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LEFT: ‘ Liking’ and ‘disliking’ expressions to taste in human, orangutan and rat. Brain map showing pleasure site in accumbens where opioid neurotransmission causes sweetness ‘liking’. Bars show morphine microinjections increase ‘liking’ reactions.

RIGHT: Fearful defensive treading displayed by ground squirrel and rat to threats (rattlesnake or shockprod). Brain map (side view) shows gradient of desire versus dread in nucleus accumbens, where microinjections cause either feeding or fearful treading. Bars show fearful defensive treading caused especially by posterior microinjections.

Description of pictures from Kelley & Berridge, Neuroscience of natural rewards, Journal of Neuroscience (2002).

See movie files: Affective expressions to taste: Human Babies, adult apes, monkeys, and rats (15MB) & Fearful defensive treading in the wild: squirrels & rattlesnakes (2MB).