Interview Questions for EEG

EEG montages refer to the way EEG signals from different electrodes are displayed and arranged. The choice of montage significantly impacts the interpretation of the data. Different montages emphasize different aspects of brain activity.

• Referential Montage: Each electrode’s activity is referenced to a single point, often a mastoid or earlobe. This provides a general overview of brain activity, but can be affected by the reference point’s own activity. Imagine it like taking a picture of a landscape – you get a broad view, but might miss subtle details.
• Bipolar Montage: The difference in voltage between adjacent electrodes is displayed. This montage is excellent for highlighting localizing patterns and identifying sharp transients because it emphasizes voltage *differences*. Think of it as comparing adjacent areas to see relative differences in activity. This is very useful in identifying the source of focal epileptiform activity.
• Average Reference Montage: The activity of each electrode is compared to the average activity of all electrodes. This helps to minimize the influence of artifacts and provides a more balanced representation of brain activity. This is analogous to taking an average of all the data points before analyzing any individual point, reducing biases from unusual data points.
• Laplacian Montage: This calculates the difference between an electrode and the average of its surrounding electrodes. It’s particularly effective in identifying localized sources of activity by essentially filtering out more widespread activity. It acts as a spatial filter, giving better source resolution.

The application of a particular montage depends on the clinical question. For example, a bipolar montage is often preferred for identifying epileptic discharges, while an average reference montage might be used for sleep studies.

EEG waves are classified by their frequency, measured in Hertz (Hz). Each frequency band is associated with different states of consciousness and brain activity.

• Delta Waves (0.5-4 Hz): These are the slowest waves and are typically seen during deep sleep and in infants. They are often associated with slow-wave sleep and can indicate organic brain damage if present excessively in waking adults.
• Theta Waves (4-8 Hz): These waves are usually seen during drowsiness, light sleep, and meditative states. Increased theta activity can sometimes be associated with emotional distress or cognitive impairment.
• Alpha Waves (8-13 Hz): These waves are most prominent when a person is relaxed and awake with their eyes closed. They are often considered a marker of relaxed wakefulness, and their presence can indicate a healthy neurological state. They’re suppressed by opening your eyes or engaging in mental tasks.
• Beta Waves (13-30 Hz): These waves are associated with alertness, concentration, and active thinking. Increased beta activity is common during active cognitive processes, but excessive beta activity might reflect anxiety or stress.

Think of it like a musical scale: delta waves are the deep, slow bass notes, while beta waves are the high-pitched, fast notes representing active mental processing.

EEG recordings are susceptible to various artifacts, which are non-cerebral signals that contaminate the EEG data. These can make interpretation difficult.

• Electrode Artifacts: Poor electrode contact, electrode movement, or improperly applied gel cause noisy signals. Mitigation: Proper electrode placement, secure fixation, and sufficient gel application.
• Muscle Artifacts: EMG (electromyographic) activity from jaw clenching, eye blinks (EOG), and other muscle movements. Mitigation: Instructing the patient to relax, using EMG or EOG electrodes to identify and remove the artifact, and signal processing techniques.
• Eye Blink Artifacts: These are very common and appear as large deflections. Mitigation: EOG electrodes or signal processing techniques that remove eye blink artifacts.
• Environmental Artifacts: Power line interference (60 Hz in the US, 50 Hz in Europe), electrical equipment interference, and other external sources. Mitigation: Shielding of the recording room, proper grounding of equipment, and digital filtering techniques.
• Cardiac Artifacts: Electrical activity from the heart can be seen as periodic waves on the EEG. Mitigation: ECG electrodes or signal processing to remove cardiac components.

Identifying and mitigating artifacts requires a combination of careful recording techniques and advanced signal processing methods. It’s like cleaning up a noisy audio recording; you need to identify the source of noise and then use tools to remove or reduce it.

Performing an EEG involves careful patient preparation and precise electrode placement.

1. Patient Preparation: Explain the procedure to the patient and ensure they are comfortable. Their hair should be clean and free of hair products to ensure good electrode contact. The patient typically lies down or sits in a relaxed position with their eyes closed.
2. Electrode Placement: Electrodes are placed on the scalp according to the International 10-20 system, a standardized system ensuring consistent electrode placement across studies. This system is based on percentages of the distance between anatomical landmarks such as the nasion and inion. The number of electrodes used varies depending on the clinical question.
3. Electrode Impedance: The impedance, or resistance to the flow of electrical current, at each electrode site is measured and should be below a certain threshold (usually <5kΩ) to ensure optimal signal quality. High impedance leads to noisy data.
4. Recording: The EEG is recorded while the patient is awake and resting with their eyes closed and open and potentially during sleep or various stimuli such as photic stimulation.
5. Data Review: Post-recording, a neurophysiologist reviews the EEG tracing, identifying artifacts and interpreting brainwave patterns.

