Ongoing fluctuations of neuronal activity have long been considered intrinsic noise that
introduces unavoidable and unwanted variability into neuronal processing, which the
brain eliminates by averaging across population activity (Georgopoulos et al., 1986;
Lee et al., 1988; Shadlen and Newsome, 1994; Maynard et al., 1999). It is now
understood, that the seemingly random fluctuations of cortical activity form highly
structured patterns, including oscillations at various frequencies, that modulate evoked
neuronal responses (Arieli et al., 1996; Poulet and Petersen, 2008; He, 2013) and affect
sensory perception (Linkenkaer-Hansen et al., 2004; Boly et al., 2007; Sadaghiani et al.,
2009; Vinnik et al., 2012; Palva et al., 2013). Ongoing cortical activity is driven by
proprioceptive and interoceptive inputs. In addition, it is partially intrinsically generated
in which case it may be related to mental processes (Fox and Raichle, 2007; Deco
et al., 2011). Here we argue that respiration, via multiple sensory pathways, contributes
a rhythmic component to the ongoing cortical activity. We suggest that this rhythmic
activity modulates the temporal organization of cortical neurodynamics, thereby linking
higher cortical functions to the process of breathing