11.3: Brain - Cerebrum

By the end of this section, you will be able to:

• Name the major regions of the adult brain
• Identify the anatomical structures of the cerebrum
• Identify the tracts associated with the white matter of the cerebrum and describe their functions
• Describe the components of the cerebral nuclei
• Describe the functional areas of the cerebral cortex and their locations

The organs of the central nervous system are the brain and spinal cord. The brain is described in terms of four major regions: the cerebrum, the diencephalon, the brainstem, and the cerebellum (Figure \(\PageIndex{1}\)). The iconic gray mantle of the human brain, which appears to make up most of the mass of the brain, is the cerebrum. Many of the higher neurological functions, such as memory, emotion, and consciousness, are the result of cerebral function. The cerebrum is divided into different regions called lobes. Overall, the functions of the cerebrum are initiation and coordination of movement, processing of general and special senses, and high level functions such as judgment, reasoning, problem solving, and learning.

Figure \(\PageIndex{1}\): Major Brain Regions.  On the external, lateral surface only three of the four major regions are visible: the cerebrum, the brainstem, and the cerebellum.  The diencephalon is deep within the brain and can be seen in both inferior and midsagittal views. (Image credit: "Major Brain Regions" by Justin Greene and Jennifer Lange is licensed under CC BY-NC-SA 4.0)

Cerebrum

The cerebrum is covered by a continuous layer of gray matter that wraps around either side of the forebrain—the cerebral cortex. This thin, extensive region of wrinkled gray matter is responsible for the higher functions of the nervous system. A gyrus (plural = gyri) is the ridge of one of those wrinkles, and a sulcus (plural = sulci) is the groove between two gyri (Figure \(\PageIndex{2}\) and Figure \(\PageIndex{3}\)). The pattern of these folds of tissue indicates specific regions of the cerebral cortex. The brain must fit inside the cranial cavity of the skull. Extensive folding in the cerebral cortex enables more gray matter to fit into this limited space. If the gray matter of the cortex were peeled off of the cerebrum and laid out flat, its surface area would be roughly equal to one square meter. The folding of the cortex maximizes the amount of gray matter in the cranial cavity. During embryonic development, as the telencephalon expands within the skull, the brain goes through a regular course of growth that results in everyone’s brain having a similar pattern of folds.

The surface of the brain can be mapped on the basis of the locations of large gyri and sulci. Three deep sulci are visible: the central sulcus, the lateral fissure (sulcus) and the parietoccipital sulcus. Anterior to the central sulcus is the precentral gyrus, while posterior to the central sulcus is the postcentral gyrus (Figure \(\PageIndex{2}\)). There is a large separation between the two sides of the cerebrum called the longitudinal fissure (Figure \(\PageIndex{3}\)). It separates the cerebrum into two distinct halves, a right and left cerebral hemispheres.

Figure \(\PageIndex{2}\): Cerebrum: Major Gyri and Sulci, Lateral View. The cerebrum presents ridges called gyri and grooves called sulci. The main sulci are the central sulcus, lateral fissure (sulcus) and parieto-occipital sulcus. The gyrus anterior to the central sulcus is called precentral gyrus, while the posterior one is the postcentral gyrus. (Image credit: "Gyrus and Sulcus - Lateral and Midsagittal Views" by Justin Greene and Jennifer Lange is licensed under CC BY-NC-SA 4.0)

Figure \(\PageIndex{3}\): Superior View of the Brain. The cerebrum is medially divided by the longitudinal fissure into left and right hemispheres. The central sulcus is visible cutting the cerebrum in a coronal section. The gyrus anterior to the central sulcus is called precentral gyrus, while the posterior one is the postcentral gyrus.  The enlargement shows a human brain tissue block containing the central sulcus and the two adjacent gyri. (Image credit: "Gyrus and Sulcus - Superior View" by Justin Greene and Jennifer Lange is licensed under CC BY-NC-SA 4.0; inset image: "Pre- and Post-central gyrus" by Geyer S, Weiss M, Reimann K, Lohmann G and Turner R, via Wikimedia Commons, as modified by Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

The cerebrum comprises the outer wrinkled gray matter that is the cerebral cortex (from the Latin word meaning “bark of a tree”), the inner white matter that forms tracts, and several deep (subcortical) nuclei called basal ganglia (Figure \(\PageIndex{4}\)). Deep within the cerebrum, the white matter of the corpus callosum provides the major pathway for communication between the two hemispheres of the cerebral cortex.

