A new study sheds further light on the biology of motivation.

People vary in the level of their work ethic. We all know that. Whether it’s a friend, a co-worker or an employee, we see examples of this play out everyday. But the real question is why? Why do these differences exist in the first place? Does it have to do with our upbringing? Is it just our “personality”? Could these differences be due to brain chemistry? If so, the origin of these individual differences in the brain have remained a scientific mystery… until now.

The veil has recently been pushed back by a new brain imaging study that has found an individual’s work ethic is strongly influenced by the chemistry in three specific areas of the brain. In addition to shedding new light on how the brain works, the research could have important implications for the treatment of attention-deficit disorder, depression, schizophrenia and other forms of mental illness characterized by decreased motivation.

The study was performed by a team of Vanderbilt scientists including post-doctoral student Michael Treadway and Professor of Psychology David Zald. Their results were recently published  in the Journal of Neuroscience.

Using a brain mapping technique called positron emission tomography (PET scan), the researchers found that “go-getters” willing to work hard for rewards had higher release of the neurotransmitter dopamine in specific areas of the brain, known as the striatum and ventromedial prefrontal cortex. These brain regions are known to play an important role in reward and motivation. On the other hand, “slackers” who are less willing to work hard for a reward had high dopamine levels in a different brain area – the anterior insula – which plays a role in emotion and risk perception.

Answers Raise New Questions

“Past studies in rats have shown that dopamine is crucial for reward motivation,” said Treadway, “but this study provides new information about how dopamine determines individual differences in the behavior of human reward-seekers.”

The role of dopamine in the anterior insula came as a complete surprise to the researchers. The finding was unexpected because it suggests that more dopamine in the insula is associated with a reduced desire to work, even when it means earning less money. The fact that dopamine can have opposing effects in different parts of the brain complicates the picture regarding the use of psychotropic medications that affect dopamine levels for the treatment of attention-deficit disorder, depression and schizophrenia because it calls into question the general assumption that these dopaminergic drugs have the same effect throughout the brain.

“At this point, we don’t have any data proving that this 20-minute snippet of behavior corresponds to an individual’s long-term achievement,” said Zald, “but if it does measure a trait variable such as an individual’s willingness to expend effort to obtain long-term goals, it will be extremely valuable.”

The research is part of a larger project designed to search for objective measures for depression and other psychological disorders where motivation is reduced. “Right now our diagnoses for these disorders is often fuzzy and based on subjective self-report of symptoms,” said Zald. “Imagine how valuable it would be if we had an objective test that could tell whether a patient was suffering from a deficit or abnormality in an underlying neural system. With objective measures we could treat the underlying conditions instead of the symptoms.”

Further research is needed to examine whether similar individual differences in dopamine levels help explain the altered motivation seen in forms of mental illness such as depression and addiction. Additional research is under way to examine how medications specifically impact these motivational systems.

May 1, 2012
The Healthy Mind Network

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