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Verbal Description Rules for EEG Pattern Labels

These rules define how to generate a concise verbal description from the model outputs for LRDA, GRDA, LPD, and GPD patterns.

Templates:

LRDA / LPD:   {type} at {X} Hz, {laterality}; maximal in {top regions}.
GRDA / GPD:   {type} at {X} Hz, {regional predominance}.

Rule 1 — Event type

Use the acronym exactly as output by the model. Do not spell it out.

Model output Use in description
LRDA LRDA
GRDA GRDA
LPD LPD
GPD GPD

The model type label is never overridden by other outputs (e.g., a high laterality index does not change GRDA to LRDA).

Rule 2 — Frequency

Report the median detected frequency rounded to 1 decimal place. No band name.

Example: at 2.1 Hz

Rule 3 — Laterality (LRDA / LPD only)

Derived from laterality_index = (right_mean_score − left_mean_score) / (right_mean_score + left_mean_score).

The left/right mean scores are computed as equal-weighted means over the 4 anatomical regions per side (LF, LT, LCP, LO for left; RF, RT, RCP, RO for right), so that frontal regions (4 channels) do not dominate over occipital/centro-parietal (1 channel).

Ranges from −1 (fully left) to +1 (fully right).

For LRDA / LPD (per ACNS 2021 nomenclature, L = Lateralized):

Laterality index Label
< −0.15 unilateral left
−0.15 to −0.10 bilateral asymmetric, left-predominant
−0.10 to +0.10 bilateral/symmetric
+0.10 to +0.15 bilateral asymmetric, right-predominant
> +0.15 unilateral right

ACNS 2021 definitions (qualitative, Section C1b, p.9–10):

  • Unilateral: pattern seen in only one hemisphere
  • Bilateral asymmetric: seen bilaterally but clearly and consistently (>80% of the time) higher amplitude in one hemisphere
  • No quantitative amplitude ratio or LI threshold is given; the ±0.15 cutoff is calibrated to clinical judgment.

For GRDA / GPD: Laterality is not reported. See Rule 5.

Rule 4 — Spatial extent

Not included in the verbal description. Spatial extent is available as a numeric field but is not reported in the verbal summary.

Rule 5 — Regional description

For LRDA / LPD:

Report top 1–2 active regions on the dominant side only (side already stated in the laterality term). Use bare names without the side prefix.

  • Threshold for "active": mean region score > 2.0
  • Use bare names: "frontal", "temporal", "centro-parietal", "occipital"
  • If no qualifying region: "no region clearly dominant"

Example: maximal in the centro-parietal and temporal regions

For GRDA / GPD (ACNS 2021, Section C1b):

Report regional predominance using one of three ACNS-specified categories:

Predominance group Regions used
frontally predominant mean(LF, RF)
occipitally predominant mean(LO, RO)
midline predominant mean(Fz-Cz, Cz-Pz channel scores)

Pick the group with the highest mean score. If that score is ≤ 2.0 (not above the active threshold), use "no regional predominance" instead.

Rule 6 — Modifiers (+F, +S, etc.)

Deferred. No method currently exists to detect fast activity or sharp wave morphology. Do not add modifiers until a detection method is implemented.

Examples

LRDA at 2.1 Hz, unilateral left; maximal in the centro-parietal and temporal regions.

LRDA at 2.1 Hz, bilateral asymmetric, left-predominant; maximal in the centro-parietal regions.

LPD at 1.2 Hz, unilateral right; maximal in the temporal region.

GRDA at 1.8 Hz, frontally predominant.

GRDA at 2.3 Hz, no regional predominance.

GPD at 1.5 Hz, occipitally predominant.