Temporal strategy for discriminating noxious from non-noxious electrical stimuli by cortical and thalamic neural ensembles in rats

Considerable evidence supports that pain is encoded in a large, widespread network that consists of the thalamus, cortex, as well as limbic system. However, the temporal properties of the neural matrix in pain processing were largely unknown. In the present study, we simultaneously recorded thalamic and cortical neuronal discharges elicited by brief noxious or innocuous electrical stimulus in awake rats. The discrimination performance of the neural ensembles in differentiating noxious from innocuous inputs was calculated using different window sizes at the millisecond and second level, respectively. The results demonstrated that coding information emerged in a quantum-like manner; the minimum spike-train length for discriminating noxious from innocuous inputs was 40 ms. The nociceptive coding activity was temporally dynamic, and could be preserved for a relatively long time (3–4 s) within the thalamocortical loops, independent of the initial brief stimuli. These results suggest that the nociceptive signals may be reverberatory within the thalamocortical loops, hence keeping the neurosignature for central pain representation.