Mental blocks to starting an unpleasant task explained in monkeys

Researchers in Japan have identified, in macaques, a brain circuit that acts like a "motivation brake", helping to explain why it can be hard to start unpleasant tasks. 

Many people experience motivational difficulty: knowing what they should do but being unable to begin the task. In clinical settings, this extreme inability to initiate action — termed avolition — is observed in conditions such as major depression, schizophrenia and Parkinson’s disease. 

Scientists from the Institute for the Advanced Study of Human Biology (WPI-ASHBi) at Kyoto University examined brain activity in macaque monkeys performing tasks with two different motivational costs: a reward-only task and the same task combining the reward (water) with a punishment (a bad-odour puff). Additionally, the team was able to control a circuit connecting two brain regions known to be involved in motivation – the ventral striatum and the ventral pallidum. 

Temporarily disabling the connection makes monkeys more willing to start the avoided tasks, but it doesn’t affect their motivation for reward-only tasks. When these two regions are connected, monkeys are less likely to initiate the unpleasant tasks, suggesting that they function as a motivational brake. 

These findings, published in Current Biology, are now ready to be validated in humans and might help understand motivation paralysis in depression and other disorders.