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Brainlobes
Lobes of the human brain (Frontal Lobe is shown in red)
LifeartistAdded by Lifeartist

The frontal lobe is an area in the brain of mammals. It is located at the front of each cerebral hemisphere and positioned anterior to (in front of) the parietal lobes and above and anterior to the temporal lobes. It is separated from the parietal lobe by the primary motor cortex, which controls voluntary movements of specific body parts associated with the precentral gyrus.

The frontal lobe reaches full maturity around age 25, marking the cognitive maturity associated with adulthood. Arthur Toga, UCLA, found increased myelin in the frontal lobe white matter of young adults compared to that of teens. A typical onset of schizophrenia in early adult years correlates with poorly myelinated and thus inefficient connections between cells in the fore-brain.

The frontal lobe contains most of the dopamine-sensitive neurons in the cerebral cortex. The dopamine system is associated with reward, attention, long-term memory, planning, and drive. Dopamine tends to limit and select sensory information arriving from the thalamus to the fore-brain. A report from the National Institute of Mental Health says a gene variant that reduces dopamine activity in the prefrontal cortex is related to poorer performance and inefficient functioning of that brain region during working memory tasks, and to slightly increased risk for schizophrenia.

Anatomy

Gray729
Gray's Fig. 729 - Orbital surface of left frontal lobe.
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File:Frontal lobe animation.gif
Animation. Frontal lobe (red) of left cerebral hemisphere.

On the lateral surface of the human brain, the central sulcus separates the frontal lobe from the parietal lobe. The lateral sulcus separates the frontal lobe from the temporal lobe.

The frontal lobe can be divided into a lateral, polar, orbital (above the orbit; also called basal or ventral), and medial part. Each of these parts consists of particular gyri:

The gyri are separated by sulci. E.g., the precentral gyrus is in front of the central sulcus, and behind the precentral sulcus. The superior and middle frontal gyri are divided by the superior frontal sulcus. The middle and inferior frontal gyri are divided by the inferior frontal sulcus.

In humans, the frontal lobe reaches full maturity around only after the 20s,[1] marking the cognitive maturity associated with adulthood. A small amount of atrophy, however, is normal in the aging person’s frontal lobe. Fjell, in 2009, studied atrophy of the brain in people aged 60–91 years. The 142 healthy participants were scanned using MRI (magnetic resonance imaging). Their results were compared to those of 122 participants with Alzheimer’s disease. The participants returned one year later, and the researchers noted that although volumetric decline was clearly evident in large amounts in the AD participants, it was also evident in small quantities in the healthy individuals. A decline in frontal lobe volume of approximately .5% over that year seemed to be average.[2] These findings corroborate those of Coffey, who in 1992 indicated that the frontal lobe decreases in volume approximately .55%-1% per year.[3]

Dr. Arthur Toga, a UCLA professor of neurology, found increased myelin in the frontal lobe white matter of young adults compared to that of teens. A typical onset of schizophrenia in early adult years correlates with poorly myelinated and thus inefficient connections between cells in the fore-brain.


Function

Main article: Frontal lobe functions

In the human brain, the precentral gyrus and the related cortical tissue that folds into the central sulcus comprise the primary motor cortex, which controls voluntary movements of specific body parts associated with areas of the gyrus.

Executive control

Frontal lobes assist in planning, coordinating, controlling and executing behavior. People that have damaged frontal lobes may experience problems with these aspects of cognitive function, being at times impulsive; impaired in their ability to plan and execute complex sequences of actions; perhaps persisting with one course of action or pattern of behavior when a change would be appropriate (perseveration).

The executive functions of the frontal lobes involve the ability to recognize future consequences resulting from current actions, to choose between good and bad actions (or better and best), override and suppress unacceptable social responses, and determine similarities and differences between things or events.Therefore, it is involved in higher mental functions.


