Uncinate fasciculus
Encyclopedia
The uncinate fasciculus is a white matter
tract in the human brain
that connects parts of the limbic system
such as the hippocampus
and amygdala
in the temporal lobe
with frontal ones such as the orbitofrontal cortex
. Its function is unknown though it is affected in several psychiatric conditions. It is the last white matter tract to mature in the human brain.
and the lower surfaces of the frontal lobe
. It does this by arising lateral to the amygdala
and hippocampus
in the temporal lobe
curving in an upward pathway behind the external capsule
inward of the insular cortex
and continuing up into the posterior part of the orbital gyrus
.
The average length of the uncinate fasciculus is 45 mm with a range 40–49 mm. Its volume in adults is 1425.9±138.6 mm3, being slightly larger in men, at 1504.3±150.4, than women 1378.5±107.4.
It has three parts: a ventral or frontal extension, an intermediary segment called the isthmus or insular segment and a temporal or dorsal segment.
.
The uncinate fasciculus on the left side shows greater fractional anisotropy
(a measure of microstructural integrity) than on the right, and this has been argued to possibly link to the left hemispheric specialization for language. However, the use of electrical brain stimulation
upon it fails to disrupt language, suggesting it might not be involved in language, though it is possible that this disruption failed to happen because it was functionally compensated by alternative pathways.
The capacity for autonoetic self awareness that is re-experiencing previous events as part of one's past as a continuous entity across time has been linked to the right uncinate fasciculus as has proficiency in auditory-verbal memory and declarative memory
to the integrity of the left uncinate fasciculus.
It seems to be developmentally vulnerable. In 12 year-old males that were preterm, abnormalities measured by fractional anisotropy in the left anterior uncinate correlated with verbal IQ, full-scale IQ
, and Peabody Picture Vocabulary Test
-Revised scores. In 10 year-old children who have suffered socioemotional deprivation, the left uncinate fasciculus shows reduced fractional anisotropy compared to that in other children, and this might underlie their cognitive, socioemotional, and behavioral difficulties.
, Alzheimer's disease
, bipolar disorder
, and depression in the elderly that had first had it in adolescence or early adulthood.
Such abnormalities also link to schizophrenia
, In those with schizotypal personality disorder
, reduced fractional anisotropy in the right uncinate fasciculus associates personality traits and clinical symptoms of ideas of reference
, suspiciousness, restricted affect, reduced extraversion and social anxiety
, while those on the left side associate with general intelligence, verbal and visual memory, and executive performance. The greater left than right fractional anisotropy of the uncinate fasciculus is missing in those with schizophrenia.
In 2009 it was implicated in psychopathy
—individuals with a high score in the Psychopathy Checklist Revised and an associated history of violent behavior appeared to have abnormalities in it.
White matter
White matter is one of the two components of the central nervous system and consists mostly of myelinated axons. White matter tissue of the freshly cut brain appears pinkish white to the naked eye because myelin is composed largely of lipid tissue veined with capillaries. Its white color is due to...
tract in the human brain
Human brain
The human brain has the same general structure as the brains of other mammals, but is over three times larger than the brain of a typical mammal with an equivalent body size. Estimates for the number of neurons in the human brain range from 80 to 120 billion...
that connects parts of the limbic system
Limbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
such as the hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
and amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
in the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
with frontal ones such as the orbitofrontal cortex
Orbitofrontal cortex
The orbitofrontal cortex is a prefrontal cortex region in the frontal lobes in the brain which is involved in the cognitive processing of decision-making...
. Its function is unknown though it is affected in several psychiatric conditions. It is the last white matter tract to mature in the human brain.
Anatomy
The uncinate fasciculus is a hook-shaped bundle that links the forward portions of the temporal lobe with the inferior frontal gyrusInferior frontal gyrus
The inferior frontal gyrus is a gyrus of the frontal lobe . It is labelled gyrus frontalis inferior, its Latin name...
and the lower surfaces of the frontal lobe
Frontal lobe
The frontal lobe is an area in the brain of humans and other mammals, located at the front of each cerebral hemisphere and positioned anterior to the parietal lobe and superior and anterior to the temporal lobes...
. It does this by arising lateral to the amygdala
Amygdala
The ' are almond-shaped groups of nuclei located deep within the medial temporal lobes of the brain in complex vertebrates, including humans. Shown in research to perform a primary role in the processing and memory of emotional reactions, the amygdalae are considered part of the limbic system.-...
and hippocampus
Hippocampus
The hippocampus is a major component of the brains of humans and other vertebrates. It belongs to the limbic system and plays important roles in the consolidation of information from short-term memory to long-term memory and spatial navigation. Humans and other mammals have two hippocampi, one in...
in the temporal lobe
Temporal lobe
The temporal lobe is a region of the cerebral cortex that is located beneath the Sylvian fissure on both cerebral hemispheres of the mammalian brain....
curving in an upward pathway behind the external capsule
External capsule
The external capsule is a series of white matter fiber tracts in the brain. These fibers run between the most lateral segment of the lentiform nucleus and the claustrum....
inward of the insular cortex
Insular cortex
In each hemisphere of the mammalian brain the insular cortex is a portion of the cerebral cortex folded deep within the lateral sulcus between the temporal lobe and the frontal lobe. The cortical area overlying it towards the lateral surface of the brain is the operculum...
and continuing up into the posterior part of the orbital gyrus
Gyrus rectus
The portion of the frontal lobe medial to the medial orbital gyrus is named the gyrus rectus , and is continuous with the superior frontal gyrus on the medial surface....
.
