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Browse courses and booksModule 3
Chapter 3 · 3 h · 8 quiz items · pass at 80%
This module carries the anatomy core of IQCB Domain II (Neuroscience), 15% of the exam. The IQCB explicitly tests behavioral correlates of brain regions and networks, and this module names them at exam resolution. The cytoarchitecture and interneuron content supports later reading of where rhythms come from. The quiz confirms the learner can connect a region or Brodmann area to its function.
The previous chapter built the signal from charge held across a membrane to a voltage at the scalp. This chapter builds the tissue that generates it. A QEEG practitioner reasons constantly from a site to a function: a deviation at Fz is a question about cognitive control, a slowed peak at O1 and O2 a question about the thalamocortical clock, an asymmetry at F3 and F4 a question about affective style. That reasoning is only as good as your anatomy, and the IQCB tests anatomy harder than the BCIA track does, including the cortical microanatomy, the subcortical structures at both macro and micro scale, the ascending sensory pathways, and the behavioral correlates of regions and networks that Domain II names explicitly.
This is a working set, not an anatomy course. The goal is enough structure to place every generator the rest of the book refers to, and enough function to read a site as a hypothesis. Where the depth runs past what you need at the map, the fuller treatment is in Neurophysiology for Neurofeedback. What is here is what the exam asks and what the database comparison requires.
Gross anatomy is the neighborhoods. Cytoarchitecture is the masonry, and the masonry is why the EEG exists at all (Chapter 2). The neocortex is not a uniform slab. Through its depth, from the pial surface down to the white matter, it is organized into roughly six horizontal layers (laminae), conventionally numbered with Roman numerals from the surface. They differ in which cells they contain and what those cells connect to, and the division of labor among them is what gives the cortex its open-field geometry and shapes what the scalp hears.
The functional summary a QEEG practitioner should carry is a flow: input arrives mainly in layer IV, output to other brain regions leaves from layers V and VI, and the superficial layers (I to III) carry cortico-cortical coordination and sit closest to the scalp. Because the surface signal falls off steeply with distance (Chapter 2's forward model), the EEG is weighted toward this superficial, cortico-cortical activity, the cortex coordinating with cortex, more than toward the deep output layers. The regional differences in this layering are exactly what let Brodmann divide the cortex into numbered areas, taken up later in this chapter.
Two broad classes of neuron build and shape the cortical signal.
Pyramidal cells are the principal excitatory (glutamatergic) projection neurons and the source of the EEG. Their long apical dendrite runs perpendicular to the surface, their basal dendrites spread near the soma, and their axon descends toward the white matter. The apical-versus-basal geometry matters for the dipole: a synapse on the apical tuft and a synapse on the basal dendrites produce currents separated along the cell's length, and their summed orientation is what the open-field geometry of Chapter 2 depends on. Pyramidal cells in different layers project to different targets: layer III pyramids drive cortico-cortical and callosal connections, layer V pyramids project subcortically, and layer VI pyramids feed back to the thalamus.
Stellate (granule) cells are small, locally projecting neurons concentrated in layer IV. The spiny excitatory subtype is the main recipient of specific thalamic input and the first cortical stage of sensory processing. Their compact, star-shaped geometry is unaligned, so they contribute little directly to the surface field. Their role is to receive and distribute thalamic input to the pyramidal cells that do.
Inhibitory interneurons are the GABAergic cells that pace and gate the pyramidal population. They are a varied family, and three subtypes carry most of the rhythm-shaping work the QEEG practitioner needs to know. Parvalbumin-positive (PV) cells are fast-spiking. Their synapses land on the pyramidal soma and axon initial segment, the sites with the most control over whether a spike fires, and their rapid feedback inhibition (the recurrent-inhibition motif of Chapter 2) paces gamma (Cardin et al., 2009). Somatostatin-positive (SOM) cells, including the Martinotti type, target the distal apical dendrites, gating what long-range input reaches the cell and shaping slower, theta-range timing. Vasoactive-intestinal-peptide (VIP) cells inhibit the SOM cells, a double negative that disinhibits the dendrite and tilts the column toward receptivity when attention or top-down signals arrive. The lesson is the one Chapter 2 stated as a principle: EEG rhythms are not passive summations of pyramidal firing but are actively sculpted by inhibitory timing, and the band you read reflects which kind of timing is dominating.