Memory

The frontal lobes also play an important part in retaining longer term memories which are not task-based. Memories associated with emotions of input from the brain's limbic system are modified by the higher frontal lobe centers to generally fit socially acceptable norms (see executive functions above)[citation needed]. The frontal lobes have rich neuronal input from both the alert centers in the brainstem and the limbic regions.

Role in mental health

A report from the National Institute of Mental Health says a gene variant that reduces dopamine activity in the prefrontal cortex is related to poorer performance and inefficient functioning of that brain region during working memory tasks, and to slightly increased risk for schizophrenia.


Dopamine-sensitive neurons in the cerebral cortex are found primarily in the frontal lobes. The dopamine system is associated with pleasure, long-term memory, planning and drive. Dopamine tends to limit and select sensory information arriving from the thalamus to the forebrain. Poor regulation of dopamine pathways has been associated with schizophrenia.

Psychosurgery

In the early 20th century, a medical treatment for mental illness, first developed by Portuguese neurologist Egas Moniz, involved damaging the pathways connecting the frontal lobe to the limbic system. Frontal lobotomy (sometimes called frontal leucotomy) successfully reduced distress but at the cost of often blunting the subject's emotions, volition and personality. The indiscriminate use of this psychosurgical procedure, combined with the severe side effects and dangerous nature of the operation gained it a bad reputation and the frontal lobotomy has largely died out as a psychiatric treatment.

More precise psychosurgical procedures are still occasionally used, although are now very rare occurrences. They may include procedures such as the anterior capsulotomy (bilateral thermal lesions of the anterior limbs of the internal capsule) or the bilateral cingulotomy (bilateral thermal lesions of the anterior cingulate gyri) and might be used to treat otherwise untreatable obsessional disorders or clinical depression.


Other

Frontal lobes have been found to play a part in impulse control, judgment, language, memory, motor function, problem solving, sexual behavior, socialization and spontaneity.

Developmental aspects

Cognitive maturity associated with adulthood is marked by related maturation of cerebral fibers in the frontal lobes between late teenager years and early adult years. Research by Dr. Arthur Toga, UCLA, found increased myelin in the frontal lobe gray matter of young adults compared to that of teens, whereas gray matter in parietal and temporal lobes was more fully matured by teen years. Typical onset of schizophrenia in early adult years correlates with poorly myelinated and thus inefficient connections between cells in the forebrain.

Assessment of function

Psychological tests that measure frontal lobe function include Finger Tapping, Wisconsin Card Sorting, and measures of verbal and figural fluency.

Theories of function

Theories of frontal lobe function can be differentiated into four categories:

  • Single-process theories. Posit "that damage to a single process or system is responsible for a number of different dysexecutive symptoms” (Burgess, 2003, p. 309).
  • Multi-process theories. Propose “that the frontal lobe executive system consists of a number of components that typically work together in everyday actions [(heterogeneity of function)]“ (Burgess, 2003, p. 310).
  • Construct-led theories. Assume “that most if not all frontal functions can be explained by one construct (homogeneity of function) such as working memory or inhibition” (Stuss, 1999, p. 348; cf. Burgess & Simons, 2005).
  • Single-symptom theories. Suggest that a specific dysexecutive symptom (e.g., confabulation) is related to the processes and construct of the underlying structures (cf. Burgess & Simons, 2005)

Stuss (1999) suggests a differentiation into two categories according to homogeneity and heterogeneity of function.

Further theoretical approaches to frontal lobe function include:

  • Grafman's managerial knowledge units (MKU) / structured event complex (SEC) approach (cf. Wood & Grafman, 2003)
  • Miller & Cohen's integrative theory of prefrontal functioning (e.g. Miller & Cohen, 2001)
  • Rolls's stimulus-reward approach and Stuss's anterior attentional functions (Burgess & Simons, 2005; Burgess, 2003; Burke, 2007).

