The Cerebrum and the

UNIT 4 CEREBRAL LOBES AND THE Cerebral Hemispheres and

their Functions
LIMBIC SYSTEM

Structure
4.0 Introduction
4.1 Objectives
4.2 The Lobes of the Brain
4.3 The Frontal Lobe
4.3.1 The Location of the Frontal Lobe
4.3.2 Anatomy of Frontal Lobe
4.3.3 Different Functions of Frontal Lobes
4.3.4 Frontal Lobe Damage
4.4 The Occipital Lobe
4.4.1 Occipital Lobe Anatomy
4.4.2 Location of the Occipital Lobe
4.4.3 Functions of the Occipital Lobe
4.4.4 Occipital Lobe Damage and Its Effects
4.5 The Parietal Lobe
4.5.1 Location of Parietal Lobe
4.5.2 Anatomy of Parietal Lobe
4.5.3 Functions of Parietal Lobe
4.5.4 Damage to Parietal Lobe and Its Effects
4.6 The Temporal Lobe
4.6.1 Location of Temporal Lobe
4.6.2 Anatomy of Temporal Lobe
4.6.3 The Functions of Temporal Lobe
4.6.4 Temporal Lobe Damage and Its Effects
4.7 The Limbic System
4.8 The Amygdala
4.9 Let Us Sum Up
4.10 Unit End Questions
4.11 Suggested Readings

4.0 INTRODUCTION
In this unit we will be dealing with the lobes of the brain. This consists of the
frontal, occipital, parietal and temporal lobes. Then we take up in detail the
frontal lobe and discuss its anatomy, location and functions. Then we deal with
the damage caused to the frontal lobe and what are the effects of the same. This
section is followed by the section on Occipital lobe. We take up the anatomy,
location and functions of occipital lobe, and discuss the consequences of any
damage to any part of the occipital lobe. Then we take up the issue of parietal
lobe and discuss its location, anatomy and functions. We also mention about the
damages caused to the parietal lobe and the consequences of the same. This is
followed by a section on temporal lobe in which we discuss then location, anatomy
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Basics of the Central and functions of the temporal lobe and point out how damage to this lobe ma
Nervous System
cause myriads of problems. Then we present the limbic system and amygdala
and their effects on behaviour.

4.1 OBJECTIVES
After completing this unit, you will be able to:
• Define lobes of the brain;
• Categorize the structural divisions of the brain;
• Describe the general structure of the frontal lobe;
• Describe the primary functions of the frontal lobe;
• Explain what would happen if the frontal lobe is damaged;
• Describe the location, anatomy and functions of the occipital lobe;
• Analyse the problems that may arise as a result of damage to the occipital
lob;
• Elucidate the functions, location and anatomy of temporal lobe; and
• Explain the behaviours that may be affected as a result of damage to the
lobe.

4.2 THE LOBES OF THE BRAIN

The human brain is not only one of the most important organs in the human
body but it is also the most complex. In the following sections, We will discuss
the basic structures that make up the brain as well as how the brain works.

The cerebral cortex is a part of the brain that functions to make human beings
unique. Distinctly human traits including higher thought, language, human
consciousness, as well as the ability to think, reason, and imagine all originate in
the cerebral cortex.
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The cerebral cortex is what we see when we look at the brain. It is the outermost Cerebral Lobes and the
Limbic System
portion that can be divided into the four lobes of the brain. Each bump on the
surface of the brain is known as a gyrus, while each groove is known as a sulcus.

The Four Lobes (Source: Kendra Van Wagner)

The cerebral cortex can be divided into four sections, which are known as lobes
(see figure above). The frontal lobe, parietal lobe, occipital lobe and temporal
lobe. These lobes have been associated with different functions ranging from
reasoning to auditory perception.
The frontal lobe is located at the front of the cerebrum. This section reaches
maturity when a person is about 25 years old. It handles the functions of planning,
emotions, and parts of speech. It is associated with reasoning, motor skills, higher
lever cognition, and expressive language. It is also where most of the personality
is based. This means that it controls a lot of a person’s behaviour and expressions.
Because this lobe is so large and located in the front of the skull, the majority of
injuries to the brain occur to this lobe. At the back of the frontal lobe, near the
central sulcus, lies the motor cortex. This area of the brain receives information
from various lobes of the brain and utilises this information to carry out body
movements.
The parietal lobe above the occipital lobe and behind the frontal lobe. It is
located in the middle section of the brain and is associated with processing tactile
sensory information This part of the cerebellum handles information related to
touch, temperature, pain and pressure. This lobe coordinates sensory information
and enables the person to correctly perceive their environment as one complete
whole. If this area is damaged, a person may have difficulty with coordination,
movement or recognition that his or her body is in pain. A portion of the brain
known as the somatosensory cortex is located in this lobe and is essential to the
processing of the body’s senses.
The temporal lobe is located on the side of the cerebrum and at the bottom
section of the brain. This lobe is also the location of the primary auditory cortex,
which is important for interpreting sounds and the language we hear. The
hippocampus is also located in the temporal lobe, which is why this portion of
the brain is also heavily associated with the formation of memories. The main
purpose of this lobe is to interpret auditory data. This means that it processes
information that a person receives through their sense of hearing. This lobe also
plays a role in both speech and memory. It is believed that the temporal lobe
helps when the brain is transferring memories from short term to long term.
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Basics of the Central The occipital lobe is the part of the brain that manages data received through
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the sense of vision. This lobe is located behind and below the parietal and temporal
lobes. It is located at the back portion of the brain and is associated with
interpreting visual stimuli and information. This part of the brain allows us to
distinguish shapes and colours and to process what our eyes see. The primary
visual cortex, which receives and interprets information from the retinas of the
eyes, is located in the occipital lobe.

