BA 4 - primary motor

In the volumetric brain

The Territory

Structure. Brodmann area 4: the agranular strip of precentral cortex with giant Betz cells in layer V — the primary motor cortex's cytological signature, somatotopically ordered (leg medial, face lateral).

Function. Voluntary movement's final common cortical path: lowest-threshold stimulation evokes discrete contralateral movements; it launches the corticospinal volley that the basal ganglia and cerebellum shape in advance.

The Levers — graded instruments & the levers to come

Experiences of record: Sequence-tap motor trainer

Behaviour · Action · Thought — the tagged profile

Modulating Experiences

The Network — what fires with this region

Papers on disk — 242 full texts

The Evidence — Neurosynth studies (914)

The Evidence — NeuroQuery studies (862)

The Exploration Guide

*Frontal lobe · Mai atlas of record · 914 studies · 196 papers on disk*

The giant Betz cells of area 4 are the largest neurons the cortex owns, and their job is the simplest to state: launch movement. This right-hemisphere strip commands the left body — lowest-threshold stimulation evokes discrete contralateral twitches, somatotopically ordered from foot (medial) to face (lateral).

The Territory

Brodmann area 4: the agranular strip of precentral cortex with giant Betz cells in layer V — the primary motor cortex's cytological signature, somatotopically ordered (leg medial, face lateral).

*— {'source': 'Gazzaniga, Ivry & Mangun', 'work': 'Cognitive Neuroscience: The Biology of the Mind, 4th ed., W. W. Norton', 'kind': 'textbook', 'locator': 'ch. 8, Action'}*

What It Does

Voluntary movement's final common cortical path: lowest-threshold stimulation evokes discrete contralateral movements; it launches the corticospinal volley that the basal ganglia and cerebellum shape in advance.

The functional record: the final common cortical path — the corticospinal volley that the basal ganglia and cerebellum shape in advance. The decoded profile is the working body: motor, hand, finger, movement. The graded matrix carries the reaction-time family — simple-RT as both stimulator and assessor, choice-RT as stimulator — and the coactivation map is the sensorimotor loop itself: primary somatosensory (841 shared studies), postcentral gyrus and sulcus, SMA (511). Move and feel, firing together.

*— {'source': 'Gazzaniga, Ivry & Mangun', 'work': 'Cognitive Neuroscience: The Biology of the Mind, 4th ed., W. W. Norton', 'kind': 'textbook', 'locator': 'ch. 8, Action'}*

The Network

Read the loop: M1 ↔ S1 ↔ SMA ↔ premotor, the closed circuit every grip and tap travels. The ipsilateral vocabulary in its decoded profile marks the bilateral coordination studies.

Co-activation partners of record: BA 1-3 - primary somatosensory:841, Postcentral gyrus:550, Precentral gyrus:525, Supplementary motor area:511, Postcentral sulcus:489, BA 6 - premotor/SMA:467, Thalamus:388, Cingulate gyrus, anterior:387.

When It Fails

Contralateral weakness from the strip's damage; the subtler clinical dissociations live downstream (spasticity vs. flaccidity by lesion stage). The record's plainness here is the point — this is the cortex's simplest and most measurable output.

The Evidence

• Role of the supplementary motor area and the right premotor cortex in the c (1997)
• Functional-anatomic correlates of object priming in humans revealed by rapi (1998) — 10.1016/S0896-6273(00)80456-0
• Activation of Heschl's gyrus during auditory hallucinations. (1999) — 10.1016/S0896-6273(00)80715-1
• Fast reaction to different sensory modalities activates common fields in th (2000)
• Partially overlapping neural networks for real and imagined hand movements. (2000) — 10.1093/cercor/10.11.1093
• Error-related brain activation during a Go/NoGo response inhibition task. (2001) — 10.1002/1097-0193(200103)12:3<131::AID-HBM1010>3.0.CO;2-C

914 studies total touch this region in the Neurosynth corpus of record; the full literature lives beside this dossier.

The Levers

• simple-rt — stimulator · standard-scientific
• simple-rt — assessor · standard-scientific
• choice-rt — stimulator · standard-scientific
• choice-rt — assessor · standard-scientific
• finger-sequence-learning — stimulator · standard-scientific
• finger-sequence-learning — assessor · standard-scientific

Candidate levers (Neurosynth-decoded terms — motor(action-motor), hand(action-motor), movement(action-motor), movements(action-motor), m1(anatomy-reference), finger(action-motor), premotor(anatomy-reference), sensorimotor(method-other) …) are the foundation for the thousands of instruments to come; they are ungraded by law.

Explore Further

BA 1-3 - primary somatosensory:841, Postcentral gyrus:550, Precentral gyrus:525, Supplementary motor area:511 — each name is a dossier stop in this explorer.

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