CorpusHuman Anatomy
NervousBrain region

Frontal lobe

Lobus frontalis

The largest lobe, anterior to the central sulcus and above the lateral sulcus; it contains the primary motor, premotor and supplementary motor cortex, the frontal eye field, Broca's area and the prefrontal cortex for executive function and personality.

Show on body map Brain — Lateral View

Overview

Share of cerebral cortex≈1/3 (largest lobe)
Primary motor areaBrodmann 4 (precentral gyrus)
Broca's areaBrodmann 44, 45

The frontal lobe forms roughly the anterior third of each hemisphere. It is bounded behind by the central sulcus and below by the lateral sulcus, and it extends onto the medial surface as far as the paracentral lobule and onto the orbital surface above the orbit. Its gyri are:
• the precentral gyrus;
• the superior, middle and inferior frontal gyri. The inferior gyrus is divided by rami of the lateral sulcus into the pars orbitalis, triangularis and opercularis.
• the orbital gyri and the gyrus rectus, with the olfactory bulb and tract on the orbital surface.

Function is arranged as a gradient from movement execution at the back to abstract control at the front. The primary motor cortex (area 4) in the precentral gyrus sends a large share of the corticospinal and corticobulbar fibres and is laid out as the motor homunculus:
• the leg and foot lie on the medial surface (paracentral lobule);
• the trunk, arm and a large hand area lie on the dorsolateral convexity;
• the face, tongue and larynx lie lowest, next to the lateral sulcus.
The premotor and supplementary motor areas (area 6) plan and sequence movements. The frontal eye field (area 8) drives voluntary saccades to the opposite side. Broca's area (44/45, dominant hemisphere) programmes speech production.

The prefrontal cortex occupies everything in front of these areas and is one of the last regions to mature, myelinating into the mid-20s. The dorsolateral prefrontal cortex supports working memory, planning, set-shifting and judgement. The orbitofrontal and ventromedial cortex regulate social behaviour, impulse control, reward valuation and emotion. The medial frontal and anterior cingulate cortex support motivation and initiation. The paracentral lobule also provides cortical inhibitory control of micturition.

Location

Anterior part of each hemisphere: anterior to the central sulcus and superior to the lateral sulcus; occupies the anterior cranial fossa (orbital surface).

Parts & subdivisions

  1. Primary motor cortex (area 4)
    Precentral gyrus and anterior paracentral lobule. Pyramidal (Betz) cells of layer V; contralateral voluntary movement; somatotopic motor homunculus with disproportionately large hand, face and tongue representations.
  2. Premotor cortex (lateral area 6)
    Anterior to the precentral gyrus on the lateral surface; selects and prepares movements guided by external (e.g. visual) cues; contains mirror neurons.
  3. Supplementary motor area (medial area 6)
    On the medial surface; planning of internally generated, sequential and bimanual movements; active even when movements are only imagined.
  4. Frontal eye field (area 8)
    Middle frontal gyrus; voluntary conjugate saccades to the contralateral side. A destructive lesion deviates the eyes towards the lesion; an irritative (seizure) focus drives them away.
  5. Broca's area (areas 44, 45)
    Pars opercularis and pars triangularis of the inferior frontal gyrus, usually in the left hemisphere. Motor programming of speech and syntax; connected to Wernicke's area by the arcuate fasciculus.
  6. Prefrontal cortex
    Dorsolateral (areas 9, 46): working memory, planning, flexibility. Orbitofrontal/ventromedial (areas 10–12, 47): social behaviour, inhibition, reward, decision-making. Medial/anterior cingulate: motivation and drive.
  7. Paracentral lobule (anterior part)
    Medial-surface continuation of the precentral gyrus: motor control of the contralateral leg and foot, and cortical control of bladder and bowel voiding.

Anatomy

Arterial supply

Middle cerebral artery (superior division): lateral surface, including Broca's area and the face/arm motor cortex. Anterior cerebral artery: medial and orbital-medial surfaces, including the leg area and the paracentral lobule.

Relations

Anterior cranial fossa below (orbital surface on the orbital plates of the frontal bone, olfactory bulbs on the cribriform plate); falx cerebri medially; parietal lobe behind; temporal lobe and insula below the lateral sulcus.

Function

  • Initiation and control of contralateral voluntary movement
  • Planning and sequencing of motor acts
  • Voluntary eye movements (saccades)
  • Speech production (dominant hemisphere)
  • Executive functions: working memory, planning, judgement, problem-solving
  • Regulation of personality, social behaviour, motivation and emotion
  • Voluntary control of micturition and defecation

Clinical significance

Broca's (expressive) aphasia

Speech is non-fluent, effortful and telegraphic with agrammatism, while comprehension is relatively preserved. Repetition is impaired and the patient is aware of the problem and frustrated. It is usually caused by an infarct of the superior division of the left MCA and is often accompanied by right face and arm weakness.

Frontal lobe syndromes

• Orbitofrontal lesions: disinhibition, impulsivity, inappropriate jocularity and poor social judgement. Phineas Gage (1848) is the classic case.
• Dorsolateral lesions: dysexecutive syndrome with poor planning, perseveration, concreteness and impaired set-shifting.
• Medial lesions: apathy, abulia and, when bilateral, akinetic mutism.
Primitive reflexes (grasp, pout) may return. Causes include trauma, tumours (meningioma, glioma), ACA infarction and frontotemporal dementia.

Compiled from standard anatomy and physiology references — see the Nervous System sources. For education only; not medical advice.