Delta Wave
Denition
-Frequency: <4 Hz
-Physiology: Large‑amplitude, slow oscillatory activity
Mechanism
-2 major neuronal generators:
>Thalamocortical networks→ synchronous, rhythmic delta (particularly in sleep)
>Intrinsic cortical circuits→ focal, polymorphic delta (often pathological)
-Modulators:
>Glial/astrocytic networks influence slow oscillations
*Delta is never generated by purely neuronal mechanisms
Interpretation
-Depends age, vigilance state, topographic distribution, morphology, reactivity, and clinical context
Age
-Infancy: abundant delta→ physiologic
~10 years: <10% of background
-Adults: largely absent in awake state
-Elderly: up to ~1% may persist as physiologic
State
-Delta↑ w/ ↓alertness
>Drowsiness: ↑, often temporal
-Hyperventilation: ↑ generalized delta
-N3 sleep: high‑amplitude, synchronous, generalized delta (“slow‑wave sleep”)
Topography and morphology
-Polymorphic focal delta
>Persistent, non‑reactive, state‑independent→ strong marker of structural lesion (subcortical lesions or large cortical lesions)
-Generalized polymorphic delta
>Suggests diffuse encephalopathy
Rhythmic patterns
-FIRDA (Frontal Intermittent Rhythmic Delta Activity)
>Bilateral, symmetric, intermittent rhythmic delta
>Associated w/ diffuse cerebral dysfunction, ↑ICP, or metabolic encephalopathy
>Benign in children/teens
-TIRDA (Temporal Intermittent Rhythmic Delta Activity)
>Focal, typically unilateral
>Associated w/ TLE, even w/o interictal spikes
-OIRDA (Occipital Intermittent Rhythmic Delta Activity)
>Mainly in children
>Associated w/ CAE and others idiopathic generalized epilepsies
-LRDA (Lateralized Rhythmic Delta Activity)
>Critically ill patients
>IIC pattern
-GRDA (Generalized Rhythmic Delta Activity)
>Seen in: encephalopaty, sedation, post‑anoxic injury
>Not epileptiform unless evolving
-SIRPIDs (Stimulus‑Induced Rhythmic, Periodic, or Ictal‑appearing Discharges)
>Often rhythmic delta following stimulation
>Occur in comatose, septic, or anoxic patients
>Falls under IIC spectrum
-Delta brush pattern
>Fast activity riding on delta
-Seen in: Anti‑NMDA encephalitis (extreme delta brush), premature neonates (physiologic delta brush)
Clinical significance
-Excess generalized delta→ diffuse encephalopathy
-Focal persistent delta→ structural pathology
-Intermittent rhythmic delta→ epilepsy or prior brain injury (location matters)
>Temporal→ TLE
>Occipital→ CAE
>Frontal→ diffuse dysfx
Clinical pearl
-Delta alone is never inherently normal or abnormal — context determines meaning
-Persistent focal polymorphic delta has the highest specificity for structural lesions
-Rhythmic delta is more associated with epilepsy or IIC than polymorphic delta
-Non‑reactive generalized delta in an awake adult→ think encephalopathy