Figure \(\PageIndex{4}\): Coronal Section of the Brain. The coronal section shows the layers of the cerebrum. The superficial gray matter is called cerebral cortex, while the deep gray matter is composed of multiple nuclei called the basal ganglia (nuclei). The superficial and deep regions are connected by myelinated axons (white matter) called tracts. These tracts include the corpus callosum and the internal capsule.  The corona radiata contains tracts of multiple fibers leading to and from the cortex. (Image credit: "Brain Coronal Section - Grey and White Matter" by Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

Cerebral Cortex

The cortex can be separated into major regions called lobes (Figure \(\PageIndex{5}\)). The lateral sulcus separates the temporal lobe from the other regions. Deep to the lateral sulcus is another lobe called insula (shown in Figure \(\PageIndex{5}\)). Superior to the lateral sulcus are the parietal lobe and frontal lobe, which are separated from each other by the central sulcus. The posterior region of the cortex is the occipital lobe, which has no obvious anatomical border between it and the parietal or temporal lobes on the lateral surface of the brain. From the medial surface, an obvious landmark separating the parietal and occipital lobes is called the parieto-occipital sulcus (Figure \(\PageIndex{2}\)).

Figure \(\PageIndex{5}\): Lobes of the Cerebral Cortex. The cerebral cortex is divided into four lobes by the major sulci. The central sulcus separates the frontal and parietal lobes. The parieto-occipital sulcus separates the parietal and occipital lobes. The lateral sulcus separated the temporal and parietal lobes. The fifth lobe is the insula which is deep to the frontal and temporal lobes (not shown here). Each lobe corresponds to specific functions of the cerebral cortex. (Image credit: "Lobes of the Cerebral Cortex" by Justin Greene and Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

Figure \(\PageIndex{6}\): Insular Lobe. The insula is one of the five lobes of the cerebral cortex and is located deep in the lateral fissure, between the parietal and temporal lobes. (Image credit: "Insular Lobe - Coronal Section" by Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

DISORDERS OF THE

Cerebral Cortex: Concussion

A concussion, also known as a mild traumatic brain injury (mTBI), is a head injury that temporarily affects brain functioning. The mechanism of injury involves either a direct blow to the head or forces elsewhere on the body that are transmitted to the head. The brain is surrounded by cerebrospinal fluid, which protects it from light trauma, but more severe impacts, or the forces associated with rapid acceleration and/or deceleration, may not be absorbed by this cushion and these forces are transferred to the brain.  Such forces can occur when the head is struck by an object or surface (a 'direct impact'), or when the torso rapidly changes position (i.e. from a body check) and force is transmitted to the head (an 'indirect impact').  These strong forces cause the brain to move within the cerebral cavity and come in contact with the skull.  Which part of the cerebral cortex strikes the cranial bones depends on the direction of the force, but the most common is an anterior movement followed by a reactive posterior movement that will affect both the frontal lobe and the occipital lobe.  Many of the stereotypical concussion checks are examining the functioning of these two lobes:  'how many fingers am I holding up' checks for blurred vision, 'what day is today' and 'who is the president' are checking for memory recall and clarity of thinking.  More serious injury may occur involving damage to the brainstem.

Figure \(\PageIndex{7}\): Concussion.  A strong, sudden impact with an object can cause the brain to swing forward and then backward, causing the frontal and occipital/partial lobes to contact the skull.  (Image credit: "Concussion" by Jennifer Lange is licensed under CC BY-NC-SA 4.0, modification of original by Scientific Animations.)

