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.

Several recent studies have shown that respiration modulates oscillatory neuronal activity in the neocortex and hippocampus on a cycle-by-cycle basis. It was suggested that this respiratory influence on neuronal activity affects cognitive functions, including memory. Sharp-wave ripples (SWRs) are high-frequency local field potential activity patterns characteristic for the hippocampus and implicated in memory consolidation and recall. Here we show that the timing of SWR events is modulated by the respiratory cycle, with a significantly increased probability of SWRs during the early expiration phase. This influence of respiration on SWR occurrence was eliminated when olfactory bulb activity was inhibited. Our findings represent a possible neuronal mechanism for a direct influence of the respiratory cycle on memory function.

SUMMARY The cerebellum has long been implicated in tasks involving precise temporal control, especially in the coordination of movements. Here we asked whether the cerebellum represents temporal aspects of oscillatory neuronal activity, measured as instantaneous phase and difference between instantaneous phases of oscillations in two cerebral cortical areas involved in cognitive function. We simultaneously recorded Purkinje cell (PC) single-unit spike activity in cerebellar lobulus simplex (LS) and Crus I and local field potential (LFP) activity in the medial prefrontal cortex (mPFC) and dorsal hippocampus CA1 region (dCA1). Purkinje cells in cerebellar LS and Crus I differentially represented specific phases and phase differences of mPFC and dCA1 LFP oscillations in a frequency-specific manner, suggesting a site- and frequency-specific cerebellar representation of temporal aspects of neuronal oscillations in non-motor cerebral cortical areas. These findings suggest that cerebellar interactions with cerebral cortical areas involved in cognitive functions might involve temporal coordination of neuronal oscillations.

Background Respiration is one of the essential rhythms of life. The precise measurement of respiratory behavior is of great importance in studies addressing olfactory sensory processing or the coordination of orofacial movements with respiration. An ideal method of measurement should reliably capture the distinct phases of respiration without interfering with behavior. New Method This new method involves chronic implantation of a thermistor probe in a previously undescribed hollow space located above the anterior portion of the nasal cavity without penetrating any soft epithelial tissues. Results We demonstrate the reliability and precision of the method in head-fixed and freely moving mice by directly comparing recorded signals with simultaneous measurements of chest movements and plethysmographic measurements of respiration. Comparison with Existing Methods Current methods have drawbacks in that they are either inaccurate or require invasive placement of temperature or pressure sensors into the sensitive nasal cavity, where they interfere with airflow and cause irritation and damage to the nasal epithelium. Furthermore, surgical placement within the posterior nasal cavity adjacent to the nasal epithelium requires extensive recovery time, which is not necessary with the described method. Conclusions Here, we describe a new method for recording the rhythm of respiration in awake mice with high precision, without damaging or irritating the nasal epithelium. This method will be effective for measurement of respiration during experiments requiring free movement, as well as those involving imaging or electrophysiology.