Dr. Manoj Rathi *
MD(Ped),FICMCH Aashirwad Children Hospital, Mudholkar Peth, Amravati *
Major Frequency Range of Rhythms:
Electrical activity from the brain consists primarily of rhythms and these rhythms are named according to their frequency in cycles per second (c/sec), also called Hertz (Hz).

  • Delta refers to all rhythms less than 4 c/sec
  • Theta is between 4 to <8 c/sec
  • Alpha is between 8 to 13 c/sec
  • Beta is > 13 c/sec

      Normal Background Rhythms- Introduction
      Usually, there is one dominant frequency that is called the 'background rhythm'.

1. Background rhythm in wake

    In infants = 4 to 5 c/sec (Delta and Theta waves)
    In children = 5 to 8 c/sec (Theta)
    In adults = 8 to 10 c/sec (Alpha)

2. Background rhythm is sleep

    In light sleep = 5 to 6 c/sec (Theta)
    In deep sleep = 2 to 3 c/sec (Delta)

(A) Abnormal Patterns - Introduction:
Abnormal patterns are mainly divided into two types:

    1. Slow waves and
    2. Spikes (or sharp waves)

Also, depression of normal rhythm's may be abnormal.

(I) Slow Waves:
Slow waves are rhythms appearing especially during wakefulness that are slower than in the normal. Abnormal slow waves appear when the brain cells are damaged.

(II) Paroxysms: Spikes (Sharp Waves):
The spike (or Sharp wave) is a suddenly appearing electrical explosion that looks like a spike of large nail, spikes are <70 m sec and sharp wave 70 to 200 m sec in duration. These two patterns signify an epileptogenic region of the brain.

(III) Depression of normal Rhythms - Decreased amplitude of any normal rhythms.

    Diffuse slow - suggestive of metabolic, toxic, infectious etiologies.
    Focal slow-very slow - space occupying lesion.

(B) Summary of Abnormal EEG Patterns and associated clinical conditions:

  1. Multi focal spikes - (non-specific) seizures

  2. Repetitive spike - Clonic seizure

  3. Slow delta discharge - Tonic seizure


  1. Hypsarrhythmias-Infantile spasms
  2. Slow (1 to 2/sec.) spike and wave-Lennox-Gastaut syndrome (tonic seizure)
  3. 3.3/sec spike and wave complex-absence (Multiple spike-generalized tonic clonic seizure)
  4. Occipital spikes - Visual perceptual disorders
  5. Centro-temporal sharp waves-benign epilepsy of childhood
  6. Periodic Lateralized epileptiform discharge - Cerebrovascular emboli and also epilepsia partialis continua, meta static to mores
  7. Temporal sharp waves

    Mid temporal
    Navigate Symptoms & Seizures
    P Psychomotor & generalized
    Tonic clonic seizures


    These are diffuse slow waves, decreased frequency of background rhythm.


    • Carotid - Frontal and temporal slow waves

    • Vertibrobasilar - Temporal and occipital show waves and low amplitude

    • Haemorrhage-Sharr J-waves or spikes with slow waves

    • Space occupying lesion - highly localized abnormal slow waves


    Occipital slow waves and extreme spindles

    Decreased frequency of back ground rhythm and temporal slow waves on the left side of brain.
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