Table 2.
Summary of study characteristics.
| Author and year | Study design | Inter-vention | M/EEG | Entity | Total sample size | Assess-ment tool | M/EEG Analysis | Main result (M/EEG) |
|---|---|---|---|---|---|---|---|---|
| Bruno 1998 (Bruno et al., 1998) | Descriptive | – | EEG | PVFS | 33 | PFQ | Power | Power equal between hemispheres across all frequency bands EEG slow wave power in the right hemisphere significantly correlated with daily fatigue scores |
| Buyukturkoglu 2017 (Buyukturkoglu et al., 2017) | Cross-sectional observational | – | EEG | MS | 29 | mFIS | Connectivity | FC (Coherence) differing in various frequency bands and brain regions between fatigued MS patients and healthy participants Coherence in the theta and beta band in the fronto-frontal region as well as in the beta band in the temporo-parietal region positively correlated with fatigue scores |
| Cogliati Dezza 2015 (Cogliati Dezza et al., 2015) | Cross-sectinal observational | – | EEG | MS | 35 | mFIS | Power | Lower right hemisphere power in patients with high but not low fatigue compared to healthy participantsInter-hemispheric total power (L > R) of homologous sensorimotor (SM1) areas positively correlated with fatigue scores |
| Duffy 2011 (Duffy et al., 2011) | Cross-sectional observational | – | EEG | CFS | 460 | – | Other (Classification) | Highly significant group discrimination in unmedicated females (86.8% patients and 89.8% HC accuracy) and males (88.9% patients and 82.4% healthy participants accuracy)Less accurate discrimination in patients taking psychoactive medications (females 77.8%, males 60.0%) Bilateral temporal lobe involvement in 9/10 discrimination factors |
| Fallon 2018 (Fallon et al., 2018) | Cross-sectional observational | – | EEG | FMS | 37 | – | Power | Higher theta power in prefrontal and anterior cingulate cortices in patients compared to healthy participants Positive correlation of theta changes with tiredness, tenderness and pain scores |
| Flor-Henry 2010 (Flor-Henry et al., 2010) | Cross-sectional observational | – | EEG | CFS | 137 | – | Power/PF/Other (Classification) | Lower alpha power in the parieto-occipital region and lower beta power in the fronto-temporal region in patients compared to healthy participants No significant PF differences Classification approach using spectral current density in the alpha and beta band with 72% and 71% accuracy, respectively |
| Golonka 2019 (Golonka et al., 2019) | Cross-sectional observational | – | EEG | Other (Burnout) | 95 | – | Power/PF | Lower alpha power in patients compared to healthy participants Alpha power negatively correlated with exhaustion symptoms in anterior and posterior region No significant PF difference |
| Gschwind 2016 (Gschwind et al., 2016) | Cross-sectional observational | – | EEG | MS | 102 | FSMC | Other (Microstate) | Cognitive fatigue significantly predicted by short duration of class B microstate |
| Jensen 2018 (Jensen et al., 2018) | (Randomized) Controlled Trial | NFB + Hypnosis vs. MM+ Hypnosis vs. Hypnosis | EEG | MS | 32 | FSS | Power | Hypnosis increased theta, beta and gamma power only in patients who received NFB and decreased beta and gamma in those who received MM |
| Kayiran 2010 (Kayıran et al., 2010) | (Randomized) Controlled Trial | NFB vs. Escitalopram | EEG | FMS | 36 | VAS | Power | No power changes in NFB compared to control group Decrease in theta/sensory motor rhythm ratio in NFB group |
| Kravitz 2006 (Kravitz et al., 2006) | (Randomized) Controlled Trial | NFB vs. Sham | EEG | FMS | 47 | Fibro-myalgia Symptom Scales | Power | Pre-treatment delta/alpha amplitude ratio > 1 associated with participant rated but not clinician rated global impression response, independent of intervention |
| Loganovsky 2000 (Loganovsky, 2011) | Cross-sectional observational | – | EEG | CFS | 38 | – | Power | Lateralized (left-sided) in- crease of theta and beta as well as decrease of alpha power |
| Lopez 2015 (Navarro Lopez et al., 2015) | Cross-sectional observational | – | EEG | FMS | 26 | – | Power/PF | Ratios of theta/alpha and beta/alpha power as indicators of disease severity PF higher in patients compared to healthy participants |
| Moore 2014 (Moore et al., 2014) | Longitudinal descriptive | Chemo-therapy | EEG | CRF | 18 | BFI | Power | Total spectrum power increased after a physical task in patients during chemotherapy but not healthy participants |
