AMYGDALA, HİSLERİN DAĞARCIĞI

AMYGDALA, HİSLERİN DAĞARCIĞI

By Ali R+ SARAL – arsaral(at)yahoo.com

 

Denizde kayıktasınız.  Açılmışsınız.  Hava patlıyor.  Buna benzer bir ciddi zorlukla karşılaştığınızda hayatta kalmak için mücadele ederken hiç “İçimde bir his var kurtulmağı başaracağım” dediğiniz oldu mu?  Hiç bir mantıksal açıklaması olması gerekmeyen. Kelimelerle ifade edilemeyen bu şey, bu his ‘güven’dir.

 

“Çocukların duygusal gelişimi onların çeşitli duyguları nasıl kazandıkları ...[1]” ’na bağlıdır.  “Bakımın tutarlı olması, duygusal güvenin korunmasında en önemli bileşkendir[1].”  Güven duygusu (bağlılık ile birlikte) insanın ilk öğrendiği duygudur.  Bakım, yani sevgi, beslenme ve diğer ihtiyaçlar bebeğin güven duygusunu koşullanma yolu ile sağlar.

 

Pavlov’un koşullama deneyleri aslında Amygdala’ya belirli bir işaretten sonra belirli bir tepki vermeği öğretir.  Amygdala’sı çıkartılmış ya da olmayan hayvan ve insanlarla yapılan deneyler işaret verilse bile ilgili tepkinin denek tarafından verilemediğini göstermiştir[Q1, Q2].

 

Amygdala algıların vücutsal tepkilerle eşleştirildiği beyin parçası ya da alt-organımızdır.  Amygdala algıları hissel karşılıkları ile eşleştirir ve bu eşlemeyi hatırlar.  Örneğin, bir köpek saldırısına uğrayan çocuğun amygdalası, kan basıncının, kalp atışlarının arttığını, terleme ve panik dürtüsünü bünyesine kayıt eder.  Sonradan bir köpek ile karşılaşma durumunda çocuk bu hisleri amygdala sayesinde otomatik olarak duyar.

 

Sinirlendiğiniz zaman içinde bulunduğunuz durumun farkına varır ve ifade ederseniz ‘sinirlenme duygusu’ kaybolur.  Çünkü artık amygdala’nız ve onun sağladığı saklı-implicit hatıralar[Q3] devreden çıkmış, önbeyin – PFC ve Hippocampus’taki açık-expilicit bellek doğrudan iletişime geçerek kontrolü ele almıştır[Q6,Q7].

 

Amygdala ile Hippocampus arasındaki bağlantılar belirli bir hissi oluşturan algıların isimlendirilmesine olanak tanır.  Hippocampus’tan geri Amygdala’ya olan bağlantılar ise belirli bir duyguyu anmanın ona ilişkin vücutsal ve algısal hisleri zayıfta olsa hissetmek sonucunu doğurur[Q7].

 

İnsan amygdalası bebeklikten itibaren karşılaştığı bütün durumlara ilişkin hisleri zaman içinde kayıt eder.  Böylece amygdala her olayın duygusal önemini ve gerektirdiği hissel uyanıklığı-salience içeren bir repertuar [Q4]oluşturur. 

 

Amygdala dikkat, algılama, ve açık-expilicit bellek gibi muhakemesel işlevlerin ayarlanması ve değişikliğe uğratılmasını da yerine getirir[Q5].  Harici uyarıcıların duygusal önemini işleyen amygdala tarafından bu muhakemesel işlevlerin ayar ve değişime uğratıldığı genellikle kabul edilir.

 

Amygdala bağlantıları bakımından önbeyin-PFC’ye benzer şekilde beynin hemen hemen her kısmı ile temas halindedir.  İnsan yaşamında her eylemin az ya da çok duygusal bir rengi olduğu ve amygdala ile dikkat[Q8], algılama, bellek gibi muhakemesel yetenekler arasındaki ilişki(*) düşünülürse, zihinsel yüklü ve stresli çalışan kişilerde affektif-hazsal bozuklukların çok sayıda olması tesadüf değildir[Q9, Q10, Q11].

 

(*) Aklınızda tutamadığınız bir şeyi hatırlamak için ona ilişkin ortamı, hissi canlandırmağa çalışınız.  Bu şekilde amygdalanız hippocampusünüzün arama yeteneklerini arttırır.

