Part I. Experimental Studies: 2. Experiment in psychology 3. Experiments on perceiving III Experiments on imaging 4-8. Experiments on remembering: (a) The method of description (b) The method of repeated reproduction (c) The method of picture writing (d) The method of serial reproduction (e) The method of serial reproduction picture material 9. Perceiving, recognizing, remembering 10. A theory of remembering 11. Images and their functions 12. Meaning Part II. Remembering as a Study in Social Psychology: 13. Social psychology 14. Social psychology and the matter of recall 15. Social psychology and the manner of recall 16. Conventionalism 17. The notion of a collective unconscious 18. The basis of social recall 19. A summary and some conclusions.

Remembering. A Study in Experimental and Social Psychology, Cambridge (University Press) 1964.

Neurogenesis occurs in the dentate gyrus of the hippocampus throughout the life of a rodent, but the function of these new neurons and the mechanisms that regulate their birth are unknown. Here we show that significantly more new neurons exist in the dentate gyrus of mice exposed to an enriched environment compared with littermates housed in standard cages. We also show, using unbiased stereology, that the enriched mice have a larger hippocampal granule cell layer and 15 per cent more granule cell neurons in the dentate gyrus.

More hippocampal neurons in adult mice living in an enriched environment

The relationship between cognition and action: performance of children 3 1/2-7 years old on a Stroop-like day-night test.

Childhood trauma has profound impact on the emotional, behavioral, cognitive, social, and physical functioning of children. Developmental experiences determine the organizational and functional status of the mature brain. The impact of rruumufic experiences on the development and function of the brain are discussed in context of basic principles of neurodevelopment. There are various adaptive mental and physical responses to trauma, including physiological hyperarousal and dissociation. Because the developing brain organizes and internalizes new information in a use-dependent fashion, the more a child is in a state of hyperarousal or dissociation, the more likely they are to have neuropsychiatric symptoms following trauma. The acute adaptive states, when they persist, can become maladaptive traits. The clinical implications of this new neurodevelopmental conceptualization of childhood trauma are discussed.

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Childhood trauma, the neurobiology of adaptation, and "use-dependent" development of the brain: How "states" become "traits."

Neurons are continually born from endogenous stem cells and added to the dentate gyrus throughout life, but adult hippocampal neurogenesis declines precipitously with age. Short-term exposure to an enriched environment leads to a striking increase in new neurons, along with a substantial improvement in behavioral performance. Could this plastic response be relevant for explaining the beneficial effects of leading "an active life" on brain function and pathology? Adult hippocampal neurogenesis in mice living in an enriched environment from the age of 10 to 20 months was fivefold higher than in controls. Relatively, the increase in neuronal phenotypes was entirely at the expense of newly generated astrocytes. This cellular plasticity occurred in the context of significant improvements of learning parameters, exploratory behavior, and locomotor activity. Enriched living mice also had a reduced lipofuscin load in the dentate gyrus, indicating decreased nonspecific age-dependent degeneration. Therefore, in mice signs of neuronal aging can be diminished by a sustained active and challenging life, even if this stimulation started only at medium age. Activity exerts not only an acute but also a sustained effect on brain plasticity.

Neuroplasticity in old age: sustained fivefold induction of hippocampal neurogenesis by long-term environmental enrichment.

Four studies are reported examining the development of spontaneous alternation behavior in rats. Spontaneous alternation was found to increase from a rate of around 20% in 15-16 day old rats to around 90% in 100-day olds. Increasing the length of confinement in the 1st chosen goal arm did not affect alternation rats. Spontaneous alternation could be disrupted or facilitated in mature animals by the administration of either scopolamine hydrobromide or physostigmine sulphate, drugs which had no effect on the typical alternation pattern of 16-day olds, but appeared to begin to have an effect at around 24 days. Dose response curves revealed certain age-dose level interactions which were consistent with the hypothesis that cholinergic inhibitory mechanisms in the brain develop gradually in the rat.

Ontogenetic aspects of central cholinergic involvement in spontaneous alternation behavior

The differential brain development induced by sensory enrichment or deprivation is most apparent in rats with low brain weights. These differences are hypothesized to represent the retarded development of environment-dependent neurons in the isolated animals.

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A developmental theory of environmental enrichment

Three groups of 8 male albino rats within each of the age ranges 24, 50, and 100 days were trained on an active avoidance task to a criterion of 10 successive avoidances. The number of trials to criterion was found to be a monotonic function of age. One group at each age was tested immediately thereafter for passive avoidance of the conditioning chamber, another group was tested for passive avoidance after 25 days, and the third was tested for retention of active avoidance after 25 days. Groups at 50, 75, and 125 days were used as controls for the active avoidance retention groups. All animals took significantly fewer trials to relearn the active avoidance after 25 days than did controls on the acquisition of the original learning task. On passive avoidance 24-day olds performed less efficiently than the older groups and failed to show any retention after 25 days.

Age effects in the acquisition and retention of active and passive avoidance learning by rats.

The learning of multiple choice discrimination tasks of 3-, 4-, 5-, and 6-year-old children was compared using the components of learning of cue significance and response regulation. No significant differences between age groups were found in the occurrence of cue significance learning, although the younger children's cue significance responses were less accurately related to task solution. On the two easier tasks, the component of response regulation improved significantly over the age range of 3-5 years. On the two more difficult tasks 6-year-olds' response regulation was significantly better than that of 4- and 5-year-olds. In a second experiment involving two different training procedures, 5-year-olds performed better than 4-year-olds. Only for 5-year-olds was performance with the procedure emphasizing response regulation superior to performance with the procedure emphasizing cue significance. These results are discussed in terms of an association between development of response regulation and maturation of hippocampal-prefrontal cortex systems.

Cue significance and response regulation in 3‐ to 6‐year‐old children's learning of multiple choice discrimination tasks

Wistar rats at 7 (mature), 16 (aging), and 22 (old) months of age spent 70 days in normal laboratory (Social), impoverished (Isolated) or dynamic Enrichment cages. The Enriched cage emphasized spatial re-arrangements of significant items, and the learning of new routes. Subsequently, Enriched rats at all ages entered a novel environment and escaped from a bright light with significantly shorter latencies than rats from either of the other environments. Mature, aging and some of the old Enriched rats also significantly outperformed their Isolated and Social counterparts in the radial maze. However old Enriched and Isolated animals showed significant variability in relation to the measure of the proportion reaching criterion on this task, and a significantly lower proportion than of old Social rats reached criterion. Enriched rats had a significantly higher survival rate than Social and Isolated animals. These findings are discussed in terms of learning efficiency and behaviors that conserve energy and thereby enhance survival. s 2009 Wiley Periodicals, Inc. Dev Psychobiol 51: 564-578, 2009.

P. J. Livesey

Papers

Ontogenetic aspects of central cholinergic involvement in spontaneous alternation behavior

A developmental theory of environmental enrichment

Age effects in the acquisition and retention of active and passive avoidance learning by rats.

Cue significance and response regulation in 3‐ to 6‐year‐old children's learning of multiple choice discrimination tasks

Environmental Enrichment Influences Survival Rate and Enhances Exploration and Learning But Produces Variable Responses to the Radial Maze in Old Rats