Accurate electrode placement is crucial, like setting up the right coordinates on a map to accurately pinpoint a location. The International 10-20 system ensures consistency and comparability across different studies.

Epileptiform discharges are abnormal electrical patterns in the brain that are characteristic of epilepsy. Identifying them on EEG requires experience and expertise.

• Spike: A sharp, transient wave with a duration of less than 70 milliseconds.
• Sharp Wave: Similar to a spike, but with a slightly longer duration (70-200 milliseconds).
• Spike-and-Wave Complex: A spike followed immediately by a slow wave. This is highly suggestive of epileptic activity.
• Polyspike-and-Wave Complex: Multiple spikes followed by a slow wave. Indicates more severe epileptic activity.

Interpretation involves considering the morphology (shape), amplitude, location (focal or generalized), frequency, and associated clinical symptoms. For example, a focal spike-and-wave discharge might indicate a seizure focus in a specific brain region. It’s like recognizing a specific musical phrase that indicates a particular piece of music.

Seizure localization involves identifying the brain region responsible for generating a seizure. EEG is a crucial tool for this.

By analyzing the EEG, a neurophysiologist can determine the origin of epileptiform discharges. For example, if there are focal discharges in the temporal lobe, this suggests a temporal lobe epilepsy. This determination can guide surgical planning or influence therapeutic interventions.

However, it’s crucial to note that EEG alone is not always sufficient for accurate localization. Other techniques such as MRI and neuropsychological testing might be needed for a complete evaluation.

EEG procedures require adherence to strict safety measures.

• Electrical Safety: Ensure proper grounding of equipment to prevent electrical shocks. The equipment should be checked regularly and maintained according to manufacturer guidelines.
• Patient Safety: Monitor the patient’s vital signs, especially during prolonged recordings. Ensure the patient’s comfort and explain the procedure clearly. The patient shouldn’t be left unattended.
• Infection Control: Maintain proper hygiene and use sterile techniques to prevent infection. This includes proper disinfection of electrodes and equipment.
• Allergic Reactions: Be mindful of any potential allergies to the electrode gel or other materials used. This may necessitate the use of hypoallergenic alternatives.
• Seizure Monitoring: If performing EEG for seizure monitoring, be prepared for the possibility of a seizure. Personnel should be trained on how to manage seizures.

Safety is paramount. A careful and organized approach is required to ensure that the procedure is both safe and effective.

Troubleshooting EEG equipment malfunctions requires a systematic approach. First, always ensure the equipment is properly powered and connected. Check all cables for damage or loose connections – a surprisingly frequent source of issues. Look at the impedance levels displayed on the machine; high impedances (typically above 5 kΩ) indicate poor electrode contact and need attention. This often involves improving electrode paste application or repositioning electrodes. If you encounter artifacts, determine their source. Muscle activity manifests as high-frequency activity, often easily identified. Line noise, typically 60 Hz interference, appears as a rhythmic wave. Electrode pops or movement artifacts are usually transient spikes. Solving these requires addressing the root cause: ensuring patient comfort and minimal movement, checking for loose wiring near electrical sources, or re-geling electrodes.

If these simple checks don’t resolve the problem, more complex steps might be needed. Verify the settings on the EEG machine, ensuring they’re appropriate for the recording. Consult the equipment manual for troubleshooting specific errors. If the problem persists, contact the biomedical engineering department or manufacturer for support. Regular preventative maintenance, including calibration and cleaning of the equipment, is crucial to minimize malfunctions.

Encephalopathies are disorders that affect brain function. Their EEG correlates vary widely depending on the cause and severity. Metabolic encephalopathies, such as those caused by hepatic or renal failure, often present with diffuse slowing – a decrease in the frequency of brainwave activity. This slowing can range from mild slowing of the background rhythm to the presence of delta waves, which are slow waves associated with deep sleep or dysfunction. In severe cases, there may be burst suppression, where periods of activity alternate with periods of electrical silence. Infectious encephalopathies (like encephalitis), conversely, can demonstrate more focal slowing or epileptiform discharges (abnormal, seizure-like activity) depending on the location of the infection in the brain.

