Critical Thinking

The mitosis (the production of somatic cells- Scott

The Limbic System and related disorders


possess the greatest variety of emotions and feelings, among all species around
the world. The brain structure that deals with emotions and memory is the
limbic system. It is a group of different structures within the brain that are
involved in the way in which the body responds to certain stimuli from the
outside world. This complex system has a great importance in day to day life
due to its ability to remind feelings related to different events, use learning
outcomes based on previous experience, improve the way to control emotions such
as: anger, fear, excitement, sadness etc. The limbic system is composed of the
following structures: limbic lobe, dentate gyrus, amygdala, septal nuclei,
mammillary bodies and olfactory bulbs (Derrickson and
Tortora-2014, pp 496). Each of them plays an extremely important role in
memory, fear, instinct, consciousness etc. Limbic system is a very complicated
brain system and all of its components link together when it comes to their
functions. For example, it is said that the sense of smell is included in the
limbic system because the smell of a certain thing can trigger different emotions
which are a part of the limbic system. An example is the smell of a baby which
activate the maternal affection (Dr. Abrahams-2007, p.58-59). Given the fact
that the limbic system is quite a small structure of the human brain people
tend to ignore the fact that major disorders are related particularly to this


The limbic system is
located on top of the brain stem, on both sides of the thalamus and underneath
the cerebrum. Its connections with the cerebral cortex allow human beings to
process the information from the outer world in order to keep under control their
emotional state. The hippocampus (structure included in the limbic system) is a
unique structure thanks to its cells which are capable of mitosis (the
production of somatic cells- Scott Freeman-2014, p.299).

system or “the emotional brain” has many functions within the brain and some of
them include: controlling blood pressure, eating, hydration, emotions,
responding to sensory information, to pain, sensing sexual satisfaction,
controlling violent behaviour etc. The hippocampus is a structure included in
the limbic system and its main concerns are memory and learning. Thus, the
hippocampus helps with short-term and long-term memory, visual and acoustic
memory, learning new things by practicing and so on.

or removal of some parts of the limbic system leads to certain behaviours which
affect humans’ and animals’ daily life. For example, stimulation of a cat’s
amygdala or some nuclei of the hippocampus make the cat rage: it extends its
claws, raises its tail, hisses and spits (Derrickson and Tortora-2014, pp 496).
On the other side, the removal of an animal’s amygdala makes it lack of fear
and aggression which means it has no power to fight and no ability to defend
itself in emergency situations. Not being able to use fully every sense of the
body or express emotions provoke stress and frustration which cause damage to
the internal organism.


The limbic system has an
important role in regulating memories, behaviors and emotions. Damaging of the
limbic system leads to psychiatric disease such as: obsessive-compulsive
disorder (OCD), bipolar disorder and major depressive disorder (MDD). Usually,
patients who are immune to existing medicines are given ablative surgery (A
generic term for an operative procedure in which tissue is destroyed) as a
neurosurgical treatment option. The major ablative limbic system procedures
currently used are: anterior capsulotomy, dorsal anterior cingulotomy,
subcaudate tractotomy and limbic leucotomy (Sinha, S., McGovern, R.A., Mikell,
C.B., Banks, G.B., Sheth, S.A. (2015).

(CSTC) loops bind together regions of the cortex, basal ganglia and thalamus.
Alexander, DeLong and Strick said that there are a number of circuits projecting
from the cortex to the striatum to the thalamus back to the cortex, but their
exact number is still under discussion. One circuit, along with ventral
striatum, hippocampus, amygdala, orbitofrontal cortex, dorsal anterior
cingulate cortex integrates the limbic system, basal ganglia and frontal
circuits in a feedback-dependent manner to regulate behavior (Sinha, S.,
McGovern, R.A., Mikell, C.B., Banks, G.B., Sheth, S.A. (2015). Functional and
metabolic neuroimaging of OCD showed that there are some dysfunctions in
regions which are part of the CSTC loops. Hyperactivity of the orbitofrontal
cortex (OFC), dorsal anterior cingulate cortex (dACC), caudate and thalamus has
been described with demonstrable decreases in metabolism on PET after
treatment. Hyperconnectivity within CSTC circuit regions has been seen in the
OFC, dACC, thalamus and striatum, although pathological hypoconnectivity has
also been reported. The concept underlying ablative surgery for OCD is thus
based on this pathological hyperactivity and dysfunctional connectivity within
the limbic CSTC loop (Sinha, S., McGovern, R.A., Mikell, C.B., Banks, G.B.,
Sheth, S.A. (2015).

system does not seem to be a very interesting part of the human brain but the
truth is that any damage to a structure within the limbic system can lead to
dangerous disorders (as mentioned above): obsessive compulsive disorder (OCD),
bipolar disorder, major depressive disorder (MDD) and multiple sclerosis (MS).
Next, this diseases will be presented in more depth for the understanding of
the importance of the limbic system and the negative effects that it has on

