2 Neuroscience2.6 Neuroanatomy

2.6.4 Internal anatomy of the frontal lobes and cingulate gyrus

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Written by Resident Doctor Committee · Published

Surfaces and landmarks

Surface

Landmarks

Lateral

Precentral gyrus in front of the central sulcus; superior, middle and inferior frontal gyri

Medial

Paracentral lobule, supplementary motor area, cingulate gyrus above the corpus callosum

Orbital

Gyrus rectus and orbital gyri, separated by the olfactory sulcus

  • Loss of smell localises to the orbital surface of the frontal lobe, where the olfactory bulbs and tracts lie beneath the gyrus rectus.

Motor cortex and white matter

  • Primary motor cortex lies in the precentral gyrus of the posterior frontal lobe. Damage causes contralateral upper motor neurone weakness because corticospinal fibres cross at the medullary pyramids.

  • Prefrontal subcortical white matter makes up only about 12 to 15% of total subcortical white matter in humans.

Prefrontal syndromes

Each prefrontal region drives a loop through the striatum and mediodorsal thalamus. The same syndrome can follow damage to the cortex, the deep nuclei or the white matter joining them.

Region

Striatal target

Syndrome

Features

Dorsolateral prefrontal

Dorsal caudate

Dysexecutive

Failure of planning and set shifting, poor working memory, perseveration; IQ may be normal

Orbitofrontal

Ventromedial caudate

Disinhibited, formerly pseudopsychopathic

Impulsivity, tactlessness, facetiousness, poor social judgement

Medial frontal and anterior cingulate

Ventral striatum

Apathetic, formerly pseudodepressed

Lost drive: apathy, abulia and, at the extreme, akinetic mutism

Find the dorsolateral prefrontal cortex, whose damage gives the dysexecutive syndrome, and the orbitofrontal cortex below it, whose damage gives the disinhibited syndrome. The motor cortex sits further back, just in front of the central sulcus. Eko321, CC0, via Wikimedia Commons

  • Orbitofrontal cortex regulates social conduct and assigns reward value to social information.

  • Phineas Gage became disinhibited, profane and impulsive, with poor social judgement but intellect and memory spared, after a tamping-iron injury. His case is the founding evidence that orbitofrontal cortex governs personality and social conduct.

  • A frontal lobe lesion is suggested by a change in character with disinhibition, poor judgement and apathy, together with urinary incontinence that the patient is unconcerned about.

Cingulate gyrus

Subdivision

Position

Function

Subgenual

Below the callosal genu

Visceral regulation, mood

Rostral (affective) anterior cingulate

Around the genu

Emotional appraisal, motivation

Dorsal (cognitive) anterior cingulate and midcingulate

Above the callosal body

Conflict and error monitoring, effort

Posterior cingulate and retrosplenial

Around the splenium

Memory, orientation, context

Follow the cingulate gyrus round the corpus callosum: the rostral anterior cingulate sits at the genu, the caudal anterior cingulate above the callosal body, and the posterior cingulate and isthmus towards the splenium. The atlas boundaries only roughly match the divisions in the table. Patric Hagmann et.al., CC BY 2.5, via Wikimedia Commons

Release and dependency behaviours

These are frontal release signs. Loss of frontal inhibitory control frees actions that the environment triggers.

Behaviour

What the patient does

Utilisation behaviour

Uses objects within reach automatically and appropriately, but out of context

Imitation behaviour

Copies the examiner's gestures without being asked

Manual groping

Seeks and reaches for a stimulus with the hand, and cannot stop on request

Environmental dependency syndrome

Lets the whole setting dictate behaviour, such as taking on the doctor's role; combines utilisation and imitation

  • Utilisation behaviour follows orbitofrontal damage with caudate involvement, and is also localised to medial frontal damage.

Revision material for the MRCPsych examinations. Not clinical guidance, and not for use in patient care.