Re-test reliability and internal consistency of EEG alpha-band oscillations in older adults with chronic knee pain

Abstract

Objective: Chronic pain studies investigating the ability to detect sensory processing differences related to thalamic gating using electroencephalographic (EEG) alpha have yielded conflicting results. Alpha's basic psychometric properties in pain populations requires further study. The present study reports on the test-retest reliability and internal consistency of EEG alpha power in older adults with chronic knee pain.

Methods: Repeated EEG alpha power measurements were taken of older adults (N = 31) with chronic knee pain across two sessions separated by a ten-day period associated with a pilot clinical trial study. Recordings included resting periods (eyes open and eyes closed) as well as periods involving a pain management activity.

Results: Most single alpha-power measures and all within-participant averages of alpha obtained within a session showed high internal consistency (Cronbach's α > 0.7) and satisfactory-to-excellent re-test reliability (Pearson's rs > 0.6) of both alpha power and alpha blocking (eyes closed minus eyes open) across repeated conditions.

Conclusions: EEG alpha power seems mostly reliable and consistent, particularly when participants' eyes are closed, after a period of habituation, and when alpha measures are averaged as within-participant estimates.

Significance: This analysis suggests that within-subject averages of EEG alpha are the most reliable for developing indices of chronic knee pain.

Keywords: Chronic pain; EEG alpha; Internal consistency; Reliability.

Figure 1:

From left to right, each of two experimental sessions started with the recording of a 3-minute electroencephalography (EEG) resting block, followed by a somatosensory stimulation block, a period of relaxation breathing/guided imagery/positive affect activity, another tactile stimulation block, and a final resting block. The resting blocks comprised an initial 90-second eyes-closed condition, followed by 90-second eyes-open condition. Each block from which alpha measures were taken is presented in white. These blocks were used as items for calculating Cronbach’s α and Pearson’s correlation coefficients. Somatosensory stimulation blocks included a 3-minute stimulation for each of four sites: the left wrist, right wrist, left knee, and right knee.

Figure 2:

The grand mean spectrum (N=31) across resting conditions computed using a fast Fourier transform (FFT). The graph shows a distinct peak between 8 and 12 Hz, where the alpha band was expected to appear in older adults.

Figure 3:

A grand mean (n = 30) spline-interpolated topographical distribution of eyes open-minus-closed difference scores of alpha-band power signal-to-noise ratios (SNR, unitless). One participant was excluded due to lack of eyes open/closed data. The EEG sensors are represented as white dots on the scalp. Blue suggests areas in which eyes-closed alpha power was greater than eyes-open alpha power (alpha blocking). As expected, the alpha blocking effect is observed most strongly at the occipital pole between Pz and Oz.

Figure 4:

A spline-interpolated topographical distribution of Cronbach’s αs of alpha-band power. The electroencephalography (EEG) sensors are represented as white dots on the scalp. The first session (top) and final session (bottom) internal consistency scores were high across all sensors (>0.7). Left and right hemispheres are both shown for clear viewing.

Figure 5:

Signal-to-noise ratios (SNRs) of baseline alpha power. These scatterplots show baseline participant alpha signal-to-noise ratios (averaged between sensors at Pz and Oz) for each of two EEG sessions, approximately one week apart. Each dot represents one participant, with the x-axis representing alpha power during the first session and the y-axis representing alpha power during the last session. A. The baseline eyes-closed condition (left) shows a pronounced cross-session stability compared to B. the baseline eyes-open condition (right).

Figure 6:

A spline-interpolated topographical distribution of test-retest correlation coefficients of alpha-band power is shown for corresponding conditions across the two sessions. The left panel shows conditions preceding the relaxation breathing/guided imagery activity. White and yellow indicate poor test-retest reliability, particularly for the eyes-open condition. Pale orange-to-red indicate moderate-to-excellent reliability, as in the eyes-closed condition pre-activity. The right panel shows the corresponding topographies for post-activity blocks. Alpha at all sensors had moderate to excellent retest reliability after pain management activity, as shown on the same scale.

Figure 7:

A spline-interpolated topographical distribution of test-retest correlation coefficients of alpha-band power is shown for corresponding conditions across the two sessions. The top panel shows the first block of the pain management activity for the respective sessions, which included relaxation breathing, guided imagery, and positive words (positive words were analyzed separately). White and yellow indicate poor test-retest reliability. Pale orange-to-red indicate moderate-to-excellent reliability, as in the guided-imagery block, which had mostly excellent retest reliability across sensors. The bottom panel shows the topographies for the positive-words block, which showed mostly better-than-moderate reliability across sensors.