The neurobiology of safety and threat learning in infancy

What an animal needs to learn to survive is altered dramatically as they change from dependence on the parent for protection to independence and reliance on self-defense. This transition occurs in most altricial animals, but our understanding of the behavioral neurobiology has mostly relied on the infant rat. The transformation from dependence to independence occurs over three weeks in pups and is accompanied by complex changes in responses to both natural and learned threats and the supporting neural circuitry. Overall, in early life, the threat system is quiescent and learning is biased towards acquiring attachment related behaviors to support attachment to the caregiver and proximity seeking. Caregiver-associated cues learned in infancy have the ability to provide a sense of safety throughout lifetime. This attachment/safety system is activated by learning involving presumably pleasurable stimuli (food, warmth) but also painful stimuli (tailpinch, moderate shock). At about the midway point to independence, pups begin to have access to the adult-like amygdala-dependent threat system and amygdala-dependent responses to natural dangers such as predator odors. However, pups have the ability to switch between the infant and adult-like system, which is controlled by maternal presence and modification of stress hormones. Specifically, if the pup is alone, it will learn fear but if with the mother it will learn attachment (10-15days of age). As pups begin to approach weaning, pups lose access to the attachment system and rely only on the amygdala-dependent threat system. However, pups learning system is complex and exhibits flexibility that enables the mother to override the control of the attachment circuit, since newborn pups may acquire threat responses from the mother expressing fear in their presence. Together, these data suggest that the development of pups' threat learning system is not only dependent upon maturation of the amygdala, but it is also exquisitely controlled by the environment. Most notably the mother can switch pup learning between attachment to threat learning in a moment's notice. This enables the mother to navigate pup's learning about the world and what is threatening and what is safe.

Antipredator behaviour of domestic guinea pigs (Cavia porcellus)

The objective of this study was to test the reactions of domestic guinea pigs to the presence of aerial and terrestrial predators in a laboratory setting. We measured the behavioural reactions of 27 adolescent guinea pigs to the presence of a dog, imitation of a bird of prey and an unknown human as control. Kruskal-Wallis ANOVA and Mann-Whitney U Test were used to analyse the differences in duration and frequency of responses (freezing, fleeing, and vigilance) to predators. When confronted with the dog, guinea pigs reacted for the longest time and most frequently by freezing. In presence of the bird of prey, they responded for the longest time and most often by freezing and fleeing. In presence of a human, they showed mostly vigilance. When comparing reactions to the dog and human, there were differences in duration and frequency of freezing and fleeing. When comparing reactions to the bird of prey and control test, we observed differences between fleeing and vigilance. The durations and frequencies of freezing, fleeing and vigilance to the dog and bird of prey were different. The only differences in reactions of males and females occurred in duration and frequency of fleeing in presence of the bird of prey. No vocalization was observed except for two occurrences, of a “drrr” and a “chirrup”. Our results indicate that domestic guinea pigs tested under laboratory conditions can discriminate between a terrestrial and an aerial predator, when exposed to them individually. Their antipredator behaviours remained functional, although their vocalizations may have been affected by the absence of signal receivers.

Directional selective neurons in the awake LGN: response properties and modulation by brain state

Directionally selective (DS) neurons are found in the retina and lateral geniculate nucleus (LGN) of rabbits and rodents, and in rabbits, LGN DS cells project to primary visual cortex. Here, we compare visual response properties of LGN DS neurons with those of layer 4 simple cells, most of which show strong direction/orientation selectivity. These populations differed dramatically, suggesting that DS cells may not contribute significantly to the synthesis of simple receptive fields: 1) whereas the first harmonic component (F1)-to-mean firing rate (F0) ratios of LGN DS cells are strongly nonlinear, those of simple cells are strongly linear; 2) whereas LGN DS cells have overlapped ON/OFF subfields, simple cells have either a single ON or OFF subfield or two spatially separate subfields; and 3) whereas the preferred directions of LGN DS cells are closely tied to the four cardinal directions, the directional preferences of simple cells are more evenly distributed. We further show that directional selectivity in LGN DS neurons is strongly enhanced by alertness via two mechanisms, 1) an increase in responses to stimulation in the preferred direction, and 2) an enhanced suppression of responses to stimuli moving in the null direction. Finally, our simulations show that these two consequences of alertness could each serve, in a vector-based population code, to hasten the computation of stimulus direction when rabbits become alert.