balloon {neuRosim}

Balloon model

Description

Generates the BOLD signal based on the Balloon model of Buxton et al. (2004).

Usage

  balloon(stim, totaltime, acc, par=list(), verbose=TRUE)

Arguments

stim

Vector representing the presence/absence (1-0 coding) of a stimulus/activation in seconds.

totaltime

Total duration of stimulus vector in seconds.

acc

Microtime resolution of stimulus vector in seconds.

par

List representing the parameters of the Balloon model. The list should contain the following:

kappa

Inhibitory gain factor

tau1

Inhibitory time constant

tauf

FWHM of CBF impulse response

taum

FWHM of CMRO2 impulse resonse

deltat

Delay of CBF relative to CMRO2 response

n

Steady-state flow metabolism relation

f1

Normalized CBF response to sustained neural activation

tauMTT

Transit time through the balloon

tau

Viscoelastic time constant

alpha

Steady-state flow-volume relation

E0

baseline O2 extraction fraction

V0

baseline blood volume

a1

weight for deoxyHb change

a2

weight for blood volume change

verbose

If TRUE, warnings are displayed.

Details

Based on the provided stimulus boxcar function, a neural activation function is generated that enters the Balloon model to generate a BOLD response. The microtime resolution ensures a high-precision generation of the response. More details can be found in Buxton et al. (2004).

Value

Vector representing the values of the BOLD signal for the given stimulus vector and microtime resolution.

Author(s)

G. Verdoolaege, M. Welvaert

References

Buxton, RB, Uludag, K, Dubowitz, DJ and Liu, TT (2004). Modeling the hemodynamic response to brain activation. NeuroImage, 23, S220-S233.

See Also

canonicalHRF, gammaHRF

Examples

s <- rep(rep(0,10), rep(1,10), 5)
T <- 100
it <- 0.1
out <- balloon(s, T, it) 
#takes a couple of seconds due to solving of the differential equations