It may be highlighted that the theories described above differ in their focus on certain processes/systems or construct-lets. Stuss (1999) remarks that the question of homogeneity (single construct) or heterogeneity (multiple processes/systems) of function “may represent a problem of semantics and/or incomplete functional analysis rather than an unresolvable dichotomy” (p. 348). However, further research will show if a unified theory of frontal lobe function that fully accounts for the diversity of functions will be available.

Studies of frontal lobe damage

Main article: Studies of frontal lobe damage See also: Frontal lobe injury, Frontal lobe lesions

and Frontal lobe disorders

Evolution

For many years, many scientists thought that the frontal lobe was disproportionately enlarged in humans compared to other primates. They thought that this was an important feature of human evolution and was the primary reason why human cognition is different from that of the other primates. However, this view has been challenged by newer research. Using magnetic resonance imaging to determine the volume of the frontal cortex in humans, all extant ape species and several monkey species, Semendeferi et al. found that the human frontal cortex was not relatively larger than the cortex in the other great apes but was relatively larger than the frontal cortex in the lesser apes and the monkeys.[4]

Additional images

See also

References

  1. Giedd, Jay N. (October 1999). Brain Development during childhood and adolescence: a longitudinal MRI study. Nature Neuroscience 2 (10): 861–863.[dead link]
  2. Fjell, A. M., Walhovd, K. B., Fennema-Notestine, C., McEvoy, L. K., Hagler, D. J., Holland, D., & ... Dale, A. M. (2009). One-year brain atrophy evident in healthy aging. The Journal Of Neuroscience, 29(48), 15223-15231.
  3. Coffey, C., Wilkinson, W., Parashos, I., Soady, S., Sullivan, R., Patterson, L., & Djang, W. (1992). Quantitative cerebral anatomy of the aging human brain: a cross-sectional study using magnetic resonance imaging. Neurology, 42(3 Pt 1), 527-536.
  4. K. Semendeferi, A. Lu, S. K. GoVredi, N. Schenker, and H. Damasio (2002). Humans and great apes share a large frontal cortex. Nature Neuroscience 5 (3): 272–276.

Further reading

Key texts

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Telencephalon (cerebrum, cerebral cortex, cerebral hemispheres) - edit

primary sulci/fissures: medial longitudinal, lateral, central, parietoöccipital, calcarine, cingulate

frontal lobe: precentral gyrus (primary motor cortex, 4), precentral sulcus, superior frontal gyrus (6, 8), middle frontal gyrus (46), inferior frontal gyrus (Broca's area, 44-pars opercularis, 45-pars triangularis), prefrontal cortex (orbitofrontal cortex, 9, 10, 11, 12, 47)

parietal lobe: postcentral sulcus, postcentral gyrus (1, 2, 3, 43), superior parietal lobule (5), inferior parietal lobule (39-angular gyrus, 40), precuneus (7), intraparietal sulcus

occipital lobe: primary visual cortex (17), cuneus, lingual gyrus, 18, 19 (18 and 19 span whole lobe)

temporal lobe: transverse temporal gyrus (41-42-primary auditory cortex), superior temporal gyrus (38, 22-Wernicke's area), middle temporal gyrus (21), inferior temporal gyrus (20), fusiform gyrus (36, 37)

limbic lobe/fornicate gyrus: cingulate cortex/cingulate gyrus, anterior cingulate (24, 32, 33), posterior cingulate (23, 31),
isthmus (26, 29, 30), parahippocampal gyrus (piriform cortex, 25, 27, 35), entorhinal cortex (28, 34)

subcortical/insular cortex: rhinencephalon, olfactory bulb, corpus callosum, lateral ventricles, septum pellucidum, ependyma, internal capsule, corona radiata, external capsule

hippocampal formation: dentate gyrus, hippocampus, subiculum

basal ganglia: striatum (caudate nucleus, putamen), lentiform nucleus (putamen, globus pallidus), claustrum, extreme capsule, amygdala, nucleus accumbens

Some categorizations are approximations, and some Brodmann areas span gyri.

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