Heart rate variability (HRV) is a well-known phenomenon whose characteristics are of great clinical relevance in pathophysiologic investigations. In particular, respiration is a powerful modulator of HRV contributing to the oscillations at highest frequency. Like almost all natural phenomena, HRV is the result of many nonlinearly interacting processes; therefore any linear analysis has the potential risk of underestimating, or even missing, a great amount of information content. Recently the technique of Empirical Mode Decomposition (EMD) has been proposed as a new tool for the analysis of nonlinear and nonstationary data. We applied EMD analysis to decompose the heartbeat intervals series, derived from one electrocardiographic (ECG) signal of 13 subjects, into their components in order to identify the modes associated with breathing. After each decomposition the mode showing the highest frequency and the corresponding respiratory signal were Hilbert transformed and the instantaneous phases extracted were then compared. The results obtained indicate a synchronization of order 1:1 between the two series proving the existence of phase and frequency coupling between the component associated with breathing and the respiratory signal itself in all subjects.

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One contribution of 16 to a theme issue 'Uncovering brain-heart information through advanced signal and image processing' .

Sleep is known to contribute to motor memory consolidation. Recent studies have provided evidence that a night of sleep plays a similar functional role following motor imagery (MI), while the simple passage of time does not result in performance gains. Here, we examined the benefits of a daytime nap on motor memory consolidation after MI practice. Participants were trained by MI on an explicitly known sequence of finger movements at 11:00. Half of the participants were then subjected (at 14:00) to either a short nap (10 min of stage 2 sleep) or a long nap (60-90 min, including slow wave sleep and rapid eye movement sleep). We also collected data from both quiet and active rest control groups. All participants remained in the lab until being retested at 16:00. The data revealed that a daytime nap after imagery practice improved motor performance and, therefore, facilitated motor memory consolidation, as compared with spending a similar time interval in the wake state. Interestingly, the results revealed that both short and long naps resulted in similar delayed performance gains. The data might also suggest that the presence of slow wave and rapid eye movement sleep does not provide additional benefits for the sleep-dependent motor skill consolidation following MI practice.

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Anterograde transport of either HRP or wheat germ agglutinin-conjugated HRP was used to study the posthatching development of the retinotectal connection in the pigeon. The functional maturation of the retinotectal system was also investigated by recording electroretinographic (ERG) and tectal evoked (TEP) responses to either flash or pattern stimuli. Two main morphological changes occurred in the retinotectal system during the first 6 days after hatching: an ipsilateral retinofugal component that was present at hatching disappeared and the outer tectal layers were progressively invaded by the contralateral retinofugal axons, which at hatching were limited to the stratum griseum et fibrosum superficiale of the dorsolateral tectal quadrant. During the early posthatching period, at the same developmental stage at which an ERG to unpatterned or patterned stimulation could first be recorded, a visually evoked response could be elicited in the contralateral optic tectum. Therefore, the retina and optic tectum seem to start functioning simultaneously, the limiting factor being the late maturation of photosensitive lamellae in the outer segments of the developing photoreceptors. During the first 20 days posthatching, the retinotectal system undergoes extensive development as revealed by latency and amplitude changes of the visually evoked potentials. We suggest that the pigeon visual system serves as a useful model for studies concerning visual development and plasticity.