Most of the research on low-frequency EEG has focused on various kinds of cognitive tasks and states such as contingent stimulation (contingent negative variation, CNV) motor movements (Bereitschafts potential) and the orienting paradigm. Additionally, ISOs at a wide range of frequencies (0.02 to 0.2 Hz) are also present during non-REM sleep, phase synchronized with higher frequency EEG activities. SATs represent endogenously driven, the spontaneous activity which is crucial in shaping neuronal connectivity at an early immature stage where sensory input has little or no role at all.

Infra-slow oscillations (ISO) (less than 0.5Hz): ISOs are the dominating frequency in the preterm neonates is as low as 0.01 to 0.1 Hz and are termed as spontaneous activity transients (SAT). Based on the FbEEG recording, EEG waveforms can be characterized by various types:-ġ. However, recording EEG data at extremely high frequencies is not done routinely in clinical practice because it requires special equipment that can acquire data at higher sampling frequencies which in turn increases the space needed to store this information.

However, a broader EEG bandwidth has undergone examination by clinical neurophysiologists and researchers and has been found to be clinically significant in certain conditions. Elimination of the lower (infra-slow) or higher (ultra-fast) bands of the EEG frequency spectrum in routine EEG results in loss of several important physiological and pathological meaningful features of brain activity. A full bandwidth EEG (FbEEG) looks at the full, physiologically and clinically relevant waveforms without any trade-off that would favor one frequency band at the expense of another. This analysis occurs through the use of bandpass filtering of the EEG recordings. The conventional bandwidth of clinical EEG focuses on the analysis of waveforms ranging from 0.5Hz to 70Hz. In addition, there are other waveforms such as infra slow oscillations (ISO) (less than 0.5Hz) and high-frequency oscillations (HFOs) (greater than 30Hz) which are outside the conventional bandwidth of clinical EEG but have recently found clinical importance with the advent of digital signal processing. The most commonly studied waveforms include delta (0.5 to 4Hz) theta (4 to 7Hz) alpha (8 to 12Hz) sigma (12 to 16Hz) and beta (13 to 30Hz). However, the most frequently used method to classify EEG waveforms is by the frequency, so much so, that EEG waves are named based on their frequency range using Greek numerals. EEG waveforms may be characterized based on their location, amplitude, frequency, morphology, continuity (rhythmic, intermittent or continuous), synchrony, symmetry, and reactivity.

Normal eeg vs seizure eeg