| Frontal lobe | |
|---|---|
Principal fissures and lobes of thecerebrum viewed laterally (Frontal lobe is shown in blue.). | |
 | |
| Details | |
| Part of | Cerebrum |
| Artery | Anterior cerebral Middle cerebral |
| Identifiers | |
| Latin | lobus frontalis |
| Acronym(s) | FL |
| MeSH | D005625 |
| NeuroNames | 56 |
| NeuroLex ID | birnlex_928 |
| TA98 | A14.1.09.110 |
| TA2 | 5445 |
| FMA | 61824 |
| Anatomical terms of neuroanatomy | |
Thefrontal lobe is the largest of the four majorlobes of the brain inmammals, and is located at the front of eachcerebral hemisphere (in front of theparietal lobe and thetemporal lobe). It is parted from the parietal lobe by agroove between tissues called thecentral sulcus and from the temporal lobe by a deeper groove called thelateral sulcus (Sylvian fissure). The most anterior rounded part of the frontal lobe (though not well-defined) is known as the frontal pole, one of the threepoles of the cerebrum.[1]
The frontal lobe is covered by thefrontal cortex.[2] The frontal cortex includes thepremotor cortex and theprimary motor cortex – parts of themotor cortex. The front part of the frontal cortex is covered by theprefrontal cortex. Thenonprimary motor cortex is a functionally defined portion of the frontal lobe.
There are four principalgyri in the frontal lobe. Theprecentral gyrus is directly anterior to thecentral sulcus, running parallel to it and contains the primary motor cortex, which controls voluntary movements of specific body parts. Three horizontally arranged subsections of thefrontal gyrus are thesuperior frontal gyrus, themiddle frontal gyrus, and theinferior frontal gyrus. The inferior frontal gyrus is divided into three parts – theorbital part, thetriangular part and theopercular part.[3]
The frontal lobe contains most of thedopaminergic neurons in thecerebral cortex. Thedopaminergic pathways are associated withreward,attention,short-term memory tasks,planning, andmotivation.Dopamine tends to limit and selectsensory information coming from thethalamus to theforebrain.[4]
The frontal lobe is the largest lobe of the brain and makes up about a third of the surface area of each hemisphere.[3] On thelateral surface of each hemisphere, thecentral sulcus separates the frontal lobe from the parietal lobe. Thelateral sulcus separates the frontal lobe from thetemporal lobe.
The frontal lobe can be divided into a lateral, polar, orbital (above theorbit; also called basal orventral), andmedial part. Each of these parts consists of a particulargyrus:
The gyri are separated bysulci. E.g., the precentral gyrus is in front of the central sulcus, and behind theprecentral sulcus. The superior and middle frontal gyri are divided by thesuperior frontal sulcus. The middle and inferior frontal gyri are divided by theinferior frontal sulcus.
In humans the frontal lobe reaches full maturity only after the 20s—the prefrontal cortex, in particular, continues in maturing 'til the second and third decades of life[5]—which, thereafter, marks the cognitive maturity associated with adulthood. A small amount ofatrophy, 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 usingMRI. Their results were compared to those of 122 participants withAlzheimer's disease. Afollow-up one year later showed there to have been a marked volumetric decline in those with Alzheimer's and a much smaller decline (averaging 0.5%) in the healthy group.[6] These findings corroborate those of Coffey, who in 1992 indicated that the frontal lobe decreases in volume approximately 0.5–1% per year.[7]
The entirety of the frontal cortex can be considered the "action cortex", much as theposterior cortex is considered the "sensory cortex". It is devoted to action of one kind or another: skeletal movement, ocular movement, speech control, and the expression of emotions. In humans, the largest part of the frontal cortex, theprefrontal cortex (PFC), is responsible for internal, purposeful mental action, commonly called reasoning orprefrontal synthesis.
The function of the PFC involves the ability to project future consequences that result from current actions. PFC functions also include override and suppression of socially unacceptable responses as well as differentiation of tasks.
The PFC also plays an important part in integrating longer non-task based memories stored across the brain. These are often memories associated with emotions derived from input from the brain'slimbic system. The frontal lobe modifies those emotions, generally to fit socially acceptable norms.[citation needed]
Psychological tests that measure frontal lobe function includefinger tapping (as the frontal lobe controls voluntary movement), theWisconsin Card Sorting Test, and measures oflanguage,numeracy skills,[8] and decision making,[9] all of which are controlled by the frontal lobe.
