Title : Effect of the level of consciousness at the neuronal scale in a rat model of Parkinson ' s disease

For the interpretation of neuronal data obtained during functional neurosurgery from alert human patients with Parkinson’s disease, it is important to know to what extent the behavior of single neurons in the Basal ganglia (BG) depends on the level of consciousness, and to what degree on chronic dopamine depletion. We recorded the activity of single GPi neurons during the transition from deep anesthesia to full alertness in relaxed, head-restrained, control and 6OHDA-lesioned rats. For these recordings, we measured the rank surprise, the percentage of Burst Triggering Spikes (BTS-index), and the sample entropy. Upon an increasing level of alertness, 1) the BTS-index decreased in both healthy and dopamine-deprived GPi neurons, 2) the rate of discharge and the Sample Entropy increased in the dopamine-deprived neurons, while the opposite occurred for the control group. Upon an increased level of alertness, single neurons changed their behavior adaptively, evidencing that the measured characteristics are emergent properties of the state of the neural system rather than static, intrinsic electrophysiological properties of GPi neurons. We interpret the increment observed in the level of entropy of Parkinsonian neurons as the inability of dopamine-depleted Basal Ganglia neurons to handle increased levels of input associated with higher levels of alertness. Our results imply that the extrapolation from data obtained under anesthesia to the wake subject or animal (as required for preclinical studies) is nontrivial, as the observed changes in neural activity must carefully be taken into account.