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The Limbic System and related disorders             Humanspossess the greatest variety of emotions and feelings, among all species aroundthe world. The brain structure that deals with emotions and memory is thelimbic system. It is a group of different structures within the brain that areinvolved in the way in which the body responds to certain stimuli from theoutside world. This complex system has a great importance in day to day lifedue to its ability to remind feelings related to different events, use learningoutcomes based on previous experience, improve the way to control emotions suchas: anger, fear, excitement, sadness etc.

The limbic system is composed of thefollowing structures: limbic lobe, dentate gyrus, amygdala, septal nuclei,mammillary bodies and olfactory bulbs (Derrickson andTortora-2014, pp 496). Each of them plays an extremely important role inmemory, fear, instinct, consciousness etc. Limbic system is a very complicatedbrain system and all of its components link together when it comes to theirfunctions. For example, it is said that the sense of smell is included in thelimbic system because the smell of a certain thing can trigger different emotionswhich are a part of the limbic system. An example is the smell of a baby whichactivate the maternal affection (Dr.

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Abrahams-2007, p.58-59). Given the factthat the limbic system is quite a small structure of the human brain peopletend to ignore the fact that major disorders are related particularly to thisarea.            CharacteristicsThe limbic system islocated on top of the brain stem, on both sides of the thalamus and underneaththe cerebrum. Its connections with the cerebral cortex allow human beings toprocess the information from the outer world in order to keep under control theiremotional state.

The hippocampus (structure included in the limbic system) is aunique structure thanks to its cells which are capable of mitosis (theproduction of somatic cells- Scott Freeman-2014, p.299).            Limbicsystem or “the emotional brain” has many functions within the brain and some ofthem 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 inthe limbic system and its main concerns are memory and learning. Thus, thehippocampus helps with short-term and long-term memory, visual and acousticmemory, learning new things by practicing and so on.            Stimulationor removal of some parts of the limbic system leads to certain behaviours whichaffect humans’ and animals’ daily life. For example, stimulation of a cat’samygdala or some nuclei of the hippocampus make the cat rage: it extends itsclaws, 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 fearand aggression which means it has no power to fight and no ability to defenditself in emergency situations. Not being able to use fully every sense of thebody or express emotions provoke stress and frustration which cause damage tothe internal organism.             DiseasesThe limbic system has animportant role in regulating memories, behaviors and emotions.

Damaging of thelimbic system leads to psychiatric disease such as: obsessive-compulsivedisorder (OCD), bipolar disorder and major depressive disorder (MDD). Usually,patients who are immune to existing medicines are given ablative surgery (Ageneric term for an operative procedure in which tissue is destroyed) as aneurosurgical treatment option. The major ablative limbic system procedurescurrently 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).             Cortico-striato-thalamo-cortical(CSTC) loops bind together regions of the cortex, basal ganglia and thalamus.Alexander, DeLong and Strick said that there are a number of circuits projectingfrom the cortex to the striatum to the thalamus back to the cortex, but theirexact number is still under discussion.

One circuit, along with ventralstriatum, hippocampus, amygdala, orbitofrontal cortex, dorsal anteriorcingulate cortex integrates the limbic system, basal ganglia and frontalcircuits in a feedback-dependent manner to regulate behavior (Sinha, S.,McGovern, R.A.

, Mikell, C.B., Banks, G.B., Sheth, S.

A. (2015). Functional andmetabolic neuroimaging of OCD showed that there are some dysfunctions inregions which are part of the CSTC loops. Hyperactivity of the orbitofrontalcortex (OFC), dorsal anterior cingulate cortex (dACC), caudate and thalamus hasbeen described with demonstrable decreases in metabolism on PET aftertreatment. Hyperconnectivity within CSTC circuit regions has been seen in theOFC, dACC, thalamus and striatum, although pathological hypoconnectivity hasalso been reported. The concept underlying ablative surgery for OCD is thusbased on this pathological hyperactivity and dysfunctional connectivity withinthe limbic CSTC loop (Sinha, S., McGovern, R.A.