Symptoms may include loss of consciousness; memory loss; headaches; difficulty with thinking, concentration, or balance; nausea; blurred vision; dizziness; sleep disturbances, and mood changes. Any of these symptoms may begin immediately, or appear days after the injury.

Basal Ganglia

The basal ganglia are a group of subcortical nuclei, meaning groups of neurons that lie below the cerebral cortex. The basal ganglia is comprised of the striatum, which consists of the caudate nucleus and the putamen, the globus pallidus, the subthalamic nucleus in the diencephalon, and the substantia nigra in the brainstem.  The basal ganglia are primarily associated with motor control, since motor disorders such as Parkinson’s or Huntington’s diseases stem from dysfunction of neurons within the basal nuclei. For voluntary motor behavior, the basal ganglia are involved in the initiation or suppression of behavior and can regulate movement through modulating activity in the thalamus and cortex. In addition to motor control, the basal ganglia also communicate with non-motor regions of the cerebral cortex and play a role in other behaviors such as emotional and cognitive processing.

The caudate is a long nucleus that follows the basic C-shape of the cerebrum from the frontal lobe, through the parietal and occipital lobes, into the temporal lobe. The putamen is mostly deep in the anterior regions of the frontal and parietal lobes. Together, the caudate and putamen are called the striatum. The globus pallidus is a layered nucleus that lies just medial to the putamen. The globus pallidus has two subdivisions, the external and internal segments, which are lateral and medial, respectively. These nuclei are depicted in a frontal section of the brain in Figure \(\PageIndex{8}\). 

Figure \(\PageIndex{8}\): Frontal Section of Cerebral Cortex and Basal Ganglia. The major components of the basal ganglia, shown in a frontal section of the brain, are deep within the cerebrum. The caudate is just lateral to the lateral ventricle. The putamen is inferior to the caudate and separated by the internal capsule. The globus pallidus is medial to the putamen. (Image credit: "Basal Ganglia - Coronal Section" by Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

White Matter Tracts

The white matter lies deep to the cerebral cortex and is mainly made by myelinated axons, which gives the white appearance. The axons are grouped into bundles called tracts that connect different regions of the cerebral cortex to integrate information and motor response. The white matter tracts of the cerebrum can be classified into three groups: commissural tracts, association tracts and projection tracts (Figure \(\PageIndex{9}\)).

Commissural tracts extend between the two hemispheres to connect left and right regions of the cerebrum. The most prominent commissural tract, and largest white matter structure, is the corpus callosum. Association tracts connect different regions within the same hemisphere. Association tracts can be classified into arcuate fibers when they connect gyri of the same lobe or longitudinal fasciculi when they connect gyri in different lobes of the same hemisphere. Projection tracts extend from the cerebral cortex to the inferior regions of the brain and to the spinal cord.

Figure \(\PageIndex{9}\): White Matter Tracts. The white matter of the cerebrum is organized in tracts that connect lobes and gyri within lobes.  Association tracts include arcuate fibers (red) that connect gyri of the same lobe, while longitudinal fibers (not shown) connect different lobes of the same hemisphere. Commissural tracts (such as the corpus callosum, in purple) connect the two hemispheres. Projection tracts (in green) connect the cerebral cortex to inferior regions of the brain or spinal cord. (Image credit: ”White Matter Tracts" by Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

Everyday Connections

Left Brain, Right Brain

Popular media often refer to right-brained and left-brained people, as if the brain were two independent halves that work differently for different people. This is a popular misinterpretation of an important neurological phenomenon. As an extreme measure to deal with a debilitating condition, the corpus callosum may be sectioned to overcome intractable epilepsy. When the connections between the two cerebral hemispheres are cut, interesting effects can be observed.

If a person with an intact corpus callosum is asked to put their hands in their pockets and describe what is there on the basis of what their hands feel, they might say that they have keys in their right pocket and loose change in the left. They may even be able to count the coins in their pocket and say if they can afford to buy a candy bar from the vending machine. If a person with a sectioned corpus callosum is given the same instructions, they will do something quite peculiar. They will only put their right hand in their pocket and say they have keys there. They will not even move their left hand, much less report that there is loose change in the left pocket.

