NeuroSkill Data Reference

EEG Band Powers

Relative power — values sum to approximately 1.0. Found under scores.bands in status, or as rel_* top-level keys in metric responses.

Field	Band	Range	What it means
`rel_delta`	δ 0.5–4 Hz	0–1	Deep sleep, unconscious processes. High during N3 sleep or drowsiness.
`rel_theta`	θ 4–8 Hz	0–1	Drowsiness, meditation, creativity, memory encoding.
`rel_alpha`	α 8–13 Hz	0–1	Relaxed wakefulness, idle cortex, eyes-closed state. Drops on task engagement.
`rel_beta`	β 13–30 Hz	0–1	Active thinking, focus, arousal. High beta = cognitive effort or stress.
`rel_gamma`	γ 30–100 Hz	0–1	Sensory binding, high-level cognition.

Field	Formula	What it means
`faa`	ln(αR) − ln(αL)	Frontal Alpha Asymmetry. Positive = approach motivation / positive affect. Negative = withdrawal motivation.
`tar`	θ / α	Theta/Alpha Ratio. High = drowsy or meditative.
`bar`	β / α	Beta/Alpha Ratio. High = alert, possibly anxious.
`dtr`	δ / θ	Delta/Theta Ratio. High in deep sleep or pathological slowing.
`tbr`	θ / β	Theta/Beta Ratio. Healthy ~1.0; elevated (>1.5) indicates drowsiness or reduced cortical arousal.
`pse`	(power law slope)	Power Spectral Exponent. Steeper = more 1/f, typical of rest. Flatter = active.
`bps`	(regression slope)	Band-Power Slope. Similar to PSE; measures spectral tilt.
`apf`	Hz	Alpha Peak Frequency. 8–12 Hz typical; shifts with age and cognitive state.
`sef95`	Hz	Spectral Edge Frequency 95%. Frequency below which 95% of power falls.
`spectral_centroid`	Hz	Spectral Centroid. Weighted average frequency — rises with cognitive load.
`coherence`	0–1	Inter-channel coherence. High = coordinated brain activity.
`mu_suppression`	0–1	Mu rhythm suppression. Increases with motor imagery or observed action.
`laterality_index`	−1 to 1	Hemispheric laterality. Left vs. right hemispheric dominance.
`snr`	dB	Signal-to-Noise Ratio. > 10 dB = good signal; < 5 dB = noisy.

0–1 range unless noted. Computed per 5-second epoch by the on-device model.

Field	What it means
`focus`	Sustained attention. Driven by frontal beta and suppressed alpha.
`relaxation`	Calm, low-arousal state. High alpha, low beta.
`engagement`	Active cognitive engagement. Composite of beta, theta, alpha suppression.
`meditation`	Meditative depth. High frontal alpha, stable theta, low beta.
`mood`	Valence estimate. Positive FAA and alpha balance → positive mood.
`cognitive_load`	Mental effort. High theta + beta, low alpha.
`drowsiness`	Sleepiness. High delta + theta, alpha intrusions.

Nonlinear EEG measures — higher complexity generally means a more flexible, awake brain state.

Field	What it means
`hjorth_activity`	Signal variance (power).
`hjorth_mobility`	Mean frequency estimate.
`hjorth_complexity`	Signal shape complexity — how much the signal changes its frequency.
`permutation_entropy`	Ordinal pattern entropy. Near 1 = complex/random; near 0 = highly ordered.
`higuchi_fd`	Fractal dimension. ~1.5–1.8 during healthy wakefulness.
`dfa_exponent`	Detrended fluctuation. ~0.5 = white noise; ~1.0 = long-range correlations.
`sample_entropy`	Regularity — lower = more predictable/periodic signal.
`pac_theta_gamma`	Phase-Amplitude Coupling (θ–γ). Linked to working memory and attention.

Derived from the Muse PPG sensor (forehead).

