Quantitative Electroencephalographic Measures of Voltage Amplitude and Dominant Frequency Associated With the Stroop Color-Conflict Cognitive-Interference Task in Medical Students

Abstract

Background Cognitive load theory postulates that effective learning depends on balancing a learner's cognitive capacity with cognitive load. Medical students are required to answer complex multiple-choice questions (MCQs) that involve complex vignettes and distractors, in 90 s per question. This demands the ability to rapidly process information, filter out irrelevant data, and suppress incorrect yet tempting answer choices. The Stroop color-conflict test represents a cognitive interference task that may simulate time-limited conditions for answering MCQs. This exploratory study tested whether selected quantitative electroencephalographic (qEEG) indices could behave as biomarkers that remain stable across sequential Stroop loads. Methods Thirteen healthy adults (11 retained after outlier removal) completed a midline (Fz, Cz, Pz) qEEG protocol comprising (i) 5 minutes of resting baseline, (ii) 5 minutes after a congruent low-load (LL) Stroop test and (iii) 5 minutes after an incongruent high-load (HL) Stroop test. Voltage amplitude (µV) and mode frequency (Hz) were extracted for theta (4-7 Hz), alpha (8-12 Hz), low-beta (12-20 Hz) and high-beta (20-30 Hz) bandwidths. Derived ratios, θ/β, α/β, θ/α and high-β/low-β, plus a frontal-posterior theta ratio (Fz/Pz), were analyzed with paired t-tests and repeated-measures ANOVA. Outliers were removed using a strict |z| > 2 threshold applied to every site-specific metric. Results Significant Baseline → LL load sensitivity was found for alpha-dominant (mode) frequency. The dominant frequencies, voltage amplitudes and voltage amplitude ratios for the other bandwidths (θ, low-β, high-β) were nonsignificant and therefore not load sensitive. None of the markers exhibited significant changes from LL → HL. Alpha voltage amplitudes were found to be higher at Pz than at Cz and Fz, exhibiting posterior dominant site sensitivity. High-β/low-β and θ/β ratios were found to be higher at Fz and Cz than at Pz, exhibiting frontal dominant site sensitivity. Conclusion These findings suggest significant Stroop testing-related qEEG changes in medical students trained to answer complex MCQs under time constraints. Alpha dominant frequency was found to be load sensitive but site insensitive. Load insensitivity of alpha voltage amplitude, θ/β ratio and high-β/low-β ratio at the Cz, Fz and Pz midline recording sites suggests site specificity of these variables. These findings appear to support the hypothesis that the site-specific topographic markers alpha voltage amplitude, θ/β and high-β/low-β ratio may be useful for characterizing responses to Stroop testing. However, the load sensitivity of alpha dominant frequency measured at the Cz, Fz and Pz midline recording sites may be useful for workload tracking to identify and remediate information-processing problems. These preliminary findings should be interpreted cautiously pending larger studies of cognitive loading in other populations of learners trained to take high-stakes, time-limited examinations.

Keywords: dominant frequency; medical school students; quantitative eeg (qeeg); stroop test; voltage amplitude.

Figure 1. Alpha dominant frequency across conditions.

Bars represent site-averaged mean (± SEM) alpha dominant (mode) frequencies, expressed in Hz, measured by qEEG for baseline control and for 5 minutes immediately after congruent Stroop test low cognitive load (LL) and noncongruent Stroop test high cognitive load (HL) conditions. *Significantly different than baseline, p < 0.05.

Figure 2. Representative qEEG tracings.

Panels show one-second qEEG recordings from a 27-year-old male study participant in the same time frames. qEEG tracings are for baseline control (B) and for 5 min immediately after congruent Stroop test low cognitive load (LL) and noncongruent Stroop test high cognitive load (HL) conditions. Left panel: Raw left ear (LE) referenced EEGs (white tracings) show the qEEG load-insensitive, site-sensitive changes in alpha (8-12 Hz) voltages (green tracings) at midline fontal (Fz-LE), central (Cz-LE) and parietal (Pz-LE) sites. Right panel: LE-referenced raw EEGs (white tracings) filtered to show the theta (4-7 Hz) voltages (blue tracings), and beta (13-30 Hz) voltages (pink tracings) at the same sites and loads, reflecting the data used to compute the theta/beta voltage amplitude ratios.

Figure 3. Alpha voltage amplitude across sites.

Bars represent mean (± SEM) alpha voltage amplitudes measured by qEEG for baseline control and for 5 minutes immediately after congruent Stroop test low cognitive load (LL) and noncongruent Stroop test high cognitive load (HL) conditions. Measurements were at midline frontal (Fz), central (Cz) and parietal (Pz) electrodes. *Pz significantly different than Cz and Fz, p < 0.01.

Figure 4. Theta-beta ratio across sites.

Bars represent mean (± SEM) theta/beta voltage amplitude ratios computed from qEEG measurements for baseline control and for 5 minutes immediately after congruent Stroop test low cognitive load (LL) and noncongruent Stroop test high cognitive load (HL) conditions. Measurements were at midline frontal (Fz), central (Cz) and parietal (Pz) electrodes. *Pz significantly different than Cz and Fz, p < 0.05.

Figure 5. High-β/low-β ratio across sites.

Bars represent mean (± SEM) high-β/low-β voltage amplitude ratios computed from qEEG measurements for baseline control and for 5 minutes immediately after congruent Stroop test low cognitive load (LL) and noncongruent Stroop test high cognitive load (HL) conditions. Measurements were at midline frontal (Fz), central (Cz) and parietal (Pz) electrodes. *Pz significantly different than Cz and Fz, p < 0.05.