One would expect training to have induced a learning-related change if, in addition, residual variance from the correlation i. This is because an effect of training that is related to learning would add to the variance in control chicks and would reveal itself in a significant correlation with preference score; residual variance about the regression line would have the same origin as in untrained chicks.
In contrast, a variance about the regression line that is significantly lower than the control variance is evidence, not for an effect of training, but merely a resorting of the control values. For example, chicks with high levels of the physiological measurement could be predisposed to learn well and chicks with low levels of the measurement predisposed to learn poorly.
Evidence of this kind for a predisposition was found by Margvelani et al. In addition, the residual variance about the regression line was significantly lower than the variance of untrained control chicks. For the reasons outlined above, it was inferred that this micro-RNA was not affected by training but was present at control levels in poor learners and low levels in good learners.
That is, its concentration reflects a predisposition to learn well or badly and is a predictor of how well chicks will learn when trained with an imprinting stimulus — see Margvelani et al.
Interestingly, levels of a protein controlled by this miRNA, cytoplasmic polyadenylation element binding protein 3 CPEB-3 , was positively correlated with preference score this direction of correlation is expected because miRNA inhibits protein translation , and the data indicate that training affect CPEB-3 level in a learning-related manner.
The miRNA, as one of the factors controlling protein level, reflects a predisposition and is not affected by training. It is not known whether the predisposition to learn referred to above is related to the other predispositions discussed in this review: there are clearly several types of predisposition and their relationships to one another remain to be elucidated.
The correlational technique outlined here see also Margvelani et al. There has been little investigation of the neural mechanism underlying a temporary preference for slight novelty during the early phase of imprinting.
There may be other possibilities, for example, metaplastic modification of the Hebbian synapses in the recognition layer, namely reducing the efficacy of Hebbian modification by recent activation of the synapses involved Abraham and Richter-Levin, The demonstration by lesion studies that the IMM is necessary for both acquisition and retention of a preference acquired through imprinting also revealed a functional difference between the left and right sides of this region.
A series of experiments indicated that the left IMM is responsible for long-term storage of a representation of the imprinting stimulus and that the right IMM also has a storage function, but of a different nature.
Conversely, if the order of lesioning is reversed, i. Presentation of two imprinting stimuli to chicks in close temporal juxtaposition results in behavior indicating that the two stimuli are classified together Chantrey, , Johnson and Horn found that chicks can learn to distinguish between two different jungle fowl models after being imprinted to one of them; moreover, this ability was abolished by lesions to the IMM.
Town a socially reared chicks in groups of six and then recorded the responses of IMM neurons, in these chicks, to video recordings of familiar and unfamiliar chicks in groups, in the presence of conspecific calls. Note that both testing and social rearing involved simultaneous visual and auditory stimulation. Under these conditions, neuronal responsiveness to the familiar chicks was lower than to novel chicks, this effect predominating in the right IMM.
Although a group of chicks rather than an individual animal was used in this experiment, the results provide evidence of remarkable learning-dependent discrimination between naturalistic stimuli, such as may be engaged in learning the features of an individual.
As noted previously, responsiveness of IMM neurons to the visual and auditory components of a familiar audio-visual imprinting stimulus are different Nicol and Horn, Responsiveness to a bisensory stimulus may be different again and not necessarily in linear combination of the constituent modalities.
As reported previously e. Responsiveness to unisensory auditory stimuli was equivocal: there was a significant interaction between stimulus familiarity and training condition but no clear indication of how either of these factors contributed, possibly because of the small number of animals involve. A particularly strong increase in responsiveness was observed when the familiar visual stimulus was presented with a novel maternal call, leading to the suggestion that IMM neurons may be sensitive to changes in the context of a familiar visual stimulus Town and McCabe, It is also apparent from these results that a response to a bisensory stimulus is not necessarily the sum of responses to its unisensory components: there can be considerable interaction between the underlying processes.
Despite the obvious need for caution in comparing neuronal activity in the IMM with behavior arising from imprinting and despite the different timescales involved, there is a noteworthy parallel between increased neuronal responsiveness to a familiar visual stimulus in a novel auditory context Town and McCabe, and the behavioral preference for slight novelty observed in the early stages of imprinting Jackson and Bateson, ; Bateson and Jaeckel, Such behavior was incorporated into the model of Bateson , Bateson and Horn consider such behavior when discussing their neural network model, postulating, in addition to the formal implementation of the model, attenuation of input into recognition modules as a result of continuous exposure to the same stimulus.
