How we are motivated to find rewards seems dependent on forgetfulness, to a certain extent.
Although the mechanisms by which learning, reward, and motivation, occur are not well understood, the neurotransmitter dopamine is known to be heavily involved.
The current study adds to our knowledge of how dopamine translates to reward and how this information is processed in the brain; it attempts to answer some pressing questions.
It builds on previous work that demonstrated how forgetting might actually aid certain forms of learning.
The recent findings are another building block in the push to explain the neuroscience of motivation and reward.
One important theory within this field of neuroscience is known as reward-prediction-error (RPE).
RPE appears to form the neurological basis of how the brain assesses rewards and drives an organism towards a goal.
Certain dopaminergic neurons in the brain have been shown to fire in situations where a task is being carried out and a reward is at stake. If a received reward is expected, these neurons do not fire, however, if the reward is not expected, they do fire. Rather than coding whether a reward is received or not, it splits the difference between expectation and reality; this is RPE.
In simple terms, if a rat, for instance, presses a lever at random, not expecting a reward, but gets one, these neurons will fire - dopamine increases. If a rat presses a lever, expecting a reward, they will not fire. So, if the reward is expected, dopamine levels will decrease.
However, other recent studies have shown that this dopamine response can sometimes remain high even when working toward a predictable reward in certain types of task - even if it is expected; researchers believe that this long-lasting signal might represent motivation.
It is thought that the way in which dopamine is released helps switch between these two modes: pulses of dopamine influence the RPE aspect of reward, whereas a longer, more sustained dopamine signal creates and maintains a motivation to find the prize.
The current study, published this week in PLOS Computational Biology, set out to better understand how this dual action of dopamine might work.
Dopamine, forgetting, and reward
To investigate this odd conundrum, Ayaka Kato and Kenji Morita, from the University of Tokyo in Japan, summoned the investigative power of mathematical modeling.
The Japanese duo created a model that involved solving a puzzle through a series of decisions, much like a computer-based maze; to incorporate a degree of forgetfulness, they programmed the reward-related connections between neurons to gradually weaken over time.
Once the model had been designed, they ran the trial hundreds of times and analyzed the results. Contrary to general expectations, inbuilt forgetting actually enhanced motivation and increased the speed with which the goal was achieved.
In a nutshell, a little bit of forgetfulness helped keep motivation high and increased the speed at which the model reached the goal.
The authors conclude that a small amount of forgetting could help to keep even small rewards surprising and help to keep up the motivation to reach routine goals. Forgetfulness effectively reduced the level of expectation.
When discussing the results, Morita said: "Nietzsche said, 'blessed are the forgetful.' Our computational study shows it may indeed be the case, even if for a different reason."
Previously, scientists had found that a drop in levels of the neurotransmitter dopamine reduced motivation. These findings help to understand the earlier findings that had perplexed researchers.
The authors hope that, eventually, the results could be used to help treat certain dopamine-based neurological conditions:
"This could potentially be related to neuropsychiatric and neurological disorders, in particular, Parkinson's disease, which is characterized by motor and motivational impairments that are suggested to be independently associated with [dopamine].
Better understanding of the dynamic nature of biological value-learning systems will hopefully contribute to clinical strategies against these diseases."
These results will need to be replicated in a lab environment to validate them. In the future, the team hopes to investigate the effects of other internal factors such as age, mood, and health. It will be interesting to see how these might affect the rates of forgetting and whether they could be manipulated to improve motivation.