The cells are organized vertically as well as horizontally. The cortex is built from functional columns: vertical cylinders of cells, spanning the layers, that share inputs and act as local processing units, with the pyramidal cells in each column oriented the same way, perpendicular to the surface. Columns sit side by side across the cortical sheet like the pile of a carpet, all pointing outward, so when a patch of them is active together their dipoles point the same direction and add. This columnar alignment is what makes the open-field summation of Chapter 2 possible. Without it, the pyramidal dendrites would point every which way and cancel.
Two classical examples make the column concrete. In primary visual cortex, ocular dominance columns alternate across the surface, each responding preferentially to one eye, an orderly mapping of input that experiments revealed by following which columns lit up to which eye. In the rodent somatosensory cortex, barrel columns each correspond to a single facial whisker, a one-to-one anatomical map of the sensory periphery onto cortical units. The general point for a QEEG practitioner is that the EEG is a columnar, population signal by construction: it is weighted toward activity that spans many adjacent columns at once, while isolated single-column events are too small and too local to register, which is part of why a scalp finding is always a statement about a patch of cortex rather than a point.
Under the cortex sit structures that shape and pace cortical activity even though their closed-field geometry keeps them nearly silent at the scalp (Chapter 2). You reason about them by their consequences on the cortical signal, not by reading them directly, and the IQCB expects both their gross identity and a working sense of their internal organization.
The thalamus is not one relay but a set of nuclei with a division of labor that matters for QEEG. Specific (relay) nuclei each relay one channel of information: the lateral geniculate nucleus for vision, the medial geniculate for hearing, the ventral posterior nucleus for body sense, the ventral anterior and ventral lateral nuclei for motor signals from the basal ganglia and cerebellum. Their cells project in a focused, point-to-point way to layer IV of one primary cortex. Nonspecific (matrix) nuclei, including the intralaminar and midline groups, project diffusely to the superficial layers across wide cortical territory and drive general activation. These are the nuclei whose repetitive stimulation produces the recruiting response of Chapter 2. Wrapping the whole thalamus is the thalamic reticular nucleus, a thin shell of GABAergic cells that does not project to cortex at all but inhibits the relay cells, acting as the pacemaker that gates the rhythms. Relay cells themselves have two firing modes set by ion channels and arousal: a tonic transmission mode when depolarized and a burst mode when hyperpolarized (the next section develops this), which is the cellular basis of the alpha-to-spindle-to-slow-wave ladder.
The basal ganglia are deep gray-matter nuclei that select and gate motor and habit programs, releasing intended actions and suppressing competing ones. The components the exam names are the striatum (caudate and putamen, the input stage), the globus pallidus (internal and external segments), the subthalamic nucleus (STN), and the substantia nigra, divided into the pars compacta (SNc, the dopamine source that biases the loop) and the pars reticulata (SNr, an output stage). The loop runs from cortex into the striatum, through the pallidum and nigra to the thalamus, and back to cortex, carrying opposing release-and-suppress influences whose balance lets a single smooth action emerge. Their dysfunction is instructive: dopamine depletion in the SNc (Parkinson's) lets the suppressing side dominate and movement becomes hard to start, while a tilt the other way lets unwanted movements through.
The amygdala is a cluster of nuclei in the medial temporal lobe that assigns emotional salience and threat value. Its basolateral nuclei receive sensory and cortical input and its central nucleus drives the autonomic and arousal responses that follow, the link to the fast-desynchronized cortex and the low, rigid heart-rate variability a stressed client presents. The amygdala is invisible at the scalp, but its influence shows up in arousal and in the autonomic measures a practitioner may pair with the map.
