Why are individuals so different from each other?

An important contributor to the differences between individuals derives from their plasticity. Such plasticity is widespread in organisms from the simple to the most complex. Adaptability plasticity enables the organism to cope with a novel challenge not previously encountered by its ancestors. Conditional plasticity appears to have evolved from repeated challenges from the environment so that the organism responds in a particular manner to the environment in which it finds itself. The resulting phenotypic variation can be triggered during development in a variety of ways, some mediated through the parent's phenotype. Sometimes the organism copes in suboptimal conditions trading off reproductive success against survival. Whatever the adaptedness of the phenotype, each of the many types of plasticity demonstrates how a given genotype will express itself differently in different environmental conditions-a field of biology referred to as the study of epigenetics. The ways in which epigenetic mechanisms may have evolved are discussed, as are the potential impacts on the evolution of their descendants.

Developmental shifts in the behavioral phenotypes of inbred mice: the role of postnatal and juvenile social experiences.

The interaction between genotype and environment is an important feature of the process of development. We investigate this interaction by examining the influence of postnatal cross-fostering and post-weaning cross-housing on the behavioral development of 129S and B6 mice. Following cross-fostering, we found significant alterations in the frequency of maternal care as a function of maternal strain and pup type as well as interactions between these variables. In adulthood, we find there are sex-specific and strain-specific alterations in anxiety-like behavior as a function of rearing environment, with males exhibiting more pronounced rearing-induced effects. Mixed-strain housing of weanlings was found to lead to alterations in home-cage social and feeding behavior as well as changes in adult anxiety-like responses of 129S mice. Anxiety-like behavior in B6 mice was altered as a function of the interaction between housing condition and weaning weight. These data illustrate the complex pathways through which early and later social experiences may lead to variations in behavior.

Unusual complications of ballooned feeding tubes.

Percutaneous Endoscopic Gastrostomy (PEG) and Feeding Jejunostomy (FJ) with a Foley catheter are well-established techniques for providing long-term nutritional support. Mechanical complications of these procedures are well recognised. We report two unusual complications of feeding tubes related to the balloon. Patient 1: A 23 years old female cerebral palsy patient had a PEG tube changed to a ballooned gastrostomy tube. Following this she developed abdominal cramps, vomiting and later on haematemesis. Contrast study showed migration of the balloon causing pyloric obstruction and a small prepyloric ulcer. Partially deflating the balloon and pulling it back to the original position corrected this. Patient 2: A 39 years old male cerebral palsy patient with a Foley catheter feeding jejunostomy developed obstructive symptoms within 48 hours of surgery. The balloon was deflated repeatedly without resolution. The catheter was impossible to withdraw and irrigate. Contrast instilled via the balloon channel demonstrated that the catheter was significantly stretched and the balloon was in terminal ileum. The balloon was fully deflated and easily withdrawn to be replaced with uninflated Foley catheter. Enteral feeding was easily reestablished. If a patient with a ballooned feeding tube develops intestinal symptoms balloon complications should be suspected. Contrast study through the feeding channel or balloon inflation channel is useful in diagnosing tube related complication. The threshold for imaging should be low, particularly in patients who are difficult to assess clinically.

Genes, environment and the development of behavior.

Explanations of where our behaviour comes from are frequently presented in terms of the exclusive importance of one set of factors, either genetic or environmental. Unravelling the external and internal sources of individual differences is a useful first step in analysing behavioural development. Nevertheless, the analytical method that was well designed for extracting influences from a confusing mass of data was never a substitute for a theory. It was simply a means to an end. Descriptive statements about the genetic and environmental sources of variation in the population do not offer an adequate basis for understanding what happens to individuals. That awareness was an important step in moving towards an adequate theory of behavioural development. As an example of how that may be done, I discuss the interplay between the developing individual and its environment in highly regulated learning processes such as imprinting. Getting the level of explanation right is crucial. A purely molecular or synaptic account of the processes involved in the development of behaviour is inadequate. Nevertheless, those connectionist models that are properly rooted in a thorough knowledge of behaviour and physiology do provide a promising route out of the reductionism and the empty interactionism that characterized the old nature-nurture debates.

Physiological effects of hunting red deer (Cervus elaphus).

When red deer (Cervus elaphus) were hunted by humans with hounds the average distance travelled was at least 19 km. This study of 64 hunted red deer provides the first empirical evidence on their state at the time of death. Blood and muscle samples obtained from hunted deer after death were compared with samples from 50 non-hunted red deer that had been cleanly shot with rifles. The effects on deer of long hunts were (i) depletion of carbohydrate resources for powering muscles, (ii) disruption of muscle tissue, and (iii) elevated secretion of beta-endorphin. High concentrations of cortisol, typically associated with extreme physiological and psychological stress, were found. Damage to red blood cells occurred early in the hunts; possible mechanisms are discussed. Taken together, the evidence suggests that red deer are not well-adapted by their evolutionary or individual history to cope with the level of activity imposed on them when hunted with hounds.