 

QUOTATIONS:

Pavlovian Conditioning and Amygdala

Q1. “Monkeys without amygdalas have difficulty learning to associate a light-signal with an electric shock — and also have difficulty associating a neutral stimulus with a food reward. It has been suggested that the amygdala functions to associate sensation with reward or punishment.[2]”

“Figure 7: Auditory fear conditioning paradigm. Studies using this paradigm have helped elaborate the functional role of amygdala nuclei. Rats are habituated to the chamber on day 1 (no stimulation). On day 2, the rat receives a small number of training trials (typically 1-5) in which a tone CS is paired with a footshock US. Controls receive unpaired presentations of the CS and US. On day 3, the CS is presented in a novel chamber with a unique odor (peppermint) and fear responses (freezing) to the CS assessed. Animals receiving pairings on day 2 show high levels of freezing but animals receiving unpaired training show little freezing.”

 

Q2.“In Pavlovian fear conditioning a neutral conditioned stimulus (CS) that is paired with a painful shock unconditioned stimulus (US) comes to elicit fear responses such as freezing behavior and related physiological changes ( Figure 7). Studies in rodents have mapped the inputs to and outputs of amygdala nuclei and subnuclei that mediate fear conditioning.[3]”

 

Amygdala, the Implicit Memory

Q3.“Although fear is the emotion best understood in terms of brain mechanisms, the amygdala has also been implicated in a variety of other emotional functions. A relatively large body of research has focused on the role of the amygdala in processing of rewards and the use of rewards to motivate and reinforce behavior. As with aversive conditioning, the lateral, basal, and central amygdala have been implicated in different aspects of reward learning and motivation, though the involvement of these nuclei differs somewhat from their role in fear. The amygdala has also been implicated in emotional states associated with aggressive, maternal, sexual, and ingestive (eating and drinking) behaviors. Less is known about the detailed circuitry involved in these emotional states than is known about fear.

 

Because the amygdala learns and stores information about emotional events, it is said to participate in emotional memory. Emotional memory is viewed as an implicit or unconscious form of memory and contrasts with explicit or declarative memory mediated by the hippocampus. 

 

Amygdala, the Repertoire of Feelings

Q4.“When a person looks at the world, he or she is confronted with an overwhelming amount of sensory information—sights, sounds, smells, and so on. After being processed in the brain's sensory areas, the information is relayed to the amygdala, which acts as a portal to the emotion-regulating limbic system. Using input from the individual's stored knowledge, the amygdala determines how the person should respond emotionally—for example, with fear (at the sight of a burglar), lust (on seeing a lover) or indifference (when facing something trivial). Messages cascade from the amygdala to the rest of the limbic system and eventually reach the autonomic nervous system, which prepares the body for action. If the person is confronting a burglar, for example, his heart rate will rise and his body will sweat to dissipate the heat from muscular exertion. The autonomic arousal, in turn, feeds back into the brain, amplifying the emotional response. Over time, the amygdala creates a salience landscape, a map that details the emotional significance of everything in the individual's environment. [4]“

 

Additional Roles of Amygdala

Q5.In addition to its role in emotion and unconscious emotional memory, the amygdala is also involved in the regulation or modulation of a variety of cognitive functions, such as attention, perception, and explicit memory. It is generally thought that these cognitive functions are modulated by the amygdala's processing of the emotional significance of external stimuli. Outputs of the amygdala then lead to the release of hormones and/or neuromodulators in the brain that then alter cognitive processing in cortical areas. For example, via amygdala outputs that ultimately affect the hippocampus, explicit memories about emotional situations are enhanced. For example, glucocorticoid hormone released into the blood stream via amygdala activity travels to the brain and then binds to neurons in the basal amygdala. The latter then connects to the hippocampus to enhance explicit memory. There is also evidence that the amygdala can, through direct neural connections, modulate the function of cortical areas.

 

Further, exposure to emotional faces potently activates the human amygdala. Both conditioned stimuli and emotional faces produce strong amygdala activation when presented unconsciously, emphasizing the importance of the amygdala as an implicit information processor and its role in unconscious memory. Studies of humans and non-human primates also implicate the amygdala in soical behavior. Findings regarding the human amygdala are mainly at the level of the whole region rather than nuclei. [3]”

 

Amygdala – Hippocampus Relation

Q6.“the amygdala is indispensable for emotional conditioning and for the coupling for extroceptive sensory information with introceptive information concerning somatic states (emotion and effect).[5]”

 

Q7.“PLEASURE, ELATION, EUPHORIA, ecstasy, sadness, despondency, depression, fear, anxiety, anger, hostility, and calm—these and other emotions color our lives. They contribute to the richness of our experiences and imbue our actions with passion and character. Moreover, as we shall learn in Chapter 61, disorders of emotion contribute importantly to several major psychiatric illnesses. An emotional state has two components, one evident in a characteristic physical sensation and the other as a conscious feeling—we sense our heart pounding and we consciously feel afraid. To maintain the distinction between these two components, the term emotion sometimes is used to refer only to the bodily state (ie, the emotional state) and the term feeling is used to refer to conscious sensation.[6]”...

