Modulation of cortical activity by visual and proprioceptive sensory demand in knee movement

Abstract

The field of neurorehabilitation has grown with our understanding of the human brain in recent decades. Regions and networks of the adult brain are now known reorganize following cerebral injury, a process enhanced through performance of complex tasks with specific sensory and motor challenges. Current rehabilitation therapies commonly involve performance of visually guided movements with various degrees of movement assistance or resistance. These tasks require the sensorimotor system to process and integrate information from both the visual and proprioceptive domains, each modality having unique effects on regional cortical activity. However, our understanding of cortical responses to unimodal and bimodal sensory processing demand remains incomplete, especially in the context of lower extremity motor control. The current work used electroencephalography (EEG) to evaluate regional brain activity during planning and execution of knee movements as the complexity of visual and proprioceptive sensory demand was increased. These results showed that the healthy brain required widespread activation of the sensorimotor network (e.g. premotor and primary sensorimotor areas) to perform unimodal visual and proprioceptive information processing, and that activation of these regions was not modality specific. Further studies demonstrated that sensorimotor structures increased activation to intermediate levels of bimodal sensory demand, but not in the transition from intermediate to maximal sensory demand, suggesting involvement of other brain regions in tasks with maximal complexity. High order cortical regions (e.g. prefrontal, parietal and occipital) were then evaluated in unimodal and bimodal conditions to determine if these regions assist in motor control as sensory demand and task complexity increase. Activation of these regions was increased to both visual and proprioceptive sensory modalities, and may reflect increased attentional requirements and the external projection of attention in visual sensory demand. Furthermore, the anterior frontal regions were most active to simultaneously increased visual and proprioceptive demands, implicating these regions in tasks with increased complexity. Lastly, the effect of unimodal visual and proprioceptive sensory demand on cortical activation was evaluated in a subcortical stroke patient. Anterior frontal regions, but not the sensorimotor network, were robustly activated, suggesting that high order cortical regions may provide a viable substrate for future neurorehabilitation therapy.