Stimulus comparison and perceptual learning: further evidence and evaluation from an imprinting procedure.

Two experiments used chicks to investigate the role of stimulus comparison in perceptual learning. In Experiment 1, chicks received exposure to two views of a jungle fowl, SV (side view) and BV (back view), intermixed within a session (mixed exposure), exposure to SV in one session and BV in a different session (separate exposure), or no exposure to either view. All chicks then received a heat-reinforced discrimination with SV and BV serving as discriminanda. Chicks given mixed exposure acquired the discrimination more readily than did either those given separate exposure or those given no exposure. In Experiment 2, all chicks received mixed exposure to the two stimuli. For one group the interval between presentations of the stimuli was short (short-mixed), for the other group it was long (long-mixed). Subjects in the long-mixed condition acquired the heat-reinforced discrimination more rapidly than those in the short-mixed condition. These results suggest that the intermixed nature of stimulus exposure is an important determinant of the magnitude of perceptual learning effects.

Functionally distinct memories for imprinting stimuli: behavioral and neural dissociations.

Precocial chicks exposed to a stimulus subsequently approach that stimulus in preference to other, novel stimuli. Previous investigations of the neural basis of these imprinting preferences suggest that imprinting training results in the formation of two memories. The first memory is formed rapidly and is located in the intermediate and medial part of the hyperstriatum ventrale (IMHV) of the left hemisphere; the formation of the second, in another memory system, S', takes several hours and can be prevented by a lesion placed in the right IMHV soon after training. The results of the present study suggest that the functional characteristics of these memories differ. Although memories in both left IMHV and S' supported imprinting preferences (Experiments 1a and 2a), only memories in S' influenced the acquisition of a heat-reinforced discrimination in which imprinted objects served as discriminanda (Experiments 1b and 2b).

The role of stimulus comparison in perceptual learning: an investigation with the domestic chick.

In two experiments an imprinting procedure was used to familiarize chicks with two stimuli, A and B, that subsequently served as the discriminanda in a simultaneous discrimination. On the first day of each experiment, subjects either received presentations of A and B that were intermixed within a session (mixed exposure) or presentations of A in one session and of B in another (separate exposure). For half of the subjects in each of the exposure conditions, A and B differed in both colour and form; for the remainder A and B differed in form alone. On the second day of the experiments, the chicks were placed into a cool test apparatus and given training in which approaching A was rewarded by the delivery of a stream of warm air, but approaching B was not. Acquisition of this discrimination was more rapid when A and B differed in two respects than when they differed in form alone. When A and B differed in both colour and form, the heat-reinforced discrimination was acquired more rapidly after separate exposure than after mixed exposure; but when A and B differed in form alone, discrimination learning was more rapid following mixed exposure than separate exposure. The latter finding, that the opportunity to compare stimuli differing in only one dimension facilitates subsequent discrimination learning, is consistent with earlier suggestions (Gibson, 1969) regarding the conditions that promote perceptual learning.

The dynamics of parent-offspring relationships in mammals.

Evolutionary theories about parent-offspring relationships have predicted that young will aggressively demand food and care from their parents at the time of weaning - when the parents should, in their own interests, reserve their efforts for future offspring. Detailed studies of the behavioural development of mammals have given only limited support for these expectations. Often the mother is more amenable to the needs of her offspring than evolutionary theory predicts, and often offspring are sensitive to the state of their mother, tuning the pattern of their own development accordingly. Such aggression as is seen between mother and offspring tends to occur at stages other than weaning. The mismatch between theory and evidence may arise because a mother needs to monitor her offspring's state as well as her own and respond appropriately in order to maximize her own reproductive success. Similarly, an offspring needs to monitor its mother and prepare for the world in which it will grow up, in order to maximize its chances of surviving to breed.

Laparoscopic cholecystectomy: experience in a district general hospital.

In many centres laparoscopic cholecystectomy has become the procedure of choice for symptomatic gallbladder stones. By comparison with conventional cholecystectomy it appears to be associated with minimal morbidity, shorter hospital stay, earlier return to work and a better cosmetic result. The present study reviews the results of the first 50 laparoscopic cholecystectomies performed at Altnagelvin Area Hospital.

Stimulus representation: a subprocess of imprinting and conditioning.

We suggest a way to reconcile imprinting and associative learning that respects the real differences between the two phenomena but helps to recognize underlying commonalities. Rather than treating each type of learning as the manifestation of a unitary mechanism, we approach learning as a combination of separate subprocesses. Exploration of the literature regarding one of these subprocesses, namely, that governing the representation of stimuli, revealed striking similarities between imprinting and conditioning. These similarities suggest predictions for fresh experimental work that will help to uncover the general rules by which combinations of stimulus features are represented in memory.