The average length of the uncinate fasciculus is 45 mm with a range 40–49 mm. Its volume in adults is 1425.9±138.6 mm3, being slightly larger in men, at 1504.3±150.4, than women 1378.5±107.4.
It has three parts: a ventral or frontal extension, an intermediary segment called the isthmus or insular segment and a temporal or dorsal segment.
Function
The function of the uncinate fasciculus is not known, though it is traditionally considered to be part of the limbic systemLimbic system
The limbic system is a set of brain structures including the hippocampus, amygdala, anterior thalamic nuclei, septum, limbic cortex and fornix, which seemingly support a variety of functions including emotion, behavior, long term memory, and olfaction. The term "limbic" comes from the Latin...
.
The uncinate fasciculus on the left side shows greater fractional anisotropy
Fractional anisotropy
Fractional anisotropy is a scalar value between zero and one that describes the degree of anisotropy of a diffusion process. A value of zero means that diffusion is isotropic, i.e. it is unrestricted in all directions. A value of one means that diffusion occurs only along one axis and is fully...
(a measure of microstructural integrity) than on the right, and this has been argued to possibly link to the left hemispheric specialization for language. However, the use of electrical brain stimulation
Electrical brain stimulation
Electrical brain stimulation , also referred to as focal brain stimulation , is a form of electrotherapy and technique used in research and clinical neurobiology to stimulate a neuron or neural network in the brain through the direct or indirect excitation of its cell membrane by using an electric...
upon it fails to disrupt language, suggesting it might not be involved in language, though it is possible that this disruption failed to happen because it was functionally compensated by alternative pathways.
The capacity for autonoetic self awareness that is re-experiencing previous events as part of one's past as a continuous entity across time has been linked to the right uncinate fasciculus as has proficiency in auditory-verbal memory and declarative memory
Declarative memory
Declarative memory is one of two types of long term human memory. It refers to memories which can be consciously recalled such as facts and knowledge. Its counterpart is known as non-declarative or Procedural memory, which refers to unconscious memories such as skills...
to the integrity of the left uncinate fasciculus.
Development
The uncinate fasciculus has the longest period of development in terms of fractional anisotropy as it alone amongst the major white fibre tracks continues to develop beyond the age of 30It seems to be developmentally vulnerable. In 12 year-old males that were preterm, abnormalities measured by fractional anisotropy in the left anterior uncinate correlated with verbal IQ, full-scale IQ
Wechsler Adult Intelligence Scale
The Wechsler Adult Intelligence Scale intelligence quotient tests are the primary clinical instruments used to measure adult and adolescent intelligence. The original WAIS was published in February 1955 by David Wechsler, as a revision of the Wechsler-Bellevue Intelligence Scale...
, and Peabody Picture Vocabulary Test
Peabody Picture Vocabulary Test
The PPVT-IV, updated in 2007, is an untimed, individual intelligence test. The test measures an individual's receptive vocabulary for Standard American English and provides a quick estimate of their verbal ability or scholastic aptitude. It was created in 1959 by two pioneers in special education,...
-Revised scores. In 10 year-old children who have suffered socioemotional deprivation, the left uncinate fasciculus shows reduced fractional anisotropy compared to that in other children, and this might underlie their cognitive, socioemotional, and behavioral difficulties.
Clinical significance
Abnormalities within the fiber bundles of the uncinate fasciculus associate with social anxietySocial anxiety
Social anxiety is anxiety about social situations, interactions with others, and being evaluated or scrutinized by other people...
, Alzheimer's disease
Alzheimer's disease
Alzheimer's disease also known in medical literature as Alzheimer disease is the most common form of dementia. There is no cure for the disease, which worsens as it progresses, and eventually leads to death...
, bipolar disorder
Bipolar disorder
Bipolar disorder or bipolar affective disorder, historically known as manic–depressive disorder, is a psychiatric diagnosis that describes a category of mood disorders defined by the presence of one or more episodes of abnormally elevated energy levels, cognition, and mood with or without one or...
, and depression in the elderly that had first had it in adolescence or early adulthood.
Such abnormalities also link to schizophrenia
Schizophrenia
Schizophrenia is a mental disorder characterized by a disintegration of thought processes and of emotional responsiveness. It most commonly manifests itself as auditory hallucinations, paranoid or bizarre delusions, or disorganized speech and thinking, and it is accompanied by significant social...
, In those with schizotypal personality disorder
Schizotypal personality disorder
Schizotypal personality disorder, or simply schizotypal disorder, is a personality disorder that is characterized by a need for social isolation, anxiety in social situations, odd behavior and thinking, and often unconventional beliefs.-Genetic:...
, reduced fractional anisotropy in the right uncinate fasciculus associates personality traits and clinical symptoms of ideas of reference
Ideas of reference
Ideas of reference and delusions of reference involve people having a belief or perception that irrelevant, unrelated or innocuous phenomena in the world refer to them directly or have special personal significance: 'the notion that everything one perceives in the world relates to one's own...
, suspiciousness, restricted affect, reduced extraversion and social anxiety
Social anxiety
Social anxiety is anxiety about social situations, interactions with others, and being evaluated or scrutinized by other people...
, while those on the left side associate with general intelligence, verbal and visual memory, and executive performance. The greater left than right fractional anisotropy of the uncinate fasciculus is missing in those with schizophrenia.
In 2009 it was implicated in psychopathy
Psychopathy
Psychopathy is a mental disorder characterized primarily by a lack of empathy and remorse, shallow emotions, egocentricity, and deceptiveness. Psychopaths are highly prone to antisocial behavior and abusive treatment of others, and are very disproportionately responsible for violent crime...
—individuals with a high score in the Psychopathy Checklist Revised and an associated history of violent behavior appeared to have abnormalities in it.