Let us now take each of the lobes and discuss them in detail. Let us start with
frontal lobe.

4.3 THE FRONTAL LOBE (FIGURE BELOW)

The frontal lobes are considered our emotional control center and home to our
personality. There is no other part of the brain where lesions can cause such a
wide variety of symptoms (Kolb & Wishaw, 1990). The frontal lobes are involved
in motor function, problem solving, spontaneity, memory, language, initiation,
judgement, impulse control, and social and sexual behaviour. The frontal lobes
are extremely vulnerable to injury due to their location at the front of the cranium,
proximity to the sphenoid wing and their large size. MRI studies have shown
that the frontal area is the most common region of injury following mild to
moderate traumatic brain injury.
There are important asymmetrical differences in the frontal lobes. The left frontal
lobe is involved in controlling language related movement, whereas the right
frontal lobe plays a role in non verbal abilities. Some researchers emphasise that
this rule is not absolute and that with many people, both lobes are involved in
nearly all behaviour.
Disturbance of motor function is typically characterised by loss of fine movements
and strength of the arms, hands and fingers. Complex chains of motor movement
also seem to be controlled by the frontal lobes.
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Patients with frontal lobe damage exhibit little spontaneous facial expression, Cerebral Lobes and the
Limbic System
which points to the role of the frontal lobes in facial expression. Broca’s Aphasia,
or difficulty in speaking, has been associated with frontal lobe damage.

An interesting phenomenon of frontal lobe damage is the insignificant effect it

can have on traditional IQ testing. Researchers believe that this may have to do
with IQ tests typically assessing convergent rather than divergent thinking. Frontal
lobe damage seems to have an impact on divergent thinking, or flexibility and
problem solving ability. There is also evidence showing lingering interference
with attention and memory even after good recovery from a TBI(Traumatic Brain
Injury).
Another area often associated with frontal damage is that of “behavioural
sponteneity.” It has been noted that individual with frontal lobe damage displayed
fewer spontaneous facial movements, spoke fewer words (left frontal lesions) or
excessively (right frontal lesions).
One of the most common characteristics of frontal lobe damage is difficulty in
interpreting feedback from the environment. Perseverating on a response, risk
taking, and non compliance with rules, and impaired associated learning using
external cues to help guide behaviour are a few examples of this type of deficit.
The frontal lobes are also thought to play a part in our spatial orientation, including
our body’s orientation in space.
One of the most common effects of frontal lobe damage can be a dramatic change
in social behaviour. A person’s personality can undergo significant changes after
an injury to the frontal lobes, especially when both lobes are involved. There are
some differences in the left versus right frontal lobes in this area. Left frontal
damage usually manifests as pseudodepression and right frontal damage as
pseudopsychopathic.
Sexual behaviour can also be effected by frontal lesions. Orbital frontal damage
can introduce abnormal sexual behaviour, while dorolateral lesions may reduce
sexual interest (Walker and Blummer, 1975).
Some common tests for frontal lobe function are: Wisconsin Card Sorting
(response inhibition); Finger Tapping (motor skills); Token Test (language skills).

4.3.1 The Location of the Frontal Lobe

The frontal lobe is an area in the brain of humans and other mammals, located at
the front of each cerebral hemisphere and positioned anterior to (in front of) the
parietal lobes and above and anterior to the temporal lobes (i.e. directly behind
the forehead or “temple”).

It is separated from the parietal lobe by the post-central gyrus primary motor
cortex, which controls voluntary movements of specific body parts associated
with the precentral gyrus posteriorly.

It is associated inferiorly by lateral sulcus which separates it from the temporal

lobe.

It is associated superiorly by the superior margin of the hemisphere and anteriorly

by the frontal pole.
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Basics of the Central 4.3.2 Anatomy of Frontal Lobe
Nervous System

Frontal Lobe: Front part of the brain; involved in planning, organising, problem
solving, selective attention, personality and a variety of “higher cognitive
functions” including behaviour and emotions.

The anterior (front) portion of the frontal lobe is called the prefrontal cortex. It is
very important for the “higher cognitive functions” and the determination of the
personality.

The posterior (back) of the frontal lobe consists of the premotor and motor areas.
Nerve cells that produce movement are located in the motor areas. The premotor
areas serve to modify movements.

Ventral View (From Bottom)

Side View (Cognition and memory)

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On the lateral surface of the human brain, the central sulcus separates the frontal Cerebral Lobes and the
Limbic System
lobe from the parietal lobe.