Field	Unit	What it means
`hr`	bpm	Heart rate.
`rmssd`	ms	Root mean square of successive differences — parasympathetic HRV. High = relaxed.
`sdnn`	ms	Standard deviation of NN intervals — overall HRV.
`pnn50`	%	% of successive differences > 50 ms — parasympathetic index.
`lf_hf_ratio`	ratio	Low/High frequency power ratio — sympathetic vs. parasympathetic balance. High = stress.
`respiratory_rate`	bpm	Estimated breathing rate from PPG.
`spo2_estimate`	%	Estimated blood oxygen saturation (research only).
`perfusion_index`	%	Ratio of pulsatile to static IR signal — peripheral perfusion quality.
`stress_index`	0–100	Composite stress index. High HR + low HRV + high LF/HF → high stress.

Field	What it means
`stillness`	0–1. Head movement score; 1 = no motion.
`head_pitch`	Degrees forward/backward tilt.
`head_roll`	Degrees left/right tilt.
`nod_count`	Number of detected vertical head nods.
`shake_count`	Number of detected horizontal head shakes.
`blink_count`	Number of detected eye blinks (from frontal electrodes).
`blink_rate`	Blinks per minute.
`jaw_clench_count`	Number of detected jaw clenches (EMG artifact).
`jaw_clench_rate`	Jaw clenches per minute.

Used in sleep and status.sleep.

Stage	Code	EEG signature
Wake	`0`	High beta, present alpha when eyes closed
N1	`1`	Slow eye movements, alpha fades, theta begins
N2	`2`	Sleep spindles (12–15 Hz bursts), K-complexes, dominant theta
N3	`3`	High-amplitude delta > 50% of epoch — deep/slow-wave sleep
REM	`4`	Low-amplitude mixed frequency, sawtooth waves, suppressed delta

From neurological. All 0–100. Research use only — not diagnostic.

Index	Mechanism	Reference (verified DOI)
`headache_index`	Cortical hyperexcitability (beta)	Bjørk et al. (2009) · doi:10.1007/s10194-009-0140-4
`migraine_index`	Delta + alpha suppression	Bjørk et al. (2009) · doi:10.1007/s10194-009-0140-4

Score colour coding: < 30 = green (low), 30–60 = yellow (moderate), > 60 = red (elevated).

From neurological.consciousness. All 0–100 (higher = better).

Metric	What it measures	Reference (verified DOI)
`lzc`	Lempel-Ziv Complexity proxy — signal diversity; drops under anesthesia	Casali et al. (2013) · doi:10.1126/scitranslmed.3006294
`wakefulness`	Inverse drowsiness — high alpha relative to theta	Klimesch (1999) · doi:10.1016/s0165-0173(98)00056-3
`integration`	Composite of coherence × PAC × spectral entropy — cortical integration	Tononi (2004) · doi:10.1186/1471-2202-5-42

Consciousness: ≥ 50 = green, 25–50 = yellow, < 25 = red.

All DOIs below are verified against the Skill application reference list (HelpReferences.svelte). Only papers present in that list are cited here.

#	Citation	DOI
[69]	Bjørk, M. H., Stovner, L. J., Engstrøm, M. et al. (2009). Interictal quantitative EEG in migraine: a blinded controlled study. The Journal of Headache and Pain, 10(5), 331–339.	doi:10.1007/s10194-009-0140-4
[75]	Casali, A. G., Gosseries, O., Rosanova, M. et al. (2013). A Theoretically Based Index of Consciousness Independent of Sensory Processing and Behavior. Science Translational Medicine, 5(198), 198ra105.	doi:10.1126/scitranslmed.3006294
[6]	Klimesch, W. (1999). EEG alpha and theta oscillations reflect cognitive and memory performance. Brain Research Reviews, 29(2–3), 169–195.	doi:10.1016/s0165-0173(98)00056-3
[76]	Tononi, G. (2004). An information integration theory of consciousness. BMC Neuroscience, 5, 42.	doi:10.1186/1471-2202-5-42