Question

The amplitude of the Electroencephalograph (EEG) signal is :

• A. (0.05 - 5) millivolts (mv)
• B. (2 - 200) microvolts (\(\mu\)v)
• C. (0.1 - 5) millivolts (mv)
• D. (0 - 1) volts (v)

Hint:

Scale associations for biomedical signals are common exam topics: Brain (EEG) = Microvolts ($\mu$V, extremely weak, needs high amplification). Heart (ECG) = Millivolts (mV, moderately weak, roughly 1-2 mV). Muscle (EMG) = Millivolts (mV). Always remember the brain's signals are the hardest to detect through the skull!

Answer 1

The Correct Option is B

Step 1: Concept:
The question tests knowledge of clinical biomedical instrumentation, specifically asking for the typical electrical voltage range of signals produced by the human brain as measured non-invasively on the scalp by an Electroencephalograph (EEG).

Step 2: Step-by-step Explanation:

• An Electroencephalograph (EEG) is designed to measure the synchronized summation of electrical post-synaptic activity originating from millions of pyramidal neurons located in the cerebral cortex.

• Because these delicate electrical signals originate deep within the brain, they must physically travel through several highly resistive biological layers—including the meninges, the thick cerebrospinal fluid (CSF), the dense bone of the skull, and the skin of the scalp—before reaching the surface recording electrodes.

• Due to this massive resistance, the signals are heavily attenuated (weakened) by the time they are recorded.

• Consequently, surface EEG signals are extremely small in amplitude. Typical normal adult human EEG signals range from approximately 10 to 100 microvolts ($\mu$V). Depending on the state of arousal, age, or the presence of intense pathology (like epileptic seizures), they can peak up to about 200 $\mu$V.

• Let's evaluate the options to confirm:
- Volts (v): This is far too massive. Measuring whole volts on the scalp would imply lethal electrocution levels.
- Millivolts (mV): This range (e.g., 1 to 5 mV) represents much stronger bio-signals, specifically the heart's electrocardiogram (ECG).
- Microvolts ($\mu$V): This is the correct, highly sensitive measurement scale required for brain waves.

• Therefore, Option (B) provides the precise and accurate clinical range for these signals.

Step 3: Final Answer:
The typical EEG amplitude ranges from (2 - 200) microvolts.