The lateral sulcus separates the frontal lobe from the temporal lobe.
The frontal lobe can be divided into the following:
• a lateral part
• a polar (front almost) part
• an orbital (also called basal or ventra) part
• a medial part.
Each of these parts consists of particular gyri:
i) Lateral part: Precentralgyrus, lateral part of the superior frontal gyrus,
middle frontal gyrus, inferior frontal gyrus.
ii) Polar part: Transverse frontopolar gyri, frontomarginal gyrus.
iii) Orbital part: Lateral orbital gyrus, anterior orbital gyrus, posterior orbital
gyrus, medial orbital gyrus, gyrus rectus.
iv) Medial part: Medial part of the superior frontal gyrus, cingulate gyrus.

The gyri are separated by sulci. E.g., the precentral gyrus is in front of the central
sulcus, and behind the precentral sulcus.

The superior and middle frontal gyri are divided by the superior frontal sulcus.

The middle and inferior frontal gyri are divided by the inferior frontal sulcus.

In humans, the frontal lobe reaches full maturity around only after the 20s marking
the cognitive maturity associated with adulthood.

4.3.3 Different Functions of Frontal Lobes

The frontal lobes are considered our emotional control center and home to our
personality. There is no other part of the brain where lesions can cause such a
wide variety of symptoms.
Prefrontal area is involved in the following:
• The ability to concentrate and attend, elaboration of thought.
• The “Gatekeeper”; (judgment, inhibition).
• Personality and emotional traits.
• Deals with Movement.
• Motor Cortex (Brodman’s): voluntary motor activity.
• Premotor Cortex: storage of motor patterns and voluntary activities.
Language problems and motor speech problems include the following:
• Impairment of recent memory, inattentiveness, inability to concentrate,
behaviour disorders, difficulty in learning new information. Lack of
inhibition (inappropriate social and/or sexual behaviour). Emotional lability.
“Flat” affect.
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Basics of the Central • Contralateral plegia, paresis.
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• Expressive/motor aphasia.
The frontal lobes are involved in motor function, problem solving, spontaneity,
memory, language, initiation, judgment, impulse control, and social and sexual
behaviour.

There are important asymmetrical differences in the frontal lobes. The left frontal
lobe is involved in controlling language related movement, whereas the right
frontal lobe plays a role in non verbal abilities. Some researchers emphasise that
this rule is not absolute and that with many people, both lobes are involved in
nearly all behaviour.

The executive functions of the frontal lobes involve the ability to recognise future
consequences resulting from current actions, to choose between good and bad
actions, override and suppress unacceptable social responses, and determine
similarities and differences between things or events. Therefore, it is involved in
higher mental functions.

The frontal lobes also play an important part in retaining longer term memories
which are not task-based. These are often memories associated with emotions
derived from input from the brain’s limbic system.

The frontal lobe modifies those emotions to generally fit socially acceptable
norms.

Psychological tests that measure frontal lobe function include finger tapping,
Wisconsin Card Sorting Task, and measures of verbal and figural fluency.

4.3.4 Frontal Lobe Damage

The frontal lobes are extremely vulnerable to injury due to their location at the
front of the cranium, proximity to the sphenoid wing and their large size. MRI
studies have shown that the frontal area is the most common region of injury
following mild to moderate traumatic brain injury (Levin et al., 1987).
The frontal lobe contains most of the dopamine-sensitive neurons in the cerebral
cortex. The dopamine system is associated with reward, attention, long-term
memory, planning, and drive. Dopamine tends to limit and select sensory
information arriving from the thalamus to the fore-brain. A report from the
National Institute of Mental Health says a gene variant that reduces dopamine
activity in the prefrontal cortex is related to poorer performance and inefficient
functioning of that brain region during working memory tasks, and to slightly
increased risk for schizophrenia.
A new study has found the strongest evidence regarding what sets humans apart
from other primates. This is found in the brain’s frontal lobes, particularly in an
area the size of a “billiard ball” called the right prefrontal cortex.
Understanding the mental processes of others, that is mentalising is the basis of
our socialisation and what makes us human. It gives rise to our capacity to feel
empathy, sympathy, understand humor and when others are being ironic, sarcastic
or even deceptive. It’s a “theory of mind” that has been associated with the frontal
lobes, but until now scientists have had difficulty demonstrating this ability to
70 specific regions of the brain.
What is exciting about this study, according to Dr. Timothy Shallice of the Institute Cerebral Lobes and the
Limbic System
of Cognitive Neuroscience at University College London, is that the Rotman
study came at this challenge with two different testing methods and both generated
similar compelling evidence to show that these higher cognitive functions in
humans are “localisable” to a specific region within the frontal lobes. Dr. Shallice
wrote the lead editorial in BRAIN.

Dr. Stuss and his research colleagues tested patients who had damage to various
parts of the frontal lobes, and other areas of the brain as well. The selective
impairment in only some patients provided the ability to precisely localise those
regions that are necessary when specific mentalising tasks are performed.
Dr Strauss and his colleagues reported that in their study, the frontal lobes were
the most critical region for visual perspective taking, and the inferior medial
prefrontal region, particularly for the right, for detecting deception. Visual
perspective taking is the ability to empathise or identify with the experience of
another person.

