Social isolation in the gerbil: its effect on exploratory or agonistic behavior and adrenocortical activity.
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Adrenal Glands↗
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Rates of pediatric injuries by 3-month intervals for children 0 to 3 years of age.
OBJECTIVE: Mortality and morbidity data on childhood injury are used to construct developmentally appropriate intervention strategies and to guide pediatric anticipatory counseling on injury prevention topics. Effective anticipatory guidance depends on detailed injury data showing how risks change as children develop. Conventional age groupings may be too broad to show the relationship between children's development and their risk of various causes of injury. Previous studies revealed differences in overall rates and specific causes of injury by year of age. However, single year of age rates for children younger than 4 years may not reflect the variations in risk as a result of rapid developmental changes. This study was designed to analyze injury rates for children younger than 4 years by quarter-year intervals to determine more specifically the age period of highest risk for injury and for specific causes. METHODS: We used data from 1996-1998 California hospital discharges and death certificates to identify day of age and external cause of injury (E-code) for children younger than 4 years. The number of California residents for each day of age was estimated from US Census of estimates of California's population by year of age for the midpoints (1996-1998). Rates were calculated by 3-month intervals. We grouped the E-codes into major categories that would be particularly relevant for developmentally related risks of injury specific to young children. The categorization took into account physical, motor, behavioral, and cognitive developmental milestones of children 0 to 3 years. RESULTS: There were a total of 23,173 injuries; 636 resulted in death. The overall annual rate for children aged 0 to 3 years was 371/100,000. Beginning at age 3 to 5 months, the overall rate of injury rapidly increased with increased age, peaking at 15 to 17 months. The mean injury rate calculated for each single year of age did not reflect the variation and the highest rate of injury by quarter year of age for children younger than 1 year, 1 year, and 2 years. The leading major causes of injury in descending order were falls, poisoning, transportation, foreign body, and fires/burns. The overall rate of the major category of falls exceeded poisoning, the second leading cause of injury, by a factor of 2. Age-related differences were detected within each major cause of injury. For children 0 to 12 months of age, there was a different leading cause of specific injury for each 3-month period: other falls from height (0-2 months), battering (3-5 months), falls from furniture (6-8 months), and nonairway foreign body (9-11 months). Hot liquid and vapor injuries were the leading specific causes for children 12 to 17 months. Poisoning by medication was the leading specific cause of injury for all age groups from 18 to 35 months and exceeded poisoning by other substances. Pedestrian injury was the leading specific cause of injury for all age groups from 36 to 47 months. Fall from furniture has the highest rates of specific causes of falls from age 3 to 47 months. Fall from stairs peaked at age 6 to 8 months and 9 to 11 months. Fall from buildings was highest at 24 to 26 months. Poisoning by medication peaked at age 21 to 23 months, but poisoning by other substances peaked at 15 to 17 months. The motor vehicle occupant injury rates were fairly stable over the age span of this study. The pedestrian injury rate increased beginning at age 12 to 14 months and by 15 to 17 months was double that of the motor vehicle occupant. Foreign body had a marked peak at age 9 to 11 months. Both battering and neglect rates were highest among infants 0 to 2 and 3 to 5 months. Bathtub submersions had a narrow peak at age 6 to 11 months. Other submersions peaked at 12 to 14 months and remained high until 33 to 35 months. CONCLUSIONS: We departed from usual groupings of E-codes and devised groupings that would be reflective of age-related developmental characteristics. Differences in rates by narrow age groups for young children can be related to developmental achievements, w can be related to developmental achievements, which place the child at risk for specific causes of injury. We found marked variability in both rates and leading causes of injury by 3-month interval age groupings that were masked by year of age analyses. Children aged 15 to 17 months had the highest overall injury rate before age 15 years. This coincides with developmental achievements such as independent mobility, exploratory behavior, and hand-to-mouth activity. The child is able to access hazards but has not yet developed cognitive hazard awareness and avoidance skills. A remarkable finding was the high rate of battering injury among infants 0 to 5 months, suggesting the need to address potential child maltreatment in the perinatal period. Poisoning was the second major leading cause of injury; more than two thirds were medication. Cultural factors may influence views of medications, storage practices, use of poison control system telephone advice, and risk of toddler poisoning. The pedestrian injury rate doubled between 12 and 14 months and 15 and 17 months and exceeded motor vehicle occupant injury rates for each 3-month interval from 15 to 47 months. Pedestrian injury has not received sufficient attention in general and certainly not in injury prevention counseling for children younger than 4 years. Anticipatory guidance for pedestrian injury should be incorporated before 1 year of age. Effective strategies must be based on the epidemiology of childhood injury. Pediatricians and other pediatric health care providers are in a unique position to render injury prevention services to their patients. Integrating injury prevention messages in the context of developmental assessments of the child is 1 strategy. These data can also be used for complementary childhood injury prevention strategies such as early intervention programs for high-risk families for child abuse and neglect, media and advocacy campaigns, public policies, and environmental and product design.
