fMRI Methods
Lecture 12 – Random stuff…
Correlation/Covariance
The idea with correlation is that two variables are related, enabling you to predict one from the other.
Implies, but does not prove causality.
Tricky business:
Rat
e of
aut
ism
Rate of atheists in the population
Correlation with behavior
1. Explain between-trial variability in behavior (reaction time, accuracy, memory, decision making variables, fear, bravery) with response amplitude.
2. Explain between-subject variability in behavior with response amplitude.
In both cases: look for brain areas that predict behavior. Places where the extent of behavior is encoded by strength of response (e.g. fear in Amygdala).
Example
Mirror system responses in autism:
Dapretto et. al. Nat. Neurosci 2006
Spurious correlations?
Personality measure reliability ~ 0.8fMRI measure reliability ~ 0.7
Correlation between the two should be < 0.74
Spurious correlations?64,000 voxels and multiple subjects…
Lack of independence
Solutions/Approaches
1. Test for correlations in ROIs defined based on other criteria.
2. Split your data into two halves and show reproducibility.
Examples
Identify ROI that responds to faces using one scan.
Determine whether responses are correlated with face familiarity in this ROI and not in other ROIs using data
from another scan.
Say a word about correlations in rest scans
Planning experiments
Number of subjects and trials - power analysis
Caveats and proper controls – Signal and noise, statistical interpretation.
Auditory experiments
Issues with sound presentation.
Auditory system and language.
To the lab!
Top Related