It has long been known that some patients with frontal lobe damage have
significantly changed personalities. What is important about the study is that it
helps families, friends and caregivers of the patient to appreciate and understand
a very important reason why this occurs. This deficit in mentalising can affect
social cognition which is important in everyday human interactions. For example,
patients with damage in the specific frontal area are often less empathetic and
sympathetic, and they miss social cues which lead to inappropriate judgements.

In a study conducted by Strauss, 32 adults with lesions in frontal and non-frontal

brain regions, most commonly as a result of stroke, and a control group of 14
healthy adults, underwent two seemingly very simple tests. Both tasks required
participants to guess in which coffee cup a ball was hidden under. Participants
sat across a table from the experimenter and a table curtain was used on some
occasions to conceal which cup the experimenter hid the ball under. The
participant was asked to point to the correct cup.

The first test was on visual perspective taking. In this the participants had to
reflect on their own experience to understand and interpret the experience of
others. For example, the participants either saw the ball being hidden under a
particular cup with the curtain open, or were told that the ball was being hidden
when the curtain was closed and they could not see anything.

Then two assistants joined the task. One sat beside the experimenter, and one
beside the participant. The table curtain was drawn this time, concealing which
cup the ball was placed under. When the participant had to guess where the ball
was hidden, the assistants ‘helped’ by moving beside the examiner and each
pointed to a different cup.

Participants needed to realise that one of the assistants had not been in a position
to see where the ball was hidden (because they were sitting beside the participant
who themselves could not see where the ball was hidden).

The results of this experiment showed that the Frontal lesion subjects had a
much higher error rate on the task and it appeared that the ‘right’ frontal lobe
was most critical. While the small number of right frontal subjects (4) makes
this only a suggestion, it is still a striking finding, says Dr. Strauss.
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Basics of the Central In the second test on deception, an assistant sat at the table beside the experimenter
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and always pointed to a cup where the ball was NOT hidden. Participants had to
infer that the assistant was trying to deceive them. Those with right inferior
medial prefrontal damage had difficulty catching on to the ruse and were the
most frequently deceived.

A team of brain scientists at Carnegie Mellon University and the University of

Pittsburgh has found spontaneous reorganisation of cognitive function
immediately following brain damage caused by stroke.

The findings are based on functional magnetic resonance imaging (FMRI) scans
showing that brain function associated with language shifted away from the stroke-
damaged area of the adult brain to the corresponding area on the undamaged
side of the brain. The findings show the “healing” that happens after a stroke
occurs at a high level of organisation, demonstrating the plasticity of the human
brain long into adulthood. Such plasticity was routinely credited to the brain in
the first few years of life.

The results also indicate the organisational flexibility of the cortical systems that
underlie higher level thinking processes. The researchers say this knowledge
may be useful in designing future rehabilitation strategies that can exploit the
flexibility.

Using non-invasive FMRI, the team looked at the brains of two stroke patients,
34 and 45 years old, as they read and indicated their comprehension of normal
English sentences. Very soon after stroke, the cortical areas on the right sides of
their brains, the right-hand homologues of Broca’s area or of Wernick’s area,
showed increasing activation during the sentence comprehension, at about the
same time as the patients’ ability to process language was coming back to them.

In healthy brains, language functions are carried out by a network of mirror

image brain areas in the left and right side of the brain, with one side, usually the
left, being dominant. The subordinate side, usually the right, may spend most of
its lifetime playing an understudy role, as well as developing its own
specialisations.

But if a stroke or some other neurological damage disables one of the network
components on the dominant side, the corresponding left side component rapidly
and spontaneously emerges from its understudy role, and starts to activate to a
normally high level during language processing.

The rapid recovery of the ability to use language after stroke damage to the
language network was previously attributed to tissue healing functions, like
reduction of swelling in the brain.

