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Low rate hippocampal delay period activity encodes behavioral experience

Several cortical mechanisms have been proposed to explain the neuronal basis of short-term memory; however, the community has not reached a consensus yet. A recent publication in Hippocampus reports that hippocampal activity contains information about past behavior in brief sporadically spread, time intervals.

Animals need to remember what just happened, and retain information online in order to be able to adjust their future behavior accordingly. Theoretical work suggested that continuous high-rate activity is not required, instead information could be stored in brief activity periods. Researchers at the Bernstein Center Freiburg and the University of California San Diego analyzed neural activity of rodents during a time interval in which they need retain memory to receive future rewards, and provide evidence that short-term memory content can be found in the low-rate activity patterns of few time points. This activity can be distinguished by small increases in the firing rate of only few neurons.

We used a conventional classification based decoding methodology, to link past experience with the recorded hippocampal activity. In order to understand how these algorithms work, we developed a method that can visualize decision boundaries, and in doing so identified activity patterns from neural ensembles that correlate with previous experience”, said Markos Athanasiadis.

The developed method relies on adversarial attacks, state-of-the-art MVPA algorithms commonly used for computer vision. The identified patterns exist in both working memory and non-working memory tasks, in two rodent species, rats and Mongolian gerbils. They are postdictive of behavioral variables and are represented by only a few temporally distributed spikes. They also seem to depend on an intact functioning hippocampus, as well as the on familiarity to the sensory-motor context.

Figure Caption:
Left: Typical design of a rodent working memory task. Animals are held in a delay area before being released to collect reward in the to be remembered goal arm.
Right: What are the hippocampal activity patterns recorded during the delay period that hold information about the working memory content? 

Markos Athanasiadis and Christian Leibold
Bernstein Center Freiburg
Hansastr. 9A
79104 Freiburg

Athanasiadis M, Masserini S, Yuan L, Fetterhoff D, Leutgeb JK, Leutgeb S, Leibold C (2024)
Low Rate Hippocampal Delay Period Activity Encodes Behavioral Experience.
Hippocampus 116


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