Table 1. Correlations Between Behavioral Parameters in Experiment 1.

Variables	Group	Statistics
Withdrawal-potentiated startle on intervening days
ID1 vs ID2	Morphine	r=0.47, p=0.029*
ID1 vs ID3	Morphine	r=0.52, p=0.011*
ID1 vs ID4	Morphine	r=0.47, p=0.024*
ID2 vs ID3	Morphine	r=0.47, p=0.027*
ID2 vs ID4	Morphine	r=0.57, p=0.005*
ID3 vs ID4	Morphine	r=0.40, p=0.061
Withdrawal severity and sensitization
ID1 withdrawal vs composite  sensitization	Morphine	r=0.50, p=0.016*
ID1 withdrawal vs Final test  sensitization	Morphine	r=0.44, p=0.035*
ID1 withdrawal vs Challenge  sensitization	Morphine	r=0.42, p=0.045*
ID1 withdrawal vs Challenge  locomotion	Saline	r=−0.062, p=0.77
Other factors
Escalation of withdrawal severity vs sensitization	Morphine	r=0.21, p=0.33
ID1 baseline startle vs sensitization	Morphine	r=0.21, p=0.33
Response to novelty vs sensitization	Morphine	r=0.01, p=0.97
Response to novelty vs Initial Test locomotion	Morphine	r=0.71, p=0.001*

Abbreviation: ID, Intervening Day.

Pearson's correlation coefficient is presented for each pair of variables in the indicated group; significant correlations are shown in bold. Sensitization in the morphine group was computed by subtracting the Initial Test locomotor response from the Final Test, Morphine Challenge, or their composite average. In the saline group, the locomotor response to Morphine Challenge was analyzed. Escalation of withdrawal severity represents the difference in withdrawal-potentiated startle on the Final Test versus the Initial Test. The response to novelty was measured during the first 30 min of the initial exposure to the activity monitor context.