Researchers say the new results show that part of the recovery is due to the brain
function reorganisation, a re-balancing of the network, like the cast of a play
adjusting to the loss of a key actor. The adjustment can begin within a day or two
after the stroke, and can continue for many months.
Damage to the frontal lobes can lead to a variety of results:
• Mental flexibility and spontaneity will be impaired, but IQ is not reduced.
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• Talking may increase or decrease dramatically. Cerebral Lobes and the
Limbic System
• Perceptions regarding risk-taking and rule abiding are impaired.
• Socialisation can diminish or increase.
• Orbital frontal lobe damage can result in peculiar sexual habits.
• Dorsolateral frontal lobe damage reduces sexual interest.
• Creativity is diminished or increased as well as problem solving skills.
• Distraction occurs more frequently.
• Loss of smell and/or taste.
• One of the most common characteristics of frontal lobe damage is difficulty
in interpreting feedback from the environment.
• Perseverating on a response, risk taking, and non compliance with rules
• Impaired associated learning
• The effects of frontal damage can lead to a dramatic change in social
behaviour.
• A person’s personality can undergo significant changes after an injury to the
frontal lobes, especially when both lobes are involved.
• There are some differences in the left versus right frontal lobes in this area.
Left frontal damage usually manifests as pseudo depression and right frontal
damage as pseudo psychopathic.
• An interesting phenomenon of frontal lobe damage is the insignificant effect
it can have on traditional IQ testing. Researchers believe that this may have
to do with IQ tests typically assessing convergent rather than divergent
thinking.
• Frontal lobe damage seems to have an impact on divergent thinking, or
flexibility and problem solving ability.
• There is also evidence showing lingering interference with attention and
memory even after good recovery from a Traumatic Brain Injury (TBI).
• Disturbance of motor function is typically characterised by loss of fine
movements and strength of the arms, hands and fingers.
• Complex chains of motor movement also seem to be controlled by the frontal
lobes.
• Patients with frontal lobe damage exhibit little spontaneous facial expression,
which points to the role of the frontal lobes in facial expression.
• Broca’s Aphasia, or difficulty in speaking, has been associated with frontal
damage by Brown.

• Another area often associated with frontal damage is that of “behavioural

spontaneity.”

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Basics of the Central Kolb & Milner (1981) found that individual with frontal damage displayed
Nervous System
fewer spontaneous facial movements, spoke fewer words (left frontal lesions)
or excessively (right frontal lesions).

• The frontal lobes are also thought to play a part in our spatial orientation,
including our body’s orientation in space.

• One of the most common Sexual behaviours can also be affected by frontal
lesions. Orbital frontal damage can introduce abnormal sexual behaviour,
while dorolateral lesions may reduce sexual interest.

Self Assessment Questions

1) Discuss with a diagram the lobes of the brain.
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2) Describe the frontal lobe, its location and anatomy.
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3) What are the functions of the different frontal lobes?
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4) What all would happen if the frontal lobe is damaged?
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 Cerebral Lobes and the
4.4 THE OCCIPITAL LOBES Limbic System

The occipital lobes are the center of our visual perception system.

The Per striate region of the occipital lobe is involved in visuospatial processing,
discrimination of movement and color discrimination.

The primary visual cortex is called the Brodmann area 17, commonly called V1
(visual one). Human V1 is located on the medial side of the occipital lobe within
the calcarine sulcus.

The full extent of V1 often continues onto the posterior pole of the occipital
lobe.

V1 that is Visual one is often also called striate cortex because it can be identified
by a large stripe of myelin, the Stria of Gennari.

Visually driven regions outside V1 are called extrastriate cortex.

There are many extrastriate regions, and these are specialised for different visual
tasks, such as visuospatial processing, color discrimination and motion perception.

4.4.1 Occipital Lobe Anatomy

The occipital lobes are one of the four main lobes or regions of the cerebral
cortex. They are positioned at the back region of the cerebral cortex and are the
main centers for visual processing. In addition to the occipital lobes, posterior
portions of the parietal lobes and temporal lobes are also involved in visual
perception. Located within the occipital lobes is the primary visual cortex. This
region of the brain receives visual input from the retina. These visual signals are
interpreted in the occipital lobes.

4.4.2 Location of the Occipital Lobe

The occipital lobes are the smallest of four lobes in the human cerebral cortex.
Located in the rearmost portion of the skull, the occipital lobes are part of the
forebrain. It should be noted that the cortical lobes are not defined by any internal
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Basics of the Central structural features, but rather by the bones of the skull that overlie them. Thus,
Nervous System
the occipital lobe is defined as the part of the cerebral cortex that lies underneath
the occipital bone.

The lobes rest on the tentorium cerebelli, a process of dura mater that separates
the cerebrum from the cerebellum. They are structurally isolated in their respective
cerebral hemispheres by the separation of the cerebral fissure.

At the front edge of the occipital are several lateral occipital gyri, which are
separated by lateral occipital sulcus.

The occipital aspects along the inside face of each hemisphere are divided by the
calcarine sulcus.

Above the medial, Y-shaped sulcus lies the cuneus, This cuneus is also called the
Brodman’s area 17 and the area below the sulcus is the lingual gyrus.

4.4.3 Functions of the Occipital Lobe

The most important functional aspect of the occipital lobe is that it contains the
primary visual cortex.

Retinal sensors convey stimuli through the optic tracts to the lateral geniculate
bodies, where optic radiations continue to the visual cortex.

Each visual cortex receives raw sensory information from the outside half of the
retina on the same side of the head and from the inside half of the retina on the
other side of the head.

The cuneus (Brodman’s area 17) receives visual information from the contralateral
superior retina representing the inferior visual field.

The lingula receives information from the contralateral inferior retina representing
the superior visual field.

The retinal inputs pass through a “way station” in the lateral geniculate nucleus
of the thalamus before projecting to the cortex.

Cells on the posterior aspect of the occipital lobes’ gray matter are arranged as a
spatial map of the retinal field. Functional neuroimaging reveals similar patterns
of response in cortical tissue of the lobes when the retinal fields are exposed to a
strong pattern.

