Critical Period For Imprinting Research Articles

Development of two transmitter release components during the critical period for imprinting in the chick IMHV.

Transmitter release at an excitatory synapse has two components, fast synchronous and slow asynchronous transmitter release. Using the whole cell recording technique, we investigated the developmental properties of neurotransmitter release, which is composed of the two components in the intermediate and medial part of the hyperstriatum ventral (IMHV) of chicks during the critical period for imprinting. Analysis of the paired-pulse responses revealed that the depression of the excitatory postsynaptic currents (EPSCs), driven mainly by fast synchronous release, was frequently observed in P0-1 chicks but not in those at P5-8. The spontaneous excitatory postsynaptic currents (sEPSCs) after the paired-pulse stimulation, which were thought to be driven by asynchronous transmitter releases, were observed more frequently in P0-1 chicks than P5-8 chicks. Furthermore, examination of Ca2+ dependency in the evoked EPSCs showed that the amplitudes in P5-8 chicks were more sensitive to reduction of the extracellular Ca2+ concentration than younger chicks. Considering that the Ca2+ dependency of EPSCs is defined by both Ca2+ sensitivity and the proportion of each type of release machineries at the release site, these results indicate that the ratio of fast synchronous to slow asynchronous transmitter release machinery changed during the critical period. These changes may play critical roles in the capacity of the avian brain to consolidate novel experience in the immediate period after hatching.

Homing of Rainbow Trout Transplanted in Lake Michigan: A Comparison of Three Procedures Used for Imprinting and Stocking

We compared the homing ability of three groups of rainbow trout (Salmo gairdneri) stocked in Lake Michigan by different procedures. One group of juvenile rainbow trout was imprinted to a synthetic chemical, morpholine, during the presmolt and smolt stages, and a second group was not imprinted. Both groups were stocked directly into Lake Michigan, 1 km north of the Little Manitowoc River. A third group of trout was retained in a pond on the Little Manitowoc River during the presmolt and smolt stages and then released into Lake Michigan at the same location as the other two groups. During the adult spawning migration, morpholine was metered into the Little Manitowoc River. This river and 16 other locations were monitored for returning fish. The morpholine-imprinted fish returned to the Little Manitowoc River in greater numbers and strayed less than did fish from the other two treatment groups. This result is a consequence of exposure to a unique odor cue at the critical period for imprinting.

Following and visual imprinting in ducklings across a wide age range.

Ducklings ranging in age from 20-125 hr were exposed to a moving silent object in an open circular apparatus until a criterion of 300 sec of following was met. All ducklings met the criterion, and age did not correlate with the time required. In subsequent choice tests most ducklings approached the imprinting object over a novel object, and age did not correlate with choice behavior. Results indicate that imprinting can occur over a fairly wide age range, and that the traditional critical period for imprinting may, in part, be an artifact of laboratory methods.

Imprinting: A Reassessment

Chicks exposed to a moving model during their critical period for imprinting will subsequently demonstrate a preference for that model if it is stationary. In preference tests with moving models, other preferences appear to over-ride the effects of the imprinting experience.

Parameters of Imprinting

Imprinting involves the rapid establishment of perceptual preferences. It is clearly distinct from the "following-response," though most experimenters have tended to confuse the two. It is in motorically precocial forms requiring parental care that imprinting generally occurs, or in cases where the pattern upon which imprinting should occur is only briefly present. Neither the factors that initiate nor those that terminate the critical period for imprinting, nor those that determine the stability of the imprinted bond are known. The social and ecologic consequences of imprinting may include fetishism, the maintenance of barriers to hybridization, and of species-characteristic habitat preferences. Imprinting also permits these latter to change with extreme rapidity.

A possible relationship between the imprinting critical period and arousal

Observations are reported on changes in wakefulness of chicks over the first 24 hour period after hatching. The course of these changes, from a low level of apparent arousal shortly after hatching to a high peak in the middle of the period and returning to a low level again by the end of the period, corresponds strikingly with the course of the critical period for imprinting reported by at least one previous investigator. It is suggested that these results for the critical period may be accounted for by change in arousal. Existing evidence for the tenability of this suggestion is examined.

Some Relationships Between Early Experience and Later Social Behavior in Ducklings 1)

Three experiments were performed to investigate the effects of certain kinds of early experiences upon the later behavior, primarily social, of Peking ducklings. 1. Experiment I investigated whether the age at which exposure to a green cube occurred and whether any exposure that occurred had any effect upon the later preference shown by the Ss for the cube versus a duck model. Also varied was whether Ss were raised as pairs or as isolates. Subjects exposed to the cube during the age for imprinting showed stronger following of the cube than did Ss exposed during the age for avoidance. However, these groups did not differ in their later preference for the cube in the choice test. Whether Ss were raised as pairs or isolates did not affect their following scores or their preference scores but had a marked effect upon their later flocking behavior. Pair raised Ss flocked readily, while isolate reared Ss ran from each other. However, isolate reared Ss that were exposed to a moving cube during the critical period for imprinting showed stronger flocking behavior than other Ss. The fear shown by the isolate reared birds was readily overcome by 22 hours confinement in groups of 3 or 4 in a 3 foot cubicle. 2. Experiment II investigated the effects of primacy versus recency upon later preference behavior. Subjects were exposed daily to a moving cube or a companion duckling, some Ss experiencing the cube the first five days and the duck the next 5 days. Other Ss experienced them in the reverse order, while a third group had no exposure the first 5 days and were exposed to the cube the next 5 days. All Ss were then given a choice between the moving cube and a live duckling. The results of this experiment showed that exposure to an object early in life leads to better following of another object later than does no early exposure. Also there was evidence that both primacy and recency are important, but, other things being equal, a live duckling is a stronger stimulus for approach behavior than is a green cube. 3. Experiment III was designed to determine whether the age at which exposure to another duckling occurred would affect the rate at which a S would later run to get to a stimulus duckling. It was found that the age of exposure was not nearly so important as the length of the exposure-test interval. Apparently the shorter this interval, the faster the S will run. 4. In general it was found that imprinting is not necessary to later social behavior, since birds raised in isolation show flocking behavior after confinement in close quarters. There was also evidence that imprinting is not necessarily object specific for Ss exposed during the critical period for imprinting can transfer to other objects more successfully than Ss not so exposed. There was some evidence that, other things being equal, a S is likely to prefer the imprint object to other objects. The question of relative potency of stimulus objects was raised when Ss showed a marked preference for a sibling duck over a green cube, regardless of the pattern of previous exposure to the two objects. If Ss have not had the opportunity to imprint and establish social behavior before the fear response occurs, it is still possible to socialize these Ss by confining them for a period of time in close quarters. The social behavior thus established is not apparently different from that established during the critical period for imprinting. In fact, the fertile eggs, from which the subjects of these experiments were hatched, came from a flock of ducks which had been raised as isolates until 25 days of age.

The influence of patterned-light deprivation on the critical period for imprinting.

The influence of patterned-light deprivation on the critical period for imprinting.

An electrical investigation of effects of repetitive stimulation on mammalian neuromuscular junction.

An electrical investigation of effects of repetitive stimulation on mammalian neuromuscular junction.