FortuneFavors the Bold

Interpreting the BOLD signal.

The development of functional magnetic resonance imaging (fMRI) has brought together a broad community of scientists interested in measuring the neural basis of the human mind. Because fMRI signals are an indirect measure of neural activity, interpreting these signals to make deductions about the nervous system requires some understanding of the signaling mechanisms. We describe our current und...

Detectability of the BOLD signal

Introduction The BOLD signal is a weak signal, and hence if no BOLD signal is found in an area this does not automatically mean there is no neural activity in that area. Signal dropout, artifacts, instability, physiological noise, RF-coil inhomogeneity etc. can all reduce the SNR locally leading to decreased detectability of the BOLD signal. Here we illustrate that calculation of the spatial di...

The Negative BOLD Signal Unmasked

Many fMRI experiments show regions of cortex that seem to respond in antiphase with the primary stimulus. In this issue of Neuron, Shmuel et al. show that this "negative BOLD response" is spatially and temporally linked to reductions in blood flow. By combining BOLD and blood flow data to model the energy consumption in cortex, they conclude that the NBR is primarily due to active neuronal inhi...

Bold Aspirations

Quantitative Combined ASL/BOLD Imaging: Implications for the Interpretation of the BOLD Post-stimulus Undershoot

Purpose A dual-echo spiral arterial spin labeling (ASL) technique provides simultaneous measurements of cerebral blood flow (CBF) and BOLD responses to brain activation, and has been applied in a calibrated-BOLD methodology to assess the coupling of CBF and the cerebral metabolic rate of O2 (CMRO2) [1-3]. However, the potential of this approach to provide a quantitative probe of the CBF and BOL...