Introduction
In evolutionary terms the frontal cortex has been the most recent to evolve, and the frontal lobes are the area of brain which has developed greatly in humans, differentiating us from other mammals. These lobes integrate the other brain areas, and are particularly responsible for higher level thinking and cognitive skills such as planning, evaluating likely outcomes, multitasking, performing risk assessment and the niceties of social interaction; it is the area of brain which deals in abstract concepts.
Anatomy
The Frontal Lobes account for approximately one third of human brain mass.
They lie at the front of the brain, anterior to the parietal lobes and superior to the temporal lobe.
Each frontal lobe (left and right) is generally considered to have several distinct divisions:
- Motor cortex
- Premotor cortex
- Supplementary motor cortex
- Prefrontal cortex
- Orbital cortex AKA frontal eye fields
- Broca’s Area
Vascular Supply
Medial frontal lobe = anterior cerebral artery
Deep & lateral regions = superior division of middle cerebral artery
Function
Author Mesulam suggests that the frontal lobe is the part of the brain which modifies and imposes constraints on reflexive behaviours[1], and this control develops as the infant brain grows[2] and the frontal lobes become larger and more active.
- Motor cortex = voluntary movement
- Premotor cortex = storage of motor patterns & voluntary activities
- Prefrontal cortex = ability to concentrate; inhibition of reflexive behaviours; personality & emotional traits; abstract thinking
- Broca’s Area = Motor control of speech
Primary Motor Cortex
Input: Basal gangliam thalamus, premotor cortex (in the frontal lobe), sensory cortex (in the parietal lobe)
Output: Motor fibres to spinal cord and brainstem, travelling in the corticospinal tract
Function: Movement
Pre motor Cortex
Input: Basal ganglia, thalamus, sensory cortex
Output: Primary motor cortex
Function: storage of motor programs, sensorimotor integration, facilitation of controlled, smooth movements
Supplementary Motor Cortex
Input: Thalamus, cingulate gyrus, sensory & prefrontal cortex
Output: Premotor cortex, primary motor cortex
Function: Intentional preparation for movement, procedural memory
Prefrontal Cortex
Function: working memory, executive functions including the ability to plan & implement (& monitor/evaluate) a series of goal-directed actions.
Frontal Eye Fields
Input: Parietal cortex, temporal cortex
Output: Caudate, superior colliculus, paramedian pontine reticular formation
Function: Control of voluntary scanning movements of the eye
Broca’s Speech Area
Input: Wernicke’s area
Output: Primary motor cortex
Function: Dominant hemisphere = speech production. Non-dominant hemisphere = emotional & melodic component of speech
Pathology/Injury – Symptoms
It has been found that in traumatic brain injury contusions typically occur on the poles and the inferior aspects of the frontal lobes[3].
Disturbances of Motor Function
- Loss of fine movements, strength & speed [damaged area = primary motor cortex]
- Changes in voluntary gaze [damage to frontal eye field]
- Changes in speech [damaged area = Broca’s speech area), usually slow, hesitant speech, difficulties in word finding, perseveration
3 Frontal Lobe Syndromes
Orbitofrontal syndrome = lack of inhibition
Frontal convexity syndrome = apathetic
Medial frontal syndrome = akinetic
Orbitofrontal syndrome
Patient demonstrates disinhibited, impulsive behaviour; difficulty in controlling their emotions; difficulty in maintaining concentration; lacking in judgement; failure to appreciate/anticipate consequences of their actions; can show euphoria, hypomania or grandiosity.
Orbitofrontal damage can also lead to abnormal sexual behaviour.
Frontal convexity syndrome
Patient shows disinterest and is apathetic; slowing of motor functions; unable to plan ahead; lacks motivation; lacks concern about the world around them.
Medial frontal syndrome
Reduced movement; loss of sensation in lower limbs; urinary incontinence; occasional mutism; profound apathy; sometimes show indifference to thirst or hunger
Resources
References
References will automatically be added here, see adding references tutorial.
- ↑ Mesulam MM. DT Stuss and RT Knight. The Human Frontal Lobes: Transcending the Default Mode through Continent Encoding. Principles of Frontal Lobe Function. Oxford: 2002. 8-30
- ↑ Luciana, ed. by Charles A. Nelson. Handbook of developmental cognitive neuroscience. Monica (2001). Cambridge, Mass. [u.a.]: MIT Press.
- ↑ Flint AC, Manley GT, Gean AD, et al. Post-operative expansion of hemorrhagic contusions after unilateral decompressive hemicraniectomy in severe traumatic brain injury. J Neurotrauma. Mar 17 2008