The reason for this is that the language functions of the cerebral cortex are localized to the left hemisphere in 95 percent of the population. Additionally, the left hemisphere is connected to the right side of the body through the corticospinal tract and the ascending tracts of the spinal cord. Motor commands from the precentral gyrus control the opposite side of the body, whereas sensory information processed by the postcentral gyrus is received from the opposite side of the body. For a verbal command to initiate movement of the right arm and hand, the left side of the brain needs to be connected by the corpus callosum. Language is processed in the left side of the brain and directly influences the left brain and right arm motor functions, but is sent to influence the right brain and left arm motor functions through the corpus callosum. Likewise, the left-handed sensory perception of what is in the left pocket travels across the corpus callosum from the right brain, so no verbal report on those contents would be possible if the hand happened to be in the pocket.

Functional Areas of the Cerebrum

The cerebrum is responsible for the perception of sensation and for controlling the skeletal muscles. The cerebrum is also the seat of many of the higher mental functions, such as memory and learning, and language. These higher functions are distributed across various regions of the cortex, and specific locations can be said to be responsible for particular functions.

The frontal lobe is responsible for motor functions, from planning movements through executing commands to be sent to the spinal cord and periphery. The most anterior portion of the frontal lobe is the prefrontal cortex, which is associated with aspects of personality through its influence on motor responses in decision-making. The other lobes are responsible for sensory functions. The main sensation associated with the parietal lobe is somatosensation, meaning the general sensations associated with the body. The occipital lobe is where visual processing begins, although the other parts of the brain can contribute to visual function. The temporal lobe contains the cortical area for auditory processing, but also has regions crucial for memory formation. The insula is responsible for processing of taste sensation.

In the early 1900's, a German neuroscientist named Korbinian Brodmann performed an extensive study of the microscopic anatomy—the cytoarchitecture—of the cerebral cortex and divided the cortex into 52 separate regions on the basis of the histology of the cortex. His work resulted in a system of classification known as Brodmann’s areas, which is still used today to describe the anatomical distinctions within the cortex (Figure \(\PageIndex{7}\)). Continued investigation into these anatomical areas over the subsequent 100 or more years has demonstrated a strong correlation between the structures and the functions attributed to those structures. Today, we more frequently refer to these regions by their function (i.e., primary visual cortex) than by the number Brodmann assigned to them.  The primary cortical areas are where sensory information is initially received for conscious perception or where descending motor commands are sent down to the brainstem or spinal cord to execute movements. The regions near the primary areas are each referred to as association areas.

Figure \(\PageIndex{7}\): Brodmann's Areas of the Cerebral Cortex. On the basis of cytoarchitecture, the anatomist Korbinian Brodmann described the extensive array of cortical regions called areas and assigned to them a number, as illustrated in this figure. This is the original image from his 1909 book:  Brodmann, Korbinian (1909) (in German) Vergleichende Lokalisationslehre der Grosshirnrinde in ihren Prinzipien dargestellt auf Grund des Zellenbaues, Leipzig: Johann Ambrosius Barth OCLC: 1040552818.

The cortical areas in the parietal, temporal, and occipital lobes are involved in conscious sensation of stimuli. In the postcentral gyrus of the parietal lobe, we find the first three areas in Brodmann’s list which compose the primary somatosensory cortex (Figure \(\PageIndex{8}\)). All of the tactile senses are processed in this area, including touch, pressure, tickle, pain, itch, and vibration, as well as more general senses of the body such as proprioception and kinesthesia, which are the senses of body position and movement, respectively. Next to it in the parietal lobe there is the sensory association area which helps the primary area to process somatosensation.

In the most posterior part of the occipital lobe the primary visual cortex receives and begins processing visual information.  Adjacent regions are visual association areas, which constitute subsequent regions of visual processing.

In the temporal lobe is the primary auditory cortex, where information regarding sounds detected by the inner ear are first processed, and the auditory association area, which further processes auditory information. Also, deep in the temporal lobe is the primary olfactory cortex that processes smell.