, Mikell, C.B., Banks, G.B.

,Sheth, S.A. (2015).

            Limbicsystem does not seem to be a very interesting part of the human brain but thetruth is that any damage to a structure within the limbic system can lead todangerous 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 ofthe importance of the limbic system and the negative effects that it has onhumans.            Obsessive-compulsive disorderObsessive-compulsivedisorder (OCD) is a neuropsychiatric disorder characterized by obsessions orcompulsions (or both). The World Health Organization (WHO) has identified OCDas a leading global cause of nonfatal illness. Obsessions are repetitive andpersistent thoughts, images or urges.

They are unwanted and cause stress,anxiety, frustration to the person who is suffering from it. People tend toignore these thoughts with another action (compulsion). Compulsions arerepetitive 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 persistmore than one hour each day. Studies conducted in Brazil and Middle Easterncountries have showed that environment, culture, religion are some importantfactors in causing OCD. It starts to appear at an early age, during childhood (approximately 10 years) or during adolescence or young adulthood (around 21years). Onset is earlier in boys than girls, but after 30 years is unusual.Obsessive compulsive disorder can often be misdiagnosed as anxiety ordepression due to the similar symptoms and patients receive wrong medicationand they are not treated for their real problem.             Therapyis one of the techniques used for patients who are suffering from this kind ofdisorder.

They are exposed to certain situations in which they feeluncomfortable and in which they would start using a compulsive behavior. Thetherapist instruct the patients to abstain from compulsive activities in orderto reduce stress and anxiety. These types of exercises are performedcontinuously, as long as the patient needs. The exposure level increases fromsession to session, anytime the patient shows progression. Controlled trialsshowed have shown that 60 to 85% of patients report a significant reduction insymptoms after using the method of exposure and response prevention. Also,their improvement is maintained up to 5 years after interrupting thetreatment(Jon E. Grant, J.

D., M.D., M.P.

H, Solomon, Caren G., 2014, pp.646-650).            Bipolar disorder            Bipolardisorder is characterized with anatomical and functional abnormalities in brainregions that mediate emotion regulation. Changes of mood and strong emotionssuggest 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.,2011).            Bipolardisorder affects more than 1% of the world’s population, no matter whatnationality, ethnic origin or socioeconomic status and represent one of theleading 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 healthcare, because of the costs, especially in low-income countries. ( MerikangasKR, Jin R, He J-P, et al. Prevalence and correlates of bipolar spectrumdisorder in the world mental health survey initiative.

Arch Gen Psychiatry2011; 68: 241–51.). As OCD, bipolar disorder is diagnosed in young adulthood.

In the past, bipolar disorder was known as maniac depressive illness. It isassociated with episodes of mania, hypomania and alternating episodes ofdepression. Manic or hypomanic episodes are states of elevated mood andincreased 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 andit can lead to hospital admission. On the other hand, a hypomanic episode doesnot typically cause severe impairment and it does not require admission tohospital. Moreover, a hypomanic episode lasts about 4 consecutive days, whereasa manic episode lasts for at least 1 week. About a third to a half of patients with bipolar disorder attemptsuicide 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 BipolarDisorders Task Force on Suicide: meta-analyses and meta-regression ofcorrelates of suicide attempts and suicide deaths in bipolar disorder. BipolarDisord 2015; 17: 1–16.). The most important thing in diagnosing bipolardisorder is to make distinction between mania and hypomania.              Major depressive disorder            Majordepressive disorder (MDD) is a medical condition that includes abnormalities ofmood, 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 isthe most common of psychiatric disorders and the most common of majorbiomedical condition in “first-world” countries such as the United States.

