Effects of cognitive load on cortical oscillations during a pattern learning task using MEG and pupillometry

Silvia L. Isabella (1,2,3), Allan J. Cheyne (1,2,3), Douglas O. Cheyne (4)

1. Institute of Medical Sciences, University of Toronto

2. Institute of Biomaterials and Biomedical Engineering, University of Toronto

3. Neurosciences and Mental Health, Hospital for Sick Children

4. Department of Psychology, University of Waterloo

Although studies involving use of cognitive control demonstrate changes in brain activity, the functional roles of these signals remain unknown. The objective of this study is to characterize cortical oscillations related to increases in cognitive and motor demands. We hypothesize that frontal θ (4-8 Hz) and sensorimotor γ (60-90 Hz) power will increase with cognitive effort (speed + load) required by the task (as measured by reaction time, RT, and pupil diameter, PD) while post-movement β (15-30 Hz) rebound (PMBR) will decrease with effort. We measured neuromagnetic (MEG) brain activity in 16 right-handed healthy adults performing 6 blocks of a go/switch task (Switch=25%). We manipulated stimulus predictability using fixed stimulus sequences (P=90%, d=10%) that were unknown to the participants. There was a main effect of response hand (Go/Switch) and pattern (all p<0.01) on RT and PD. Given that PD was more sensitive than RT to the task parameters, subjects likely increased cognitive load (PD) to reduce differences in performance (RT). We found that θ activity was more sensitive to the pattern (p<0.001) than to the Switch response (p<0.02), indicating a role in surprise detection. Furthermore, PMBR and γ increased with cognitive load, but did not correlate with RT or PD, indicating a role in integrating cognitive and motor parameters together. This study is the first to distinguish these roles for these cortical oscillations, while demonstrating a role for frontal activity in surprise detection over cognitive control, and a role for sensorimotor activity in integrating cognitive and motor control.