# The Development of Trait Anxiety in Nonhuman Primates During the First Year of Life

## TL;DR

The study tracks how anxious behavior develops in baby monkeys during their first year, showing it becomes stable by age one.

## Contribution

The study reveals that anxious temperament in nonhuman primates becomes stable and reaches maturity by one year of age.

## Key findings

- Anxious temperament increases linearly and reaches mature levels by 52 weeks.
- Individual differences in anxious temperament and its components remain stable across development.
- Threat-related freezing, reduced cooing, and increased cortisol are consistent markers of anxious temperament.

## Abstract

Anxious temperament (AT) is a nonhuman primate phenotype that models childhood behavioral inhibition, a prominent risk factor for anxiety disorders and stress‐related psychopathology. To understand its earliest antecedents, we characterized AT's developmental trajectory over the first year of life. Infant monkeys (n = 35, 24 females) were longitudinally phenotyped for AT by assessing threat‐related increases in freezing behavior, reductions in coo‐calling, and increases in circulating cortisol at 1.5, 6, 12, 24, and 52 weeks. AT levels increased linearly, reaching mature levels by 52 weeks. Individual differences in AT, and its components, were stable across development. These findings support further studies during early primate life aimed to uncover neurobiological factors mediating development of this phenotype, which in humans is linked to stress‐related psychopathology.

Anxious temperament (AT) or behavioral inhibition (BI), a trait‐like characteristic in humans associated with later development of anxiety‐related psychopathology, is evident during earliest weeks of primate life.Developmental patterns of AT and its components (threat‐related freezing, reductions in cooing, increases in plasma cortisol) across the first year of primate life are presented.Individual differences in AT and its behavioral and hormonal components are relatively stable across the first year of life, reaching maturity by one year.

Anxious temperament (AT) or behavioral inhibition (BI), a trait‐like characteristic in humans associated with later development of anxiety‐related psychopathology, is evident during earliest weeks of primate life.

Developmental patterns of AT and its components (threat‐related freezing, reductions in cooing, increases in plasma cortisol) across the first year of primate life are presented.

Individual differences in AT and its behavioral and hormonal components are relatively stable across the first year of life, reaching maturity by one year.