EEG Neuroanatomy and Physiology 5 — Questions and Answers
Question 1: Inhibitory postsynaptic potentials (IPSPs) on apical dendrites of cortical pyramidal neurons generate which polarity at the overlying scalp electrode?
- Negative deflection
- Positive deflection (Correct answer)
- No detectable signal
- Biphasic spike
Correct answer: Positive deflection
IPSPs at apical dendrites create a current sink deeper in the cortex and a source near the surface, resulting in a positive polarity at the scalp electrode above.
Question 2: Which ascending arousal pathway originating in the locus coeruleus modulates cortical excitability and EEG background through norepinephrine release?
- Mesolimbic dopamine pathway
- Dorsal noradrenergic bundle (Correct answer)
- Raphe-cortical serotonin pathway
- Nigrostriatal pathway
Correct answer: Dorsal noradrenergic bundle
The dorsal noradrenergic bundle from the locus coeruleus projects widely to cortex, modulating neuronal excitability and promoting EEG desynchronization during alertness.
Question 3: The dentate gyrus, CA fields of the hippocampus, and entorhinal cortex form the primary circuit for memory encoding. EEG theta rhythms (4-8 Hz) recorded over temporal regions are thought to reflect activity in which of these structures?
- Entorhinal cortex only
- Dentate gyrus only
- Hippocampus (Correct answer)
- CA3 exclusively
Correct answer: Hippocampus
Hippocampal theta rhythm (4-8 Hz) is strongly associated with memory encoding and spatial navigation and can be detected with depth or surface EEG over temporal regions.
Question 4: Cortical spreading depression (CSD), associated with migraine aura, is characterized by what EEG finding?
- Diffuse beta activation
- Transient high-amplitude slow wave followed by sustained suppression (Correct answer)
- Persistent 3 Hz spike-and-wave
- Focal mu rhythm
Correct answer: Transient high-amplitude slow wave followed by sustained suppression
CSD produces a brief increase in slow activity followed by prolonged EEG suppression as a wave of depolarization-then-silence propagates across the cortex.
Question 5: The insula, buried within the lateral sulcus, is involved in autonomic regulation. Seizures arising from insular cortex most likely affect which EEG electrode chain?
- Fp1-F3-C3-P3
- F7-T7-P7-O1 (Correct answer)
- Fz-Cz-Pz
- F8-T8-P8-O2
Correct answer: F7-T7-P7-O1
The insula is accessed via the lateral sulcus and is closest to temporal chain electrodes (F7/T7/P7), making this chain most likely to reflect insular seizure activity.
Question 6: Cajal-Retzius cells in cortical layer I release reelin, which guides neuronal migration. Dysfunction in this process can result in lissencephaly, which characteristically produces what EEG pattern?
- Normal background with occasional spikes
- High-amplitude fast activity (>14 Hz) diffusely
- Very high voltage slow activity with multifocal spikes (Correct answer)
- Persistent alpha coma pattern
Correct answer: Very high voltage slow activity with multifocal spikes
Lissencephaly produces disorganized cortical architecture with very high-voltage slow waves and multifocal epileptiform discharges due to abnormal cortical lamination.
Question 7: The perisylvian language network includes Broca's area (IFG) and Wernicke's area connected by the arcuate fasciculus. EEG-based language mapping uses which technique to identify these regions before epilepsy surgery?
- Routine scalp EEG with hyperventilation
- Electrocorticography (ECoG) with cortical stimulation mapping (Correct answer)
- Photic driving response analysis
- Z-score normalization of alpha power
Correct answer: Electrocorticography (ECoG) with cortical stimulation mapping
Electrocorticography with direct cortical stimulation (extraoperative or intraoperative) is the gold-standard EEG-based method to map language-eloquent cortex before resection.
EEG Neuroanatomy and Physiology 5
Inhibitory postsynaptic potentials (IPSPs) on apical dendrites of cortical pyramidal neurons generate which polarity at the overlying scalp electrode?