The primary gustatory cortex is located in the insula and is responsible for processing taste information.

The regions that control motor functions are located within the frontal lobes. In the precentral gyrus is the primary motor cortex. Cells from this region of the cerebral cortex are the upper motor neurons that instruct cells in the brainstem and spinal cord to move skeletal muscles.  Anterior to the precentral gyrus are the motor association areas of the premotor cortex and the supplementary motor cortex.  These regions help to plan and coordinate complex movements and are also involved in speech production and memory.

Figure \(\PageIndex{8}\): Functional Cortical Areas. The functions of the cerebral cortex are localized within their respective lobes.  Although the exact boundaries can vary from person to person, their general area and their relative positions remain the same.  (Image credit: ”Functional Areas of the Cerebral Cortex" by Justin Greene and Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

The primary somatosensory and motor cortices provide an example of the mapping of the human body in different regions of the cortex. The term homunculus comes from the Latin word for “little man” and refers to a map of the human body that is laid across a portion of the cerebral cortex. The sensory receptors are mapped onto the somatosensory cortex and this mapping is called a sensory homunculus (Figure \(\PageIndex{9.A}\)). In the somatosensory cortex, the external genitals, feet, and lower legs are represented on the medial face of the gyrus within the longitudinal fissure. As the gyrus curves out of the fissure and along the surface of the parietal lobe, the body map continues through the thighs, hips, trunk, shoulders, arms, and hands. The head and face are just lateral to the fingers as the gyrus approaches the lateral sulcus. The representation of the body in this topographical map is medial to lateral from the lower to upper body. Note that this correspondence does not result in a perfectly miniature scale version of the body, but rather exaggerates the more sensitive areas of the body, such as the fingers and lower face. Less sensitive areas of the body, such as the shoulders and back, are mapped to smaller areas on the cortex. Likewise, the motor cortex contains a similar representation of neurons that control the respective body regions called the motor homunculus (Figure \(\PageIndex{9.B}\)).

Figure \(\PageIndex{9}\): Homunculus. Cartoon representations of the sensory homunculus (A) and motor homunculus (B) are shown. A homunculus refers to a map of the human body that is laid adjacent to the corresponding cerebral cortex region: the sensory receptors from various areas of the body are mapped to regions in which their processing takes place and the motor neurons for muscle groups are mapped to the regions that control them. For both, the most medial region of the cortex processes information regarding the toes and feet, while the most lateral region processes sensory information regarding the face, and in particular the mouth. (Image credits: "Sensory Homunculus" by Jennifer Lange and "Motor Homunculus" by Jennifer Lange are licensed under CC BY-NC-SA 4.0.  Created from components from "Sensory Homunculus" by OpenStax via Wikimedia Commons and from "Slagter - Drawing Cortical motor and sensory homunculus - Dutch labels" by Ron Slagter.)

A number of other regions, which extend beyond these primary or association areas of the cortex, are referred to as integrative areas. These areas are found in the spaces between the domains for particular sensory or motor functions, and they integrate multisensory information, or process sensory or motor information in more complex ways. Consider, for example, the posterior parietal cortex that lies between the somatosensory cortex and visual cortex regions. This area is called gnostic area and has been ascribed to the coordination of visual and motor functions, such as reaching to pick up a glass. The somatosensory function that would be part of this is the proprioceptive feedback from moving the arm and hand. The weight of the glass, based on what it contains, will influence how those movements are executed.

Memory and Learning

Where in the brain are memories made and stored? This is not an easy question to answer as "memory" is not a single entity and because multiple brain regions handle different parts of processes.  One of the most important brain regions in explicit memory is the hippocampus, which serves as an initial processor and director of information. Damage to this area of the temporal lobe prevents the formation of new declarative memories (information that can be stated - facts, events, experiences).  The hippocampus also helps us recall information about spatial relationships and the context of events.  These roles arise because the hippocampus serves to hold the information as a short term memory and then projects information to cortical regions that give memories meaning and connect them to other bits of information. In addition, it also plays a main role in memory consolidation: the process of transferring new learning from short-term memory into long-term memory.

