Experimental and modeling studies were used to estimate the effect of different sampling rates (repetition times, TR) and different sampling positions on the estimates of the temporal properties of the hemodynamic response function (HRF) derived from fMRI studies. Data were acquired at a TR of 250 ms and then subjected to various degrees of undersampling. Using a gaussian fitting function it is...

Introduction Brain areas are additionally activated in elderly subjects [1,2]. It was suggested that this additional recruitment of brain areas in elderly subjects was consistent with the compensation hypothesis and characterized neuroplasticity at the systems level in the aging brain, rather than dedifferentiation hypothesis [2]. On the other hand, age-related reduction of BOLD signal (hemodyn...

INTRODUCTION Prior studies comparing Hemodynamic Response Function (HRF) in the young and elderly adults based on fMRI data have reported inconsistent findings for brain vision and motor regions in healthy aging. It is shown that the averaging method employed in all previous works has caused this inconsistency. The averaging is so sensitive to outliers and noise. However, fMRI data are obscured...

The specificity of the hemodynamic response function (HRF) is determined spatially by the vascular architecture and temporally by the evolution of hemodynamic changes. The stimulus duration has additional influence on the spatiotemporal evolution of the HRF, as brief stimuli elicit responses that engage only the local vasculature, whereas long stimuli lead to the involvement of remote vascular ...

BACKGROUND Substance dependence is associated with impaired decision-making and altered fronto-striatal-limbic activity. Both greater and lesser brain activity have been reported in drug users compared to controls during decision-making. Inconsistent results might be explained by group differences in the temporal profile of the functional magnetic resonance imaging (fMRI) response. While most p...

We present a new algorithm to estimate hemodynamic response function (HRF) and drift components of fMRI data in wavelet domain. The HRF is modeled by both parametric and nonparametric models. The functional Magnetic resonance Image (fMRI) noise is modeled as a fractional brownian motion (fBm). The HRF parameters are estimated in wavelet domain by exploiting the property that wavelet transforms ...

The development of brain function in young infants is poorly understood. The core challenge is that infants have a limited behavioral repertoire through which brain function can be expressed. Neuroimaging with fMRI has great potential as a way of characterizing typical development, and detecting abnormal development early. But, a number of methodological challenges must first be tackled to impr...

Many fMRI analysis methods use a model for the hemodynamic response function (HRF). Common models of the HRF, such as the Gaussian or Gamma functions, have parameters that are usually selected a priori by the data analyst. A new method is presented that characterizes the HRF over a wide range of parameters via three basis signals derived using principal component analysis (PCA). Covering the HR...

Introduction The important role of fMRI in geriatrics is to assess the change of brain activation related to early signs of cognitive impairments. Various cognitive tasks increased the activation in the frontal or parietal areas in elderly subjects. On the other hand, age-related reduction of BOLD signal in the primary visual area (V1) has been discussed [1 3]. In this study, we investigated th...

Introduction It has been demonstrated in our previous study [1] that spontaneous cerebral blood flow (CBF) and electroencephalography (EEG) simultaneously recorded from rat primary somatosensory cortex are tightly coupled under burst-suppression anesthesia induced by isoflurane. On the other hand, other studies [2-3] have reported that the rat brain can exhibit distinct hemodynamic responses to...