Accidental Falls↗
Posterior internal capsule infarction associated with neglect.
A persistent hemispatial neglect developed in a patient following a small infarction of the posterior limb of the right internal capsule. This defect was restricted to tasks requiring spontaneous motor performance on the contralateral hemispace, especially when carried out under visual control. It was not associated with an extinction phenomenon. Verbal cues improved exploratory behavior, suggesting that hemispatial akinesia in this case was due to an intentional disorder. A pulvinar-parietal disconnection, depriving the right parietal cortex from relevant visuospatial information from the contralateral hemispace, was probably the anatomic basis of hemispatial neglect in this case.
Attention↗
In vivo observations of timecourse and distribution of morphological dynamics in Xenopus retinotectal axon arbors.
Changes in neuronal structure can contribute to the plasticity of neuronal connections in the developing and mature nervous system. However, the expectation that they would occur slowly precluded many from considering structural changes as a mechanism underlying synaptic plasticity that occurs over a period of minutes to hours. We took time-lapse confocal images of retinotectal axon arbors to determine the timecourse, magnitude, and distribution of changes in axon arbor structure within living Xenopus tadpoles. Images of axons were collected at intervals of 3 min, 30 min, and 2 h over total observation periods up to 8 h. Branch additions and retractions in arbors imaged at 3 or 30 min intervals were confined to shorter branches. Sites of additions and retractions were distributed throughout the arbor. The average lifetime of branches was about 10 min. Branches of up to 10 microns could be added to the arbor within a single 3 min observation interval. Observations of arbors at 3 min intervals showed rapid changes in the structure of branchtips, including transitions from lamellar growth cones to more streamlined tips, growth cone collaps, and re-extension. Simple branchtips were motile and appeared capable of exploratory behavior when viewed in time-lapse movies. In arbors imaged at 2-h intervals over a total of 8 h, morphological changes included longer branches, tens of microns in length. An average of 50% of the total branch length in the arbor was remodeled within 8 h. The data indicate that the elaboration of the arbor occurs by the random addition of branches throughout the arbor, followed by the selective stabilization of a small fraction of the new branches and the retraction of the majority of branches. Stabilized branches can then elongate and support the addition of more branches. These data show that structural changes in presynaptic axons can occur very rapidly even in complex arbors and can therefore play a role in forms of neuronal plasticity that operate on a timescale of minutes.
Animals↗
Longitudinal investigation of changes in interviewing performance of medical students.
The purposes were to determine the direction and extent of change in a medical student's ability to relate to patients between the sophomore and senior years, to assess the degree of predicted senior year performance from the sophomore year, and to determine the reliability of two major methods: interaction analysis (IA) and global faculty ratings. Twenty-two students were video-taped conducting two 10-minute interviews with a programmed patient: one as a sophomore, the other as a senior. The results for the interaction analysis method showed that the students were more directive, used more exploratory behaviors, were less supportive and more highly rated by the patients (actors) in the senior year. The physician-evaluators' global ratings indicated the students were more supportive, empathetic and open-ended, had fewer uncommon words, but conducted better overall interviews as seniors. The IA method was more reliable than global faculty ratings.
Aptitude↗
Changes in catecholamine-controlling enzymes in response to psychosocial activation of the defence and alarm reactions.
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Adrenal Medulla↗
Protein malnutrition in the rat: its effects on maternal behavior and pup development.
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Animals↗
Presurgical dietary history and the behavior of control and septal lesioned rats.