The hippocampus sits in the medial temporal lobe, curved like a seahorse, organized into sectors (CA1 through CA4 and the dentate gyrus) that form a trisynaptic circuit: the entorhinal cortex funnels processed cortical information through the perforant path to the dentate granule cells, which pass it to CA3, which recombines it and sends it to CA1, which returns it through the entorhinal cortex into the broader limbic (Papez) loop. During memory encoding and navigation the hippocampus generates its own theta rhythm (four to eight hertz) that organizes the timing of neural sequences (Buzsáki & Moser, 2013). The scalp cannot read hippocampal theta directly. The structure is deep and its geometry largely cancels. When you see theta over temporal or frontal sites in an alert, engaged person, it reflects cortical theta generators, not the hippocampus per se, a distinction that matters because cortical theta under load and drowsy theta from falling arousal look superficially alike and mean different things.
The brainstem is stacked in three tiers, midbrain over pons over medulla, and holds the arousal nuclei and the vital controls. The micro-detail the exam rewards is the set of chemically defined nuclei that set cortical tone: the locus coeruleus in the pons (norepinephrine), the raphe nuclei along the midline (serotonin), the ventral tegmental area and substantia nigra in the midbrain (dopamine), and the pedunculopontine and laterodorsal tegmental nuclei plus basal-forebrain groups (acetylcholine). A few thousand cells in each of these compact sources broadcast across wide cortical territory, which is why a small change at one of them moves the whole recording. The cerebellum, tucked behind the brainstem, coordinates and times movement but is nearly EEG-invisible because its tightly folded geometry cancels at a distance and it sits deep in the posterior fossa.
Close the client's eyes and the back of the head fills with a rhythm near ten cycles a second. Open them and it drops away. Posterior alpha is the most reliable feature in human EEG, and the cortex on its own does not keep such steady time. The metronome is the thalamus, working in a loop with the cortex it drives, and this engine is the single most important generator a QEEG practitioner reasons about.
The loop is the engine. Thalamic relay cells project up to the cortex, the cortex projects back down (from its layer VI pyramids), and the inhibitory reticular nucleus regulates the traffic. A circuit with excitation one way, inhibition another, and feedback between them can oscillate, and the relay cells add a second ingredient: membrane properties that make them prone to rhythmic bursting on their own. Two channels create the switch between the relay cell's two modes. The T-type calcium channel is low-threshold, priming when the cell is hyperpolarized. When inhibition releases the primed cell, calcium rushes in and launches a burst. The HCN (Ih) channel carries a slow inward current after hyperpolarization that returns the cell toward threshold and sets the interval to the next burst, which is why it is called the pacemaker channel. The balance between how deeply the cell is hyperpolarized and how quickly Ih brings it back sets the oscillation frequency, and arousal-system neurotransmitters that act on Ih change the clock speed (McCormick & Pape, 1990).
Arousal sets which mode dominates. Alert and engaged, the relay cells sit in transmission mode, the loop is loosely coupled, and the cortex runs fast and desynchronized. As arousal falls, the cells slip toward burst mode, the loop tightens, and the rhythms grow slower and larger, alpha giving way to spindles and then to the slow waves of deep sleep. Posterior alpha is the clearest product: eyes-closed, posterior, and it blocks (attenuates) the moment the eyes open and the visual cortex engages, because the idling synchronized population desynchronizes. The frequency at which an individual's alpha peaks, the individual alpha peak frequency, is a stable trait that reflects the clock's speed, generally eight to thirteen hertz, slowing with age (Klimesch, 1999; Scally et al., 2018). Sleep spindles are the same engine in another state. The QEEG payoff is a distinction you will apply at the map: too much alpha power and a slow alpha peak are different findings, one a question about how much a region idles, the other about how fast the clock runs, and collapsing them into "alpha problem" loses the more useful reading.