Figure \(\PageIndex{10}\): Hippocampus and Amygdala.  Both the hippocampus and the amygdala are located within the medial aspect of the temporal lobe.  The hippocampus serves as the floor of the inferior portion of the lateral ventricle.  (Image credit: "Hippocampus and Amygdala" by Functional Neuroanatomy at the University of British Columbia is licensed under CC BY-NC-SA 4.0; labels added by Jennifer Lange.)

The storage of many of our most important emotional memories, and particularly those related to fear, is initiated and controlled by the amygdala.  The amygdala is also located in the temporal lobe, just anterior and medial to the hippocampus.  These two centers have many neuronal interconnections and the signaling between them can both enhance or suppress detailed memory formation.

The cerebellum plays a large role in implicit memories (procedural memory, motor learning, and classical conditioning).  These are memories for motor responses that we learn through practice, such as playing the piano or writing.  The cerebellum also maintains internal representations of the external world, which allow you to complete tasks such as navigating through your house in the dark and driving to work on "autopilot". 

The prefrontal cortex is the location for our working memory.  It's many interconnections with other brain regions allows it to access and temporarily hold and limited amount of information so we can "work" with it.  This work could be something as simple as remembering a numerical code sent to verify our electronic identity to mentally manipulating complex concepts such as determining cancer treatment options.  This region allows for reasoning and the guidance of decision-making and behavior.

Case Study - H.M.

Much of our early understanding of the locations of memory in the brain come from studying patients with memory disorders.  The most famous patient in neuroscience, known for years only as H.M., had the medial portion of both his left and right temporal lobes surgically removed in 1953 in an attempt to help control the debilitating seizures he had been suffering from since a bicycle accident when he was a child.  Following the surgery his seizures resolved, but also his declarative memory was significantly affected and he could not form new semantic knowledge. He lost the ability to form new memories, yet he could still remember information and events that had occurred prior to the surgery as well as form new short-term and procedural memories.  Work with H.M. established fundamental principles about how memory functions are organized in the brain.  After his death, patient H.M.'s identity was released.  Henry Molaison, died in 2008 at the age of 82.

View this Slate video for a closer look at how memory works, as well as how researchers are now studying H.M.’s brain.

Language and Speech

Adjacent to the auditory association cortex, at the end of the lateral sulcus just anterior to the visual cortex, is Wernicke’s area (Figure \(\PageIndex{8}\)). Wernicke's area is responsible for the understanding of language, both written and verbal. In the lateral aspect of the frontal lobe, just anterior to the region of the motor cortex associated with the head and neck, is Broca’s area. Broca’s area is responsible for the production of language and controlling movements responsible for speech. Both areas are located only in the left hemisphere in the majority of people. The tendency for some brain functions to be specialized in one side of the brain is called lateralization of function.  Both regions were originally described on the basis of losses of language, both verbal and written, which is called aphasia. The aphasia associated with Broca’s area is known as an expressive aphasia, which means that speech production is compromised. This type of aphasia is often described as non-fluency because the ability to say some words leads to broken or halting speech. Grammar can also appear to be lost. The aphasia associated with Wernicke’s area is known as a receptive aphasia, which is not a loss of speech production, but a loss of understanding of content. Patients, after recovering from acute forms of this aphasia, report not being able to understand what is said to them or what they are saying themselves, but they often cannot keep from talking.

The two regions are connected by white matter tracts that run between the posterior temporal lobe and the lateral aspect of the frontal lobe. Conduction aphasia associated with damage to this connection refers to the problem of connecting the understanding of language to the production of speech. This is a very rare condition, but is likely to present as an inability to faithfully repeat spoken language.

Figure \(\PageIndex{11}\): Functional Cortical Areas - Language and Executive Functions.  Broca's area in the frontal lobe and Wernicke's area in the temporal lobe are crucial for creating and understanding language.  The prefrontal cortex is responsible for executive functions such as decision making, reasoning, and working memory. (Image credit: ”Functional Areas of the Cerebral Cortex - Language and Executive Functions" by Justin Greene and Jennifer Lange is licensed under CC BY-NC-SA 4.0.)