            Obsessive-compulsive disorder

disorder (OCD) is a neuropsychiatric disorder characterized by obsessions or
compulsions (or both). The World Health Organization (WHO) has identified OCD
as a leading global cause of nonfatal illness. Obsessions are repetitive and
persistent thoughts, images or urges. They are unwanted and cause stress,
anxiety, frustration to the person who is suffering from it. People tend to
ignore these thoughts with another action (compulsion). Compulsions are
repetitive actions (washing, cleaning, sanitizing) or mental acts (Jon E. Grant, J.D., M.D., M.P.H, Solomon, Caren G., 2014,
pp. 646-650) . They are meant to reduce the stress caused by obsessions.
For someone to suffer from real OCD, the obsessive thoughts have to persist
more than one hour each day. Studies conducted in Brazil and Middle Eastern
countries have showed that environment, culture, religion are some important
factors in causing OCD. It starts to appear at an early age, during childhood (
approximately 10 years) or during adolescence or young adulthood (around 21
years). Onset is earlier in boys than girls, but after 30 years is unusual.
Obsessive compulsive disorder can often be misdiagnosed as anxiety or
depression due to the similar symptoms and patients receive wrong medication
and they are not treated for their real problem.

is one of the techniques used for patients who are suffering from this kind of
disorder. They are exposed to certain situations in which they feel
uncomfortable and in which they would start using a compulsive behavior. The
therapist instruct the patients to abstain from compulsive activities in order
to reduce stress and anxiety. These types of exercises are performed
continuously, as long as the patient needs. The exposure level increases from
session to session, anytime the patient shows progression. Controlled trials
showed have shown that 60 to 85% of patients report a significant reduction in
symptoms after using the method of exposure and response prevention. Also,
their improvement is maintained up to 5 years after interrupting the
treatment(Jon E. Grant, J.D., M.D., M.P.H, Solomon, Caren G., 2014, pp.

            Bipolar disorder

disorder is characterized with anatomical and functional abnormalities in brain
regions that mediate emotion regulation. Changes of mood and strong emotions
suggest dysfunction of brain networks that maintain emotional homeostasis (
limbic system) (Leow, A., Ajilore, O., Zhan, L.,
Arienzo, D., GadElkarim, J., Zhang, A., Moody, T., Van Horn, J.,  Feusner, J., Kumar, A., Thompson, P.,
Altshuler, L. (2012), pp.183-193). By using the diffusion tensor imagining
(DTI), it was seen that abnormalities occurred in prefrontal, parietal,
temporal and occipital lobes, as well as within the anterior-limbic network.
(Benedetti F, Absinta M, Rocca MA, Radaelli D, Poletti S, Bernasconi A, et al.,

disorder affects more than 1% of the world’s population, no matter what
nationality, ethnic origin or socioeconomic status and represent one of the
leading causes of disability among young people. (Alonso J, Petukhova M,
Vilagut G, et al. Days out of role due to common physical and mental conditions:
results from the WHO World Mental Health surveys. Mol Psychiatry 2011; 16:
1234–46.). It is very difficult for some people to benefit from mental health
care, because of the costs, especially in low-income countries. ( Merikangas
KR, Jin R, He J-P, et al. Prevalence and correlates of bipolar spectrum
disorder in the world mental health survey initiative. Arch Gen Psychiatry
2011; 68: 241–51.). As OCD, bipolar disorder is diagnosed in young adulthood.
In the past, bipolar disorder was known as maniac depressive illness. It is
associated with episodes of mania, hypomania and alternating episodes of
depression. Manic or hypomanic episodes are states of elevated mood and
increased motor drive which differ in severity and length. (Grande, I., Berk, M., Birmaher, B., Vieta, E. (2016), pp.
1571-1572) A manic episode impairs social or occupational functioning and
it can lead to hospital admission. On the other hand, a hypomanic episode does
not typically cause severe impairment and it does not require admission to
hospital. Moreover, a hypomanic episode lasts about 4 consecutive days, whereas
a manic episode lasts for at least 1 week. 
About a third to a half of patients with bipolar disorder attempt
suicide at least once in their lifetime, and 15-20% of attempts are completed.
(Schaff er A, Isometsä ET, Tondo L, et al. International Society for Bipolar
Disorders Task Force on Suicide: meta-analyses and meta-regression of
correlates of suicide attempts and suicide deaths in bipolar disorder. Bipolar
Disord 2015; 17: 1–16.). The most important thing in diagnosing bipolar
disorder is to make distinction between mania and hypomania. 