Damage to the frontal lobe can occur in a number of ways and result in many different consequences.Transient ischemic attacks (TIAs) also known as mini-strokes, andstrokes are common causes of frontal lobe damage in older adults (65 and over). These strokes and mini-strokes can occur due to the blockage ofblood flow to the brain or as a result of the rupturing of ananeurysm in acerebral artery. Other ways in which injury can occur includetraumatic brain injuries incurred following accidents, diagnoses such asAlzheimer's disease orParkinson's disease (which causedementia symptoms), andfrontal lobe epilepsy (which can occur at any age).[10] Very often, frontal lobe damage is recognized in those withprenatal alcohol exposure.
Common effects of damage to the frontal lobe are varied. Patients who have experienced frontal lobe trauma may know the appropriate response to a situation but display inappropriate responses to those same situations in real life[citation needed]. Similarly, emotions that are felt may not be expressed in the face or voice. For example, someone who is feeling happy would not smile, and the voice would be devoid of emotion. Along the same lines, though, the person may also exhibit excessive, unwarranted displays of emotion. Depression is common in stroke patients. Also common is a loss of or decrease in motivation. Someone might not want to carry out normal daily activities and would not feel "up to it".[10] Those who are close to the person who has experienced the damage may notice changes in behavior.[11] The case ofPhineas Gage was long considered exemplary of these symptoms, though morerecent research has suggested that accounts of his personality change have been poorly evidenced. The frontal lobe is the same part of the brain that is responsible forexecutive functions such as planning for the future, judgment, decision-making skills,attention span, and inhibition. These functions can decrease in someone whose frontal lobe is damaged.[10]
Consequences that are seen less frequently are also varied.Confabulation may be the most frequently indicated "less common" effect. In the case of confabulation, someone gives false information while maintaining the belief that it is the truth. In a small number of patients, uncharacteristic cheerfulness can be noted. This effect is seen mostly in patients with lesions to the right frontal portion of the brain.[10][12]
Another infrequent effect is that ofreduplicative paramnesia, in which patients believe that the location in which they currently reside is a replica of one located somewhere else. Similarly, those who experienceCapgras syndrome after frontal lobe damage believe that an identical "replacement" has taken the identity of a close friend, relative, or other person and is posing as that person. This last effect is seen mostly in schizophrenic patients who also have a neurological disorder in the frontal lobe.[10][13]
In the human frontal cortex, a set of genes undergo reduced expression after age 40 and especially after age 70.[14] This set includes genes that have key functions insynaptic plasticity important in learning and memory,vesicular transport andmitochondrial function. Duringaging,DNA damage is markedly increased in thepromoters of the genes displaying reduced expression in the frontal cortex. In cultured human neurons, these promoters are selectively damaged by oxidative stress.[14]
Individuals withHIV associated neurocognitive disorders accumulate nuclear andmitochondrial DNA damage in the frontal cortex.[15]
A report from theNational Institute of Mental Health says agene variant of(COMT) that reduces dopamine activity in theprefrontal cortex is related to poorer performance and inefficient functioning of that brain region during working memory, tasks, and to a slightly increased risk forschizophrenia.[16]
In the early 20th century, a medical treatment formental illness, first developed byPortugueseneurologistEgas Moniz, involved damaging the pathways connecting the frontal lobe to thelimbic system. A frontallobotomy (sometimes called frontal leucotomy) successfully reduced distress but at the cost of often blunting the subject's emotions, volition andpersonality. The indiscriminate use of thispsychosurgical procedure, combined with its severe side effects and amortality rate of 7.4 to 17 per cent,[17] earned it a bad reputation. The frontal lobotomy has largely died out as a psychiatric treatment. More precise psychosurgical procedures are still used, although rarely. They may include anterior capsulotomy (bilateral thermal lesions of the anterior limbs of theinternal capsule) or thebilateral cingulotomy (involving lesions of the anteriorcingulate gyri) and might be used to treat otherwise untreatableobsessional disorders orclinical depression.
Theories of frontal lobe function can be separated into four categories:
Other theories include:
It may be highlighted that the theories described above differ in their focus on certain processes/systems or construct-lets.[clarification needed] 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.
Many scientists had thought that the frontal lobe was disproportionately enlarged in humans compared to other primates. This was thought to be an important feature of human evolution and seen as the primary reason why human cognition differs from that of other primates. However, this view in relation to great apes has since been challenged byneuroimaging studies. Usingmagnetic resonance imaging to determine the volume of the frontal cortex in humans, all extant ape species, and severalmonkey species, it was found that the human frontal cortex was not relatively larger than the cortex of othergreat apes, but was relatively larger than the frontal cortex oflesser apes and the monkeys.[22] The higher cognition of the humans is instead seen to relate to a greater connectedness given byneural tracts that do not affect the cortical volume.[22] This is also evident in thepathways of thelanguage network connecting the frontal and temporal lobes.[23]
