Network dynamics underlying the formation of sparse, informative representations in the hippocampus

By Mattias P. Karlsson, Loren M. Frank. 2008

214 citations recorded by the source corpus.

During development, activity-dependent processes increase the specificity of neural responses to stimuli, but the role that this type of process plays in adult plasticity is unclear. We examined the dynamics of hippocampal activity as animals learned about new environments to understand how neural selectivity changes with experience. Hippocampal principal neurons fire when the animal is located in a particular subregion of its environment, and in any given environment the hippocampal representation is sparse: less than half of the neurons in areas CA1 and CA3 are active whereas the rest are essentially silent. Here we show that different dynamics govern the evolution of this sparsity in CA1 and upstream area CA3. CA1, but not CA3, produces twice as many spikes in novel compared with familiar environments. This high rate firing continues during sharp wave ripple events in a subsequent rest period. The overall CA1 population rate declines and the number of active cells decreases as the environment becomes familiar and task performance improves, but the decline in rate is not uniform across neurons. Instead, the activity of cells with initial peak spatial rates above ∼12 Hz is enhanced, whereas the activity of cells with lower initial peak rates is suppressed. The result of these changes is that the active CA1 population comes to consist of a relatively small group of cells with strong spatial tuning. This process is not evident in CA3, indicating that a region-specific and long timescale process operates in CA1 to create a sparse, spatially informative population of neurons.

Subfields: Cellular and Molecular Neuroscience, Cognitive Neuroscience

How researchers see this paper

The researchers whose trusted networks rank it highest, strongest advocate first. Every researcher gets a different order.

In Cellular and Molecular Neuroscience

In Cognitive Neuroscience

Citations in the corpus

Hippocampal replay in the awake state: a potential physiological substrate of memory consolidation and retrieval (2011, background): “In general, hippocampal place cells form unique maps of each experienced environment, and only about 40–50% of CA1 place cells are active in any given environmen”
Awake replay of remote experiences in the hippocampus (2009, neutral): “1)20.”
Cortical firing and sleep homeostasis. (2009, background): “, 2003) relative to sleep before, suggesting that hippocampal global firing rates are stable across behavioral states and learning conditions (Buzsaki et al., 2007; Karlsson and Frank, 2008; Pavlides and Winson, 1989).”
Rewarded Outcomes Enhance Reactivation of Experience in the Hippocampus (2009, unknown): “For each cell, we calculated peak firing rate and mean firing rate as described previously (Karlsson and Frank, 2008) for all rewarded or unrewarded trials.”