Table 1.

Studies using spectral analysis.

General study information (spectral analysis)	Study design				Results
	mTBI group (n)	Control group (n)	qEEG recording condition	Criteria for TBI patient	Measures	Statistical test/comparison/significance
Chen et al. (2006a) “Electroencephalogram and evoked potential parameters examined in Chinese mild head injury patients for forensic medicine”	60	30	Eyes closed, resting, wakeful	Glasgow coma scores (13–15)	Frequency band average power	Unpaired t-test
						1. α1 (p < 0.001)
						2. θ, α2, β1, β2 (all p > 0.05) (NS)
					Frequency band power ratios	Unpaired t-test
						1. θ/α1 and θ/α2 (both p < 0.05)
						2. α1/α2 (p < 0.01)
					Frequency band power ratios and average power	Paired t-test Initial vs. 3 month retest (p > 0.05 for all comparisons) (NS)
Notes: this study supports qEEG as a more sensitive method for detecting mTBI compared to evoked potential recording (auditory and flash). This conclusion is somewhat contradictory to other studies in the field
Coutin-Churchman et al. (2003) “Quantitative spectral analysis of EEG in psychiatry revisited: drawing signs out of numbers in a clinical setting” Notes: qEEG was reported to bin normal subjects and psychiatric patients with good specificity and sensitivity. However, this study does not find any clear association between particular qEEG measures and specific disorders. In addition, the patient group mostly consisted of individuals with mood and psychological disorders, not cognitive impairments due to injury	4 (Post-traumatic headache 336 With other neurological disorders	67	Eyes closed, resting, wakeful	Post-traumatic headache diagnosis	Power spectra (all bands), converted to Z-score (all disorders combined)	Z-score abnormality defined as Z-score >3 or <−3
						1. Sensitivity (0.838)
						2. Specificity (0.9104)
						3. Positive predictive value (0.979)
						4. Negative predictive value (0.526)
					Absolute power and power asymmetry (all disorders combined)	Various tests
						Overall correspondence between qEEG abnormality pattern and clinical diagnosis (χ2 = 315.8, Cramer’s V = 0.305, Contingency coefficient = 0.694; p = 0.00001)
					Beta activity increase (all disorders combined)	Pearson’s correlation
						Medication use in all patients (Pearson χ2 = 7.865, df = 1, p = 0.005)
					Slow band decrease (all disorders combined)	Pearson’s correlation
						Medication use in all patients (χ2 = 2.963, df = 1, p = 0.085) (NS)
Gosselin et al. (2009) “Sleep following sport-related concussions” Notes: while this report did not find differences in sleep architecture (frequency activities) between concussed and control athletes, concussed athletes showed significant increased delta and reduced alpha activities in the waking qEEG analysis. This study also demonstrates effective combinatorial technology use (fMRI and ERP)	10	11	Eyes closed, resting, wakeful Eyes closed, asleep Frontal region (Fz, F3, F4), central region (CZ, C3, C4), parietal region (Pz, P3, P4), occipital region (O1 and O2), temporal region (T7, T8, P7, P8)	Glasgow coma scores (13–15)	Relative spectral power (all frequencies) (eyes closed asleep)	Two-way ANOVA (no significance for any region)
					Relative delta power (eyes closed, wakefulness)	Two-way ANOVA (F1, 14 = 12.7, p < 0.01) (all regions)
					Relative alpha power (eyes closed, wakefulness)	Two-way ANOVA (F1, 14 = 8.8, p < 0.05) (all regions)
					Slow to fast frequencies ratio (eyes closed, wakefulness)	Two-way ANOVA (F1, 14 = 11.5, p < 0.01) (all regions)
Haglund and Persson (1990)	47	50	Eyes closed, resting, wakeful	High number of boxing matches (>25)	Average power spectrum (grand averages from each frequency)	Chi square (no significant differences between all groups)
“Does Swedish amateur boxing lead to chronic brain damage? A retrospective clinical neurophysiological study”	22 High-match boxers	25 Soccer players
Notes: study reports no differences in qEEG measures between patient groups, but the effort was exploratory and used grand averages for each frequency band. Importantly, inter-rater reliability was reported to be sufficient