            Major depressive disorder

depressive disorder (MDD) is a medical condition that includes abnormalities of
mood, neurovegetative functions (such as appetite and sleep disturbances),
cognition (such as inappropriate guilt and feelings of  worthlessness) and psychomotor activity
(agitation, retardation). (Fava, M., Kendler, K.S. (2000), pp. 335-341). MDD is
the most common of psychiatric disorders and the most common of major
biomedical condition in “first-world” countries such as the United States. Some
of the main risk factors that can contribute to this disease are: gender,
stressful life events, adverse childhood experiences and certain personality
traits. After many studies, scientists discovered that women are at more risk
than men to manifest major depressive disorder. Environmental adversities such
as job loss, marital difficulties, major health problems and loss of personal
relationships are associated with a significant increase in risk for the onset
of MDD. Also, difficulties in childhood, including physical and sexual abuse,
poor parent-child relationships and parental discord and divorce are other
substantial dangers for MDD.  (Fava, M.,
Kendler, K.S. (2000), pp. 335-341)

As bipolar disease and
obsessive compulsive disorder, MDD occurs for the first time in childhood. The
patients keep having episodes during early adulthood. This is a life-long
episodic disorder, usually one episode in every 5-year period. Several
treatment approaches to MDD are currently available. These approaches include
psychotherapy, antidepressant medications, electroconvulsive treatment (ECT)
and other somatic therapies. (Fava, M., Kendler, K.S. (2000), pp. 335-341).

Multiple sclerosis

It is known that a
substantial number of patients with multiple sclerosis (MS) display variable
levels of depression during their life span, although the brain mechanisms of
this disease are not fully understood. There has been a study made on
seventy-seven MS patients with different levels of depression. (Riccelli, R.,
Passamonti, L., Cerasa, A., Nigro, S., Cavalli, S.M., Chiriaco, C., Valentino,
P., Nisticò, R., Quattrone, A. (2015), pp.1094-1105). They did functional
magnetic resonance imaging while performing an emotional processing task. They
chose the bilateral amygdala and hippocampus to conduct the functional
connectivity analyses. Also, multiple regression models were used to see how
depression in multiple sclerosis patients was associated with the activity of
the limbic system. The results have shown that individual differences in
depression in MS patients were associated with altered regional acitivity and
functional connectivity patterns within the limbic system. (Riccelli, R., Passamonti, L., Cerasa, A., Nigro, S.,
Cavalli, S.M., Chiriaco, C., Valentino, P., Nisticò, R., Quattrone, A. (2015),


Even though the limbic
system does not occupy a large part in the brain, it has some important roles
in an everyday life. Scientists say that the limbic system is one of the oldest
systems discovered within our brains while other structures have come up as a
result of many innovative techniques and procedures. However, the brain is in a
permanent change and it has to adapt to various factors through its entire
life. This means that all of the structures included in the human brain change
and need to adapt to environments. Thus, a clear definition has never been
given to this particular brain structure. Some people say that the limbic
system cannot control emotions by itself and others claim that it represents a
unique structure which can function fully independent.

Nonetheless, limbic system
does not seem to have a great role in people’s life. But, as mentioned above,
damaging to any part of the limbic system can lead to severe conditions which
involve loss of different sense and loss of conscious sometimes. For instance,
people who have major depressive disorder have many episodes of depression and
anger when they lose their mind and become aggressive.








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B. (2014) Principles of anatomy and physiology ,  14th edn, United States of America:John

Dr. Abrahams, P. (2007)
“Limbic System” (ed.) London: Amber Books Ltd, p.58-59.

Freeman, S. (2014)
Biological Science, 5th edn, United States of America: Pearson Education

Sinha, S., McGovern, R.A.,
Mikell, C.B., Banks, G.B., Sheth, S.A. (2015) ‘Ablative Limbic System Surgery:
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November 2017

Jon E. Grant, J.D., M.D.,
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(Accessed: 17 November 2017)

Benedetti F, Absinta M,
Rocca MA, Radaelli D, Poletti S, Bernasconi A, et al., 2011: Tract-specific
white matter structural disruption in patients with bipolar disorder. Bipolar
Disord 13:414–424

Leow, A., Ajilore, O.,
Zhan, L., Arienzo, D., GadElkarim, J., Zhang, A., Moody, T., Van Horn, J.,  Feusner, J., Kumar, A., Thompson, P.,
Altshuler, L. (2012), ‘Impaired Inter-Hemispheric Integration in Bipolar
Disorder Revealed with Brain Network Analyses’, Biological Psychiatry, 73(2), pp.183-193. ScienceDirect Online. Available at:
(Accessed: 14 November 2017)

Grande, I., Berk, M.,
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Fava, M., Kendler, K.S.
(2000), ‘Neuron’, Cell Pres, 28(2),
pp. 335-341, ScienceDirect Online.
Available at: (Accessed: 17 November

Riccelli, R., Passamonti,
L., Cerasa, A., Nigro, S., Cavalli, S.M., Chiriaco, C., Valentino, P., Nisticò,
R., Quattrone, A. (2015), ‘ Individual differences in depression are associated
with abnormal function of the limbic system in multiple sclerosis patients’, Multiple Sclerosis Journal, 22(8),  pp.1094-1105, Sage Journals Online. Available at: (Accessed: 19 November