Hypoxic-ischemic encephalopathy, which results from a lack of oxygen to the brain, usually shows diffuse slowing, often with sharp waves or even status epilepticus (a prolonged seizure). Toxic encephalopathies, caused by drug overdose or exposure to toxins, present a spectrum of changes, ranging from subtle slowing to significant abnormalities, again depending on the toxin and severity. Identifying the specific EEG correlate requires considering the patient’s clinical presentation and history. It’s vital to remember that EEG alone doesn’t diagnose encephalopathy; it provides crucial supportive data in conjunction with clinical findings.

Long-term EEG monitoring (usually >24 hours) is indicated for several reasons. The most common is the evaluation of patients with recurrent seizures or epilepsy that are difficult to control. This allows clinicians to capture seizure activity that may not occur during a shorter routine EEG. Another indication is the monitoring of patients in the ICU following severe neurological injuries (e.g., stroke, traumatic brain injury). This helps assess the evolution of brain function and identify potential complications like non-convulsive seizures or status epilepticus, which may not be apparent through other clinical means. Long-term EEG is also helpful in diagnosing certain types of encephalopathies, particularly those with fluctuating symptoms.

Patients with unexplained alterations in consciousness, such as those with altered mental status or coma, can benefit from long-term EEG monitoring to identify the cause. Sometimes, subtle epileptiform activity only becomes apparent during continuous monitoring. Furthermore, long-term EEG helps in assessing the efficacy of treatment for seizures or other neurological conditions by monitoring changes in brainwave patterns in response to medication or other interventions.

The key difference between video-EEG monitoring and a routine EEG lies in the addition of video recording. A routine EEG is a relatively short recording (usually 20-30 minutes) that assesses the brain’s electrical activity. It provides a snapshot of brain function at a specific point in time. In contrast, video-EEG monitoring continuously records both the EEG and a video of the patient over a prolonged period, typically 24 hours or more. This simultaneous recording is critical for correlating neurological events, primarily seizures, with their corresponding behavioral manifestations.

Video-EEG is crucial when there’s uncertainty about the origin of events, particularly those that might appear similar clinically but have different underlying mechanisms. For example, a patient experiencing periods of altered consciousness could have non-convulsive seizures, behavioral episodes, or a purely psychiatric cause. Video-EEG helps differentiate these, as the EEG can identify subtle seizure activity even if the patient shows no overt motor convulsions. This allows clinicians to accurately diagnose the condition and tailor treatment accordingly. Routine EEGs might miss these intermittent events, making video-EEG indispensable in complex cases.

Interpreting an EEG in a suspected sleep disorder involves careful analysis of sleep stages and the identification of any abnormalities during those stages. The EEG will show characteristic patterns for the different sleep stages (N1, N2, N3, REM). Abnormal findings in sleep disorders could include excessive slow-wave activity (delta waves), indicative of deep sleep disorders, or frequent arousals during sleep. Furthermore, the EEG may reveal the presence of periodic limb movements, particularly during non-REM sleep, which are frequently seen in patients with restless leg syndrome or periodic limb movement disorder (PLMD).

Sleep-related epilepsy may present with epileptiform discharges that are only apparent during sleep. Certain parasomnias, which are unusual behaviors that occur during sleep, can sometimes be associated with abnormal EEG patterns. The interpretation always needs to be correlated with polysomnography (PSG), which includes other measures like eye movements (EOG), muscle activity (EMG), and respiratory patterns. The combined data from EEG and PSG provides a comprehensive picture of the sleep architecture and can differentiate between various sleep disorders.

EEG plays a crucial role in the diagnosis of coma and brain death. In coma, the EEG typically shows diffuse slowing, and the degree of slowing can correlate with the severity of the coma. However, the presence of coma doesn’t automatically indicate brain death. Brain death is defined by the irreversible cessation of all brain function, and the EEG in this condition exhibits a characteristic pattern of electrical silence or isoelectricity, also known as a flat EEG. This absence of any detectable brain activity is a critical criterion in the diagnosis of brain death.

