#EEG

Electrophysiological methods

Which wave replaces alpha during excitement?

Alpha rhythm at 8-13 Hz indicates synchronous idling of visual cortex during eyes-closed relaxed wakefulness maintained by thalamic pacemaker activity. When attention increases, eyes open, or emotional excitement occurs, thalamocortical circuits desynchronize due to enhanced reticular activation, cholinergic drive and increased synaptic bombardment, suppressing alpha amplitude. Faster low-amplitude beta activity spanning 13-30 Hz emerges reflecting active information processing and increased cortical excitability. Theta and delta dominate drowsiness and sleep, gamma appears during binding, but classical electrophysiological shift from relaxed alpha to alert excitement is replacement by beta.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Electrophysiological methods

What is the correct placement system for EEG electrodes?

Reproducible comparison of EEG recordings across patients and laboratories requires standardized scalp coordinates independent of head size. Internationally accepted placement positions electrodes at intervals of 10 and 20 percent of total nasion-inion and interaural distances, creating systematic frontal, central, parietal, temporal and occipital sites labeled F, C, P, T, O with odd numbers left hemisphere and even right. This 10-20 montage documented in some textbooks and software as 20-Oct shorthand ensures consistent coverage and reliable localization. Notations like 10-Feb or 20-30 lack anatomical validity entirely.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Electrophysiological methods

Which brain scan is preferred for identifying epileptic seizures?

Epileptic seizures result from abrupt, excessive, synchronous discharges of interconnected cortical neurons generating high-amplitude spike and sharp-wave complexes. Diagnostic preference focuses on capturing these transient electrical paroxysms with millisecond accuracy. Electroencephalography amplifies ongoing scalp potentials continuously, identifying interictal epileptiform discharges, ictal onset patterns and focal slowing without radiation or contrast. Computed tomography primarily excludes hemorrhage, MRI identifies hippocampal sclerosis or cortical dysplasia as structural cause, PET shows interictal hypometabolism, but only EEG directly displays real-time seizure electricity essential for syndrome classification.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Electrophysiological methods

Which wave is associated with deep sleep in EEG?

Electroencephalographic frequencies correlate closely with behavioral states across sleep-wake cycle. Deep non-rapid eye movement sleep stage N3, also termed slow-wave sleep, exhibits synchronized high-amplitude slow oscillations reflecting alternating hyperpolarized down states and depolarized up states in extensive thalamocortical networks with reduced consciousness. Beta rhythm around 13-30 Hz indicates alert active cognition, alpha at 8-13 Hz marks relaxed eyes-closed wakefulness, theta at 4-8 Hz appears in drowsiness. Predominant activity during restorative deep sleep below 4 Hz is designated delta rhythm essential for memory consolidation.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Electrophysiological methods

Which of the following techniques offers the highest temporal resolution?

Temporal resolution defines minimal interval needed to separate successive events. Neuronal communication occurs in milliseconds, requiring recording systems with kilohertz sampling. Electroencephalography directly measures scalp voltage fluctuations at 250-2000 Hz, instantly capturing evoked potentials, epileptic spikes and oscillatory changes. In contrast, computed tomography requires seconds for gantry rotation and reconstruction, magnetic resonance imaging needs seconds for pulse sequences and hemodynamic lag, positron emission tomography depends on tracer accumulation over minutes. Therefore EEG offers superior temporal precision among structural and metabolic imaging methods.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Electrophysiological methods

In a typical EEG, alpha waves represent:

Alpha rhythm consists of regular 8-13 Hz oscillations most prominent over occipito-parietal cortex when a person is awake but resting quietly with eyes closed, minimizing visual input and mental effort. The rhythm arises from synchronized thalamocortical feedback loops in an idling yet alert cortex, suppressed by eye opening, mental arithmetic, attention or anxiety. Excited states replace alpha with low-amplitude fast beta activity, deep sleep produces high-amplitude slow delta, drowsiness shows theta, and focal damage causes pathological slowing. Thus alpha signifies relaxed wakefulness, not sleep or excitation.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details

Electrophysiological methods

What is detected using EEG?

Electroencephalography records summed extracellular fields generated by thousands of aligned cortical pyramidal neurons. Action potentials are too brief, approximately one millisecond, and occur asynchronously, so their currents cancel at distant scalp electrodes. Sustained excitatory and inhibitory postsynaptic potentials lasting tens of milliseconds can summate temporally and spatially across cortical columns, creating dipoles detectable noninvasively. Thus raw EEG reflects integrated synaptic drive, not individual spikes, simple ion flux or radioisotope emission. This principle explains sensitivity to arousal, cognition and epileptic hypersynchrony linked to postsynaptic currents.

Ref: NCERT Biology Class XII Principles on Klenow fill-in labeling, Lehninger Chapter 9 DNA cloning techniques, and Molecular Cloning by Sambrook Chapter 10 documenting end-labeling of cohesive termini.

View Details