 

“The Hippocampus Has Only an Indirect Role in Emotion

Early theories of the neural control of emotional states accorded the hippocampus a major role in coordinating the activity of the hypothalamus and cerebral cortex (see Figure 50-5). Subsequent experimental studies on both monkeys and humans showed that the coordinating role is carried out by the amygdala rather than the hippocampus. The hippocampal system is involved in explicit (declarative) memory (Chapter 62).

 

The distinctive roles of the amygdala and the hippocampus were clearly demonstrated in a study of three patients with selective damage to the amygdala, the hippocampus, or both. These patients were shown monochromatic slides (green, blue, yellow, or red) and their autonomic responses were measured. After some of the colored slides a frightening loud horn was sounded. Patients with the amygdala lesion did not become conditioned to the associated color. Yet when asked how many different colors they observed and how many were followed by the loud horn, the patients responded correctly and had clearly acquired explicit knowledge about the testing situation. Patients with hippocampal damage, on the other hand, became conditioned to colors associated with the loud horn but did not learn how many colors were associated with the sound of the loud horn. Patients with lesions in both the amygdala and hippocampus showed neither autonomic conditioning nor knowledge of the testing situation.[6]”

 

Attention and Other Amygdala Functions

Q8.“The amygdala in attention. Most proposals describe this structure in terms of affective functions. Indeed, the amygdala is often categorized as an affective region strongly linked to fear processing.  Evidence concerning fear conditioning in rats, deficits in the recognition of fearful expressions in patients with bilateral amygdala lesions and the robust responses evoked by fearful faces in neuroimaging studies, have popularized the view of the amygdala as a ‘fear centre’. However, this structure is also involved in several functions that are closely linked to cognition, including attention and associative learning. 

 

A central function of attention, a paradigmatic cognitive process, is to modulate sensory processing. For instance, attention to a stimulus increases neuronal firing rates in sensory cortex and is believed to improve behavioural performance.  Such ‘competitive advantage’ also occurs during the viewing of emotion-laden visual stimuli. The amygdala probably underlies these effects.

 

 Indeed, recent studies have provided evidence that the amygdala mediates the processing advantage of emotional items. Furthermore, in neuroimaging studies, amygdala activation is correlated with activation in the visual cortex and this correlation is attenuated in patients with amygdala damage. Thus, the amygdala might underlie a form of emotional modulation of information that in many ways parallels the attentional effects observed in the visual cortex.[7]”

 

Occupational Risks

Q9.“Another example of kindling  is the effects of stress on the hippocampi. ... studies in rats and primates suggest that glucocorticoids are the culprit. Robert Sapolsky explains that glucocorticoids "may be neurotoxic to the hippocampus at the massive levels that are released under extreme stress or during trauma.[4]”

 

Q10.“Like the hippocampus, the amygdala is rich in receptors for cortisol (hydrocortisone, ie, stress hormone). While prolonged stress (prolonged cortisol exposure) impairs LTP in the hippocampus, the same stresses facilitate LTP (Long-Term Potentiation) in the amygdala [NEUROCHEMICAL RESEARCH 28(1):1735-1742 (2003)]. [2]“

 

Q11.“the work of Joseph LeDoux of NYU: "Suppose a major traumatic stressor occurs, of a sufficient magnitude to disrupt hippocampal function while enhancing amygdaloid function. At some later point, in a similar setting, you have an anxious, autonomic state, agitated and fearful, and you haven't a clue why—this is because you never consolidated memories of the event via your hippocampus while your amygdala-mediated autonomic pathways sure as hell remember." [4]”

 

KAYNAKLAR:

[1] İnanç, B. Y., Bilgin M., Atıcı M. K.; “Gelişim Psikolojisi”, Nobel Kitabevi, ISBN: 975-8561-31-6, s 162, 164

[2] Best, B.; “Amygdala and the Emotions”, from “The Amygdala”, Ed. by John P. Aggleton (Wiley-Liss, 1992).

[3] LeDoux, J. E.; Scholarpedia, “Amygdala”, Center for Neural Science, NYU, New York, NY.

[4] Koch, S. N.; “Subcortical Brain Structures, Stress, Emotions, and Mental Illness”, MyBrainNotes™.com

[5] Vale C. I. et al.; “Knowing the Amygdala: Its Contribution to Psychiatric Disorders”, Psicosssomatica, ISBN: 0874-4696
[6] Kandel E. R., et al;  “Emotional States and Feelings”, “Principles of Neural Science”, 4th Edition, p.994.

[7] Pessoa, L.; “On the relationship between emotion and cognition”, “Perspectives”, “Nature”, february 2008, volume 9.