Someof the main risk factors that can contribute to this disease are: gender,stressful life events, adverse childhood experiences and certain personalitytraits. After many studies, scientists discovered that women are at more riskthan men to manifest major depressive disorder. Environmental adversities suchas job loss, marital difficulties, major health problems and loss of personalrelationships are associated with a significant increase in risk for the onsetof MDD. Also, difficulties in childhood, including physical and sexual abuse,poor parent-child relationships and parental discord and divorce are othersubstantial dangers for MDD.

  (Fava, M.,Kendler, K.S.

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

S. (2000), pp. 335-341). Multiple sclerosisIt is known that asubstantial number of patients with multiple sclerosis (MS) display variablelevels of depression during their life span, although the brain mechanisms ofthis disease are not fully understood. There has been a study made onseventy-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 functionalmagnetic resonance imaging while performing an emotional processing task. Theychose the bilateral amygdala and hippocampus to conduct the functionalconnectivity analyses. Also, multiple regression models were used to see howdepression in multiple sclerosis patients was associated with the activity ofthe limbic system. The results have shown that individual differences indepression in MS patients were associated with altered regional acitivity andfunctional 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),pp.1094-1105).ConclusionEven though the limbicsystem does not occupy a large part in the brain, it has some important rolesin an everyday life. Scientists say that the limbic system is one of the oldestsystems discovered within our brains while other structures have come up as aresult of many innovative techniques and procedures. However, the brain is in apermanent change and it has to adapt to various factors through its entirelife.

This means that all of the structures included in the human brain changeand need to adapt to environments. Thus, a clear definition has never beengiven to this particular brain structure. Some people say that the limbicsystem cannot control emotions by itself and others claim that it represents aunique structure which can function fully independent. Nonetheless, limbic systemdoes 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 whichinvolve loss of different sense and loss of conscious sometimes. For instance,people who have major depressive disorder have many episodes of depression andanger when they lose their mind and become aggressive.

      References:Tortora, G. and DerricksonB. (2014) Principles of anatomy and physiology ,  14th edn, United States of America:JohnWiley&SonsDr.

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 EducationLimitedSinha, S.

, McGovern, R.A.,Mikell, C.B., Banks, G.B., Sheth, S.A.

(2015) ‘Ablative Limbic System Surgery:Review and Future Directions’, Springer Link, Current Behavioral NeurosciencesReports Online. Available at: https://link.springer.com/ (Accessed: 17November 2017Jon E. Grant, J.D., M.

D.,M.P.H, Solomon, Caren G., (2014),’Obsessive-compulsive disorder’, The New England Journal of Medicine,371(7), pp. 646-650. ProQuestOnline. Available at: https://search-proquest-com.

ergo.southwales.ac.uk/?accountid=15324(Accessed: 17 November 2017) Benedetti F, Absinta M,Rocca MA, Radaelli D, Poletti S, Bernasconi A, et al., 2011: Tract-specificwhite matter structural disruption in patients with bipolar disorder. BipolarDisord 13:414–424Leow, 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 BipolarDisorder Revealed with Brain Network Analyses’, Biological Psychiatry, 73(2), pp.

183-193. ScienceDirect Online. Available at: https://www-sciencedirect-com.ergo.southwales.

ac.uk/(Accessed: 14 November 2017)Grande, I., Berk, M.,Birmaher, B., Vieta, E.

(2016), ‘Bipolar disorder’, The Lancelet, 387(10027) pp. 1571-1572, ScienceDirect Online. Available at: https://www-sciencedirect-com.ergo.southwales.ac.

uk/ (Accessed: 18 November2017)Fava, M., Kendler, K.S.(2000), ‘Neuron’, Cell Pres, 28(2),pp. 335-341, ScienceDirect Online.Available at: https://www-sciencedirect-com.ergo.southwales.

ac.uk/ (Accessed: 17 November2017)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 associatedwith abnormal function of the limbic system in multiple sclerosis patients’, Multiple Sclerosis Journal, 22(8),  pp.1094-1105, Sage Journals Online. Available at: http://journals.sagepub.com.ergo.southwales.ac.uk/ (Accessed: 19 November2017) 

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