Every sense except smell reaches the cortex the same way: up a dedicated pathway, through a relay in the thalamus, and on to a primary sensory cortex built for that modality. The thalamic relay is an active gate, not a passive junction, because the reticular nucleus and the cortex's own descending feedback decide moment to moment how much of each pathway's traffic passes. Because each pathway ends in a known place, a finding at a site over that place carries a specific functional meaning, and the rhythm idling over that cortex reports whether the system beneath is at rest or engaged.
The exception that proves the rule is olfaction, which passes from the olfactory bulb directly to olfactory cortex without a thalamic relay, reaching cortex before any gate. It sits deep and medial, far from the scalp, and contributes almost nothing to the surface EEG, which confirms how central the thalamic relay is for everything the electrode can hear.
Map the four lobes onto function, because this is what lets a site stand for a function. The frontal lobe holds executive control: planning, working memory, impulse regulation, and the approach-versus-withdrawal balance that distinguishes the left frontal cortex (biased toward approach and positive engagement) from the right (withdrawal and avoidance), the physiological basis of frontal alpha asymmetry. The parietal lobe handles spatial integration and attentional allocation, with a posterior-midline default-mode hub. The temporal lobe handles hearing, language on the left, prosody and social tone on the right, and, through medial structures the scalp cannot reach, memory. The occipital lobe handles vision and is where alpha is strongest.
A century ago Brodmann divided the cortex into numbered areas by differences in their layering (the cytoarchitecture above), and the numbering survives because those structural divisions correspond reasonably well to functional ones. You do not memorize all fifty-some areas, but a working handful, grouped by function, repays knowing: primary motor cortex (BA 4) and the somatosensory strip (BA 1, 2, 3) around the central sulcus, with premotor and supplementary motor areas (BA 6) just ahead; the dorsolateral prefrontal cortex (BA 9, 46) for working memory and executive control, the frontal eye fields (BA 8) for gaze and attention, and Broca's area (BA 44, 45, left) for speech production; the anterior cingulate (BA 24, 32) for conflict and error monitoring and the posterior cingulate (BA 23, 31) as a default-mode hub; the auditory and language association cortex (BA 22) including Wernicke's area on the left; the angular and supramarginal gyri (BA 39, 40) for symbolic and spatial processing; and primary and association visual cortex (BA 17, 18, 19). The relationship between a scalp electrode and a Brodmann area is approximate, blurred by volume conduction, gyral folding, and individual variation, drawn from MRI studies that projected electrode positions onto cortex (Homan et al., 1987; Okamoto et al., 2004; Koessler et al., 2009). A finding at a site implicates a neighborhood, not a coordinate.
The IQCB tests behavioral correlates explicitly, so hold the function-to-region map for the domains a clinical question most often concerns:
The clearest way to confirm what a region does is to see what breaks when it is damaged. Damage to the left angular gyrus (BA 39, near P3) can produce Gerstmann syndrome, the co-occurring cluster of agraphia, acalculia, finger agnosia, and left-right confusion, a demonstration that one patch of association cortex carries several high-order functions at once. Damage to the right inferior parietal cortex and temporo-parietal junction (under roughly P4 and T6) can produce hemispatial neglect, unawareness of the left side of space, strong evidence for the right hemisphere's dominance in spatial attention. These lesions name the functions behind the sites a QEEG practitioner reads.
Facing each other across the central sulcus are the primary motor cortex (precentral gyrus, BA 4) and the primary somatosensory cortex (postcentral gyrus, BA 1, 2, 3), together the sensorimotor cortex. Both are organized as a body map, the homunculus, running from the legs and feet at the top of the head down through trunk, arm, and hand to the face near the lateral sulcus, distorted in proportion to control and innervation density so that the hand and face occupy far more cortex than the trunk. The hand and lower-face territory sits roughly under the central electrodes (C3, C4), which is why the rhythms trained there relate to bodily stillness and readiness.