If one occipital lobe is damaged, the result can be homonomous vision loss from
similarly positioned “field cuts” in each eye.

4.4.4 Occipital Lobe Damage and Its Effects

They are not particularly vulnerable to injury because of their location at the
back of the brain, although any significant trauma to the brain could produce
subtle changes to our visual perceptual system, such as visual field defects and
scotomas.

Damage to one side of the occipital lobe causes homonomous loss of vision with
exactly the same “field cut” in both eyes.
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Disorders of the occipital lobe can cause visual hallucinations and illusions. Cerebral Lobes and the
Limbic System
Lesions in the parietal temporal occipital association area are associated with
color agnosia, movement agnosia, and agraphia.

Visual hallucinations (visual images with no external stimuli) can be caused by

lesions to the occipital region or temporal lobe seizures.

Visual illusions (distorted perceptions) can take the form of objects appearing
larger or smaller than they actually are, objects lacking color or objects having
abnormal coloring.

Lesions in the parietal temporal occipital association area can cause word
blindness with writing impairments (alexia and agraphia).

Self Assessment Questions

1) Describe the occipital lobe and its importance.
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2) Where is occipital lobe located?
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3) Describe the anatomy of the occipital lobe and its functions.
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4) If there is damage to the occipital lobe what functions are affected?
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Basics of the Central
Nervous System 4.5 THE PARIETAL LOBE

THE MEDICAL DETAILS

Senator Edward M. kennedy has been diagnosed with a malignant
glioma in his left parietal lobe.
Malignant:
Relatively fast-growing
tumor.

Glioma:
Tumor originating in the
brain. It can spread within
the nervous system, but
not outside.
Left Parietal Lobe:
Region of the brain
registering sensory
perception; involved in
understanding written and
spoken words.
Treatment:
Kennedy’s doctors say that
chemotherapy and radiation are
usual in similar cases, but that the best
options for Kennedy have not yet been
determined. The doctors did not mention surgery.
Some tumor locations preclude surgery.
SOURCES: Mayo Clinic; neurskills.com: Massachusetts General Hospital DAVID BUTLER/GLORE STAFF

4.5.1 Location of Parietal Lobe

The parietal lobes are positioned above (superior to) the occipital lobe and behind
(posterior to) the frontal lobe.
This lobe is divided into two hemispheres left and right.
The left hemisphere plays a more prominent role for right handers and is involved
in symbolic functions in language and maths.
The right hemisphere plays a more prominent role for left handers and is
specialised to carry out images and understanding of maps i.e. spatial relationships.

4.5.2 Anatomy of Parietal Lobe

The parietal lobe is defined by four anatomical boundaries: the central sulcus
separates the parietal lobe from the frontal lobe.
The parieto occipital sulcus separates the parietal and occipital lobes.
The lateral sulcus is the most lateral boundary separating it from the temporal
lobe.
The medial longitudinal fissure divides the two hemispheres.
Immediately posterior to the central sulcus, and the most anterior part of the
parietal lobe, is the postcentral gyrus the primary somatosensory cortical area.
Dividing this and the posterior parietal cortex is the postcentral sulcus.
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The posterior parietal cortex can be subdivided into the superior parietal lobule Cerebral Lobes and the
Limbic System
and the inferior parietal lobule separated by the intraparietal sulcus (IP).
The intraparietal sulcus (IP) and adjacent gyri are essential in guidance of limb
and eye movement, and based on cytoarchitectural and functional differences is
further divided into medial (MIP), lateral (LIP), ventral (VIP), and anterior (AIP)
areas.

4.5.3 Functions of Parietal Lobe

The parietal lobe can be divided into two functional regions.
• One involves sensation and perception and the other is concerned with
integrating sensory input, primarily with the visual system.
• The first function integrates sensory information to form a single perception
(cognition).
• The parietal lobe plays important roles in integrating sensory information
from various parts of the body, knowledge of numbers and their relations
(Blakemore & Frith (2005) and in the manipulation of objects.
• The second function constructs a spatial coordinate system to represent the
world around us.
• Individuals with damage to the parietal lobes often show striking deficits,
such as abnormalities in body image and spatial relations (Kandel, Schwartz
& Jessel, 1991).
• Portions of the parietal lobe are involved with visuospatial processing.
• Although multisensory in nature, the posterior parietal cortex is often referred
to by vision scientists as the dorsal stream of vision (as opposed to the
ventral stream in the temporal lobe).
• Various studies in the 1990s found that different regions of the posterior
parietal cortex in Macaques represent different parts of space.
• The lateral intraparietal (LIP) contains a map of neurons (retinotopically-
coded when the eyes are fixed representing the saliency of spatial locations,
and attention to these spatial locations.
• It can be used by the oculomotor system for targeting eye movements, when
appropriate.
• The ventral intraparietal (VIP) area receives input from a number of senses
(visual, somatosensory, auditory, and vestibular).
• Neurons with tactile receptive fields represented space in a head-centered
reference frame. The cells with visual receptive fields also fire with head-
centered reference frame but possibly also with eye-centered coordinate.
• The medial intraparietal (MIP) area neurons encode the location of a reach
target in eye-centered coordinates.
• The anterior intraparietal (AIP) area contains neurons responsive to shape,
size, and orientation of objects to be grasped as well as for manipulation of
hands themselves, both to viewed and remembered stimuli.
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Basics of the Central 4.5.4 Damage to Parietal Lobe and Its Effects
Nervous System
Damage to the left parietal lobe can result in what is called “Gerstmann’s
Syndrome.”
It includes right-left confusion,
difficulty with writing (agraphia) and
difficulty with mathematics (acalculia).
It can also produce disorders of language (aphasia) and the inability to perceive
objects normally (agnosia).