| Neu 2011 (Neu et al., 2011) | Cross-sectional observational | – | EEG | CFS | 30 | FSS | Power | Higher theta power in electrodes Fp1 and F4 as well as higher beta power in electrode O2 in patients compared to healthy participants |
| Park 2019 (Park et al., 2019) | Descriptive | – | EEG | CRF/CFS | 45 | BFI/FSS | Power | FSS scores positively correlated with frontal delta, theta, alpha power in CFS group |
| Porcaro 2019 (Porcaro et al., 2019) | (Randomized) Controlled Trial | tDCS vs. Sham | EEG | MS | 30 | mFIS | Connectivity | Before treatment, more severely impaired resting state dynamics in S1 than in M1 in fatigued patients Left S1 fractal dimension at rest impaired compared to healthy participants before but not after tDCS treatment |
| Sherlin 2007 (Sherlin et al., 2007) | Cross-sectional observational | – | EEG | CFS | 34 | – | Power | Higher delta power in the left uncus and parahippocampal gyrus as well as higher theta power in the cingulate gyrus and right precentral gyrus of the frontal lobe in patients compared to HC twins |
| Sjøgård 2021 (Sjogard et al., 2021) | Cross-sectional observational | – | MEG | MS | 146 | FSMC | Connectivity | Lower alpha FC within the DMN and between the DMN, SMN and LAN as well as lower interhemispheric beta FC among nodes of the SMN in patients compared to healthy participants Significant negative correlation of FC with cognitive fatigue |
| Vecchio 2017 (Vecchio et al., 2017) | Cross-sectional observational | – | EEG | MS | 38 | mFIS | Other (Graph measures) | Fatigue symptoms positively correlated with beta smallworldness in SN |
| Wu 2016 (Wu et al., 2016) | Cross-sectional observational | – | EEG | CFS | 47 | – | Power | Delta, theta and alpha power increased in frontal and prefrontal brain regions of patients compared to healthy participants Overall decrease in intensity and complexity of the brain electrical signals in patients |
| Zinn 2016 (Zinn et al., 2016) | Cross-sectional observational | – | EEG | CFS | 18 | – | Power/Connectivity | Decreased alpha power in bilateral parietal, occipital and posterior temporal lobes in patients compared to healthy participants Significantly decreased lagged phase synchronization for delta and alpha including the DMN and CEN |
| Zinn 2017 (Zinn et al., 2017) | Cross-sectional observational | – | EEG | CFS | 29 | DSQ | Connectivity/Other (Graph measures) | Lower delta smallworldness in patients compared to healthy participants Delta smallworldness negatively correlated with neurocognitive impairment scores on the DSQ |
| Zinn 2018 (Zinn et al., 2018) | Cross-sectional observational | – | EEG | CFS | 100 | MFI-20/FSS | Power | Increased delta power predominately in the frontal lobe, and decreased beta power in the medial and superior parietal lobe in patients compared to healthy participants Left- lateralized, frontal delta sources associated with a clinical reduction in motivation |
| Zinn 2021a (Zinn et al., 2021) | Cross-sectional observational | – | EEG | CFS | 13 | DSQ | Power | Higher delta and lower alpha and beta power in patients compared to healthy participants |
| Zinn 2021b (Zinn and Jason, 2021) | Cross-sectional observational | – | EEG | CFS | 68 | DSQ | Other (Graph measures) | Significant group differences in baseline CAN organization Cognitive, affective, and somato-motor symptom cluster ratings associated with alteration to CAN topology in patients, depending on the frequency band |
Note. M/EEG, Magneto-/Electroencephalography; PF, Peak Frequency; mFIS, modified Fatigue Impact Scale; FSS, Fatigue Severity Scale; FSMC, Fatigue Scale for Motor and Cognitive Funktions; DSQ, DePaul Symptom Questionnaire; BFI, Brief Fatigue Inventory; PFQ, Post-Polio Fatigue Questionnaire; NFB, Neurofeedback; MM, Mindfulness Meditation; tDCS, transcranial direct current stimulation; FC: Functional Connectivity; CEN, Central executive network; DMN: Default-mode network; SN, Salience Network; SMN; Sensory-motor network; CAN, Central autonomic network; LAN, language network; rsFC, resting-state functional connectivity; S1, primary somatosensory cortex; M1, primary motor cortex; CFS, chronic fatigue syndrome; CRF, cancer-related fatigue; FMS, fibromyalgia syndrome; MS, multiple sclerosis; PVFS, post-viral fatigue syndrome.