Heart rate variability is encoded in the spontaneous discharge of thalamicsomatosensory neurones in cat

1. Wie studied the spontaneous discharge variability of thalamocortical som atosensory neurones in the awake cat in order to disclose its possible info rmation content. The presence of slow (0.09-1.39 Hz) regular fluctuations i n the discharge rate of these cells during the waking state has been previo usly reported. Oscillations in a similar frequency range are known to chara cterize the activity of central and peripheral neurones pertaining to the a utonomic nervous system and the variability of heart period (RR interval va riability). 2. A surrogate data test, performed on our database, confirmed the presence of slow (0.05-1 Hz) non-random fluctuations in firing rate. 3. Linear regression detected the presence of an inverse relationship betwe en the values of RR interval and the concurrent levels of neural discharge. 4. Frequency domain analysis indicated that a significant coupling between the two variability signals preferentially occurred in two frequency bands: in the frequency of the respiratory sinus arrhythmia and in correspondence with a slower rhythm (0.07-0.3 Hz), the two signals being in phase opposit ion in most of the cases. 5. Coherent fluctuations could also be observed when epochs of evoked activ ity were analysed, while coupling between the two variability signals appea red to be disrupted after sleep onset. 6. We conclude that RR interval variability, an internally generated dynami c related to basic visceral regulation, is encoded in the discharge of sing le somatosensory thalamocortical neurones during wakefulness. A possible in teraction with the transmission of somatosensory information has to be eval uated.