Rats reared under dietary enrichment or standard diet from 25 days of age underwent septal or control surgery 2 months later. Enrichment differentially altered septal or control behavior as measured by: exploration tests: fluid consumption of water, saccharin, and quinine; and the acquisition of an active avoidance task.
Animals↗
Self-conscious behavior of infants: a videotape study.
The reactions of 4 infants each at ages 10, 15, and 20 months were recorded on videotape as they responded to their own simultaneous video image, their own previously taped video image, the image of a control infant, and that of a female stranger. The subjects' responses were coded by 2 research assistants, ignorant of the original stimuli and the purpose of the study. The following behavioral categories were used: attends, sociable behavior, curiosity, unhappiness-withdrawal, and self-consciousness. The 1st-step discriminant according to a matrix algebra analysis between age groups was self-conscious behavior in response to the simultaneous video image. Twenty month-old infants were significantly different in their display of self-consciousness from the 10 and 15 month-old groups; the latter did not differ from each other.
Age Factors↗
Paternal effects on the development of social behavior in Mus musculus.
In order to extend the determination and description of effects of the father's phenotype on the development of social behavior in male mice, we tested 24 males from each of 2 highly inbred strains of Mus musculus, A/J and C57BL/6J. Approximately 1 week before the birth of the subjects, we replaced natural fathers with a foster parent such that, within each strain, 8 subjects had preweaning experience with same-strain males, 8 with other-strain males, and 8 with same-strain females, in addition to their natural mothers. Observations of social behavior were conducted at 21, 50, and 60 days of age. The results showed effects of the foster parent's phenotype on the development of social exploration in both strains and, possibly, on agonistic behavior in C57BL/6J mice. The different effects in the 2 strains indicate mechanisms dependent on genotype.
Aggression↗
Deficits in spatial memory performance induced by early undernutrition.
Recent studies have shown that rats have a remarkable ability to keep track of their spatial location. Explanations stress the involvement of a form of short-term (working) memory in which the hippocampus appears to play a major role. The hippocampus appears to be vulnerable to early undernutrition and preliminary investigations indicate that Areas CA3 and CA4 suffer the most. Ninety-day-old rats, previously undernourished prenatally and throughout lactation, were tested in an 8- and, then, a 16-arm radial maze. Significant differences were observed between the experimental and control groups on both tests, especially in the 16-arm maze. Error distributions were also significantly different with experimental animals tending to perseverate in 1 area of the maze. Differences were also observed in the time taken to make the choices and in exploratory behavior. We conclude that early undernutrition affected the spatial learning ability of the animals and that this may be due to the distortions observed in the normal growth pattern of the hippocampus.
Animals↗
Neurogenesis may relate to some but not all types of hippocampal-dependent learning.
The hippocampal formation generates new neurons throughout adulthood. Recent studies indicate that these cells possess the morphology and physiological properties of more established neurons. However, the function of adult generated neurons is still a matter of debate. We previously demonstrated that certain forms of associative learning can enhance the survival of new neurons and a reduction in neurogenesis coincides with impaired learning of the hippocampal-dependent task of trace eyeblink conditioning. Using the toxin methylazoxymethanol acetate (MAM) for proliferating cells, we tested whether reduction of neurogenesis affected learning and performance associated with different hippocampal dependent tasks: spatial navigation learning in a Morris water maze, fear responses to context and an explicit cue after training with a trace fear paradigm. We also examined exploratory behavior in an elevated plus maze. Rats were injected with MAM (7 mg/kg) or saline for 14 days, concurrent with BrdU, to label new neurons on days 10, 12, and 14. After treatment, groups of rats were tested in the various tasks. A significant reduction in new neurons in the adult hippocampus was associated with impaired performance in some tasks, but not with others. Specifically, treatment with the antimitotic agent reduced the amount of fear acquired after exposure to a trace fear conditioning paradigm but did not affect contextual fear conditioning or spatial navigation learning in the Morris water maze. Nor did MAM treatment affect exploration in the elevated plus maze. These results combined with previous ones suggest that neurogenesis may be associated with the formation of some but not all types of hippocampal-dependent memories.
