Theta frequency band activity and attentional mechanisms in visual and proprioceptive demand.

In a companion manuscript we reported reduced electroencephalographic (EEG) activation at traditional sensorimotor areas in knee movements with high levels of task difficulty modulated by varying visual and proprioceptive sensory demands. Given that reduced cortical activity with more complex tasks is counter-intuitive, we suggested that high order cognitive-motor areas may show increased EEG activation to compensate for the observed decrease in sensorimotor regions. To test this hypothesis, we evaluated theta band activation at anterior frontal regions in a secondary analysis of our previous data. Unlike activation at sensorimotor areas, anterior frontal responses increased with each level of task difficulty as modulated by precision of visual targeting and/or proprioceptive demands from adding masses to the leg. Activity was increased as both unimodal visual and proprioceptive requirements became more demanding, but showed greater sensitivity to visual over proprioceptive processing requirements. Each level of bimodal task demands showed increasing activation, which was consistently greater when modulated through visual demands. These results are consistent with our hypothesis of increased contribution of anterior frontal regions for motor control in lower extremity movements with increasing sensory demands and further support different mechanisms for internally and externally guided movement.