Memory relies on different timescales that must all be available at once in order to be useful, new research argues. Both short- and long-term memory are thus equally important to the way in which our brains function.

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A key factor in the formation of short- and long-term memory is time, research shows.

Short- and long-term memory have been the subject of many studies seeking to explore how, what, and why we remember. Medical News Today have previously reported on research identifying memory formation mechanisms, and revealing the impact of sleep deprivation on how much we can learn and recall.

Drs. Thomas Carew and Nikolay Kukushkin, from the Center of Neural Science at New York University in New York City, have recently undertaken a study aiming to furnish us with a better understanding of how memory works in humans.

Their findings are published in the current issue of Neuron.

Short- and long-term memories 'collaborate'

The researchers point out that short-term and long-term memories coexist with the experience lived in the present moment. They offer the example of music, saying that we experience a song both as it is played to us in the present, and through the lens of our past recollections about it.

When we listen to our favorite song on the radio, we process the short-term memory of the notes and lyrics that we have just heard and link it to memories of listening to that same song at various points in the past.

Drs. Carew and Kukushkin compare the formation of long-term memories with the way in which human beings process sound.

"Much like sound is broken down by the auditory system into many discrete bins of frequencies that are perceived simultaneously, an experience as a whole is parsed by the brain into many 'time windows' that collectively represent the past."

The researchers view this process as reliant on a "temporal hierarchy," wherein various related "time windows," or recalled information, work together simultaneously.

Both short-term and long-term memories, therefore, do two things at once: they preserve past information and determine our current perception of events.

'Many timescales of memory'

One key goal of the current study was to understand under what circumstances short-term memory becomes long-term memory.

This ties in with questions of whether memories move between "repositories" in the brain, whether long-term memory is modified short-term memory, or whether the two are completely independent of each other.

These issues may need further investigation, but the research undertaken by the specialists at New York University suggest a way forward, indicating that time is a key factor in the formation of memories.

Drs. Carew and Kukushkin explain that the brains of many creatures, including both sea slugs and human beings, are able to "spread" experience onto different timescales. This is how we remember things that happened over very long periods of time and spanning many years, as well as those that took place just moments before.

Every different timescale refers to particular deviations from homeostasis, which is a state of stabilized internal conditions.

According to the scientists, any departure from this "stabilized state" determines the opening of a new "time window," which closes again once homeostasis is regained.

A "temporal hierarchy" is established when enduring changes occur in the system as a result of alterations on the fastest timescales, the researchers explain.

"Changes occurring on the fastest timescales combine with other changes to produce more lasting, emergent changes, creating a 'temporal hierarchy' of time windows that collectively alter the state of the brain at each given instant," say the researchers.

The team concludes that memories are dependent on the way that external stimuli play out in time, adding that "time is the only physical variable that is 'inherited' by the brain from the external world."

Memory, they say, is free-flowing and engages several timescales, making both long-term and short-term recollections equally important.

"In effect, the entire biological utility of memory relies on the existence of many dimensions of homeostasis, some shorter-term and some longer-term. The many timescales of memory represent many timescales of past experience and must be simultaneously available to the organism to be useful."