Animals↗
Hippocampal synaptic plasticity is modulated by theta rhythm in the fascia dentata of adult and aged freely behaving rats.
A modulatory role for the hippocampal theta rhythm in synaptic plasticity is suggested by the observations that theta occurs during exploratory behaviors, spatial learning is impaired when the theta rhythm is disrupted, and excitation of hippocampal principal cells is phase-coupled to the theta wave. The theta phase affects the nature of the plasticity induced in urethane-anesthetized rats and in the carbachol-treated in vitro slice preparation, but these oscillations are phenomenologically different from natural theta, and the effects of theta phase on plasticity under natural conditions have not been reported. We therefore examined the effects of theta phase on the magnitude of long-term potentiation (LTP) in awake rats running on a linear track for a food reward. Twelve adult and 10 aged F344 male rats were implanted with a stimulating electrode in the perforant path and a recording electrode in the hilus of the fascia dentata. Stimuli were delivered at the peak or trough of the hilar theta rhythm. In both adult and aged, memory-impaired rats, LTP lasting at least 48 h was induced when stimuli were delivered at the positive theta peak, whereas LTP was not induced when stimuli were delivered at the negative troughs. Consistent with the finding that the threshold for LTP induction is increased at this synapse in old rats, the magnitude of LTP induced at the peak of theta rhythm was significantly lower in old animals. These data confirm that LTP can be modulated by locomotion-induced theta, and that this modulation is at least qualitatively preserved across age.
Aging↗
Rhythmic hippocampal slow oscillation characterizes REM sleep in humans.
Hippocampal rhythmic slow activity (RSA) is a well-known electrophysiological feature of exploratory behavior, spatial cognition, and rapid eye movement (REM) sleep in several mammalian species. Recently, RSA in humans during spatial navigation was reported, but systematic data regarding human REM sleep are lacking. Using mesio-temporal corticography with foramen ovale electrodes in epileptic patients, we report the presence of a 1.5-3-Hz synchronous rhythmic hippocampal oscillation seemingly specific to REM sleep. This oscillation is continuous during whole REM periods, is clearly observable by visual inspection, and appears in tonic and phasic REM sleep episodes equally. Quantitative analysis proved that this 1.5-3-Hz frequency band significantly differentiates REM sleep from waking and slow-wake sleep (SWS). No other frequency band proved to be significant or showed this high rhythmicity. Even in temporo-lateral surface recordings, although visually much less striking, the relative power of the 1.5-3-Hz frequency band differentiates REM sleep from other states with statistical significance. This could mean that the 1.5-3-Hz hippocampal RSA spreads over other cortical areas in humans as in other mammals. We suggest that this oscillation is the counterpart of the hippocampal theta of mammalian REM sleep, and that the 1.5-3-Hz delta EEG activity is a basic neurophysiological feature of human REM sleep.
Adult↗
Responses of excitatory hippocampal synapses to natural stimulus patterns reveal a decrease in short-term facilitation and increase in short-term depression during postnatal development.
Schaffer collateral excitatory synapses onto CA1 pyramidal cells are subject to significant modulation by short-term plasticity. This presynaptic, history-dependent modulation of neurotransmitter release causes synaptic transmission to be sensitive to the frequency of the input. As a result, temporally irregular input patterns, such as those observed in vivo, produce synaptic responses over a very wide dynamic range that reflect a balance of short-term facilitation and short-term depression. The neonatal period is an important developmental period in the hippocampus, when functional representations of an animal's environment are being established through exploratory behavior. The strength of excitatory synapses and their modulation by short-term plasticity are critical to this process. One form of short-term plasticity, paired-pulse facilitation, has been shown to decrease as juvenile rats mature into young adults. However, little is known about the neonatal modulation of other forms of short-term plasticity, including the responses to temporally complex stimuli. We examined developmental modulation of the short-term dynamics of Schaffer collateral excitatory synapses onto CA1 pyramidal cells in acute hippocampal slices, using both constant frequency stimuli and natural stimulus patterns that were taken from in vivo recording of spike patterns of hippocampal cells. In response to constant frequency stimulation, synapses in slices from young adult rats (P28-P35) showed less short-term depression than did those in slices from juveniles (P12-P18). However, when the natural stimulus pattern (containing a wide mix of frequencies) was used, synapses from young adults instead showed more short-term depression and less short-term facilitation than did juveniles. Comparing the natural stimulus pattern responses with constant frequency stimulation of a similar frequency, we found that the average responses were similar in young adults (both showed modest depression). However, in juveniles, the natural pattern produced robust facilitation while constant frequency stimulation caused a large short-term depression. Our results reveal that there are developmental changes both in individual forms of short-term plasticity and in the relative balance between short-term facilitation and short-term depression that will alter the signal transfer characteristics of these synapses.
