Another study found that during non-rapid eye movement (N-REM) sleep following training on the texture discrimination task, a significantly higher BOLD signal was observed in the trained visual quadrant of V1 than in another quadrant (Yotsumoto et al. 2009). It has been found that BOLD signals are better correlated with field potential than action potential and reflect the input of activity to intracortical processing of a given area from another area(s) rather than the area’s action potential output