Table 1.

Summarized examples of impaired postural responses and associated cortical function.

Condition	Major reported impairments of postural responses	Cortical function during impaired standing postural responses
Stroke involving cortex	Feet-in-place responses: change in the distal-to-proximal muscle pattern and delayed muscle onset as well as delayed and slowed rates of force development in the more severely involved limb (Di Fabio et al., 1986; Ikai et al., 2003)	Unaware of studies utilizing measures of cortical neurophysiology during standing postural responses post-stroke
	Stepping responses: paretic limb exhibits delayed foot-lift, low clearance, need for multiple steps, or an inability to initiate a step (Lakhani et al., 2011; Martinez et al., 2013). Steps are non-paretic limb dominant, even when obstacles block the limb (Lakhani et al., 2011; Mansfield et al., 2012). Impairments associate with increased fall risk and, in contrast, greater use of the paretic limb associates with better recovery (Mansfield et al., 2012, 2013)
Advanced age	Age associates with delays and antagonistic co-contraction of muscles, as well as greater displacement and instability (Halicka et al., 2012)	Electroencephalographic (EEG) PEP delayed, bifid (double-peaked), and decreased with age—effects larger in balance impaired elders (Duckrow et al., 1999)
	Dual task costs greater for elderly only in late-phase in-place and stepping responses, more so for stepping and more so if balance impaired elder (Brown et al., 1999; Rankin et al., 2000; Brauer et al., 2001, 2002; Zettel et al., 2008)
Parkinson's disease	Falls, instability, antagonistic co-contraction and lack of modulation based on knowledge of perturbation. Stepping responses may exhibit freezing or have decreased velocity and step length (Jacobs et al., 2005, 2009b; Jacobs and Horak, 2006; Smith et al., 2012)	Increased desynchronization of EEG beta signal, and this increase associates with decreased response adaptation to perturbation magnitude (Smith et al., 2012)
	With dual tasking, in-place responses are not modulated, and falls increase during stepping responses, but postural preparation or freezing unchanged (de Lima-Pardini et al., 2012; Jacobs et al., 2014a)
Low back pain	Increased pre-perturbation muscle activation, increased activation amplitude at distal muscle, but decreased or delayed trunk muscle activation (Jacobs et al., 2011)	Late positive peak PEP larger with LBP; larger PEP correlates with less postural instability, disability, and fear of activity (Jacobs et al., 2014b)