Definitions

severing connections

Frontal lobe disorder

The frontal lobe of the brain plays a key role in higher mental functions such as motivation, planning, social behaviour, and speech production. A frontal lobe syndrome can result from a range of causes inlcuding head trauma, tumours, degenerative diseases and cerebrovascular disease. Impairment of frontal lobe functioning is also found in a range of psychiatric conditions including schizophrenia, attention deficit disorder and antisocial personality disorder. Frontal lobe impairment can be detected by recognition of typical clinical signs, use of simple screening tests, and specialist neuropsychiatric testing.

Anatomy and functions

The frontal lobe has three main areas, known as the precentral cortex, prefrontal cortex and the orbitofrontal cortex. These three areas are represented in both the left and the right cerebral hemispheres.

The precentral cortex or primary motor cortex is concened with the planning, initiation and control of physical movement. The dorsolateral part of the frontal lobe is concerned with planning, strategy formation, and other executive functions. The prefrontal cortex in the left hemisphere is involved with verbal memory while the prefrontal cortex in the right hemisphere is involved in spatial memory. The left frontal operculum region of the prefrontal cortex, or Broca's area, is responsible for expressive language, in other words language production. The orbitofrontal cortex is concerned with response inhibition, impulse control , and social behaviour.

Clinical assessment

History

Frontal lobe disorders may be recognised through a sudden and dramatic change in a person's personality, for example with loss of social awareness, disinhibition, emotional instability, aggression, irritability or impulsiveness (for example sexually inappropriate behaviour or spending money impulsively). Alternatively the disorder may become apparent because of mood changes such as depression, anxiety or apathy.

Examination

On mental state examination a person with frontal lobe damage may show reduced speech , with reduced verbal fluency and impaired expressive language. The person might have flattened or blunted affect. Typically the person is lacking in insight and judgment, but does not have marked cognitive abnormalities or memory impairment (as measured for example by the mini-mental state examination). With more severe impairment there may be echolalia or mutism. Neurological examination may show primitive reflexes (also known as frontal release signs) such as the grasp reflex or the rooting reflex. These are reflexes normally found in babies, but normally suppressed and absent in adults. Akinesia (lack of spontaneous movement) and urinary incontinence will be present in more severe and advanced cases. The frontal assessment battery (FAB), which includes simple tests of sequencing, behavioural inhibition, planning and frontal release signs, can be used as a screening test to elicit typical neurological and cognitive features.

Further investigation

A range of neuropsychological tests are available for clarifying the nature and extent of frontal lobe dysfunction. For example, concept formation and ability to shift mental sets can be measured with the Wisconsin card sort test, planning can be assessed with the Mazes subtest of the WISC, switching between plans is assessed with the Trail-making test, and screening out distracting stimuli is assessed with the Stroop test.

Individuals with frontotemporal dementia and Pick's disease will show frontal cortical atrophy on Computerised tomography or magnetic resonance imaging. Frontal impairment due to head injuries, tumors or cerebrovascular disease will also be apparent on brain imaging.

Causes of Frontal lobe dysfunction

Head trauma

Closed head injuries, for example from motor vehicle accidents, can cause damage to the orbitofrontal cortex. Pre-frontal lobotomies severing connections between the pre-frontal cortex and the rest of the brain, were effectively a form of iatrogenic trauma resulting in a frontal lobe syndrome.

Cerebrovascular disease

Cerebrovascular disease may cause a stroke in the frontal lobe.

Tumours

Tumours such as meningiomas may present with a frontal lobe syndrome.

Degenerative diseases

Frontal lobe impairment is a feature of Alzheimer's disease, frontotemporal dementia and Pick's disease.

Psychiatric disorders

There is evidence for frontal lobe impairment in schizophrenia, depression, attention deficit disorder, and antisocial personality disorder or psychopathy

A large number of studies have documented abnormalities in working memory in schizophrenia, associated with disrupted functioning of the dorso-lateral prefrontal cortex. There is also evidence for disruption of neuronal connections between the temporal and frontal lobes in people with schizophrenia. The characteristic dorso-lateral prefrontal cortex morphological abnormalities are said to be related to a general impaired ability to control and regulate behavior, which would correspond to deficits in several functional areas in schizophrenia. A study of people with schizophrenia using MRI scanning and psychological assessment has also found that longer duration of illness was associated with lower gray matter volume in the left dorsomedial prefrontal cortex and the right middle frontal cortex, and these changes were associated with impaired working memory, attention and psychomotor speed. Another MRI study of schizophrenia has found an association between orbitofrontal cortex volume reduction and a longer duration of illness, impaired executive functioning, and greater formal thought disorder.

See also

Frontal lobe

Executive system

Notes

References

Gelder, M; López-Ibor J; Andreasen N (2000). New Oxford textbook of psychiatry. Oxford: Oxford University Press.

External links

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