How does the human brain keep track of time? The question fascinates professor Hedderik van Rijn: ‘Timing is crucial in many aspects of human behavior, also in higher cognitive processes. In order to understand those, we need to understand how timing works.’ A Vici grant helps him track down the temporal workings of the brain.
You ring your neighbor’s doorbell and at a certain moment decide to turn away because she’s not home. You’re in a conversation and know exactly when to nod or pause or pose the next question. Or – in a more dramatic situation – a police officer commands a suspect to put away his weapon and at a certain moment decides to pull his trigger. How do we keep track of time in these kinds of situations? We don’t look at our watch to tell us how long we have been waiting at the door, some internal mechanism helps us determine when it’s time to take the next step in what we are doing.
For decades, scientists speculated this temporal behavior is managed by an internal clock, a kind of stopwatch that starts running when we ring the doorbell and gives a signal when the appropriate ‘waiting at the door time’ has passed. But despite many efforts, researchers have not been able to identify any traces of this neural stopwatch. This lead Van Rijn to suspect our conception of how the brain keeps track of time is fundamentally mistaken.
‘The information associated with the actions we’re involved in is temporarily stored by oscillations in our working memory. Why would we assume that besides these oscillations, there would be a separate brain mechanism involved in tracking the temporal aspects of the things we do?’ Van Rijn asks. ‘That does not seem efficient to me.’
His idea; the decay in working memory oscillations that occurs over time, could function as a time stamp for the items represented. And the striatal region known to be involved in action selection, the basal ganglia, have specific cells that read the changes in working memory oscillations and signal timing information about those oscillations.
That theory would also explain our ability to keep track of the multitude of different things we might be doing simultaneously, Van Rijn argues. Whiles driving for example, we keep track of the timing of speech in a conversation with our passenger, we check our mirrors and speed indicator with a certain frequency and meanwhile we also regularly check-in with the toddler snoozing in the back seat. ‘Rather than having separate stopwatches running for all these actions, the time sensitive cells in the basal ganglia could keep track of all of them.’
The Vici grant allows Van Rijn and his research group to test this theory in different ways. For example, they will use a high definition fMRI scanner in an attempt to pinpoint the striatal cells that correspond to different time stamps. Van Rijn explains that this is the riskiest part of the study, which he can only afford to undertake because the grant allows him enough time to also cover other research paths. ‘It is a bit of a leap of faith because we really don’t know whether the measurement will be sensitive enough to distinguish the cells we expect to be involved in timing.’
In another research line, Van Rijn tries to unravel how external factors like heat and internal factors like emotions can influence the perception of time. ‘We experience time to go relatively fast when we are emotional. Could that be caused by faster decay in the working memory oscillations? Insight into that question might also help us find ways to teach people to not make rushed decisions, the relevance of which becomes crystal clear when we think about the example of a police officer deciding to pull the trigger.’
Text: Marieke Buijs