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Browse courses and booksModule 10
Chapter 10 · 2 h · 8 quiz items · pass at 80%
This module satisfies BCIA II.B.4 (lobe functions, Brodmann areas, electrode mapping) and the IQCB brain-function and behavioral-correlates topics. It builds the function-to-site bridge that turns this into a neurofeedback course; the quiz proves the learner reads a 10-20 site as an approximate functional hypothesis, not a fixed label.
A protocol says to train the sensorimotor rhythm at C4. Why there, and not somewhere else? The answer is the subject of this chapter, and it is the move that turns neuroanatomy into something a brain trainer uses at the cap. An electrode site is not arbitrary. It is a bet about which functional cortex sits underneath, and the quality of that bet depends on knowing what each region does and how loosely a scalp site maps to the tissue below it.
Map the four lobes of Chapter 5 onto 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, biased toward withdrawal and avoidance. This asymmetry is the basis of the frontal alpha asymmetry that brain trainers read in mood work. Just in front of the central sulcus runs the primary motor cortex. Just behind it, in the parietal lobe, sits the primary somatosensory cortex. These two strips, facing each other across the central sulcus, are the sensorimotor cortex.
The parietal lobe handles spatial integration and attentional allocation, and its posterior midline is a hub of the default mode network covered in Chapter 12. The temporal lobe handles hearing, language on the left, prosody and social tone on the right, and, through its medial structures that the scalp cannot reach directly, memory. The occipital lobe handles vision, and it is where alpha is strongest, which is no accident: a visual cortex at rest is an idling cortex, and idling cortex synchronizes.
The motor and somatosensory strips facing each other across the central sulcus are organized as a map of the body, the homunculus, running from the legs and feet at the top of the head down through the trunk, arm, and hand to the face near the lateral sulcus. The map is distorted in proportion to use and innervation density: the hand and the face occupy far more cortex than the trunk, because they are richly controlled and richly sensed. For a brain trainer the practical point is that the hand and lower-face territory sits roughly under the central electrodes, which is part of why the sensorimotor rhythm trained there relates to a state of bodily stillness and readiness.
Most of the cortex, though, is neither primary motor nor primary sensory. It is association cortex, the territory that integrates across the primary regions and holds the higher functions: the prefrontal cortex for executive control, the parietal association cortex for spatial integration and attention, the temporo-parietal junction for social cognition. Association cortex is where the clinically interesting phenotypes mostly live, and it is also where the function-to-site mapping is loosest, because association functions are distributed and individually variable. A brain trainer should hold primary-region mappings (motor strip, visual cortex) more firmly than association-region mappings, which are real but fuzzier.
[[FIG: FIG-15 – Cortical function by lobe – HALF PAGE – the lobes color-blocked by primary function: motor, sensory, language, executive, visual HERE]]
A century ago Korbinian Brodmann divided the cortex into numbered regions by the microscopic differences in their layering, the micro-anatomy of Chapter 5 (Purves et al., 2018). The numbering survives because those structural divisions correspond reasonably well to functional ones. A brain trainer does not memorize all fifty-some areas, but a working handful repays knowing, grouped by what they do rather than by number.
Around the central sulcus sit the primary motor cortex (area 4) and the somatosensory strip (areas 1, 2, 3), with the premotor and supplementary motor areas (area 6) just ahead, planning movement. In the frontal lobe, the dorsolateral prefrontal cortex (areas 9 and 46) does working memory and executive control, the frontal eye fields (area 8) direct gaze and attention, and on the left the inferior frontal gyrus (areas 44 and 45) is Broca's area for speech production. Along the midline, the anterior cingulate (areas 24 and 32) monitors conflict and error, and the posterior cingulate (areas 23 and 31) anchors the default mode network. In the temporal lobe, the auditory and language association cortex (area 22) includes Wernicke's area on the left for language comprehension. At the parietal-temporal-occipital junction, the angular and supramarginal gyri (areas 39 and 40) handle the symbolic and spatial processing of Chapter 5's inferior parietal lobule. At the back, the primary visual cortex (area 17) and the visual association areas (18 and 19) process sight. Use the numbers to reason about what a region does, not to overclaim precision. The relationship between a scalp electrode and a specific Brodmann area is approximate, blurred by volume conduction, by the folding of cortex into sulci, and by individual variation in anatomy. A finding at a site implicates a neighborhood, not a coordinate.
The clearest way to learn what a region does is to see what breaks when it is damaged, and the association cortex offers three lessons a brain trainer should carry, because each names a function behind a site rather than a syndrome to treat.
The left angular gyrus (area 39), near P3 and the inferior parietal lobule, sits at the crossroads of language, number, and body-space (Blumenfeld, 2021). Damage there can produce Gerstmann syndrome, a cluster of four deficits that travel together because they share that cortex: difficulty writing (agraphia), difficulty calculating (acalculia), an inability to identify one's own fingers (finger agnosia), and left-right confusion. The cluster is instructive less as a diagnosis than as a demonstration that a single patch of association cortex can carry several high-order functions at once, which is why a parietal finding is rarely about one thing.
