Bayesian Comparison of Neurovascular Coupling Models Using EEG-fMRI

Functional magnetic resonance imaging (fMRI), with blood oxygenation level-dependent (BOLD) contrast, is a widely used technique for studying the human brain. However, it is an indirect measure of underlying neuronal activity and the processes that link this activity to BOLD signals are still a topic of much debate. In order to relate findings from fMRI research to other measures of neuronal activity it is vital to understand the underlying neurovascular coupling mechanism. Currently, there is no consensus on the relative roles of synaptic and spiking activity in the generation of the BOLD response. Here we designed a modelling framework to investigate different neurovascular coupling mechanisms. We use Electroencephalographic (EEG) and fMRI data from a visual stimulation task together with biophysically informed mathematical models describing how neuronal activity generates the BOLD signals. These models allow us to non-invasively infer the degree of local synaptic and spiking activity in the healthy human brain. In addition, we use Bayesian model comparison to decide between neurovascular coupling mechanisms. We show that the BOLD signal is dependent upon both the synaptic and spiking activity but that the relative contributions of these two inputs are dependent upon the underlying neuronal firing rate. When the underlying neuronal firing is low then the BOLD response is best explained by synaptic activity. However, when the neuronal firing rate is high then both synaptic and spiking activity are required to explain the BOLD signal

Measurement of B(d)0 - anti-B(d)0 oscillations

Bd 0meson oscillations are measured in hadronic Z0decays using the charge of a lepton or the mean charge of an event hemisphere to sign the presence of a b or a b quark when it is produced, and using the charge of a lepton emitted at large ptor of a D∗±to sign the presence of a B or a B meson when it decays. With 3.2 million hadronic Z0decays registered by DELPHI between 1991 and 1994, the mass difference Δmdbetween the two physical Bd 0states is measured in four channels: Δmd= 0.523 ± 0.072 ± 0.043 ps-1(D∗±- Qhem) Δmd= 0.493 ± 0.042 ± 0.027 ps-1(ℓ - Qhem) Δmd= 0.499 ± 0.053 ± 0.015 ps-1((π∗- ℓ) - Qhem) Δmd= 0.480 ± 0.040 ± 0.051 ps-1(ℓ - ℓ). Taking into account the statistical overlap between these measurements and the common systematic uncertainties, the combined result is: Δmd= 0.497 ± 0.035 ps-1.0info:eu-repo/semantics/publishe

Measurement of B-d(0)-(B-d(0))over-bar oscillations

B-d(0) meson oscillations are measured in hadronic Z(0) decays using the charge of a lepton or the mean charge of an event hemisphere to sign the presence of a b or a (b) over bar quark when it is produced, and using the charge of a lepton emitted at large p(t) or of a D*(+/-) to sign the presence of a B or a (B) over bar meson when it decays. With 3.2 million hadronic Z(0) decays registered by DELPHI between 1991 and 1994, the mass difference Delta m(d) between the two physical B-d(0) states is measured in four channels: Delta m(d) = 0.523 +/- 0.072 +/- 0.043 ps(-1) (D*(+/-) - Q(hem)) Delta m(d) = 0.493 +/- 0.042 +/- 0.027 ps(-1) (l - Q(hem)) Delta m(d) = 0.499 +/- 0.053 +/- 0.015 ps(-1) ((pi* - l) - Q(hem) Delta m(d) = 0.480 +/- 0.040 +/- 0.051 ps(-1) (l - l). Taking into account the statistical overlap between these measurements and the common systematic uncertainties, the combined result is: Delta m(d) = 0.497 +/- 0.035 ps(-1)