fmri_doublegamma

Description

FMRI_DOUBLEGAMMA Canonical double-gamma haemodynamic response function. Computes the double-gamma HRF at time points T. The function is the difference of two gamma functions, modelling the initial positive BOLD peak followed by the post-stimulus undershoot: h(t) = (t/t1)^d1 * exp(-d1*(t-t1)/t1) - c*(t/t2)^d2 * exp(-d2*(t-t2)/t2) where t1 = 0.9*d1 and t2 = 0.9*d2.

Usage

g = fmri_doublegamma(t)
g = fmri_doublegamma(t, d1, d2, c)

Inputs

T: Time vector in seconds (e.g. 0:TR:30). Row or column vector.
D1: Delay of response peak in seconds. Default: 6
D2: Delay of undershoot peak in seconds. Default: 12
C: Undershoot-to-peak ratio. Default: 0.35

Outputs

G: HRF values at each time point in T (same size as T).

Examples

t   = 0:0.5:30;
hrf = fmri_doublegamma(t);
plot(t, hrf)
% At TR = 2s
hrf_tr2 = fmri_doublegamma(0:2:30);