Damage to the right parietal lobe can result in neglecting part of the body or
space (contralateral neglect), which can impair many self-care skills such as
dressing and washing.

Right side damage can also cause difficulty in making things (constructional
apraxia), denial of deficits (anosagnosia) and drawing ability.

Bi lateral damage (large lesions to both sides) can cause “Balint’s Syndrome,” a
visual attention and motor syndrome.

This is characterised by the inability to voluntarily control the gaze (ocular

apraxia), inability to integrate components of a visual scene (simultanagnosia),
and the inability to accurately reach for an object with visual guidance (optic
ataxia) (Westmoreland et al., 1994).

Special deficits (primarily to memory and personality) can occur if there is damage
to the area between the parietal and temporal lobes.

Left parietal temporal lesions can effect verbal memory and the ability to recall
strings of digits (Warrington & Weiskrantz, 1977).

The right parietal-temporal lobe is concerned with non-verbal memory. Right

parietal-temporal lesions can produce significant changes in personality.

Self Assessment Questions

1) Discuss the importance of the parietal lobe.
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 Cerebral Lobes and the
3) Describe the anatomy of the parietal lobe. Limbic System
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4) What are the functions of parietal lobe?
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5) If damage occurs to parietal lobe which behaviours are affected?
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4.6 THE TEMPORAL LOBES

Temporal lobe (pink portion)

4.6.1 Location of Temporal Lobe

The temporal lobes are anterior to the occipital lobes and lateral to the Fissure of
Sylvius.

The temporal lobe is a region of the cerebral cortex that is located beneath the
Sylvian fissure on both cerebral hemispheres of the mammalian brain. 81
Basics of the Central There are two temporal lobes, one on each side of the brain located at about the
Nervous System
level of the ears. These lobes allow a person to tell one smell from another and
one sound from another. They also help in sorting new information and are
believed to be responsible for short-term memory.
Right Lobe - Mainly involved in visual memory (i.e., memory for pictures and
faces).
Left Lobe - Mainly involved in verbal memory (i.e., memory for words and
names).

4.6.2 Anatomy of Temporal Lobe

The superior temporal gyrus includes an area (within the Sylvian fissure) where
auditory signals from the cochlea (relayed via several subcortical nuclei) first
reach the cerebral cortex.
This part of the cortex (primary auditory cortex) is involved in hearing.
Adjacent areas in the superior, posterior and lateral parts of the temporal lobes
are involved in high level auditory processing.
In humans this includes speech, for which the left temporal lobe in particular
seems to be specialised.
Wernicke’s area, which spans the region between temporal and parietal lobes,
plays a key role (in tandem with Broca’s area, which is in the frontal lobe).
The temporal lobe is involved in auditory perception and is home to the primary
auditory cortex.
It is also important for the processing of semantics in both speech and vision.
The temporal lobe contains the hippocampus and plays a key role in the formation
of long-term memory.

4.6.3 The Functions of Temporal Lobe

The left temporal lobe is not limited to low level perception but extend to
comprehension, naming, verbal memory and other language functions.

Blunt trauma to the temporal lobe can result in hair-trigger violent reactions and
increased aggressive responses.

The underside (ventral) part of the temporal cortices appear to be involved in

high-level visual processing of complex stimuli such as faces (fusiform gyrus)
and scenes (parahippocampal gyrus).

Anterior parts of this ventral stream for visual processing are involved in object
perception and recognition.

The medial temporal lobes (near the Sagittal plane that divides left and right
cerebral hemispheres) are thought to be involved in episodic/declarative memory.

Deep inside the medial temporal lobes lie the hippocampi, which are essential
for memory function that is particularly the transference from short to long term
memory and control of spatial memory and behaviour.
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4.6.4 Temporal Lobe Damage and Its Effects Cerebral Lobes and the
Limbic System
Damage to this area typically results in anterograde amnesia.

Kolb & Wishaw (1990) have identified eight main symptoms of temporal lobe
damage:
1) Disturbance of auditory sensation and perception,
2) Disturbance of selective attention of auditory and visual input,
3) Disorders of visual perception,
4) Impaired organisation and categorisation of verbal material,
5) Disturbance of language comprehension,
6) Impaired long-term memory,
7) Altered personality and affective behaviour,
8) Altered sexual behaviour.
Selective attention to visual or auditory input is common with damage to the
temporal lobes.

Left side lesions result in decreased recall of verbal and visual content, including
speech perception.

