EEG Basics - Neural Generators

These flashcards cover the neurophysiological generators of EEG signals, including synaptic potentials, ion channel conductances, cortical structure, and thalamocortical rhythms.

EEG (Electroencephalography)

A continuous graphic display over time of the spatial distribution of changing voltage fields at the scalp surface.

Na+ Action potential

Rapid ion movements across the neuronal membrane resulting in a large amplitude change in membrane potential ($+20\,mV$) that is brief in duration ($1\text{--}3\,ms$).

Excitatory postsynaptic potential (EPSP)

Neurotransmitter mediated synaptic transmission involving $Na^+$ and $Ca^{++}$ that depolarizes the cell for $10\text{--}30\,ms$.

Inhibitory postsynaptic potential (IPSP)

Neurotransmitter mediated synaptic transmission involving $K^+$ and $Cl^-$ that hyperpolarizes the cell for $70\text{--}200\,ms$.

Ca2+ spikes

Inward currents on dendrites with potential changes of $20\text{--}50\,mV$ that are important in epileptic discharges.

DC shifts

Ultraslow voltage changes resulting from neuron-glia interactions through glial gap junctions.

Ripples

Ultrafast cortical rhythms involving interneurons and pyramidal neurons.

Pyramidal neurons

Large neurons located in layers III, IV, and V of the cortex whose synaptic processes are the primary contributors to scalp EEG potentials.

Sink

The site of active inward current flow into neurons (such as $Na^+$ at the site of an EPSP), resulting in a negative voltage deflection in the extracellular space.

Source

The site of outward current flow (such as passive current flow matching an inward Sink), resulting in a positive voltage deflection in the extracellular space.

Volume Conduction

The transmission of current through tissues where voltage drops off exponentially with distance and is attenuated in voltage, but not delayed in time.

Nucleus reticularis thalami (nRT)

A thalamic nucleus that provides GABAergic feedback IPSPs to thalamocortical (Th-Cx) neurons, essential for synchronizing rhythms.

Ih (Hyperpolarisation-activated cationic current)

A depolarizing pacemaker potential occurring between $-70$ and $-85\,mV$ that activates the low threshold spike (LTS).

LTS (Low threshold Ca++ spike)

A T-type calcium spike characterized by a cycle of deinactivation, activation, and inactivation, acting as an amplifier during oscillatory modes.

Oscillatory mode

A state of thalamocortical rhythms during drowsiness and sleep where neurons are hyperpolarized and the LTS is activated.

Relay mode

A state of thalamocortical rhythms for transmitting sensory information to the cortex where the membrane potential is $-50$ to $-60\,mV$ and the LTS is inactivated.