ИСТИНА

Memories are hypothesized to be encoded by distributed cell assemblies, however little is known about consistency of activation of such neuronal populations. An essential question is how similar are these activations during memory encoding and subsequent episodes of retrieval. To study this question we investigated neuronal activity of the mouse associative cortex in auditory fear conditioning and memory recall in response to conditioned sound. We used optic fiber recording and two-photon visualization of activated neurons in the cortex of awake transgenic mice in which the expression of enhanced green fluorescent protein (EGFP) was under the control of c-fos immediate early gene promoter. With optic fiber technique we characterized time course of induced fos-EGFP expression. Then we compared populations of active neurons in the same area of parietal associative cortex before learning, following learning and following memory retrieval. The largest proportion of identified neurons was active during all three conditions (79%). Most neurons, which were not active before learning, but were activated during learning, were also activated during memory retrieval (10% of all identified neurons). The small parts of identified neurons were activated only during learning or memory recall (3% or 2% respectively). Thus, our results indicate that the main part of neuronal population in the mouse parietal associative cortex that was transcriptionally activated during fear memory encoding, was then reactivated during cue-induced memory retrieval.