	25 Low-match boxers	25 Track and field players
Korn et al. (2005) “Focal cortical dysfunction and blood-brain barrier disruption in patients with post-concussion syndrome” Notes: the main purpose of this study was to correlate abnormal EEG, brain imaging, and blood–brain barrier disruptions, especially as related to localization. Arciniegas’ (2011) review provides critical perspective on this study (classification of some experimental group subjects as having mTBI, but CT scans suggest a more severe form of TBI)	17	17	N/A	Glasgow coma scale >12, post-concussion syndrome (PCS) diagnosis 1 month to 7 years post-injury	Delta frequency power Alpha frequency power	Student’s t-test Increased delta (p < 0.01) Student’s t-test Lower alpha 1 (p < 0.05) Lower alpha 2 (p < 0.05)
Montgomery et al. (1991) “The psychobiology of minor head injury” Notes: the theta band was the only abnormal frequency in the qEEG analysis. However, no normative sampling or pre-injury measures, or control group measures were used. The comparison was only between immediate post-injury (approximately 24 h) and 6 weeks later. So, reduction in theta power may be considered persistent	26	None	Eyes closed, resting, wakeful	Head injury requiring overnight hospital stay; post-traumatic amnesia >12 h	Mean theta power (comparison between day 0 and 6 weeks)	Two-tailed paired t-tests
						1. Right temporal, T4–T6 (p < 0.025)
						2. Right parietal, P4–O2 (p < 0.01)
						3. Left temporal, T3–T5 (p < 0.01)
						4. Left parietal, P3–O1 (p < 0.01)
					Mean alpha power (comparison between day 0 and 6 weeks)	Two-tailed paired t-tests
						No significance at any region
					Mean delta power (comparison between day 0 and 6 weeks)	Two-tailed paired t-tests
						No significance at any region
Slobounov et al. (2012) “Residual brain dysfunction observed 1 year post-mild traumatic brain injury: combined EEG and balance study” Notes: this study suggests qEEG and balance analysis as good prognostic tools; efficacy as a diagnostic tool was not explored	49	None (used baseline testing from mTBI group pre-injury)	Eyes closed, resting, wakeful Eyes open, resting, wakeful Eyes closed, standing, wakeful Eyes open, standing, wakeful	Grade 1 mTBI (Cantu Dad Driven Revised Concussion Grading Guideline, 2006)	Alpha power suppression (from resting to standing posture) increase	t-Test (baseline vs. day 7 post-injury) 1. Occipital region of interest: F = 11.77 (1,48), p < 0.01 2. Parietal region of interest: F = 8.2 (1,48), p = 0.038
Tebano et al. (1988) “EEG spectral analysis after minor head injury in man” Notes: this report suggests differences in power band frequencies occur between healthy and patients with mTBI. This is an early study and may be considered exploratory	9 (No loss of consciousness) 9 (Reported loss of consciousness)	9	Eyes closed, resting, wakeful (baseline recording) Eyes open, resting, wakeful (recording)	Reported loss of consciousness after injury	Alpha I band power (higher in injured group)	Mann–Whitney test U = 28, p < 0.01
					Alpha II band power (reduced in injured group)	Mann–Whitney test
						U = 47, p < 0.05
					Mean frequency of total alpha band power (reduced in injured group)	Mann–Whitney test
						U = 46, p < 0.05
					Frequency band total power (if significant, reduced in injured group)	Mann–Whitney test
						1. Alpha (alpha I and II), (NS)
						2. Delta, U = 45, p < 0.05
						3. Beta II, U = 41, p < 0.025
Thatcher et al. (2001) “Estimation of the EEG power spectrum using MRI T2 relaxation time in traumatic brain injury” Notes: Nuwer et al. (2005) criticizes this study due to lack of age-matching and broad spread of TBI severity	18 (Mild-severe TBI)	11	Eyes closed, resting, wakeful	Chronic TBI diagnosis	Correlation between relative EEG frequency power and T2 relaxation time (MRI scan) (decreased alpha and beta; increased delta and theta with MRI T2 abnormalities)	ANOVA
						1. Delta (t = 8.876, p < 0.0001)
						2. Theta (t = 8.529, p < 0.0001)
