How does the brain organize the sequence of events?
Research suggests that ‘time cells’ – neurons in the hippocampus thought to represent temporal information – could be the glue that sticks our memories together in the right sequence so that we can properly recall the correct order in which things happened.
These sequence-tracking time cells have been shown to be valid. Previously found in rats, where specific neuron assemblies are thought to support the recollection of events and the planning of action sequences – but for a long time, less was known about how episodic memory is encoded in the human brain.
A team of researchers, led by Leila Reddy, a neuroscientist from the Brain and Cognition Research Center in France, monitored the electrical activity of 15 epilepsy patients using microelectrodes placed in the hippocampus.
Researchers concluded that “Creating episodic memories requires linking distinct events with temporal fidelity.” Their study explains this.Published in the last year.
“Given its importance in sequence order order learning and temporal judgments, we tested if human hippocampal neurons represented temporal info while participants learned the sequence of items.”
The experiments were performed during medical tests, which used electrodes to pinpoint the source of seizures in the brain.
Therefore, prospective epilepsy treatment didn’t have to be performed by patients undergoing invasive or risky procedures.
Participants were given a sequence of images and asked to remember it.
The electrodes recorded the firing of specific neurons in the hippocampal hippocampus during the sessions. These were at specific times when images were shown, gaps between images, and pauses during which participants were asked to guess the next image from a sequence.
The researchers concur.These neurons are evidence of time cells, as they show that “neurons whose activity can be modulated by time context within a defined time window”
Researchers found that some neurons were active in recalling or memorizing the sequence of images, while others were active even without visual stimuli. This suggests that they were encoding time flow even when there was nothing.
“Time cells were observed that they fired at each successive moment in these blank periods.” Researchers explained.In their paper.
“Temporal modulation in these gap periods could not be driven by external events. Rather, they seem to reflect an evolving temporal signal due to changes in patients’ experiences during this period of waiting.”
Researchers found that time cells in the brain of humans are multi-dimensional, capable of both encoding and responding to different types of sensory information.
It is possible, according to the team, that these time neurons may be responsible for recording the ‘what, ‘where, and ‘when of experiences, stitching together elements to form coherent memories from a mess of inputs.
“The phenomenon of subjective mental time travel’ is a cornerstone for episodic memories.” The researchers stated.
“Central to our experience of reliving the past is our ability to vividly recall specific events that occurred at a specific place and in a specific temporal order… Our results provide further evidence that human hippocampal neurons represent the flow of time in an experience.”
These findings were reported in The Journal of Neuroscience.
A previous version of this story appeared in July 2021.