Hemispatial neglect is the right-hemisphere counterpart and the more common one. Damage to the right inferior parietal cortex and the temporo-parietal junction, under roughly P4 and T6, can leave a person unaware of the left side of space: they eat from one half of the plate, draw half a clock, and do not notice the omission. That the right hemisphere produces neglect of the left while left-hemisphere damage rarely produces the mirror image is one of the strongest pieces of evidence for the right hemisphere's dominance in spatial attention, the specialization this chapter assigned it. A right-parietal or right-TPJ finding is, in that light, a question about spatial attention and self-other processing.
Connecting the language regions is a tract worth naming because connectivity work (Chapter 12) leans on it. The arcuate fasciculus is the dorsal bundle that links the posterior language region (Wernicke's, area 22, near T5) to the frontal speech-planning region (Broca's, areas 44 and 45, near F7), arcing under the parietal cortex. It is the wiring that lets comprehension and production work together, and its disruption produces the language disconnection in which a person understands and speaks but cannot repeat. For a brain trainer the point is that a function can live in a connection rather than a region, which is exactly what the connectivity measures of Chapter 12 try to read.
Return to C4. Beneath the central electrodes lies the sensorimotor cortex, and over it sits the sensorimotor rhythm, around twelve to fifteen hertz, present when the sensorimotor system is still and suppressed the moment it engages in movement. It is the motor system's idling rhythm, the way posterior alpha is the visual system's, and it shares the thalamocortical machinery of Chapter 6. For the function-to-site bridge the point is just this: a central site means sensorimotor cortex and the rhythm it idles at. Why that rhythm became the founding target of the field, and how it behaves the moment the system engages, is the physiology of Chapter 11.
The left-right axis of Chapter 5 is more than geography. The hemispheres are functionally specialized, and the specialization is exam-relevant and clinically useful. In most people the left hemisphere is dominant for language, both production (Broca's region near the inferior frontal cortex) and comprehension (Wernicke's region in the posterior temporal cortex), and it favors sequential, analytic, detail-level processing. The right hemisphere favors spatial, global, and contextual processing, including the prosody and social tone that carry the music of speech rather than its words, and visuospatial reasoning. This is a bias, not an absolute. The "left brain, right brain" of popular culture overstates a real but graded asymmetry.
The asymmetry that matters most for a brain trainer is frontal. The left frontal cortex is associated with approach motivation and positive, engaged affect, and the right frontal cortex with withdrawal, avoidance, and the brake side of emotion. The relative balance between them, frontal alpha asymmetry, is one of the more studied EEG markers of affective style, and its physiological basis is this approach- withdrawal specialization. The neuroscience of the asymmetry belongs here. What a given asymmetry value means as a clinical phenotype is the Field Guide's call.
Along the midline runs a chain of cortex worth knowing as a unit. At the front, near the Fz electrode, sits the anterior cingulate cortex, which monitors for conflict and errors and generates frontal-midline theta, a rhythm that rises with cognitive control and working-memory load (Nakamura-Palacios et al., 2023). Behind it, near Pz, sits the posterior cingulate, a hub of the default mode network taken up in Chapter 12. The same anterior cingulate, as Chapter 9 noted, also sits in the central autonomic network, which is why cognitive control and bodily regulation are neighbors rather than strangers. Frontal-midline theta is a clean example of this chapter's whole argument: a specific rhythm, generated by a specific structure, readable at a specific electrode, and meaningful because of what that structure does.
[[FIG: FIG-16 – The function-to-site bridge – FULL PAGE – the 10-20 electrode layout overlaid with function: Cz/SMR, Fz/frontal-midline theta, Pz/default mode, O1-O2/visual alpha, F3-F4/executive, T6/social HERE]]
Putting it together gives the brain trainer the move that matters: read an electrode site as a statement about function. The central strip, C3, C4, Cz, means sensorimotor cortex and the sensorimotor rhythm. Fz means anterior cingulate and frontal-midline theta. The posterior sites, O1, O2, P3, P4, Pz, mean visual and parietal cortex and alpha. The frontal sites, F3, F4, and the prefrontal Fp positions, mean executive cortex and the approach-withdrawal balance. Overlaid on the standard ten-twenty electrode layout, this turns a montage from a set of labels into a map of function. The ten-twenty system itself, its geometry and nomenclature, is the Field Guide's territory. What this chapter adds is the meaning beneath each position.
The mapping can be made concrete. The table below pairs each standard ten-twenty site with the cortical region and the Brodmann area or areas most likely to lie beneath it, drawn from the studies that projected electrode positions onto the cortex by MRI (Homan et al., 1987; Okamoto et al., 2004; Koessler et al., 2009). Read it as a teaching aid and a prior, not a coordinate system. The correspondence is approximate and individually variable, and it is blurred by the volume conduction and gyral folding this chapter keeps returning to. A site overlies a neighborhood of cortex, often several Brodmann areas, not a single one.
