AMYGDALA, THE REPERTOIRE OF FEELINGS
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].
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.
