Tuesday, September 28, 2010

The impairment of memory consolidation in psychiatric patients

ResearchBlogging.orgGenzel L, Ali E, Dresler M, Steiger A, & Tesfaye M (2010). Sleep-dependent memory consolidation of a new task is inhibited in psychiatric patients. Journal of psychiatric research PMID: 20869069

Just a little update, since I've been slacking lately.

The authors looked at schizophrenic and depressive Ethiopian patients given a sequential finger tapping task (a motor task used often in sleep research because the timing can be measured and for the simplicity of the task). The all participants were, notably, keyboard naive - and so everyone learning the tapping task weren't used to the feeling of keys under their fingers. Trials 1-12 of the task were done on day 1, 6 more trials (13-18) on day 2, and 6 more (19-24) on day 3.

The good: the authors do clearly show an increase in performance (measured in number of correctly tapped sequences in 30 seconds) for healthy participants. So far, in line with prior studies. Now, schizophrenic patients and depressive patients do not show an increase in performance with sleep - suggesting something's going on (and I suspect it lies in the patterns of synaptogenesis that underlie sleep which have been suggested in depression and schizophrenia - but that's my speculation).

The not-so-good: The authors infer between trials one and six an increase in performance in healthy controls that they claim does not exist in the psychiatric patients. They show a nice box and whisker, and spit out the p-values, but they seem to run into the problem again that "not being able to rule out the null" (in this case, the difference between trials one and six for the psychiatric patients was not significant). Remember: just because you can't rule it out doesn't mean the null is true either. It could just as well mean you have a lot of variability and an underpowered study - which, with small ns like this, is particularly problematic.

In any case, interesting from a sleep perspective, and probably just as much so to those who deal in the neural mechanisms that underlie psychiatric disorders.