Decimal understanding in young children

Understanding number magnitude is fundamental to mathematics achievement. In this longitudinal study, researchers investigated the nature of students’ decimal understanding early in the 4^th grade, prior to them receiving formal instruction. The aim was to determine if this predicted later mathematics achievement.

Despite a lack of formal instruction, ~15% of students had a good understanding of decimal magnitudes. The ~20% who had a partial understanding made systematic errors, most commonly exhibiting a whole-number bias (e.g. believing 0.07 > 0.1) while understanding place value (e.g. 0.01 < 0.1). Notably, the authors found that decimal understanding in 4^th grade, prior to receiving formal instruction, predicted both later understanding of fractions as well as mathematics achievement in 6^th grade. They suggest that decimal instruction could occur earlier in school to improve later outcomes.

Resnick et al. (2019) Children’s reasoning about decimals and its relation to fraction learning and mathematics achievement. Journal of Educational Psychology 111(4): 604-618 DOI: http://dx.doi.org/10.1037/edu0000309

Sleep stabilises memory consolidation

In the dual-storage model of memory, consolidation is thought to involve movement of the memory trace from the hippocampus to the neocortex. Much of this consolidation is thought to occur when memories are replayed during post-learning sleep. However a 2016 article showed that for spatial memories, some consolidation occurs even prior to sleep, as learning material is repeated during mental rehearsal. This consolidation is evident as increased neocortical and decreased hippocampal activity.

In this study, the same research group first shows that mental rehearsal also consolidates non-spatial memories, in this case memory for words. They also show that such rehearsal-mediated consolidation is lost if subjects do not sleep soon after learning. Thus sleep is necessary to stabilise the early consolidation that occurs during repeated memory rehearsal.

Himmer et al. (2019) Rehearsal initiates systems memory consolidation, sleep makes it last. Science Advances 5(4): eeav1695 DOI: https://doi.org/10.1126/sciadv.aav1695

Brain stimulation improves working memory in older adults

Our cognition, including our working memory, declines as we age. Some evidence indicates this may be due to poor synchronisation of neural activity between brain regions, preventing efficient communication.

In this study, researchers first confirmed that compared to 20-29 year-olds, older adults (aged 60-76) had impaired working memory and disrupted brain wave synchronisation in the temporal and prefrontal cortices. Next, the authors stimulated the brains of older subjects in an attempt to temporarily improve working memory. Twenty-five minutes of transcranial alternating current stimulation (tACS) improved older adults’ working memory accuracy to the level of the young adults. This was accompanied by local and inter-regional synchronisation of brain waves in the prefrontal and temporal cortices. The effects lasted for at least 50 minutes, the longest time point the researchers tested.

Reinhart and Nguyen (2019) Working memory revived in older adults by synchronizing rhythmic brain circuits. Nature Neuroscience 22: 820-827 DOI: https://doi.org/10.1038/s41593-019-0371-x

Forming memories without experience

Scientists are increasingly able to manipulate memories in animals. Previous efforts have even implanted false memories in mice, something that required the mice to first link two sensory experiences. In this study, researchers go a step further, creating a completely new memory that did not require previous sensory experience.

The researchers relied on optical and genetic tools that let them artificially activate an odor pathway at the same time as pathways for either reward or aversion. As a result, the mice linked the odor to positive or negative outcomes. Indeed, after these artificial activations, mice showed a preference for (or against) a room holding that odor, even though they had never physically experienced the odor itself before.

Vetere et al. (2019) Memory formation in the absence of experience. Nature Neuroscience DOI: https://doi.org/10.1038/s41592-019-0389-0