A paper published earlier this week in the journal Molecular Psychiatry claims reactions to unfamiliar sounds, smells and objects at four-months could predict the development of anxiety disorders later in life. The authors say they’ve found the earliest examples of infant behaviour showing continuity with brain activity in adulthood.
Researchers conducted a longitudinal study with 135 four-month old male and female infants who were introduced to a set of novel or unfamiliar visual, auditory and olfactory stimuli at the start of the study.
They followed up with further research 18 years later and concluded that male infants who’d reacted with more crying and limb movement in the first part of the study (graded as highly reactive) showed more reactivity in the part of the brain known as the amygdala when presented unfamiliar faces as adults. The finding was only significant in males and the authors conclude that it may predict a predisposition to anxiety disorders.
Professor of Developmental Psychiatry and Director of the Monash University Centre for Developmental Psychiatry & Psychology, Louise Newman comments on the findings of the study.
This is a very interesting and important study that demonstrates quite a significant relationship between infant state and adult brain response patterns to unfamiliar faces. The authors see this as illustrating a link between a “temperamental variable” and adult brain function.
The role of temperamental variation and adult responses is an ongoing matter of discussion in the field with some now arguing that innate differences can predispose people to a range of future mental disorders.
The study looks at the functioning of the amygdala, which is a part of the brain very much involved in reaction to novel stimuli and to perceptions of what might potentially be a threat, and links it to a predisposition to anxious responses and even anxiety disorders in adult life.
But this sort of paper raises more interesting questions than it answers. The first one of these questions is about continuity: to what extent do mental states experienced in infancy predict ongoing states or are related to them? The authors seem to be arguing that this study illustrates that there is such a continuity.
The other point they make is that the association between infant reactions and adult anxiety is due to temperament rather than shaped by the environment. Even though the study involved quite young infants, that’s a really debatable point.
Brain development and responses are shaped from birth by interaction with carers and are influenced by the quality of emotional interaction. It’s actually very hard to say with certainty that any brain response identified at even four months of age is entirely due to innate factors and not influenced by the environment.
The third point they make (and this is even more debatable) is that temperament might be related to adult-type mental disorders – that maybe these temperamental variables are themselves related to or predict anxiety disorders. But the study authors present no evidence for the claim and I think that’s another one of the contentious issues that come out of these kinds of studies.
A matter of definitions
What they say about the temperamental variable is also puzzling. The authors define temperament in a very broad way that includes cognition and other factors only evident in later childhood when it’s even more likely that such variables reflect parenting and other environmental influences.
Obviously there is such a thing as difference in temperament and most people will concede individual difference in neuro-physiological reactivity or level of response to novel or unfamiliar stimuli but that doesn’t necessarily relate to ongoing personality traits.
The authors are using the word temperament in such a broad sense that they’re talking about personality dysfunction. And I think the problem with that is that we know temperament and its expression are very much shaped by environmental factors.
Even in infants as young as four months of age, the quality of care and parenting that infants get and the quality of emotional interaction is already shaping the expression of their individual differences, whatever they might be, as well shaping brain development.
So it’s not that easy to distinguish how much is innate versus how much is environmentally shaped or whether it’s a combination of the two. And it’s much more likely that it’s a combination of the two.
And while there are individual differences in reactivity, the capacity of parents and carers to accommodate the needs of infants and respond to those differences is really very important in shaping brain development.
The role of care
So how parents respond to a so-called reactive or anxious infant is going to be very important in shaping how the brain develops and what that infant’s personality style or management of anxiety is going to be in the future.
What’s more, how much of infant experience or infant involvement is related to later traits or functioning or even mental disorders is quite a contentious issue.
But there is a growing body of evidence that early adversity or early trauma influences early brain development, which is associated with later difficulty.
And again, that’s not to say that it’s a simple linear relationship.
Most of the evidence keeps coming back to the fact that quality of care – parenting and interaction – is a mediating variable. So attachment is an important mediating variable for these associations between infant states and anxiety disorders in adulthood.
Foretelling the future
This particular study opens up really interesting questions about how predictive early states are and what factors influence associations between these states and adult behaviours – is it related to mental disorder or is it a personality trait?
But the study also highlights that we need to get better at identifying risk factors for developmental problems and that our interventions around that very young age group will have to be neuro-protective interventions. That is, interventions will need to do things to protect brain development and optimise neurological function.
This could have huge implications for the meaning of the term early intervention, and would mean radically reforming services at that age.
In terms of society, it suggests the need for much greater support for parents who are running into difficulties or for those infants who have temperamental difficulties or infants with specific needs. It will certainly influence how services are set up.