The cortex of each cerebral hemisphere consists of five lobes: frontal, parietal, temporal, occipital, and limbic lobes (the insular cortex or insula, a portion of the cerebral cortex folded deep within the lateral sulcus, is also referred in some sources as the insular lobe).
After the frontal lobe, the temporal lobe is the second largest lobe of the brain, accounting for just over 20% of the neocortical volume. This lobe largely occupies the middle cranial fossa and its name relates to its proximity to the temporal region/bone of the skull. The temporal lobe contains the cortical areas that process hearing, as well as sensory aspects of speech and memory.
In this article, we will explore the anatomy and functions of the temporal lobe.
|Middle cranial fossa, next to the temporal region/bone
|Lateral surface: lateral sulcus (superiorly), line between the top of the parietoocipital sulcus and the preoccipital notch (posteriorly)
Inferior surface: collateral sulcus (superiorly), line between the preoccipital notch and the splenium of the corpus callosum (posteriorly)
|Lateral surface: superior, middle and inferior temporal gyri
Inferior surface: inferior temporal gyrus and occipitotemporal (fusiform) gyrus
|Lateral surface: superior and inferior temporal sulci
Inferior surface: collateral sulcus, midfusiform sulcus
|Cortical areas and function
|Primary auditory area (A1): Brodmann area 41
Secondary auditory area (A2): Brodmann area 42
Auditory association area: Brodmann area 22
Wernicke’s area: posterior part of area 22 in dominant hemisphere (comprehension of language)
- Location and boundaries
- Gyri and sulci
- Blood supply
- Medial temporal lobe
- Wernicke's aphasia
Location and boundaries
The temporal lobe is visible on the lateral, medial and basal surfaces of the cerebral hemisphere. On the lateral surface, it is demarcated superiorly by the lateral sulcus (or Sylvian fissure) and extends ventrally to the inferior surface of the cerebrum. Posteriorly, the temporal lobe extends to an arbitrary line running between the top of the parietooccipital sulcus and the preoccipital notch. On the inferior/ medial surfaces, the posterior boundary of the temporal lobe is an imaginary line that extends from the preoccipital notch to the splenium of the corpus callosum. Medially, the temporal lobe is separated from the limbic lobe (specifically the parahippocampal gyrus) by the collateral sulcus.
Gyri and sulci
Lateral surface of the temporal lobe
The lateral surface of the temporal lobe consists of three parallel gyri, the superior (contains Brodmann area 22), middle (area 21) and inferior (area 20) temporal gyri, separated by the superior and inferior temporal sulci. The temporal pole corresponds to the anterior end of the temporal lobe.
The superior temporal sulcus separates the superior and middle temporal gyri. It begins near the temporal pole and courses posteriorly and slightly superiorly, parallel to the lateral sulcus. It ends by curving up into the parietal lobe where it is capped by the angular gyrus. The inferior temporal sulcus separates the middle and inferior temporal gyri. It is parallel to the superior sulcus and its posterior end also ascends into the parietal lobe. The superior temporal gyrus is continuous along its superior margin with the transverse temporal gyri (of Heschl) (area 41, 42) which are buried on the floor of the lateral sulcus and extend anterolaterally from the circular sulcus around the insula.
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Inferior surface of the temporal lobe
The inferior temporal gyrus continues onto the inferior surface of the temporal lobe. The remainder of this surface is composed of the occipitotemporal gyri (a.k.a. fusiform gyrus), which is separated from the limbic lobe (specifically the parahippocampal gyrus) by the collateral sulcus. As their name suggests, the occipitotemporal gyri extend between the temporal and occipital lobes. The two occipitotemporal gyri, namely the medial occipitotemporal gyrus and lateral occipitotemporal gyrus are separated by a sulcus, called the midfusiform sulcus.
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The anterior transverse temporal gyrus (area 41) largely contains the primary auditory area (A1) and the posterior transverse temporal gyrus (area 42) is the secondary auditory area (A2). These areas are specialized parts of the cortex responsible for the reception of auditory information (via the auditory radiations) from the medial geniculate nucleus.
Also on the superior temporal gyrus is Brodmann area 22 which contains the auditory association area. It receives inputs from the primary auditory area and thalamus. This area is responsible for the interpretation of sounds and for the association of the auditory input with other sensory information.
In the posterior part of area 22 (in the posterior portion of the superior temporal gyrus) of the dominant hemisphere (usually the left) is the Wernicke’s area. This area is important in the comprehension of written and spoken language.
Other areas of the temporal lobe
The remainder of the temporal lobe, particularly the inferior surface, contains non auditory association cortex and is involved in the processing of visual information.
The lateral surface of the temporal lobe is supplied primarily by branches of the middle cerebral artery, the larger of the two terminal branches of the internal carotid artery. The inferior surface of the temporal lobe is supplied primarily by branches of the posterior cerebral artery arising from the vertebrobasilar system.
Medial temporal lobe
The medial temporal lobe (or mesial temporal lobe) is, as its name suggests, located on the medial aspect of the temporal lobe. It is in fact distinct from the rest of the temporal lobe, which is formed by neocortex. This term refers to several structures that are part of what is known as the limbic lobe: the amygdala, hippocampus, uncus, dentate gyrus and parahippocampal gyrus. These structures are fundamental in the processes of learning and memory, as well as in the regulation of emotions.
Destructive lesions restricted to the Wernicke's area produce a loss of ability to understand spoken and written language. This kind of aphasia can also be called receptive or fluent aphasia. Since the Broca area, another very important area for language processing, is unaffected, the patient can produce fluent speech. However, the patient is unaware of the meaning of the words used and uses incorrect or even nonexistent words. The affected patient also appears to be unaware of this deficit.
Temporal lobe: want to learn more about it?
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