Neurobiological analysis has yet to make headway with these behavioral phenomena, important though they undoubtedly are in the life of a young animal and at least implied by existing neural network models Martinho and Kacelnik, The contribution of imprinting to social cohesion is therefore of great biological importance.
Imprinting is also experimentally tractable. Therefore, much is known about its behavioral characteristics and the underlying neural mechanisms. Modeling the behavior associated with imprinting has yielded useful insights and predictions at the behavioral level, but such models also require physiological validation, which currently is incomplete. If such validation can be accomplished, the relevant models may make an important contribution to understand social behavior at the physiological level.
The author confirms being the sole contributor of this work and has approved it for publication. The author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest. Abraham, W. From synaptic metaplasticity to behavioral metaplasticity. Ambalavanar, R. Learning-related Fos-like immunoreactivity in the chick brain: time-course and co-localization with GABA and parvalbumin.
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Margvelani, G. Micro-RNAs, their target proteins, predispositions and the memory of filial imprinting. Marshall, L. Boosting slow oscillations during sleep potentiates memory. Transcranial direct current stimulation during sleep improves declarative memory. Martinho, A. Mascalzoni, E. Innate sensitivity for self-propelled causal agency in newly hatched chicks. Songbirds have a critical period for song learning, as we will see in Signaling and Communication. Humans also seem to have a critical learning period.
In children age 4 years and younger, learning a language is almost effortless. No class is needed, no specific instruction; they pick it up on their own. After age 13, it is much more difficult to learn a language. For older people, it is virtually impossible to learn to speak as well as a native. Johnson and Bolhuis identified two independent neural systems that control filial imprinting in precocial birds. Newly hatched chicks will follow almost anything that has eyes and moves.
After the chick follows something, another part of the brain, analogous to the frontal cortex, recognizes and imprints on the individual being followed. These mechanisms are independent. There is an instinct for chicks to follow, and then they learn what they are following.
It might seem odd that being able to identify and follow a mother does not have a genetic mechanism. Yet with a neural rather than genetic mechanism, the chick gains flexibility that might help in survival.
If a chick's mother dies, the chick can then be adopted by another family member or conspecific. If the chick's recognition of its mother were genetic, the chick would not follow its adoptive parent, and would die.
Imprinting is a form of learning in which an animal gains its sense of species identification. Birds do not automatically know what they are when they hatch — they visually imprint on their parents during a critical period of development.
After imprinting, they will identify with that species for life. Imprinting for wild birds is crucial to their immediate and long-term survival. For example, precocial baby birds such as ducks, geese, and turkeys begin the process of imprinting shortly after hatching so that they follow the appropriate adult, providing them with safety.
Imprinting allows baby birds to understand appropriate behaviors and vocalizations for their species, and also helps birds to visually identify with other members of their species so they may choose appropriate mates later in life. The timing of the imprinting stage varies from species to species, and some species of birds are more susceptible to imprinting inappropriately on human caregivers for reasons not fully understood.
If young birds imprint on humans, they will identify with humans for life. Reversing the imprinting process is impossible — these birds are bonded to humans for life and will identify with humans rather that of their own species. Human-imprinted birds have no fear of people, and this lack of fear can sometimes lead to aggression toward humans.
Human-imprinted birds also frequently have a difficult time communicating with other birds of their own species— vocalizations, postures, and a fear of humans are all things that birds learn from their parents, siblings, and other birds. They are typically not accepted by other birds of their species, likely because human-imprinted birds display odd behaviors and lack the ability to communicate properly. Birds who are human-imprinted are deemed unsuitable for release back into the wild due to these inappropriate interactions.
When humans must care for orphaned or injured baby birds, Wildlife Center staffs take special precautions to prevent them from inappropriately imprinting on humans.
Human contact is kept to a minimum; the rehabilitation staff only handle birds during the feeding and cleaning process. The rehabilitation staff, students, and volunteers do not talk to the patients. For songbirds, we try to keep babies together in groups of the same species, and this is typically enough to prevent them from imprinting on humans. With our young raptors, placing them with a surrogate parent provides them with the best chance of imprinting on the appropriate species.
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