% St = (# of tonic spikes) / (stim length in seconds)
% * dividing by stim length normalizes the spike counts
%
% We take the square root of St and Sb to avoid excessive weighting of spike
% rate in the equation, and instead emphasize the threshold currents.
% This is due to the physiology of rebound bursts, which typically plateau
% at 4-5 spikes despite increasing hyperpolarizing current, while tonic
% spikes plateau at much higher counts, and depend on the stim length
%
%
% >>> INPUTS >>>
% Optional:
% stimon = on time of pulse from CCIV protocol in seconds
% stimoff = off time of pulse from CCIV protocol in seconds
% Spiketimes = spiketimes from CCIV in column format.
% units of spiketimes needs to equal units of stimon/stimoff
% current = current levels used in CCIV protocol
% * if you provide these 4 optional inputs, this function
% will calculate the parametrs Ib, It, Sb, and St for you.
%
% If you already have [Ib,It,Sb,St] parameters calculated,
% leave the 1st 4 inputs blank and proceed with the following four inputs.
%
% Ib = threshold burst current
% It = threshold tonic current
% Sb = # burst spikes / length of pulse (seconds)
% St = # tonic spikes / length of pulse (seconds)
%
% <<< OUTPUTS <<<
% BI = burst index, ranging between [0,1]. Higher values = more "bursty"
% Ib = threshold burst current (optional)
% It = threshold tonic current (optional)
% Sb = normalized # rebound spikes (optional)
% St = normalized # tonic spikes (optional)
%
% By JMS, 02/12/2016
%
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