Key points• We have examined the functional organization of the neuronal ensembles involved in the generation of spontaneous cord dorsum potentials in the lumbo-sacral spinal cord of the anaesthetized cat.• These potentials appear synchronously along several spinal segments and are generated by a longitudinally distributed network of bilaterally interconnected sets of dorsal horn neurones.• Low levels of synchronization of spontaneous neuronal activity within this network appear associated with activation of spinal pathways mediating glycinergic non-reciprocal postsynaptic inhibition of motoneurones.• During states of spontaneous increased synchronization, or after the acute section of cutaneous nerves, there is a preferential activation of the GABAergic pathways producing primary afferent depolarization and presynaptic inhibition of muscle and cutaneous afferents.• It is suggested that modulation of the temporal synchronization of spontaneous activity of dorsal horn neurones might provide means for selection of alternatively operating inhibitory spinal pathways during different sensory and motor behaviours.Abstract Simultaneous recordings of cord dorsum potentials along the lumbo-sacral spinal cord of the anaesthetized cat revealed the occurrence of spontaneous synchronous negative (n) and negative-positive (np) cord dorsum potentials (CDPs). The npCDPs, unlike the nCDPs, appeared preferentially associated with spontaneous negative dorsal root potentials (DRPs) resulting from primary afferent depolarization. Spontaneous npCDPs recorded in preparations with intact neuroaxis or after spinalization often showed a higher correlation than the nCDPs recorded from the same pair of segments. The acute section of the sural and superficial peroneal nerves further increased the correlation between paired sets of npCDPs and reduced the correlation between the nCDPs recorded from the same pair of segments. It is concluded that the spontaneous nCDPs and npCDPs are produced by the activation of interconnected sets of dorsal horn neurones located in Rexed's laminae III-IV and bilaterally distributed along the lumbo-sacral spinal cord. Under conditions of low synchronization in the activity of this network of neurones there would be a preferential activation of the intermediate nucleus interneurones mediating Ib non-reciprocal postsynaptic inhibition. Increased synchronization in the spontaneous activity of this ensemble of dorsal horn neurones would recruit the interneurones mediating primary afferent depolarization and presynaptic inhibition and, at the same time, reduce the activation of pathways mediating Ib postsynaptic inhibition. Central control of the synchronization in the spontaneous activity of dorsal horn neurones and its modulation by cutaneous inputs is envisaged as an effective

The analysis of the interaction and synchronization of relatively large ensembles of neurons is fundamental for the understanding of complex functions of the nervous system. It is known that the temporal synchronization of neural ensembles is involved in the generation of specific motor, sensory or cognitive processes. Also, the intersegmental coherence of spinal spontaneous activity may indicate the existence of synaptic neural pathways between different pairs of lumbar segments. In this study we present a multichannel version of the detrended fluctuation analysis method (mDFA) to analyze the correlation dynamics of spontaneous spinal activity (SSA) from time series analysis. This method together with the classical detrended fluctuation analysis (DFA) were used to find out whether the SSA recorded in one or several segments in the spinal cord of the anesthetized cat occurs either in a random or in an organized manner. Our results are consistent with a non-random organization of the sets of neurons involved in the generation of spontaneous cord dorsum potentials (CDPs) recorded either from one lumbar segment (DFA- mean = 1.040.09) or simultaneously from several lumbar segments (mDFA- mean = 1.010.06), where  = 0.5 indicates randomness while 0.5 indicates long-term correlations. To test the sensitivity of the mDFA method we also examined the effects of small spinal lesions aimed to partially interrupt connectivity between neighboring lumbosacral segments. We found that the synchronization and correlation between the CDPs recorded from the L5 and L6 segments in both sides of the spinal cord were reduced when a lesion comprising the left dorsal quadrant was performed between the segments L5 and L6 (mDFA- = 0.992 as compared to initial conditions mDFA- = 1.186). The synchronization and correlation were reduced even further after a similar additional right spinal lesion (mDFA- = 0.924). In contrast to the classical methods, such as correlation and coherence quantification that define a relation between two sets of data, the mDFA method properly reveals the synchronization of multiple groups of neurons in several segments of the spinal cord. This method is envisaged as a useful tool to characterize the structure of higher order ensembles of cord dorsum spontaneous potentials after spinal cord or peripheral nerve lesions.