Right side lesions result in decreased recognition of tonal sequences and many
musical abilities.

Right side lesions can also effect recognition of visual content (e.g. recall of
faces).

The temporal lobes are involved in the primary organisation of sensory input.

Individuals with temporal lobes lesions have difficulty placing words or pictures
into categories.

Language can be affected by temporal lobe damage. Left temporal lesions disturb
recognition of words.

Right temporal damage can cause a loss of inhibition of talking.

The temporal lobes are highly associated with memory skills.

Left temporal lesions result in impaired memory for verbal material.

Right side lesions result in recall of non-verbal material, such as music and
drawings.

Seizures of the temporal lobe can have dramatic effects on an individual’s

personality.

Temporal lobe epilepsy can cause perseverative speech, paranoia and aggressive
rages (Blumer and Benson, 1975).

Severe damage to the temporal lobes can also alter sexual behaviour (e.g. increase
in activity) (Blumer and Walker, 1975).
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Basics of the Central
Nervous System Self Assessment Questions
1) Discuss the importance of temporal lobe.
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2) Where is temporal lobe located?
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3) Describe the anatomy of temporal lobe.
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4) What are the functions of temporal lobe?
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 Cerebral Lobes and the
4.7 THE LIMBIC SYSTEM Limbic System

The limbic system, essentially alike in all mammals, lies above the brain stem
and under the cortex and consists of a number of interconnected structures. The
limbic system, often referred to as the “emotional brain”, is found buried within
the cerebrum. Like the cerebellum, evolutionarily the structure is rather old.
This system contains the thalamus, hypothalamus, amygdala, and hippocampus.

1) The Thalamus
A large mass of gray matter deeply situated in the forebrain at the topmost
portion of the diencephalon. The structure has sensory and motor functions.
Almost all sensory information enters this structure where neurons send
that information to the overlying cortex. Axons from every sensory system
(except olfaction) synapse here as the last relay site before the information
reaches the cerebral cortex. The thalamus carries messages from the sensory
organs like the eyes, ears, nose, and fingers to the cortex.
2) Hypothalamus
It is a part of the diencephalon, ventral to the thalamus. The structure is
involved in functions including homeostasis, emotion, thirst, hunger,
circadian rhythms, and control of the autonomic nervous system. The
hypothalamus controls the pulse, thirst, appetite, sleep patterns, and other
processes in our bodies that happen automatically. It also controls the pituitary
gland, which makes the hormones that control our growth, metabolism,
digestion, sexual maturity, and response to stress.

3) Hippocampus
It is the portion of the cerebral hemispheres in basal medial part of the
temporal lobe. This part of the brain is important for learning and memory,
for converting short term memory to more permanent memory, and for
recalling spatial relationships in the world about us.

4.8 THE AMYGDALA

Amygdala is located in the temporal lobe is involved in memory, emotion, and
fear. The amygdala is just beneath the surface of the front, medial part of the
temporal lobe where it causes the bulge on the surface called the uncus.
Researchers have linked these structures to hormones, drives, temperature control,
emotion, and one part, the hippocampus to memory formation.
Neurons affecting heart rate and respiration appear concentrated in the
hypothalamus and direct most of the physiological changes that accompany strong
emotion.
Aggressive behaviour is linked to the action of the amygdala, which lies next to
the hippocampus.
The latter plays a crucial role in processing various forms of information as part
of our long term memory.
Damage to the hippocampus will produce global retrograde amnesia, or the
inability to lay down new stores of information. 85
Basics of the Central
Nervous System 4.9 LET US SUM UP
The occipital lobe is the visual processing center of the mammalian brain
containing most of the anatomical region of the visual cortex. The parietal lobe
is a lobe in the brain. It is positioned above (superior to) the occipital lobe and
behind (posterior to) the frontal lobe. The parietal lobe integrates sensory
information from different modalities. The temporal lobe is a region of the cerebral
cortex that is located beneath the Sylvian fissure on both cerebral hemispheres
of the mammalian brain. The temporal lobe is involved in auditory perception
and is home to the primary auditory cortex. The limbic system structures control
behaviour-related signals as well, such as satiety and tranquility (ventromedial
nucleus), fear, punishment (thin zone of the periventricular nuclei and central
gray area of the mesencephalon), and sexual drive (hypothalamus). Some other
limbic areas also control reward and punishment sensations.

4.10 UNIT END QUESTIONS

1) Discuss briefly the structure and anatomy of frontal lobe.
2) Describe the anatomy and functions of occipital lobe.
3) Explain the effects of parietal lobe damage.
4) What is limbic system?
5) Differentiate between thalamus and hypothalamus.
6) Discuss the role of amygdala and hippocampus in human behaviour.

4.11 SUGGESTED READINGS

Mark E. Bear, Barry W. Connors & Michael A.Paradiso (2001) (2nd edition).
Neuroscience. Exploring the Brain. Lippincott Williams & Wilkins, New York.

Restack, Richard (19096). Brainscapes: An Introduction to what Neuroscience

has Learned about the Structure, Function and Abilities of the Brain. Discover
books, NY.

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