It is essential to note that a flat EEG isn’t obtained immediately upon cessation of brain activity. There’s a time window before a flat EEG is reliably demonstrable; therefore, other clinical criteria and confirmatory tests are necessary to pronounce brain death. The EEG’s contribution is as part of a more extensive diagnostic evaluation, where clinical findings, such as the absence of brainstem reflexes, absence of spontaneous respirations, and confirmation through other imaging modalities, are also considered.

Evoked potentials (EPs) are brain responses to specific stimuli, recorded using EEG. They reflect the brain’s electrical activity in response to sensory stimulation (visual, auditory, somatosensory) or cognitive tasks. Clinically, EPs are used to assess the integrity of sensory pathways and cortical processing. Visual evoked potentials (VEPs) assess the visual pathway from the retina to the visual cortex, helping diagnose multiple sclerosis, optic neuritis, and other conditions affecting vision. Auditory evoked potentials (AEPs) evaluate the auditory pathway, used in diagnosing auditory neuropathies, brainstem lesions, and hearing impairments.

Somatosensory evoked potentials (SSEPs) test the sensory pathways from the periphery to the cortex, frequently employed to evaluate spinal cord injury or peripheral nerve damage. Cognitive evoked potentials, such as P300, measure cognitive processing speed and attention, and can help diagnose dementia or other cognitive disorders. By precisely timing and averaging the brain’s response to repeated stimuli, the EP signal can be distinguished from background EEG activity. This technique is invaluable in localizing lesions within the nervous system and quantifying the extent of neurological damage.

Ethical considerations in EEG testing center around patient rights and data privacy. Informed consent is paramount; patients must understand the procedure, its risks (minimal, but including allergic reactions to electrode gel), benefits, and alternatives before agreeing. Maintaining patient confidentiality is crucial, adhering strictly to HIPAA or equivalent regulations. Data anonymity must be ensured when sharing EEG data for research or teaching purposes. Furthermore, EEG technicians must be aware of and respect patient autonomy, particularly those with cognitive impairments, ensuring their comfort and understanding throughout the process. For instance, a patient who feels pressured to undergo a test they do not understand has their rights violated. Ethical dilemmas might arise in situations where a patient lacks capacity to consent, requiring a surrogate decision-maker involved in the process.

Quality assurance (QA) and quality control (QC) in EEG are crucial for reliable results. QC focuses on the daily checks of equipment: ensuring proper calibration of amplifiers, impedance levels below a certain threshold (e.g., 5 kΩ), and artifact rejection system functionality. Regular preventative maintenance, including cleaning and testing electrodes and cables, is essential. QA involves more extensive processes: periodic testing of the entire system using standardized signals (e.g., sinusoidal waves), comparison against established norms, and compliance with technical standards (e.g., those set by the American Clinical Neurophysiology Society). Technician competency is a significant factor, achieved through regular training, proficiency tests, and adherence to established protocols for electrode placement (e.g., 10-20 system) and artifact identification. Regular review of EEG recordings by experienced neurophysiologists ensures accuracy and consistency in interpretation. Think of it like a finely tuned instrument – regular checks and maintenance ensure it plays beautifully, producing accurate and reliable results.

Legal implications of EEG interpretation are significant, primarily concerning medical malpractice. Incorrect interpretation can lead to misdiagnosis and inappropriate treatment, potentially causing harm to the patient. Therefore, EEG reports must be accurate, complete, and clearly written. Documentation is crucial and should include all relevant clinical information, EEG findings (including descriptions of waveforms, frequency bands, and locations of abnormalities), and the interpreter’s professional opinion. The interpreter must stay within their scope of practice; for instance, diagnosing epilepsy based solely on an EEG without clinical correlation would be inappropriate and potentially legally problematic. Maintaining detailed records, including the raw EEG data and the interpretation, protects against legal challenges. Adhering to ethical guidelines and maintaining professional competence are key in mitigating legal risks. Malpractice claims frequently involve a failure to adhere to the standards of practice within the neurophysiology community.

Accurate and complete documentation of EEG findings is critical. The report should begin with patient demographics and clinical indication for the study. Then, a detailed description of the EEG recording procedure, including electrode placement (often referencing a diagram), montage used, and any technical issues encountered. The EEG findings must be systematically described, noting the background activity (e.g., frequency, amplitude, morphology), presence of any epileptiform discharges (spikes, sharp waves, spike-and-wave complexes), and other abnormalities (e.g., slowing, attenuation). The location and lateralization of these findings should be precisely specified. It’s helpful to use standardized terminology and quantitative measures where appropriate (e.g., frequency in Hz). The interpretation section summarizes the findings and relates them to the clinical presentation. Finally, the report should include the name and credentials of the interpreting neurophysiologist. This detailed approach ensures clarity and allows for future review and comparison.

