Friday, November 10, 2006

Memory enhancement by non-invasive electrical stimulation   posted by amnestic @ 11/10/2006 05:09:00 PM

Nature reported and Robert Stickgold commented on a study by Marshall et al. They trained folks to remember some wordpairs and then stuck electrodes on their scalp while they were sleeping. By providing rhythmic stimulation across the cortex they were able to increase the amount of time spent in a specific sleep stage: slow-wave sleep. You know some sleep stages, right? Like REM is the sleep stage where you're dreaming and things like that. Slow-wave sleep is a non-REM stage. The volunteers that received this stimulation remembered word pairs better than the ones who did not. Slow-wave sleep is especially interesting because a characteristic cortical rhythm called a "sleep spindle" can be recorded during that time, and other studies have shown that firing of hippocampal cells becomes coordinated with that of cortical cells during these patterns.

Our results indicate that slow oscillations have a causal role in consolidating hippocampus-dependent memories during sleep. How could slow oscillations promote the plastic neuronal changes that underlie such memory consolidation? One plausible mechanism might involve calcium transients mediated by spindle activity2, 23, 24, as spindle activity was enhanced by slow oscillation stimulation. Not only is spindle activity probably associated with massive Ca2+ influx into neocortical pyramidal cells, but there is also evidence that repeated spindle-associated spike discharges can trigger long-term potentiation in neocortical synapses25. As synchronous spindle activity occurs preferentially at synapses previously potentiated by tetanizing afferent stimulation26, slow-oscillation-driven spindle activity might contribute to the strengthening of synaptic connections in neocortical circuitry.

They ran lots of control memory tasks and found that the enhancement was specific for declarative memory (the wordpair test) as opposed to motor learning tasks. I might've like to see an attentional or working memory task on the second day to show that the sham-stimulated group weren't just groggy or something.