The Trace Conditional Learning of the Noxious Stimulus in UWS Patients and Its Prognostic Value in a GSR and HRV Entropy Study

Figures

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  Figure 1. Sequence of the stimuli: two short grave notes anticipate the musical stimulus; two short grave notes and one long acute note at an interval of 5th anticipate the noxious stimulus. From Sequence (A) 1 to 7 the stimuli were associated to the tones; the eighth without stimulus administration to verify the CR; Sequence (B) from 9 to 16 only tones for the extinction of the stimulus.

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  Figure 2. Protocol and data analysis: in the central line of the figure (between dashed lines) the entire sequence of the protocol (baseline, sequence A to test the conditional response (CR), and sequence B to test the extinction of the CR). From each sequence Galvanic Skin Response (GSR) and Electrocardiogram (ECG) were extracted. From the ECG the Inter-Beats Interval (distance between peak to peak of RR ECG signal) was extracted (Bottom the figure—HRV analysis) and Sample Entropy (SampEn) analyzed, then compared between and within groups. GSR was observed in baseline to exclude artifact movements. GRS analysis (above) was performed considering peak magnitude, time to reach the peak, and decay of the GSR signal in the last three phases of the sequence A (black box and black line MUS4, NOC3, and NOC*). It was considered the CR only if the GSR was present in NOC3 and NOC* (circle white filled). Finally, CR's (red box) extinction was observed in the sequence B. Similarly, for the SampEn, the GSR components (magnitude, time to reach the peak, and decay) were compared between and within groups (black line) and the extinction was compared for wave peak magnitude (red line).

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  Figure 3. Phasic components of GSR in the sequence A. The bold line is the mean of the GSR signal, and the filled area is the standard error. In blue the HC, green UWS patients with CR, and red UWS patients without CR. Vertical black continuous lines are the start of nociception stimulus, dashed black lines are the start of musical stimulus, vertical red line is the start of CR. MUS4, NOC3, and NOC* were considered in the statistical analysis to verify the conditional learning.

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  Figure 4. Characteristics of the wave in the GSR signal. After the stimulus, the time to reach the peak of max magnitude is calculated. The magnitude is different between values of peak and values at the start of the stimulus. The time of the wave's decay is the phase of decreasing after reaching the peak.

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  Figure 5. Sequence A: boxplot of the GSR waves components. Time to reach the peak (left), wave's magnitude (center) and wave's decay (right) of each group were compared among them in MUS4, NOC3, and NOC* (diamond markers), and the groups (HC, UWS1, and UWS0) were compared among them for each session (point markers). The box represents the first and third quartile, the whiskers are the 1.5 interquartile range, the black lines are the medians, and points are outliers. Significant statistical difference: ∙p = [0.002–0.003]; ∙∙p = 0.001; ∙∙∙p < 0.0001; circle: Statistical difference between groups .

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  Figure 6. Sequence B: boxplot of GSR magnitude. MUS4 vs. MUS1* and NOC* vs. NOC1* were compared. Only in the HC and UWS1 groups a significant difference between NOC* and NOC1* was observed (***HC: Z = −3.180, p < 0.0001, r = 0.88; **UWS1: Z = −2.666; p = 0.002; r = 0.60). The box represents the first and third quartile, the whiskers are the 1.5 interquartile range, the black lines are the medians, and points are outliers.

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  Figure 7. Boxplot of the SampEn. In the figure: baseline (white), sequence A (dark gray) and sequence B (light gray). Significant statistical difference: *p = [0.003–0.005]; **p = [0.001]; ***p < 0.0001.

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  Figure 8. Boxplot of the CRS-R and NCS. UWS0 (dark gray) and UWS1 (white) groups are compared for CRS-R and NCS. The box represents the first and third quartile, the whiskers are the 1.5 interquartile range, the black lines are the medians, and points are outliers. The statistical difference between groups is significant at the 3rd week (CRS-R: Z = −3.512; p < 0.0001 – NCS: Z = −2.964; p = 0.001) and 4th week (CRS-R: Z = −3.566; p < 0.0001 – NCS: Z = −2.214; p = 0.015).