Frontiers in Systems Neuroscience Systems Neuroscience

Abstract

disrupt interhemispheric balance; indeed, older adults demonstrate reduced inhibition between hemispheres compared to young adults (Talelli et al., 2008a,b). As callosal connections between the two motor cortices appear to have a net inhibitory effect (Ferbert et al., cal-losal degeneration with age may lead to greater activation of the ipsilateral M1 (due to reduced inhibition from the contralateral M1) during motor task performance. However, a complete section of the CC leads to an absence of ipsilateral activation during tactile stimulation (Fabri et al., 1999), suggesting that the relationship between CC integrity and ipsilateral activation in sensorimotor tasks may be nonlinear. Therefore, while some degeneration of the CC may lead to less lateralized task processing (Muller-Oehring et al., 2007), extensive damage or complete section of the CC would likely abolish ipsilateral activation. Motor task difficulty has also been shown to have an impact on recruitment of ipsilateral M1. More complex motor tasks result in greater recruitment of brain regions, particularly the ipsilateral M1 (Seidler et al., 2004; Verstynen et al., 2005). This raises the question of whether ipsilateral M1 activity in older adults is due to age differences in task difficulty. Advances in imaging analyses, such as resting state functional connectivity (fcMRI), provide a way to assess communication between cortical regions without incorporating a task. Regions with similar functions and known anatomical connections have shown strong correlations in the low-frequency blood oxygen level dependent (BOLD) signal, commonly referred to as