HC 6 Flashcards
What is functional connectivity and why is it important?
It is the relationship between functional activity of different brain regions.
It is important to study this, because no brain regions work in isolation from others. Regions receive input, give output and communicate.
What is the simplest index of functional connectivity and how should we interpret it?
The correlation between activity of two regions across time. It is direct connection, which means influence.
What is the network of functionally connected voxels?
Seed voxel/ region and its time-varying signal correlated with the signal of all voxels of the brain.
How is the time scale of neural communications?
It is in a matter of milliseconds. There is back-and-forth communication at temporal frequenies far above 1 Hz. It can be picked up through electrophysiological imaging.
How is the time scale measured with hemodynamic imaging?
Slower changes in signal are imaged. Low-pass filter is used and is cut-off at 0.1 Hz. Mostly noise at frequencies > 0.1 Hz.
Why is differentiation between the activity of brain regions difficult?
There are many causes of interest for correlation. There could be a mediated influence or shared influence. You have to be aware of confounding factors.
What is scrubbing?
To exclude time points with the most motion. This is done, because BOLD signal changes are correlated with subject motion.
What is the difference between functional connectivity and effective connectivity?
Functional connectivity is an observational approach and is hypothesis-free. It is based on correlations.
Effective connectivity is an model-based approach and is hypothesis-driven. Think of psychophysiological interactions, SEM and dynamic causal modeling.
Important to keep in mind is that effective connectivity is based on models and not real caual inference. Additional information needed goes beyond observed correlation. Think of evidence from animal models and predictions from theory and hypotheses.
What is PPI?
PsychoPhysiological Interaction. We examine the influence of one region of interest on any other part of the brain as a function of psychological context.
Aims to identify regions whose activity depends on interaction between psychological factors (context) and physiological factors (the time course of a region of interest).
What is the PPI effect?
Context-specific change in relationship between brain regions reflected by context-dependent difference in the slope of the regression between two regional time series.
What is SEM?
Structural Equation Modelling. Estimation of causal influence of multiple areas on each other, using a priori anatomical information.
What did Santens et al study regarding numerical representations?
VIS: primary visual cortex
SENS: number-sensitive area
SEL: numer-selective area
They studied direct vs indirect input from visual representations to number-selective representations.
The results showed that relative importance of two pathways were modulated by format (symbolic vs non-symbolic).
There was no proof of directionality.
What is the difference between functional and anatomical connectivity?
Functional connectivity can change (PPI), while anatomical connectivity is static during experiment.
Functional connectivity means direct influence from A to B, so anatomical connectivity means connection present between A and B.
If there is Functional connectivity that reflects mediating influence, while anatomical connection may not be present.
What is PCA?
Principal component analysis. Identify components that explain most of the variance in the data.
There is a subset of regions with high correlations in activity, this can be summarized by one component.
What is ICA?
Independent component analysis. It is a data-driven approach, in which we use the blind source seperation method.
The goal is to seperate sources given the mixed data.
The assumption is: fMRI data has to have a linear mixture of statistically independent sources.
