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Dopamine is not simply a pleasure chemical; it helps the brain learn, predict and pursue rewards before they arrive.

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Dopamine is one of the brain's chemical messengers. In 1958 the Swedish scientists Arvid Carlsson and Nils-Åke Hillarp showed that it works as one, and Carlsson later shared the 2000 Nobel Prize in Physiology or Medicine for this work. In the 1990s Wolfram Schultz recorded dopamine cells in monkeys. An unexpected sip of juice made them fire; once a light reliably came before the juice, they fired at the light instead, and they dipped below normal if the promised juice never came. This ‘reward prediction error’ signal tells the brain when things turn out better or worse than expected, which is how it learns what is worth doing. Kent Berridge's experiments separated ‘wanting’ from ‘liking’: rats with almost no dopamine left still showed pleasure at sugar but made no effort to get it. The same system shapes habits and addiction, and its loss in Parkinson's disease affects movement.

Türkçe oku
Dopamin, sanıldığı gibi yalnızca bir haz kimyasalı değildir; beynin ödülleri daha gelmeden tahmin etmesine, onlardan öğrenmesine ve peşlerinden gitmesine yardım eder.

Dopamin, beyindeki kimyasal habercilerden biridir. İsveçli bilim insanları Arvid Carlsson ile Nils-Åke Hillarp, dopaminin böyle bir haberci olarak çalıştığını 1958'de gösterdi; Carlsson bu çalışmasıyla çok sonra, 2000 yılında Nobel Fizyoloji veya Tıp Ödülü'nü paylaştı. Wolfram Schultz 1990'larda maymunlarda dopamin hücrelerinin etkinliğini kaydetti. Beklenmedik bir yudum meyve suyu bu hücreleri harekete geçiriyordu. Meyve suyundan önce hep bir ışık yanmaya başlayınca hücreler artık ışığa tepki verdi; beklenen meyve suyu gelmeyince de etkinlikleri olağan düzeyin altına düştü. “Ödül tahmin hatası” denen bu sinyal, beyne işlerin beklenenden iyi mi kötü mü gittiğini bildirir; beyin neyin uğraşmaya değer olduğunu böyle öğrenir. Kent Berridge'in deneyleri ise istemek ile hoşlanmanın ayrı şeyler olduğunu gösterdi: Beyninde neredeyse hiç dopamin kalmamış fareler şekerden hâlâ hoşlanıyor, ama onu elde etmek için hiç çaba göstermiyordu. Aynı sistem alışkanlıklarda ve bağımlılıkta rol oynar; Parkinson hastalığında bu hücrelerin kaybı hareketi etkiler.

Sources and further reading

Background reading: Dopamine
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