Lobes of the brain

Location

The frontal lobe is the largest lobe of the brain comprising almost one-third of the hemispheric surface. It lies largely in the anterior cranial fossa of the skull, leaning on the orbital plate of the frontal bone. 

The frontal lobe forms the most anterior portion of the cerebral hemisphere and is separated from the parietal lobe posteriorly by the central sulcus, and from the temporal lobe posteroinferiorly by the lateral sulcus (Sylvian fissure). The most anterior portion of the frontal lobe is known as the frontal pole.

Components and function

The frontal lobe is made up of three cortical surfaces: a lateral, medial and inferior surface. 

• The lateral surface of the frontal lobe contains four principal gyri: the precentral, superior frontal, middle frontal, and the inferior frontal gyri. 
• The medial (interhemispheric) surface extends down to the cingulate sulcus and consists mainly of the paracentral lobule (an extension of the precentral and postcentral gyri), and the medial extension of the superior frontal gyrus.
• The inferior surface contains the olfactory tract and olfactory bulb, the straight gyrus and the four orbital gyri.

Functionally, the entire frontal cortex of the frontal lobe is divided into three parts: the prefrontal cortex, motor cortex and Broca’s area.

Prefrontal cortex

The most rostral portion of the frontal cortex is known as the prefrontal cortex, which encompasses the superior, middle and inferior frontal gyri of the frontal lobe. It plays a crucial role in the processing of intellectual and emotional information, including aggression, and facilitates judgement and decision-making.

Motor cortex

The motor cortex corresponds to the precentral gyrus of the frontal lobe. The precentral gyrus contains the primary motor cortex (Brodmann area 4), which is responsible for integrating signals from different brain regions to modulate motor function. The primary motor cortex is where the corticospinal tract originates. 

Anterior to the primary motor cortex of the precentral gyrus is the premotor area, or premotor cortex (Brodmann area 6), and the supplemental motor cortex. These regions of the cortex occupy the anterior part of the precentral gyrus and the posterior parts of the superior, middle, and inferior frontal gyri. Collectively, they function to assist in organizing movements and actions.

Encompassing part of the middle and inferior frontal gyri, just rostral to the premotor region, is an area called the frontal eye fields (Brodmann area 6,8,9), which is responsible for voluntary control of conjugate (horizontal) eye movements.

Broca's area

The inferior frontal gyrus is divided into three parts: i) the pars opercularis, ii) the pars triangularis, and iii) the pars orbitalis. Pars opercularis refers to the most dorsal part of the gyrus, pars triangularis is the middle triangularly-shaped part, while the pars orbitalis represents the most ventral part of the gyrus.

Functionally, the pars opercularis and triangularis in the dominant hemisphere are referred to as  Broca’s speech area (Brodmann area 44 and 45). Broca’s area is responsible for producing the motor component of speech, which includes verbal fluency, phonological processing, grammar processing and attention during speech.

Location

The parietal lobe is located just underneath the parietal bone, lying posterior to the frontal lobe and anterior and superior to the temporal and occipital lobes. 

The anterior border of the parietal lobe is demarcated by the central sulcus, and the posterior border is formed by an imaginary line that extends between the parietooccipital sulcus (superiorly) and the preoccipital notch (inferiorly). The inferior border is formed by the lateral sulcus (Sylvian fissure), while the superior boundary of the parietal lobe ​​is formed by the medial longitudinal fissure that separates the two cerebral hemispheres.

Components and function

The parietal lobe can be divided into three regions. The most anterior portion of the parietal lobe is the postcentral gyrus which runs parallel to the central sulcus. Functionally, this area is known as the primary somatosensory cortex (Brodmann areas 1,2 and 3). This region receives sensory information from all sensory receptors that provide information related to temperature, pain (spinothalamic pathway), vibration, proprioception and fine touch (dorsal column pathway). Thus, the postcentral gyrus of the frontal lobe is mainly involved in processing various types of sensory information.

The remainder of the parietal lobe can be divided into two main regions: the superior and inferior parietal lobules, which are separated anatomically by the intraparietal sulcus. The superior parietal lobule contributes to sensorimotor integration while the inferior parietal lobule contributes to auditory and language functions.

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Location

The temporal 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 is separated from the frontal and parietal lobes superiorly by the lateral sulcus (Sylvian fissure). It extends ventrally from this fissure to the inferior surface of the cerebral cortex. Dorsally, it extends to an arbitrary line running between the parietooccipital sulcus and the preoccipital notch. 

The temporal lobe contains the cortical areas that process hearing, as well as sensory aspects of speech and memory.

Components and function

The temporal lobe consists of three main gyri, the superior, middle and inferior temporal gyri, which are visible on the lateral surface. The superior temporal sulcus separates the superior and middle temporal gyri, while the inferior temporal sulcus separates the middle and inferior temporal gyri. The inferomedial aspect of the temporal lobe forms the hippocampus. 

The primary auditory area ( Brodmann area 41), also known as the transverse gyri of Heschl, is located on the internal, superior part of the superior temporal gyrus. It is a specialized region of cortex primarily responsible for the reception of auditory information. 

