The many layers of BOLD. The effect of hypercapnic and hyperoxic stimuli on macro- and micro-vascular compartments quantified by CVR, M, and CBV across cortical depth.

Ultra-high field functional magnetic resonance imaging (fMRI) offers the spatial resolution to measure neuronal activity at the scale of cortical layers. However, cortical depth dependent vascularization differences, such as a higher prevalence of macro-vascular compartments near the pial surface, have a confounding effect on depth-resolved blood-oxygen-level dependent (BOLD) fMRI signals. In the current study, we use hypercapnic and hyperoxic breathing conditions to quantify the influence of all venous vascular and micro-vascular compartments on laminar BOLD fMRI, as measured with gradient-echo (GE) and spin-echo (SE) scan sequences, respectively. We find that all venous vascular and micro-vascular compartments are capable of comparable theoretical maximum signal intensities, as represented by the M-value parameter. However, the capacity for vessel dilation, as reflected by the cerebrovascular reactivity (CVR), is approximately two and a half times larger for all venous vascular compartments combined compared to the micro-vasculature at superficial layers. Finally, there is roughly a 35% difference in estimates of CBV changes between all venous vascular and micro-vascular compartments, although this relative difference was approximately uniform across cortical depth. Thus, our results suggest that fMRI BOLD signal differences across cortical depth are likely caused by differences in dilation properties between macro- and micro-vascular compartments.

Adiposity affects emotional information processing.

Obesity is a worldwide epidemic associated with severe health and psychological wellbeing impairments expressed by an increased prevalence of affective disorders. Emotional dysfunction is important due to its effect on social performance. The aim of the present narrative review is to provide a general overview of human research exploring emotional information processing in overweight and obese people. Evidence suggests that obesity is associated with an attenuation of emotional experience, contradictory findings about emotion recognition, and scarce research about automatic emotional information processing. Finally, we made some concluding considerations for future research on emotional information processing in overweight and obese people.

The BOLD sensitivity of rapid steady-state sequences.

PURPOSE: Relaxation and dephasing of water protons embedded in a vascular network is driven by local magnetic field inhomogeneities around deoxygenated blood vessels. These effects strongly depend on the relation between mean diffusion length and diameter of blood vessels, as well as on the chosen imaging sequence. In this work, the BOLD sensitivity of steady-state sequences as a function of vessel size, field strength, and sequence parameters are analyzed. METHODS: Steady-state magnetization within a network of artificial cylinders is simulated with Monte Carlo methods for different coherence pathways. In addition, measurements on microspheres were performed to confirm theoretical results. RESULTS: Simulations and phantom results demonstrate a vessel size-dependent signal attenuation effect of all coherence pathways. Both the FID and ECHO pathways show a signal profile similar to spin echo sequences where in the static dephasing regime the effect of larger vessels is suppressed. CONCLUSION: The BOLD effect measured in steady-state sequences is most sensitive to microvessels and might therefore be closer to the underlying neuronal event compared to gradient echo sequences.