Abstract
Our brain s potential to develop and reference long-lasting durable memories is an essential contributor to human evolutionary success. Of the multitude of experiences we encounter each day, only a very small subset go on to develop memory representations that are recallable after a delay period of weeks or months. However, little is known about whether or not neural mechanisms under the initial encoding of events potentially govern the selection of memories that will become subject to systems consolidation processes, and consequently durable. The aim of the present study was to put two accounts of durable memory formation to the test, and to replicate and extend the results of a recent between-groups investigation in a within-groups sample. A rapid event-related fMRI design was employed; 26 subjects were scanned whilst encoding 200 item-action evaluations and tested for later memory at two separate timepoints: both ~1.5 hours and ~3 weeks later. The experiment was part of a larger project within the Research Group for Lifespan Changes in Brain and Cognition, and the author was involved in the design, programming, and undertook all of the data collection. The analysis was carried out independently using a combination of self-written and pre-written scripts. Greater recruitment of hippocampus and distributed cortical episodic encoding networks predicted the formation of recollection memories tested after 1.5 hours, relative to both subsequently forgotten events and events remembered by weaker, more familiarity-based processes. In contrast, the encoding of durable memories was not underpinned by stronger recruitment in hippocampus, nor in typical episodic-related cortical structures, at least not beyond that which was necessary for successful representation in memory across a short delay. Moreover, this held for both durable recollection and durable recognition memory. Results indicate that the intensity-dependent account for memory formation was only apparent for memories that lasted a short duration, and that a critical threshold must be surpassed for a memory to potentially become durable, but that this threshold may be common both to the encoding of memories that last a short-delay, and those that go on to become more robustly represented in time. It is concluded that the selection of memories to undergo further post-encoding consolidation does not seem to be governed by processes that reflect the level of engagement of neural networks under encoding.
Our brain s potential to develop and reference long-lasting durable memories is an essential contributor to human evolutionary success. Of the multitude of experiences we encounter each day, only a very small subset go on to develop memory representations that are recallable after a delay period of weeks or months. However, little is known about whether or not neural mechanisms under the initial encoding of events potentially govern the selection of memories that will become subject to systems consolidation processes, and consequently durable. The aim of the present study was to put two accounts of durable memory formation to the test, and to replicate and extend the results of a recent between-groups investigation in a within-groups sample. A rapid event-related fMRI design was employed; 26 subjects were scanned whilst encoding 200 item-action evaluations and tested for later memory at two separate timepoints: both ~1.5 hours and ~3 weeks later. The experiment was part of a larger project within the Research Group for Lifespan Changes in Brain and Cognition, and the author was involved in the design, programming, and undertook all of the data collection. The analysis was carried out independently using a combination of self-written and pre-written scripts. Greater recruitment of hippocampus and distributed cortical episodic encoding networks predicted the formation of recollection memories tested after 1.5 hours, relative to both subsequently forgotten events and events remembered by weaker, more familiarity-based processes. In contrast, the encoding of durable memories was not underpinned by stronger recruitment in hippocampus, nor in typical episodic-related cortical structures, at least not beyond that which was necessary for successful representation in memory across a short delay. Moreover, this held for both durable recollection and durable recognition memory. Results indicate that the intensity-dependent account for memory formation was only apparent for memories that lasted a short duration, and that a critical threshold must be surpassed for a memory to potentially become durable, but that this threshold may be common both to the encoding of memories that last a short-delay, and those that go on to become more robustly represented in time. It is concluded that the selection of memories to undergo further post-encoding consolidation does not seem to be governed by processes that reflect the level of engagement of neural networks under encoding.