SWS (N3) has similar features, but less spindles, K-complexes, and POSTS are seen and even more delta frequency activity emerges (Figure 18). Artifacts are common during the wakeful EEG, and one of the first hurdles of EEG interpretation is distinguishing these from cerebral signal. Most notable is the presence of low-amplitude, high-frequency activity arising from scalp muscles, often frontally dominant but seen throughout the tracing. Rapid eye movements (REMs), resulting from saccades and spontaneous changes of gaze, may be seen as small, rapid deflections in frontal regions.
Electroencephalography (EEG) is a valuable tool used in neuroscience to monitor and analyze brain activity. EEG measures electrical activity in the brain through electrodes placed on the scalp, providing insight into different types of brain waves. There are four main types of EEG waves that are classified based on their frequency: delta, theta, alpha, and beta waves.
Delta Waves
Delta waves are the slowest brain waves, with a frequency range of 0.5 to 4 Hz. These waves are typically observed during deep sleep stages, such as in the N3 stage of non-REM sleep. Delta waves are associated with restorative functions, memory consolidation, and overall healing processes in the brain.
Typically the one electrode can display spikes of activity on the EEG, whereas the other electrodes would only pick up normal brain activity as the seizure is not happening there. The electrical activity in the brain is driven by neuronal activity (action potentials) or nerve impulses. This is how neurons pass messages to each other for behaviors, thoughts, and other conscious or unconscious processes to occur. The EEG has been used for many purposes besides the conventional uses of clinical diagnosis and conventional cognitive neuroscience. Army Air Corps to screen out pilots in danger of having seizures;[105] long-term EEG recordings in epilepsy patients are still used today for seizure prediction. Neurofeedback remains an important extension, and in its most advanced form is also attempted as the basis of brain computer interfaces.[106] The EEG is also used quite extensively in the field of neuromarketing.
Polymorphic activity must vary in frequency, amplitude and morphology. Here we see polymorphic delta activity that is characteristic of slow wave sleep. This example is actually a seizure, but for now just note that the high amplitude delta activity is monomorphic–every waveform looks essentially just like the ones around it.
Theta Waves
The importance of gamma rhythms in a large variety of cognitive functions has been well established.[16][17] Brain stem evoked potentials (BERA) is a well established and routinely measured category of ultrafast EEG signals. Alpha is 8-13 Hz, and is perhaps the frequency you’ll come to know and love best. It is the hallmark frequency of the normal awake adult brain, to the point that the posterior dominant rhythm (PDR), a key finding of the normal background, used to be called the alpha rhythm. EEG charts comprise a series of wavy lines, which represent rising and falling voltages within different groups of neurons. These ripples are measured in hertz, or cycles per second, and are classified according to their frequency. No matter the EEG type, the electrical activity of the brain is picked up by small metal discs (electrodes) that are positioned in standardized patterns on the scalp.
Your provider will talk to you about the next steps after an EEG based on your diagnosis. Small flat metal discs called electrodes are attached to your scalp with wires. The electrodes analyze the electrical impulses in your brain and send signals to a computer that records the results. This section identifies some normal waveforms, including K complex, V waves, lambda waves, positive occipital sharp transients of sleep (POSTS), spindles, mu rhythm, spikes, sharp waves, and certain delta waves (polyphasic and monophasic shapes).
Theta waves have a frequency range of 4 to 8 Hz and are often present during light sleep, deep relaxation, meditation, or when daydreaming. These waves are also associated with creativity, intuition, and emotional processing. Theta waves are crucial for forming memories and connecting different areas of the brain.
Alpha Waves
Alpha waves have a frequency range of 8 to 13 Hz and are typically seen when the brain is in a relaxed but alert state. These waves are commonly observed when individuals are awake but in a calm and reflective state. Alpha waves are linked to improved focus, attention, and overall mental coordination.
Beta Waves
Beta waves have a frequency range of 13 to 30 Hz and are most prevalent during active thinking, problem-solving, decision-making, and concentration. These waves are associated with heightened cognitive functions, alertness, and stress response. Beta waves are crucial for maintaining focus and engaging in complex mental tasks.
Overall, understanding the different types of EEG waves can provide valuable insights into brain function, cognitive processes, and mental states. By analyzing these waves, researchers and clinicians can gain a better understanding of how the brain works and develop targeted interventions for various neurological conditions.
