'Free Choice' in Primates Changed with Brain Stimulation: New Research on Addiction

Could simple brain stimulation take away "free choice?" Scientists have discovered that when applying electrical pulses to the brains of macaques and presenting them with two images, the primates changed their preference from one image to the other.

In this case, the researchers stimulated the ventral tegmental area of the brain. This region is located in the midbrain and helps regulate learning and reinforcement in the brain's reward system. More specifically, it produces dopamine, which is a neurotransmitter that plays an important role in positive feelings, such as receiving a reward.

"In this way, this small area of the brain provides learning signals," said Wim Vanduffel, one of the researchers, in a news release. "If a reward is larger or smaller than expected, behavior is reinforced or discouraged accordingly."

Yet this effect can be artificially produced, as it turns out. This can drastically change behavior patterns. In one experiment, the scientists allowed macaques to choose multiple times between two images-a star or a ball, as an example. This told the researchers which of the two pictures the macaques naturally preferred. Then, the researchers stimulated the ventral tegmental area with mild electrical currents whenever they chose the nonpreferred image. This quickly changed their preference, showing that the researchers could manipulate the macaques' behavior.

"In scans we found that electrically stimulating this tiny brain area activated the brain's entire reward system, just as it does spontaneously when a reward is received," said Vanduffel in a news release. "This has important implications for research into disorders relating to the brain's reward network, such as addiction or learning disabilities."

The findings reveal a bit more about how simple brain stimulation can alter choices. It also shows a bit more about the reward system of the brain. This could be extremely useful for future research, and could even lead to the development of treatments for addiction.

The findings are published in the journal Current Biology.