The motor system extends beyond the strip. Premotor and supplementary motor areas (BA 6) plan and sequence action before the primary cortex issues it, and their planning shows up as the readiness potential (Chapter 2) building before a voluntary movement. The corticospinal (pyramidal) tract carries skilled movement from cortex down the brainstem, crossing in the medulla so each hemisphere drives the opposite side of the body. The basal-ganglia loop gates which movements proceed, and the cerebellum tunes their accuracy and timing.
Over the sensorimotor strip, when the body is still and the mind alert, the cortex produces the sensorimotor rhythm (SMR, roughly twelve to fifteen hertz), built by the same thalamocortical engine that makes posterior alpha. The closely related mu rhythm is the same sensorimotor idling, slightly lower in frequency. Both desynchronize the moment a movement is prepared, executed, or even imagined, an event-related desynchronization that is spatially specific to the part of the strip controlling the moving limb (Pfurtscheller & Lopes da Silva, 1999). The QEEG point is that a central site means sensorimotor cortex and the rhythm it idles at, and that SMR is state-dependent, so a low value first raises the question of whether the client was actually still during the recording.
Most of the cortex is neither primary motor nor primary sensory. It is association cortex, the territory that integrates across the primary regions and holds the higher functions, and it is where the clinically interesting QEEG phenotypes mostly live. Unimodal association cortex sits next to each primary area and elaborates one modality (the visual association areas assembling objects and faces from the edges V1 registers, for example). Heteromodal (multimodal) association cortex integrates across modalities and supports the most abstract functions: the prefrontal cortex for executive control, the parietal association cortex and intraparietal region for spatial integration and attention, and the temporo-parietal junction for social cognition and reading others' intentions.
Two properties of association cortex matter for reading a map. The function-to-site mapping is loosest here, because association functions are distributed and individually variable, so you hold primary-region mappings (motor strip, visual cortex) more firmly than association-region mappings, which are real but fuzzier. And much association function lives in connections as much as in regions, which is why a finding at a temporo-parietal site is a question about a network and why the white-matter tracts and resting-state networks of the next chapter are the natural continuation of this one.
Functional neuroanatomy, for a QEEG practitioner, comes down to reading a site as a function generated by layered, columnar cortex and paced by structures the electrode cannot see. The cortex is six-layered, with input arriving in layer IV, output leaving from layers V and VI, and superficial cortico-cortical layers sitting closest to the scalp. Pyramidal cells build the dipole, stellate cells receive thalamic input, and PV, SOM, and VIP interneurons sculpt the rhythm. Columns enforce the parallel orientation that makes open-field summation possible. The thalamus relays sensation through specific nuclei, drives activation through nonspecific nuclei, and is paced by the reticular nucleus, with T-type calcium and HCN channels setting the relay cell's burst-versus-tonic modes and therefore the alpha-to-spindle-to-slow-wave ladder. The basal ganglia (striatum, pallidum, STN, SNc and SNr) gate movement; the amygdala assigns salience; the hippocampus (CA fields, dentate, entorhinal cortex) encodes memory and generates a theta the scalp cannot read directly; the brainstem nuclei (locus coeruleus, raphe, VTA, cholinergic groups) set cortical tone from compact sources. The ascending sensory pathways relay every sense but smell through the thalamus to a mapped primary cortex (retina to LGN to V1; cochlea to MGN to A1; dorsal-column and spinothalamic routes to the ventral posterior thalamus to S1). Lobes and Brodmann areas carry the behavioral correlates the exam names, attention, memory, emotion regulation, language, and executive function, each tied to specific regions and confirmed by what their lesions disrupt. The sensorimotor strip is mapped as a homunculus and idles at SMR and mu, and the heteromodal association cortex holds the distributed higher functions where most QEEG phenotypes live, with a looser site-to-function correspondence than the primary areas.
Hold every finding on three axes at once, surface versus depth, left versus right, and anterior versus posterior, and a montage stops being a row of labels and becomes a map of function. The next chapter takes the connections between these regions, the tracts and the resting-state networks, the chemistry that sets the cortex's tone, and the plasticity that lets QEEG-guided training change the map at all.