Judgment and Abstract Reasoning

Planning and producing responses requires an ability to make sense of the world around us. Making judgments and reasoning in the abstract are necessary to produce movements as part of larger responses. For example, when your alarm goes off, do you hit the snooze button or jump out of bed? Is 10 extra minutes in bed worth the extra rush to get ready for your day? Will hitting the snooze button multiple times lead to feeling more rested or result in a panic as you run late? How you mentally process these questions can affect your whole day.

The prefrontal cortex is responsible for the functions responsible for planning and making decisions. The prefrontal cortex is composed of the regions of the frontal lobe that are not directly related to specific motor functions. The most posterior region of the frontal lobe, the precentral gyrus, is the primary motor cortex. Anterior to that are the premotor cortex, Broca’s area, and the supplementary motor cortex, which are all related to planning certain types of movements. Anterior to these motor association areas are the regions of the prefrontal cortex. They are the regions in which judgment, abstract reasoning, and working memory are localized. The antecedents to planning certain movements are judging whether those movements should be made, as in the example of deciding whether to hit the snooze button.

A discredited psychiatric practice to deal with various disorders was the prefrontal lobotomy. This procedure was common in the 1940s and early 1950s, until antipsychotic drugs became available. The connections between the prefrontal cortex and other regions of the brain were severed. The disorders associated with this procedure included some aspects of what are now referred to as personality disorders, but also included mood disorders and psychoses. Depictions of lobotomies in popular media suggest a link between cutting the white matter of the prefrontal cortex and changes in a patient’s mood and personality, though this correlation is not well understood.

Explore 3D Brain Models

Explore human brain specimens in 3D!  Each of the following specimens will have slight differences in the pattern of gyri and sulci, as such variation is normal between individuals.

 

Whole brain with gross anatomy annotations by TavorLab on Sketchfab

 

Brain Before Sections by UBC Faculty of Medicine on Sketchfab

 

Hemi-Brain with Cerebellum by UBC Medicine - Educational Media on Sketchfab

---

Concept Review

The adult brain is separated into four major regions: the cerebrum, the diencephalon, the brainstem, and the cerebellum.

The cerebrum is the largest portion, it is divided into two halves called hemispheres by the longitudinal fissure.

1. cerebral cortex is the location of important cognitive functions, with functions localized to each of the five lobes:
   • frontal - responsible for motor functions, from planning movements through executing commands to be sent to the spinal cord and periphery; high order executive functions such as personality, working memory, and decision-making
   • parietal - processing of somatosensory information
   • temporal - processing of information for hearing and for smell; memory formation; fear and anxiety
   • occipital - initial processing of visual information
   • insular - initial processing of information for taste
2. Subcortical nuclei (deep cerebral nuclei) are responsible for augmenting cortical functions. The subcortical or basal nuclei receive input from cortical areas and compare it with the general state of the individual. The output influences the activity of part of the thalamus that can then increase or decrease cortical activity that often results in changes to motor commands.
3. White matter tracts are bundles of myelinated axons that connect different regions of the brain.
   • commissural tracts - extend between the two hemispheres to connect left and right regions of the cerebrum; example is corpus callosum
   • association tracts - connect different regions within the same hemisphere
   • projection tracts - extend from the cerebral cortex to the inferior regions of the brain and to the spinal cord; example is internal capsule

Losses of language and speech functions, known as aphasias, are associated with damage to the important integration areas in the left hemisphere known as Broca’s or Wernicke’s areas, as well as the connections in the white matter between them. Different types of aphasia are named for the particular structures that are damaged.

---

Review Questions

Query \(\PageIndex{1}\)

 

---

Glossary

Query \(\PageIndex{2}\)

Contributors and Attributions

OpenStax Anatomy & Physiology (CC BY 4.0). Access for free at https://openstax.org/books/anatomy-and-physiology