A new study reveals why our brains are so hooked on sugar
I imagine, like myself, many of you glorious Food Envy readers are fond of their sweet things. As soon as sugar touches your tongue, your nervous system kicks into high gear. The tongue tells the brain’s “taste centre” that you ate something sweet, relaying a message to another part of your brain that eating sweet stuff is good.
This is a problematic process for anyone who’s ever tried to shed some pounds. Working out is great but it doesn't really get you anywhere if you treat yourself to a donut for "working so hard." In reality, you probably didn't work out hard enough to burn the calories the gym machine you used says you burnt. Unless your diet is on point, that extra-sugary dopamine hit you get from that donut will almost definitely do more harm than good.
Luckily for us lazy folk, scientists studying mouse brains have found a way to disrupt the neverending cravings. As researchers write in Nature earlier in the week - just because your brain senses sweetness doesn’t mean it has to conflate sweetness with pleasure.
In their study, the Columbia University researchers disrupted the brain region called the amygdala - responsible for the pleasant or unpleasant experience linked to taste - and found that the mice could still detect bitter and sweet flavours but didn’t express a distaste for one or a preference for the other.
This demonstrates that literal taste isn’t inherently linked to the pleasurable experience of the taste, the authors write. Rather, those two experiences seem to be processed in different brain regions. With this knowledge in mind, the team additionally found that they could hack mouse brains to alter the way mice processed taste, making plain water pleasurable or distasteful and reversing the way the mice experienced sweet and bitter tastes.
In one set of experiments, the researchers altered the way the mouse brain taste center - the “gustatory cortex” - communicated with the amygdala. The gustatory cortex has separate connection neurons that relay “sweet” and “bitter” signals. So, when the team activated the neurons associated with sweetness, the mice reacted to a neutral stimulus (plain water) as if it was sweet.
Likewise, when the neurons associated with bitterness were activated, the mice responded as if it the water was bitter. In this way, they found that this switch could even reverse the mice’s emotional reactions to sweet or bitter tastes. No one's saying we're mice, but I'm pretty sure you're all thinking of the rather trivial playground science experiment: "the salt shaker test".
In another experiment, researchers trained mice to taste water from a spout and identify it as sweet or bitter by going through a door. Then, they silenced the neurons in the amygdala that determine how pleasurable a taste is. These mice were able to identify sweet and bitter, but their appetite for sweetness wasn’t activated, showing that the pleasure-making process was indeed disrupted.
In a different test, mice were trained to lick when they tasted something bitter, and not lick when they tasted something sweet - the opposite of their natural response. Again, their amygdalae were silenced, and just like the mice in the previous test, they could still recognise sweet and bitter, but they didn’t exhibit an emotional response.
These weird experiments demonstrate that tasting and enjoying are governed by separate regions of the brain, at least in mice. If anything, it serves as a reminder that flavour and pleasure aren’t entirely linked, even though most of us take this relationship for granted.
By gaining a better understanding of these pathways, which the researchers say are similar in humans, they hope to gain insight into eating disorders, which appear to result from exaggerated responses to food input.