EEG plays a vital role in diagnosing and managing traumatic brain injury (TBI). Immediately after injury, EEG can detect evidence of diffuse or focal dysfunction, like slowing or suppression of brain activity, indicative of severity. It can help differentiate between various types of TBI (e.g., concussion, contusion, diffuse axonal injury). Serial EEGs are used to monitor the patient’s condition over time, helping predict prognosis and guiding treatment decisions. For instance, the presence of status epilepticus (continuous seizure activity) is a critical finding requiring immediate intervention. In the later stages of recovery, EEG can help identify subtle abnormalities that might not be apparent clinically, potentially aiding in rehabilitation planning. EEG helps clinicians understand the extent of brain injury, predict recovery, and monitor response to treatments.

EEG’s role in dementia evaluation is primarily to rule out other conditions, rather than directly diagnose dementia itself. In patients with suspected dementia, EEG can identify epileptiform activity or other paroxysmal events that could contribute to cognitive decline. It can also detect focal slowing, which might indicate the presence of structural brain lesions, or widespread slowing, which can reflect diffuse cortical dysfunction. However, EEG findings are not specific to a type of dementia. While a normal EEG does not rule out dementia, abnormal findings can be a significant clue in the diagnostic process and guide further investigations like neuroimaging (MRI or CT scan). For example, the presence of periodic sharp waves might suggest Creutzfeldt-Jakob disease, a rapidly progressive dementia.

Differentiating between focal and generalized seizures on EEG relies on identifying the distribution of epileptiform activity. Focal seizures originate from a localized area of the brain and initially exhibit discharges confined to that region (e.g., temporal lobe, frontal lobe). These may then spread to involve other areas (secondary generalization). On EEG, this appears as localized spikes, sharp waves, or spike-and-wave complexes initially confined to a specific brain region. Generalized seizures, in contrast, involve both hemispheres from the onset. They display widespread epileptiform discharges simultaneously across multiple brain regions, often involving both hemispheres symmetrically. Examples include generalized tonic-clonic seizures, which show generalized spike-and-wave discharges on EEG. However, some seizures may have subtle or evolving features, making differentiation challenging, sometimes requiring clinical correlation to be certain.

Proper electrode impedance is crucial for obtaining high-quality EEG recordings. Impedance refers to the resistance to the flow of electrical current between the electrode and the scalp. High impedance leads to noisy signals, artifacts, and inaccurate readings, while low impedance ensures a strong and clear signal. Think of it like a water pipe – high impedance is like a clogged pipe with reduced water flow (signal), while low impedance is a clear pipe allowing for smooth, strong water flow.

Ideally, impedance should be below 5 kΩ (kiloohms) for each electrode. Values above 10 kΩ often indicate poor contact and may require adjustments such as repositioning the electrode, using more conductive gel, or even replacing the electrode. Excessive impedance introduces noise, making it difficult to distinguish true brain activity from artifacts like muscle movement or electrical interference from external sources. In clinical practice, failing to achieve appropriate impedance can lead to misinterpretations of the EEG, impacting diagnosis and treatment planning.

The 10-20 International System is a standardized method for placing electrodes on the scalp during EEG recordings. This system ensures consistency and comparability across different studies and laboratories. It’s essential for reliable research and clinical applications because it provides a consistent reference point for identifying brain regions based on electrode locations. Imagine trying to describe a location on a map without a standardized coordinate system – it would be confusing and unreliable! The 10-20 system utilizes landmarks on the skull – the nasion (bridge of the nose), inion (prominent bone at the back of the head), and preauricular points (points in front of the ears) – to calculate electrode positions. The numbers represent approximate percentages of the distance between these landmarks. For example, Fp1 (frontal pole, left) is approximately 10% of the distance between the nasion and the inion. This system allows researchers and clinicians to easily compare EEG findings and pinpoint the source of activity or abnormalities within the brain.

Several types of EEG electrodes are available, each with specific advantages and disadvantages.