Animals↗
Spatial selectivity and theta phase precession in CA1 interneurons.
Traditionally, most of the information processing of neural networks is thought to be carried out by excitatory cells. Likewise, recent evidence for temporal coding comes from the study of the detailed firing patterns of excitatory neurons. In the CA1 region of the rat hippocampus, pyramidal cells discharge selectively when the animal is in specific locations in its environment, and exhibit a precise relationship with the ongoing rhythmic activity of the network (phase precession). We demonstrate that during a spatial exploratory behavior on a linear track, inhibitory interneurons also show spatial selectivity and phase precession dynamics. We found that the firing rate of interneurons is modulated reliably up and down around an ongoing baseline activity level for specific locations in the environment, producing robust place-specific increases or decreases in discharge. On some sections of the track, the range of theta phases shifts progressively to earlier parts of the theta cycle as the rat advances, so that a negative correlation between phase and position could be demonstrated. Unlike pyramidal cells, phase and rate were not strongly correlated. We discuss the influence of the intrinsic firing properties of interneurons on a model of phase precession, as well as the influence of the detailed shape of the inhibitory oscillation. These results indicate that spatial selectivity and phase precession in CA1 are not properties restricted to pyramidal cells. Rather, they may be a more general expression of a common interaction between the different inputs impinging on both excitatory and inhibitory cells in CA1 and the intrinsic characteristics of those cells. Furthermore, they suggest that the role of interneurons may extend beyond a global damping of the network by participating in a finely-tuned local processing with the pyramidal cells.
Action Potentials↗
Maps, routes, and the hippocampus: a neural network approach.
This study describes hippocampal participation in maze navigation in terms of a real-time, biologically plausible neural network. The system is composed of (1) a goal-seeking mechanism, (2) a cognitive map system, and (3) a route system. The goal-seeking mechanism displays exploratory behavior until either the goal is found or a sufficiently strong prediction of the goal is generated. The cognitive map is a topological map that stores associations between places and views of accessible places, and between places and reward. The route system establishes associations between cues and reward. Both systems compete with each other to establish associations with the reward, with the cognitive system generally overshadowing the route system. In agreement with previous models, it is assumed that the hippocampus modulates the storage of cognitive maps in cortical areas and mediates the competition between cognitive maps and route systems. After hippocampal lesions, animals navigate through mazes making use of the route system. Computer simulations show that the network effectively describes latent learning, detour behavior, and place learning in normal and hippocampal- and cortical-lesioned animals.
Animals↗
Kinematics of goal-directed arm movements in neglect: control of hand velocity.
Do patients with unilateral neglect exhibit direction-specific deficits in the control of movement velocity when performing goal-directed arm movements? Five patients with left-sided neglect performed unrestrained three-dimensional pointing movements to visual targets presented at body midline, the left and right hemispace. A group of healthy adults and a group of patients with right-hemispheric brain damage but no neglect served as controls. Pointing was performed under normal room light or in darkness. Time-position data of the hand were recorded with an opto-electronic camera system. We found that compared to healthy controls, movement times were longer in both patient groups due to prolonged acceleration and deceleration phases. Tangential peak hand velocity was lower in both patient groups, but not significantly different from controls. Single peak, bell-shaped velocity profiles of the hand were preserved in all right hemispheric patients and in three out of five neglect patients. Most important, the velocity profiles of neglect patients to leftward targets did not differ significantly from those to targets in the right hemispace. In summary, we found evidence for general bradykinesia in neglect patients, but not for a direction-specific deficit in the control of hand velocity. We conclude that visual neglect induces characteristic changes in exploratory behavior, but not in the kinematics of goal-directed movements to objects in peripersonal space.
Adolescent↗