Figure 6

Scatter plots depicted the capability of neural ensembles in each brain area to discriminate noxious, sham and no stimulation before (A) and after morphine administration (B). The linear discriminant analysis (LDA) was used to investigate whether morphine administration affected the capability of neural ensembles to discriminate different types of sensory stimulation. The noxious thermal evoked firing rates were chosen for discriminant analysis. The firing rates of multiple principle components around noxious, sham, or no-stimulation (randomly selected points where no events occurred within 30 seconds around) events were calculated and the discriminant function coefficients were estimated. As can be seen, the three categories can be well separated before the delivery of morphine (A), as indicated by the dashed line circles. In contrast, the three categories are mixed up after morphine injection (B).