Werker - interpreting the research

So there were two possible explanations for this pattern of results. One is that SRI exposure just disrupts the circuitry in such a way that it interferes with learning or perception or performance in the tasks that we were looking at, and there is indeed evidence that exposure to SRIs does change tonotopic organization in the primary auditory cortex, so that was one possibility. The other possibility was that exposure to SRIs had moved the whole sort of sensitive period earlier in development and that changes had been taking place even before six months of age, and that had we tested the babies at a younger age, we might have seen discrimination.

So what we had in our data set, we hadn’t tested them at four months or two months or even at birth, but what we did have in our data set was we had looked at discrimination of vowels and consonants in utero, at 36 weeks of age by measuring the fetal heart rate deceleration to a change. You get a deceleration if they hear like da da da da da da over and over again and then it changes to ta you get a temporary deceleration in heart rate and previous work has shown that at 36 weeks gestation fetuses discriminate vowels, but there’s no evidence that they discriminate very similar consonant sounds that early.

 So we tested them on a da ta distinction as well as an ah e distinction and what we found is that we had babies, we had fetuses whose mothers were taking SRI in our sample and fetuses whose mothers were not depressed and were not taking SSRIs.  We didn’t have a group of non-exposed depressed moms’ babies in that sample. What we found is that both groups of babies discriminated the vowel distinction, well both groups of fetuses at 36 weeks, so discrimination was still in place in the SRI babies. They were doing exactly what had been reported in the previous literature for a typical population. Interestingly, we also replicated the inability of 36-week fetuses who had not been exposed to SRIs to discriminate the consonant distinction, but the SRI exposed fetuses did discriminate it.

So the interpretation we have for this whole set of findings then is that SRI exposure accelerates this onset of plasticity and the pathways by which it does so may not be, they may be the typical pathways by which serotonin works, but they may also instead be different pathways that have already been implicated in changing plasticity in gaba pathways that have already been implicated so it may be a different set of pathways so that sensitivity to the properties of native language and then the decline in sensitivity is all pushed earlier.

So we think then that SRI exposure accelerates the onset of plasticity, but the answer for depressed moms is not don’t take SRIs because there are also developmental implications of maternal depression that is not treated with SRIs. The take home message that we want to give mothers here is to not beat yourself up if you’re depressed, the incidence of depression is very high, people, women in particular, are much too likely to experience a period of depression in their lives. The message is that by doing this kind of research that allows us to understand what the effect is and then we collaborate with, Techau-Hinch does animal model work, where we can get into the circuits and understand exactly how depression and/or SRI exposure modify development that we’re in a position to work with moms and say okay, you’re depressed, you had this happen you had that happen, all sort of things happen to our infants and to us while we’re pregnant or while we’re raising our children that we can’t control, but by understanding more mechanistically what the effects are on the process of development we’re in a better position to optimize development for children and for their mothers.

In our lab, we haven’t so far, looked at how the quality of mother infant interactions can impact and interact with these different sort of trajectories of development but I think that’s a really interesting and important area for further research.