neuroanatomy Neuroanatomy is the study of the structure and organization of the nervous system. In contrast to animals with radial symmetry, whose nervous system consists of a distributed network of cells, animals with bilateral symmetry have segregated, defi ...

, the optic radiation (also known as the geniculocalcarine tract, the geniculostriate pathway, and posterior thalamic radiation) are

axon An axon (from Greek ἄξων ''áxōn'', axis) or nerve fiber (or nerve fibre: see American and British English spelling differences#-re, -er, spelling differences) is a long, slender cellular extensions, projection of a nerve cell, or neuron, ...

s from the

neuron A neuron (American English), neurone (British English), or nerve cell, is an membrane potential#Cell excitability, excitable cell (biology), cell that fires electric signals called action potentials across a neural network (biology), neural net ...

s in the

lateral geniculate nucleus In neuroanatomy, the lateral geniculate nucleus (LGN; also called the lateral geniculate body or lateral geniculate complex) is a structure in the thalamus and a key component of the mammalian visual pathway. It is a small, ovoid, Anatomical ter ...

to the

primary visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalamus ...

. The optic radiation receives blood through deep branches of the

middle cerebral artery The middle cerebral artery (MCA) is one of the three major paired cerebral artery, cerebral arteries that supply blood to the cerebrum. The MCA arises from the internal carotid artery and continues into the lateral sulcus where it then branches an ...

and

posterior cerebral artery The posterior cerebral artery (PCA) is one of a pair of cerebral arteries that supply oxygenated blood to the occipital lobe, as well as the medial and inferior aspects of the temporal lobe of the human brain. The two arteries originate from the d ...

. They carry visual information through two divisions (called upper and lower division) to the

visual cortex The visual cortex of the brain is the area of the cerebral cortex that processes visual information. It is located in the occipital lobe. Sensory input originating from the eyes travels through the lateral geniculate nucleus in the thalam ...

(also called ''striate cortex'') along the

calcarine fissure The calcarine sulcus (or calcarine fissure) is an anatomical landmark located at the caudal end of the medial surface of the brain of humans and other primates. Its name comes from the Latin "calcar" meaning "spur". It is very deep, and known as ...

. There is one set of upper and lower divisions on each side of the

brain The brain is an organ (biology), organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It consists of nervous tissue and is typically located in the head (cephalization), usually near organs for ...

. If a

lesion A lesion is any damage or abnormal change in the tissue of an organism, usually caused by injury or diseases. The term ''Lesion'' is derived from the Latin meaning "injury". Lesions may occur in both plants and animals. Types There is no de ...

only exists in one unilateral division of the optic radiation, the consequence is called

quadrantanopia Quadrantanopia, quadrantanopsia, refers to an anopia (loss of vision) affecting a quarter of the visual field. It can be associated with a lesion of an optic radiation. While quadrantanopia can be caused by lesions in the Temporal lobe, tempora ...

, which implies that only the respective superior or inferior quadrant of the visual field is affected. If both divisions on one side of the brain are affected, the result is a contralateral homonymous hemianopsia.

Structure

The upper division: :* Projects to the upper bank of the

, called the

cuneus The cuneus (; : cunei) is a smaller lobe in the occipital lobe of the brain. The cuneus is bounded anteriorly by the parieto-occipital sulcus and Inferior (anatomy), inferiorly by the calcarine sulcus. Function The cuneus (Brodmann area 17) r ...

:* Contains input from the superior retinal quadrants, which represents the inferior visual field quadrants :* Transection causes contralateral lower quadrantanopia :* Lesions that involve both cunei cause a lower altitudinal hemianopia (altitudinopia) The lower division: :* Loops from the lateral geniculate body anteriorly (Meyer's loop), then posteriorly, to terminate in the lower bank of the calcarine sulcus, called the lingual gyrus :* Contains input from the inferior retinal quadrants, which represents the superior visual field quadrants :* Transection causes contralateral upper quadrantanopia :* Transection of both lingual gyri causes an upper altitudinal hemianopia

Parts

A distinctive feature of the optic radiations is that they split into two parts on each side: *Note: In 2009, an anonymous medical doctor edited the "Optic Radiation" ''Wikipedia'' article and added the eponymous name "Baum's loop," referring to the dorsal bundle. Despite the information being unverified, this name subsequently entered scholarly articles and textbooks and persisted until three radiologists discovered the fabrication in 2020. Right-superior-quadrantanopia

Function

The optic radiation contains feedforward tracts that transmit visual information (from the

retina The retina (; or retinas) is the innermost, photosensitivity, light-sensitive layer of tissue (biology), tissue of the eye of most vertebrates and some Mollusca, molluscs. The optics of the eye create a focus (optics), focused two-dimensional ...

of the eye) from the geniculate nucleus to the

, and also feedback tracts from the visual cortex to the neurons in the LGN that project to them. The function of the feedback from the visual cortex back to the LGN is unknown. The optic radiation is activated during

working memory Working memory is a cognitive system with a limited capacity that can Memory, hold information temporarily. It is important for reasoning and the guidance of decision-making and behavior. Working memory is often used synonymously with short-term m ...

tasks. The optic radiations are usually unilateral and commonly vascular in origin. Field defects, therefore, develop abruptly, in contrast to the slow progression of defects associated with tumors.

Clinical significance

Examination

Tracts contained within the optic radiation are examined as part of a

cranial nerve examination The cranial nerve exam is a type of neurological examination. It is used to identify problems with the cranial nerves by physical examination. It has nine components. Each test is designed to assess the status of one or more of the twelve cranial ...

References

External links

* * https://web.archive.org/web/20070512234857/http://www2.umdnj.edu/~neuro/studyaid/Practical2000/Q34.htm
A 3D model of optic tract and optic radiation
{{DEFAULTSORT:Optic Radiation Visual system Thalamus