If we want to catch a ball, our brain has to process the current trajectory and speed of the ball in fractions of a second and at the same time compare it with previous experiences of how we caught or missed the ball in previous attempts. Each additional attempt helps us to adjust our reaction better next time. A research team has now shown that the hippocampus plays a decisive role in the processing processes required for this. This brain region has so far been more associated with long-term memory formation.
Every day, our brain solves complex tasks that require finding the perfect timing. A simple example is a ball game: if someone throws a ball at us, our brain calculates in fractions of a second how fast and in which direction the ball will fly and where and when we can best catch it. In the case of repeated attempts, it also incorporates information from previous attempts in order to make the reaction even more precise.
Virtual catch game in the MRT
"Each throw is slightly different from the previous one," says Ignatius Polti of the Norwegian University of Science and Technology in Trondheim. “Some balls arrive earlier, some later. During play, the brain learns the distribution of arrival times and uses this information to form expectations for future throws. If we combine this previous knowledge with specific information about the current litter, we can improve the timing of our catch attempts.” Together with his team, he investigated how our brain is able to do this and which brain regions are involved in processing.
In order to observe how the brain coordinates current and previous information, Polti and his team had 34 subjects play a virtual catch game in the MRI scanner. A point moves in a straight line towards the edge of a circle. Just before he reached his destination, he faded out. The subjects were asked to press a button when they assumed that the dot should have arrived at the edge of the circle. Immediately afterwards, they each received feedback on how accurate their estimate was. "We were interested in how exactly the participants learn the distribution of the time intervals in this task and how they update their beliefs about this distribution over time," explains Polti's colleague Matthias Nau. "This updating process is critical as it allows us to be flexible in adapting to changing behavioral demands in our environment."
Orientation towards the average
Overall, the participants' estimates were mostly quite close to reality. They performed best when the point was moving at a moderate speed. If he moved particularly quickly or slowly, the subjects showed a tendency to overestimate short durations and underestimate long durations. "In other words, their estimates were skewed toward the average of all trials," says Polti. "We believe this trend reflects participants' familiarity with the range of time intervals experienced in the game and that it is an important behavioral adaptation to cope with uncertainty - if one is unsure about the current trial, one might be the average of all others." Try to be a good guess.”
activity in the hippocampus
The subjects' brains must therefore have actually calculated the distribution of the time intervals experienced and included them in the decision. Using the MRI images, Polti's team tracked how this is reflected in brain activity. "We found evidence of learning-related changes throughout the brain, particularly in regions that are typically studied in connection with reward processing and memory," says Polti's colleague Christian Doeller.
The activity in the hippocampus was particularly striking. "The hippocampus has not traditionally been considered a site that controls sensorimotor functions, and its contributions to memory formation are typically discussed on longer time scales (hours, days, weeks)," the researchers explain. "In this study, however, we found a relationship between hippocampal activity and real-time behavioral performance in a fast timing task that has traditionally been thought to be independent of the hippocampus."
Statistical information and flexible behavior
The researchers found that hippocampal activity could actually be predicted from the feedback participants received in the previous experiment. Activity was highest when users received feedback that they had made a particularly accurate estimate. When they received feedback that they were way off the mark, hippocampal activity was at its lowest. In addition, activity in the hippocampus reflected behavioral tendencies to overestimate short durations and underestimate long durations.
This suggests that participants actually refined and updated their knowledge of the distribution of time intervals as they received feedback, and that the hippocampus plays a critical role in this process. “We believe that the neural mechanisms we have discovered extend beyond interval learning and largely underlie flexible behavior. Rather, they may reflect how we learn through constructive feedback in general and how the brain forms and updates beliefs in real time,” says Matthias Nau.
Source: Max Planck Institute for Human Cognitive and Brain Sciences, specialist article: eLife, doi: 10.7554/eLife.79027