We have a strong tendency to think of things like the DIO2 gene (and its variants) in terms of their impact on conversion of thyroid hormones.
Although there is widespread understanding that thyroid hormones affect foetuses and babies, that is so often thought of as a generalised effect without understanding the detailed effects.
This paper - although in chicks rather than humans - directly identifies that T3 formed by enhanced DIO2 expression has a priming effect on at least one form of memory.
telencephalon - see en.wikipedia.org/wiki/Cerebrum
Behav Brain Res. 2018 Apr 25. pii: S0166-4328(18)30380-2. doi: 10.1016/j.bbr.2018.04.039. [Epub ahead of print]
Gene expression of Dio2 (thyroid hormone converting enzyme) in telencephalon is linked with predisposed biological motion preference in domestic chicks.
Takemura Y1, Yamaguchi S2, Aoki N2, Miura M1, Homma KJ2, Matsushima T3.
1 Department of Biology, Faculty of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan.
2 Department of Life and Health Sciences, Faculty of Pharmaceutical Sciences, Teikyo University, 2-11-1 Kaga, Itabashi-ku, Tokyo, 173-8605, Japan.
3 Department of Biology, Faculty of Science, Hokkaido University, N10 W8, Kita-ku, Sapporo, Hokkaido, 060-0810, Japan.
Filial imprinting leads to the formation of social attachment if training is performed during a brief sensitive period after hatching. We found that thyroid hormone (3,5,3'-triiodothyronine, T3) acts as a critical determining factor of the sensitive period in domestic chicks. Imprinting upregulates gene expression of the converting enzyme (Dio2, type 2 iodothyronine deiodinase) in the telencephalon, leading to increased brain T3 content. If systemically applied, T3 facilitates imprinting in aged chicks even after the sensitive period is over. Imprinting is also associated with the rapid development of visual perception. Exposure to motion pictures induces a predisposed preference to Johansson's biological motion (BM), and those individuals with higher BM preference are more easily imprinted. Here, we examined whether Dio2 expression is also linked with BM predisposition. Chicks were trained by a rotating red block, and tested for imprinting (experiment 1) and BM preference (experiment 2). To examine the time courses of behavioural and physiological processes, Dio2 expression in telencephalon was compared among three groups: naïve control chicks, and chicks trained for a short (0.5 h) or long period (2 h). In experiment 1, higher Dio2 expression appeared in the 2-h group than in the 0.5-h/control groups, but it was not correlated with the individual imprinting score. In experiment 2, a significant positive correlation appeared between Dio2 expression and BM preference in 2-h-trained chicks. Memory priming by T3 is therefore functionally linked to BM preference induction, leading to successful imprinting to natural objects even when they are initially exposed to artificial objects.
Imprinting; biological motion; innate predisposition; memory; thyroid hormone