3. Brain Oscillations

Oscillation refers to the repetitive variation or fluctuation of a system or quantity around a central value or between two or more states, typically in a regular time interval.

German psychiatrist best known for inventing electroencephalography (EEG) and discovering human brain waves

He fall from the horse and his sister had a wirde feeling and insisted father too look after him.

He believed that electromagnetic forces generated by the human brain could be the carrier waves of telpathy

alpha -> first detected rhythm

also called Berger wave

An EEG (electroencephalogram) is a valuable tool in neurology used to assess and diagnose a variety of conditions by measuring brain activity through electrodes placed on the scalp.

• a summed potential difference of post synaptic potentials from 10^7-10^10 cortical neurons

• Activity from about 6cm2 cortical area per electrode

• mostly from synchronized cortical activity

Microscopic scale -> 1 msec -> spikes

Mesoscopic scale -> 10 msec -> high frequency oscillation

Macroscopic scale -> 100 msec -> slow oscillation

Brief electrical impulse in a neuron caused by rapid ion exchange across the membrane, allowing the nerve to transmit signals

1. Resting Potential (–70 mV) – Inside of the neuron is negatively charged. – Maintained by the sodium-potassium pump and leaky K⁺ channels.

2. Depolarization (–55 mV to +30 mV) – A stimulus reaches threshold (≈ –55 mV). – Voltage-gated Na⁺ channels open, Na⁺ rushes in, making the inside more positive. – Membrane potential rapidly rises to around +30 mV.

3. Repolarization (+30 mV to –70 mV) – Na⁺ channels close, K⁺ channels open. – K⁺ rushes out, restoring the negative charge inside.

4. Hyperpolarization (below –70 mV) – K⁺ channels stay open slightly too long. – Membrane becomes more negative than resting potential.

5. Return to Resting State (–70 mV) – K⁺ channels close. – Na⁺/K⁺ pump restores ion balance (3 Na⁺ out, 2 K⁺ in).

• excitatory synapse

• positiv energy from out to inside

• extracellular energy sinks on the synapse and rise in intracellular recordings

• extracellular recordings at soma rises

• Inhibitory Synapse

• negative energy from inside to outside

• extracellular energy rises on the synapse and sinks in intracellular recordings

• extracellular recordings at soma sinks

Because in unsynchronized activity, the electrical fields of individual neurons have different timings and directions, causing their voltages to cancel each other out. Only large-scale, synchronized postsynaptic potentials generate a summated field strong enough to be detected by EEG.

The gel reduces the electrical resistance between the scalp and electrodes, improves signal quality by enhancing conductivity, and minimizes noise, enabling accurate detection of the brain’s weak electrical signals.

A: Amplitude is the height of the wave and reflects the strength or intensity of the signal; higher amplitude means stronger or more synchronized neural activity.

A: Phase describes the position within a wave cycle (e.g., rising, peak, falling) and determines how oscillations align in time across brain regions.

A: Frequency is the number of wave cycles per second (measured in Hertz) and shows how fast neural oscillations occur; different frequency bands are linked to different cognitive states.

Filter with less heart frequency

Aging causes brain shrinkage and loss of white matter pathways, leading to fewer active neurons and slower signal transmission; this results in lower EEG amplitude, slower frequencies, and reduced synchrony of brain waves

During wakefulness, EEG shows alpha (8–12 Hz) waves when relaxed and beta (13–30 Hz) waves when alert; during sleep, slow delta (0.5–4 Hz) and theta (4–8 Hz) waves dominate, especially in deep (NREM) sleep, along with sleep spindles and K-complexes in lighter stages.

A: Gray matter consists of neuron cell bodies, dendrites, and synapses; it processes and integrates information.

A: White matter is made of myelinated axons; it transmits electrical signals between different brain regions.

high frequency oscillation around 100-150 Hz

(during NREM sleep)

hippocampus

• Sleep spindles by 11-16 Hz

• short bursts of rhythmic brain activity

• originate from thalamocortical circuits and are involved in memory consolidation and sleep stability

1. Pacemaker leads

2. Arise trough collective behavior

• Only one side of the brain can sleep

• The two thalsmus in the brain of a dolphin are independent (control signal/information that goes in)

• lack automatic breating

1. gamma

2. beta

3. alpha

4. theta

5. delta

32-100 Hz

learning, problem solving

• 13 - 32 Hz

• excitement

• motor function

• also detected by Berger

• 8-13 Hz

• physically and mentally relaxed

• cognitive and memory process

• eyes closed

• sleep (spindles)

• 4-8 Hz

• creativity

• Jung und Kornmüller

• hippocampus

• sleepiness and light sleep

• 0.5-4 Hz

• deep sleep

• detected ny w. grey walter

• typical sleep wave

• anasthesia wave

It is when an external signal compels neurons or brain regions to align their oscillation phases and frequencies, overriding their natural rhythms.

e.g: sleep, anasthesia, epilectic seizure

• important neurotransmitter

• leads to depolarisation/activation

• create EPSPs

• excitation

• important neurotransmitter

• Sinks activity

• creates IPSPs

Decomposition of the EEG into sine and cosine waves in the frequency domain

• Propofol causes increased frontal alpha and delta waves, progressing to burst suppression at high doses, reflecting deep unconsciousness and reduced brain connectivity.

• Propofol, a commonly used intravenous anesthetic

• GABAergic Inhibition

• Sevoflurane causes frontal alpha and slow-delta activity, progressing to dominant slow waves and possible burst suppression at deep levels, similar to but slower-acting than propofol.

• commonly used general anesthetic — especially in children and during inhaled anesthesia

• GABAergic inhibition + others

• Ketamine increases gamma and theta activity, suppresses alpha waves, and produces a desynchronized EEG — reflecting a dissociated but active brain state, unlike the slow waves or burst suppression seen with other anesthetics.

• NMDA inhibition

• Dexmedetomidine produces strong slow-delta waves and spindle-like activity, mimicking natural non-REM sleep, without burst suppression even at high doses.

• a2 Adrenergic-mediated Inhibition

1. db Wavelets

2. Morlet W

3. Biorthogonal W

4. Spline W

5. Mexican Hat

6. Haat

7. Gaussian

8. Coiflect

1. Synchrony means different brain regions show coordinated, simultaneous activity (similar EEG waveforms at the same time).

2. A frontal group coherogram measures this synchrony (coherence) between frontal EEG signals across frequencies.

3. From wake to sedation to anesthesia, synchrony (coherence) increases, especially in slow frequencies (delta, theta, alpha).

4. Wakefulness shows low/moderate coherence (asynchronous activity), sedation increases alpha/theta coherence, and anesthesia shows very high delta/alpha coherence indicating strong synchronization.

• converts a real EEG signal into a complex form, allowing extraction of instantaneous amplitude and phase.

• The phase information is crucial for measuring phase synchrony (coherence) between brain regions by examining how stable the phase difference is over time.

Information theory quantifies how neurons encode, transmit, and process information by measuring uncertainty (entropy), the shared information between stimuli and responses (mutual information), and the efficiency of neural communication—helping to understand neural coding, decoding, and brain function.

• Claude E Shannon

PSD shows how the power (energy) of a signal is distributed across different frequencies, helping identify dominant frequency components like brain waves in EEG signals.

• coherence

• coupling of two power spectra

• normalized cross power spectrum

  criteria:

• Linearity

• stationarity