The merry-go-round of time in the hippocampus

The Neuroscientist on Call here discovered during these Olympics that she has a blatant preference for sports that test the brain's ability to create its own time: synchronized swimming (“artistic swimming” is ridiculous), synchronized diving, synchronized rhythmic gymnastics with girls and their hula hoops, balls, clubs, and ribbons in the air, or, to make things even more complicated, all of this five times at once, switching “equipment” with each other. Yes, there is the part where the music helps, by giving all the girls the same external beat. But the boys in synchronized diving—and of course the girls too—don't have that luxury; at most, they count one, two, three, four out loud, which sets the rhythm for the first few steps, but after that, good luck keeping in sync.

Except that keeping a mental representation of elapsed time is not a matter of luck, but rather a capacity of the hippocampus in everyone, including rats and mice—and also in humans, according to a European study recently published in the Journal of Neuroscience.

This part of the cerebral cortex, famous for its indispensable role in forming associations between events, which is the basis of recent memory, performs multitasking: its neurons represent events, yes, but also places, sequences of events and places, and time intervals. In fact, it is precisely this overlapping of tasks that makes the hippocampus the natural aggregator of representations of space-time sequences—what we commonly call our autobiographical memory.

All this because the hippocampus is a closed circuit of neurons, like children holding hands in a circle, circulating signals among themselves and ultimately functioning like a carousel. On the hippocampus carousel, you can get on at any time, take a seat, spin around with other children for a while, and then get off. Each set of children occupying the carousel at a given moment is a memory; the sequence of sets of occupants on the carousel is the sequence of events that we continuously represent throughout the day and throughout our lives.

The spacing between recent events, and therefore the exact moment when the next event happens, is also constructed in the hippocampus—in this case, by the relay of neurons that, active in sequence, alternate, each representing a specific interval of life since a significant event.

The synchronized evidence that I like so much, therefore, celebrates the ability of one brain's carousel to choose to spin along with another's, creating a whole that is much greater than its parts: a society of brains.

Excerpt from Suzana Herculano-Houzel (2025) Neuroscience of Everyday Life, originally published in Folha de São Paulo in August 2021