Auditory information is further processed within the secondary auditory area. The secondary auditory area (Brodmann area 42) lies posterior to the primary auditory area in the superior temporal gyrus, at the parietotemporal junction (Wernicke’s region in the dominant hemisphere), and receives impulses from the primary auditory area and thalamus. 

Unlike the superior temporal gyrus, the middle and inferior temporal gyri are responsible for visual perception. The middle temporal gyrus is associated with the perception of movement within the visual field; whereas the inferior temporal gyrus contains the fusiform face area (FFA), which is necessary for face recognition.

Now that you are becoming more familiar with identifying structures of the brain from a lateral view. Test your knowledge on the lobes of the brain from a lateral perspective in the quiz below. 

Location

The occipital lobe lies just underneath the occipital bone. It forms the most posterior portion of the brain and is found behind both the parietal and temporal lobes. The occipital lobe lies over the tentorium cerebelli, while its medial surface faces the falx cerebri. 

The occipital lobe is separated superiorly from the parietal lobe by the parietoocccipital sulcus. Anteriorly, it is separated from the temporal lobe by an imaginary line called the lateral parietotemporal line, that extends from the termination of the parietooccipital sulcus superiorly, and to the preoccipital notch inferiorly.

Components and function

There is significant anatomic variability in the sulci and gyri of this lobe. The superolateral aspect of the occipital lobe presents with three notable gyri: the superior, middle and inferior occipital gyri. The superior occipital gyrus is the clearly defined gyrus on the lateral surface of the occipital lobe. The middle and inferior occipital gyri are often indistinct and may be absent. The intraoccipital sulcus, which is formed as an extension of the intraparietal sulcus, separates the superior and middle gyri (if present). The lateral occipital sulcus (also known as the inferior occipital sulcus) separates the inferior occipital gyrus from the superior, or the middle occipital gyrus (if present). 

The surface anatomy of the medial aspect of the occipital lobe is more consistent and clearly defined. A fissure known as the calcarine sulcus begins slightly above the occipital pole just behind the parietooccipital sulcus. The calcarine sulcus divides the medial aspect of the occipital lobe into the cuneate gyrus (cuneus) superiorly and the lingual gyrus inferiorly. 

The calcarine sulcus also marks the location of the primary visual cortex (Brodmann area 17) which is responsible for visual perception. 

The visual association cortex (Brodmann area 18 and 19) constitutes the remaining regions of the occipital lobe and is also known as the extrastriate visual cortex. The visual association cortex functions to interpret visual images. 

The occipital lobe is identified as the main visual processing centre. It is associated with color determination, facial recognition, depth perception, visuospatial processing and even plays a role in memory formation. The occipital lobe not only enables visual perception but allows us to process and interpret visual information.

Location

Deep within the lateral sulcus (Sylvian fissure) is the fifth lobe of the brain, the insular lobe. This lobe is not clearly visible from the outside, but can be viewed when the temporal lobe is retracted from the cortex. The parts of the frontal, parietal and temporal lobes that overlie the insula are known as the opercula.

Composition and function

When the insular operculum is opened, the first structure to be seen is the central sulcus of the insula that divides it into an anterior and a posterior part.

The anterior portion of the insular lobe is formed by three short gyri (anterior, middle and posterior short gyri) and an accessory gyrus. The posterior portion of the insular lobe is formed by two long gyri (anterior and posterior long gyri). 

The insula is associated with processing and integration of various types of information, including taste sensation, visceral sensation, pain sensation, and vestibular function.

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Location

The limbic lobe refers to a region of the cerebral cortex that borders the corpus callosum on the medial aspect of each hemisphere. This medially located lobe surrounds the rim of the ventricles of the brain and can be found just deep to the frontal, parietal and temporal lobes. 

Structures in this region play influential roles in the modulation of emotions, visceral functions, autonomic functions, hormonal functions, and in learning and memory.

Components and function

The structures which comprise the limbic lobe are the paraterminal (subcallosal), cingulate, and parahippocampal gyri, as well as the hippocampal formation. 

The paraterminal gyrus is a small gyrus which sits inferior to the rostrum of the corpus callosum. This gyrus is thought to be involved in depression. 

The cingulate gyrus is a ‘C’ shaped structure that is divided into a prelimbic and an infralimbic cortex, an anterior cingulate and a retrosplenial cortex. It is believed that the cingulate gyrus is strongly associated with the perception of neuropathic pain and nociception.

The parahippocampal gyri can be better appreciated on the inferior surface of the temporal lobe of the cerebrum. This area corresponds with several Brodmann areas such as the entorhinal cortex (Brodmann area 27, 28), and areas 35, 36, 48 and 49. Part of the anterior end of the parahippocampal gyrus projects medially, forming a structure called the uncus. 

The parahippocampal gyrus provides a path of communication between the hippocampus and all cortical association areas through which afferent impulses enter the hippocampus.

Now that you have mastered the 6 lobes of the brain, why not test your knowledge with the quiz below: