Watch the video above, the trick is nothing short of incredible!

This is due to a mechanism called the opponent-process theory, which was developed in the 1870s. It is the idea of perceiving color in terms of paired opposites such as red with green, and yellow with blue. The possible scientific explanation for this theory is that bipolar cells are excited by one set of wavelengths and inhibited by other, which are in extend attached to the cone retinal receptors.

Someone who greatly enjoys sweet foods is said to have a "sweet tooth." Experimental evidence now shows us that eating sweets forms memories that may control eating habits. In other words, people may enjoy eating sweets because the taste is correlated with positive memories.

The findings, published online in the journal Hippocampus, show that neurons in the dorsal hippocampus, the part of the brain that is critical for episodic memory, are activated by consuming sweets. Episodic memory is the memory of autobiographical events experienced at a particular time and place.

In the study, a meal consisting of a sweetened solution, either sucrose or saccharin, significantly increased the expression of the synaptic plasticity marker called activity ...

This video explains it quite well. The key hormone in question is serotonin. Serotonin is known to play a role in depression. Low serotonin levels are believed to be the reason for depression and associated symptoms of anxiety, apathy, fear, feelings of worthlessness, insomnia and fatigue. The opposite is true when a high-level of serotonin is present, you feel jovial and enthusiastic. MDMA promotes the formation of this hormone.

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An informative recapitulation of the brain's complex physiological mysteries.

I recommend you watch the whole video, but if you're anxious and eager to see what I'm referring to, skip to the fourth minute.