						3. Alpha (t = −9.276, p < 0.0001)
						4. Beta (t = 2.421, p < 0.016)
Thatcher et al. (1991)	162	None	N/A	Closed head injury and admittance to Neurotrauma hospital center	EEG relative power	Prediction accuracy (extreme outcome scores) (1 year) 67.1%
“Comprehensive Predictions of Outcome in Closed Head-Injured Patients”
Notes: a gradient of prognostic strength of diagnostic measures was EEG phase > EEG coherence > GCS-T > CT scan > EEG relative power
Thornton (2003) “The electrophysiological effects of a brain injury on auditory memory functioning. The QEEG correlates of impaired memory” Notes: twenty-seven patients of the mTBI group were on various medications. Age was statistically different between groups (mTBI group was slightly older)	85	56	Eyes closed, resting, wakeful, during auditory memory task Eyes open, resting, wakeful, during auditory memory task	Loss of consciousness <20 min	Power band frequency measures for alpha, beta, theta, and delta (includes absolute/relative magnitude, peak amplitude, peak frequency, and symmetry)	t-Test 1. Increased beta1 relative power (p < 0.05)
Tomkins et al. (2011) “Blood–brain barrier breakdown following traumatic brain injury: a possible role in posttraumatic epilepsy” Notes: study focuses mostly on blood–brain barrier localization with qEEG abnormalities	37 (19 With post-traumatic epilepsy, PTE)	13	Eyes closed, wakeful	Glasgow coma scale >13	Delta power (increase)	Mann–Whitney U test Injured vs. controls (p = 0.002) (equivalent among PTE and non-PTE mTBI patients)
					Alpha power (decrease)	Mann–Whitney U test
						Injured vs. controls (p = 0.005) (only seen in PTE group, p = 0.01)
					Theta power (increase)	Mann–Whitney U test
						PTE group of mTBI patients vs. controls (p = 0.04)
von Bierbrauer et al. (1992) “Computer assisted vs. visual EEG-analysis in patients with minor head injury (a follow-up examination)” Notes: this study also provides evidence for qEEG as a relevant technology for patient diagnosis and analysis as compared to standard EEG. Original article is in German; analysis adapted from review article (Nuwer et al., 2005)	31	None	N/A	N/A	Median posterior alpha frequency (increase over time)	t-Test
						1. 24 h vs. 1 week (NS)
						2. 24 h vs. 3 weeks (p < 0.01)
						3. 24 h vs. 2 months (p < 0.01)
					Theta/alpha ratio (decrease over time)	t-Test
						1. 24 h vs. 1 week (NS)
						2. 24 h vs. 3 weeks (p < 0.05)
						3. 24 h vs. 2 months (p < 0.01)
Watson (1995) “The post-concussional state: neurophysiological aspects” Notes: study suggests combined use of qEEG power spectral analysis and brainstem audio evoked potential (BAEP) I–V latency analysis could provide utility to diagnose mTBI symptoms (both organic and psychological)	25	None	Eyes closed, resting, wakeful	Men; aged 14–30; uncomplicated head injury with post-traumatic amnesia <12 h	Alpha/theta ratio (at day 0, day 10, and 6 weeks post-injury)	Paired two-tailed t-test (day 0 vs. day 10 post-injury)
						1. Right temporal (T4–T6), p < 0.006
						2. Right parieto-occiptal (P4–O2), p < 0.02 (day 10 vs. 6 weeks) – not significant for any region
Williams et al. (2008) “Polysomnographic and quantitative EEG analysis of subjects with long-term insomnia complaints associated with mild traumatic brain injury” Notes: this study shows limited ability of qEEG power spectra analysis to differentiate among mTBI patients suffering from sleep disorders and control groups	9	9	Eyes closed, resting, asleep	Glasgow coma scale 13–15; loss of consciousness <20 min; hospitalization <48 h; reported sleep dysfunction	Beta 2 power (decrease in injured patients)	Two-tailed t-tests with Welch’s corrections (Wilcoxon rank sum test also used if outliers were apparent)
						1. Beta 2 (F(1, 16) = 8.9, p = 0.008)
					Variability in power (greater variability in mTBI patients)	Two-tailed t-tests with Welch’s corrections (Wilcoxon rank sum test also used if outliers were apparent)
						1. Sigma (F1,16 = 10.5, p = 0.005)
						2. Theta (F1,16 = 6.8, p = 0.019)
						3. Delta (F1,16 = 9.2, p = 0.008)