• Silver/Silver Chloride (Ag/AgCl) electrodes: These are the most common type, known for their relatively low impedance, biocompatibility, and ease of use. They’re used in most routine EEG recordings because of their reliability and cost-effectiveness.
• Gold electrodes: Gold electrodes offer excellent conductivity and biocompatibility. They may be preferred in long-term recordings or situations where very high signal quality is needed, but they are more expensive.
• Needle electrodes: These are used for more invasive recordings, such as during surgery or in cases where scalp electrodes are inadequate, for instance, in patients with excessive hair.
• Active electrodes: These electrodes contain built-in amplifiers that reduce noise and improve signal quality by amplifying the signal at the point of acquisition, reducing the effects of cable noise.

The choice of electrode depends on factors like the duration of the recording, the specific clinical question being addressed, and the patient’s condition.

EEG waves are characterized by their frequency (number of cycles per second, measured in Hertz or Hz) and amplitude (wave height, measured in microvolts or µV). These two parameters provide information about the brain’s electrical activity and its underlying physiological state.

• Frequency: Different frequency bands are associated with different states of consciousness and brain functions. For example, delta waves (0.5-4 Hz) are common during deep sleep, theta waves (4-8 Hz) are often observed during drowsiness and meditation, alpha waves (8-12 Hz) are associated with relaxed wakefulness, beta waves (12-30 Hz) are prominent during active thinking and alertness, and gamma waves (30 Hz and above) are linked to higher cognitive functions.
• Amplitude: The amplitude reflects the intensity of the electrical activity. Higher amplitudes generally indicate stronger activity. For instance, increased amplitude in specific frequency bands may indicate abnormalities, such as epileptic spikes.

Interpreting the frequency and amplitude requires expertise and consideration of the clinical context. A change in the typical pattern, or the appearance of unusual waveforms, may suggest a neurological condition that needs further investigation.

Spontaneous EEG activity refers to the ongoing, background electrical activity of the brain when there is no external stimulation. It represents the brain’s intrinsic activity and reflects its current state – sleep, wakefulness, cognitive processes, etc. Evoked EEG activity, on the other hand, is the brain’s response to a specific stimulus, such as a visual flash or auditory tone. It’s a time-locked response to the stimulus, allowing researchers to investigate the brain’s processing of sensory information. A common example of evoked EEG activity is the visual evoked potential (VEP) obtained by flashing a light and recording the brain’s response.

Analyzing spontaneous EEG reveals baseline brain activity and helps diagnose conditions like epilepsy and sleep disorders. Evoked EEG studies are used to assess sensory pathways and detect neurological impairments.

Digital filtering is a crucial step in EEG analysis. It involves using mathematical algorithms to remove unwanted frequencies (noise) from the EEG signal while preserving the frequencies of interest (brain activity). This enhances the signal-to-noise ratio, making it easier to identify meaningful patterns.

Different types of filters are used, such as:

• High-pass filters: Remove low-frequency noise, such as drift or slow eye movements.
• Low-pass filters: Remove high-frequency noise, such as muscle artifacts.
• Band-pass filters: Allow only a specific range of frequencies to pass through, such as the alpha band (8-12 Hz).
• Notch filters: Remove specific frequencies, such as the 60 Hz power line interference.

Appropriate filter selection is essential for accurate EEG interpretation. Over-filtering can remove important information, while under-filtering leaves noise that obscures the signal. The choice of filter depends on the specific application and the nature of the noise present in the recording.

While EEG is a valuable diagnostic tool, it has limitations.

• Poor spatial resolution: EEG measures electrical activity from the scalp, not directly from the brain’s neurons. This makes it difficult to pinpoint the precise location of abnormal activity. Think of it like trying to determine the location of a short circuit in a house’s wiring by only measuring the voltage at the wall outlets – you might know there’s a problem but not exactly where it is.
• Susceptibility to artifacts: EEG signals can be contaminated by various artifacts, such as muscle movements, eye blinks, and electrical interference, making interpretation challenging. Careful artifact rejection techniques are crucial for accurate analysis.
• Limited sensitivity to some pathologies: EEG may not detect subtle changes or early stages of certain neurological conditions.
• Operator dependence: Proper electrode placement and data analysis require expertise and experience.

Despite these limitations, EEG is a relatively inexpensive, non-invasive, and widely available technique that provides valuable insights into brain function, particularly in the diagnosis of epilepsy and sleep disorders. It often serves as a valuable first step in neurological investigations, often followed by more focused techniques like MEG or fMRI.