| Site (10-20) | Cortex beneath | Likely Brodmann area(s) | Function |
|---|---|---|---|
| Fp1 / Fp2 | Frontopolar prefrontal | 10 | executive, prospective control |
| F3 / F4 | Dorsolateral prefrontal | 8, 9, 46 | working memory, executive control |
| F7 / F8 | Ventrolateral frontal | 45, 47 (44/45 left = Broca) | speech production (left), inhibition |
| Fz | Superior-frontal / pre-SMA | 6, 8 (24/32 deeper) | midline executive, frontal-midline theta |
| C3 / C4 | Pre- and post-central gyri | 1, 2, 3, 4 (6) | hand motor and somatosensory |
| Cz | Vertex sensorimotor / SMA | 4, 6 (5) | leg-foot motor, SMA, SMR |
| T3 / T4 (T7 / T8) | Mid-superior temporal | 21, 22 (42) | auditory association, language (left) |
| T5 / T6 (P7 / P8) | Posterior temporal / TPJ | 37, 39 (22) | comprehension (left), social-spatial (right) |
| P3 / P4 | Inferior-superior parietal | 7, 39, 40 | spatial integration, calculation (left) |
| Pz | Precuneus / posterior cingulate | 7, 31 (23) | default-mode hub, visuospatial |
| O1 / O2 | Occipital | 17, 18, 19 | primary and association vision |
The parenthetical labels in the modern ten-ten relabeling (T3/T4 become T7/T8, T5/T6 become P7/P8) name the same scalp positions. The Brodmann assignments do not change with the renaming. Where two columns disagree about a region, the disagreement is the point: the body of evidence places these sites over these neighborhoods with real but limited precision.
The three axes of Chapter 5 are the frame that keeps this disciplined, because a site carries three coordinates at once. On the surface-to-depth axis, ask whether a finding is the cortex the electrode sees or a deep structure it can only infer. On the left-to-right axis sit the asymmetries: language and analytic processing biased left, spatial and prosodic processing biased right, and the frontal approach-withdrawal balance. On the anterior-to-posterior axis, executive control sits in front, sensory and visual processing behind, with the sensorimotor strip at the divide. Reading a site on all three axes at once, rather than as a lone label, is what turns the function-to-site bridge into a habit rather than a lookup.
Take a resting record with three findings, and read each as a functional-anatomy hypothesis rather than a number. First, elevated theta at Fz. Fz overlies the anterior cingulate, the conflict-and-error monitor and the generator of frontal-midline theta, so the hypothesis is about cognitive-control engagement or, just as plausibly, about drowsiness raising frontal theta, and the history and the arousal check decide between them. Second, low SMR at C4. The central strip is sensorimotor cortex, and the sensorimotor rhythm marks calm motor readiness, so low SMR raises a question about motor regulation and impulse control, the physiological rationale behind training SMR there. Third, a slowed alpha peak at O1 and O2. The occipital sites are visual cortex, where alpha is generated, so a slow peak is a question about the speed of the thalamocortical clock (Chapter 6), read against the client's age (Chapter 14). Three sites, three functional hypotheses, each tied to the tissue underneath and each testable against history. That is the move the chapter is built to teach, and it is what separates reading a montage from reciting one.
A practitioner sees a deviation at T6 and, lacking a functional frame, treats it as a generic abnormality to normalize. The function-to-site bridge gives the finding content. T6 overlies the right temporo-parietal region involved in social cognition and reading others' intentions, so a deviation there invites questions about social processing rather than a reflexive push toward the population mean. The site is a hypothesis about function, and the clinical history tests it.
What this means for the signal: when you choose a site, you are choosing a function, with the standing caveat that scalp-to-cortex correspondence is approximate. The reader should now look at a montage and see motor cortex, cingulate, and visual cortex where they used to see C4, Fz, and O1. That shift, from labels to functional anatomy, is what lets a protocol be reasoned about rather than merely followed.
Key points
Mnemonic (midline chain, front to back): Fight, Move, Wander. Fz (anterior cingulate, conflict monitoring) to Cz (sensorimotor, movement) to Pz (posterior cingulate / default mode, mind-wandering).
Check yourself
Ch 5 (gross anatomy, micro-anatomy), Ch 6 (posterior alpha generator), Ch 8 (sensory cortices), Ch 9 (ACC in the autonomic network), Ch 11 (SMR physiology), Ch 12 (midline/DMN), Field Guide (10-20, montages), NF: Explained / Coaching (why protocols target these sites).
Frontal (F3, F4, Fz, Fp1, Fp2): executive function, planning, impulse control, approach/withdrawal. Temporal (T3-T6): language (left), prosody/social (right), memory (medial), emotional reactivity; T6 = right TPJ (social cognition); arcuate fasciculus F7-T5. Parietal (P3, P4, Pz): spatial integration, DMN hub (Pz); IPL/ angular gyrus (left = calculation/reading; right = spatial); Gerstmann syndrome. Occipital (O1, O2): vision; alpha strongest, most heritable. Central (C3, C4, Cz): motor/somatosensory; mu rhythm; SMR target. Midline (Fz, Cz, Pz): ACC (Fz) to PCC (Pz).
The deep asides (arcuate fasciculus, Gerstmann, IPL subdivisions) move here in
full in a later pass; the Field Guide keeps one-liners. See
qeeg-field-guide/meta/PRUNE-AFTER-PHYSIOLOGY-TRANSPLANT.md.