Neuroanatomy, Temporal Lobe

Article Author:
Anand Patel
Article Editor:
James Fowler
Updated:
1/28/2019 8:56:12 AM
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Neuroanatomy, Temporal Lobe

Introduction

The temporal lobe of the brain is often referred to as the neocortex. It forms the cerebral cortex in conjunction with the occipital lobe, the parietal lobe, and the frontal lobe. It is located mainly in the middle cranial fossa, a space located close to the skull base. It is anterior to the occipital lobe and posterior to the frontal lobe. It is found inferior to the lateral fissure, also known as the Sylvian fissure or the lateral sulcus. The temporal lobe subdivides further into the superior temporal lobe, the middle temporal lobe, and the inferior temporal lobe. It houses several critical brain structures including the hippocampus and the amygdala.

Structure and Function

The primary functions of the temporal lobe are to process sensory information and derive it into meaningful memories, language, and emotions. The temporal lobe is responsible primarily for declarative memory, which is memory that can be said out loud, and is subdivided into episodic (life events) and semantic (fact-like) memory. Located within the middle temporal lobe are the hippocampus and the amygdala. The hippocampus manages the formation of new memories and the conversion of short-term memories into long-term ones. The hippocampus communicates closely with the amygdala, which is responsible for the processing of emotions.

The temporal lobe also plays an essential role in processing sounds. It houses the primary auditory cortex and the superior temporal gyrus. The primary auditory cortex can process input from the ears into meaningful units like words and sentences. The sounds we hear first enter the brain in an area within the superior temporal gyrus traveling from the cochlea.

Parts of the temporal lobe aid in processing visual stimuli, primarily to allow us to recognize objects. The fusiform gyrus distinguishes faces, and the parahippocampal gyrus identifies locations and landscapes.

A specialized area of the temporal lobe, known as the Wernicke area, is found on the dominant hemisphere. It is responsible for processing written and spoken language.

Embryology

The development of the temporal lobe, part of the forebrain, is linked closely to the development of the cerebral cortex. The embryonic ectoderm contains a specialized part known as the neural plate. The neural plate folds to create the neural tube. The neural tube houses the four ventricles, which are closed spaces containing cerebrospinal fluid, within the brain. The most anterior portion of the neural plate, the prosencephalon, eventually forms the cerebral cortex. At about three and a half weeks' gestation, the three portions of the brain become apparent from the neural plate. These portions include the prosencephalon, mesencephalon, and rhombencephalon. At about six weeks, a bend in the neural plate is visible. At seven weeks, the hemispheres of the brain start to become apparent. At fourteen weeks, the hemispheres are clearly visible, and at five months they have grown to occupy most of the brain. At eight months, the characteristic gyri and sulci, the ridges and valleys, of the cerebral cortex become clear.

Blood Supply and Lymphatics

The temporal lobe receives oxygenated blood via two primary sources, the internal carotid system and the vertebrobasilar artery. The internal carotid system contains the anterior choroidal artery and the middle cerebral artery. The blood flow from the anterior choroidal artery supplies the uncus, amygdala, and the anterior parahippocampal gyrus. The middle cerebral artery branches into the temporopolar artery, anterior temporal artery, middle temporal artery, and posterior temporal artery. It supplies the temporal pole as well as the superior and inferior portions of the temporal gyri. Blood flow from the vertebrobasilar system supplies the inferior surface of the temporal lobe from the temper-occipital artery.

Blood is drained from the temporal lobe by veins via two major routes. One route involves blood passing from the temporal lobe anteriorly to superficial middle cerebral vein. From there, it moves into the inferior anastomotic vein, known as the vein of Labbe, which goes on to join the transverse sinus. The other route involves blood flowing from the interior temporal lobe into the posterior choroidal vein. This vessel then pairs up with the thalamostriate vein from behind the interventricular foramen to form the internal cerebral vein. The internal cerebral vein then joins the basal veins to create the great cerebral vein.[1]

Surgical Considerations

The temporal lobe is crucial in many essential activities such as processing of memory, language, and emotion. Therefore, surgery must be performed with due care so as not to affect the critical functions performed by the temporal lobe negatively.

Despite the risk associated with surgery of and around the temporal lobe, it is often performed to treat temporal lobe epilepsy. In this condition, patients suffer seizures originating in the temporal lobe. Physicians can remove a section of the lobe to eliminate or significantly reduce the number of seizures. Using different functional tests including Wada, functional MRI, and neuropsychological evaluations minimizes the risk of the procedure. These tests confirm critical sections of the brain and help draw surgical boundaries. Due to the use of these precautionary measures, the surgery is both effective and safe. A study of 215 patients who had temporal lobe surgery showed that 89% were either seizure-free or experienced a significantly reduced average number of seizures. No postoperative mortality was observed.[2]

Clinical Significance

Uncontrolled damage to the temporal lobe poses a significant threat to the quality of a patient's life. A review of 56 localized lesions to the temporal lobe showed widespread effects on patient lives. The most common symptoms observed are mental disturbances generally categorized as a confused state. The secondary ailment of temporal lesions is personality changes, which ranges widely from slight emotional changes to homicidal tendencies. Of lesser frequency but still reported include symptoms of muscular pareses, somatic seizures, psychical seizures, autonomic seizures, visual field defects, and speech disorders.[3]

Wernicke aphasia is one clinical presentation of damage to the temporal lobe. It is seen often in patients who have suffered an ischemic stroke to the temporal lobe. Less frequently, it affects patients with infections, trauma, tumors, central nervous system infections, and other degenerative brain conditions. Wernicke aphasia, also known as receptive aphasia, impairs language function. Patients presenting with this aphasia can still speak with normal rate and tone but will often misuse words and form nonsensical sentences. This aphasia is in contrast to Broca aphasia in which patients cannot talk with normal fluency and tone.


References

[1] Kiernan JA, Anatomy of the temporal lobe. Epilepsy research and treatment. 2012     [PubMed PMID: 22934160]
[2] Salanova V,Markand O,Worth R, Temporal lobe epilepsy surgery: outcome, complications, and late mortality rate in 215 patients. Epilepsia. 2002 Feb     [PubMed PMID: 11903464]
[3] WYKE BD, Surgical considerations of the temporal lobes; a clinical report based on a study of fifty-six verified localised lesions of the temporal lobes. Annals of the Royal College of Surgeons of England. 1958 Feb     [PubMed PMID: 13509566]