Memory development: implications for adults recalling childhood experiences in the courtroom

Adults frequently provide compelling, detailed accounts of early childhood experiences in the courtroom. Judges and jurors are asked to decide guilt or innocence based solely on these decades-old memories using 'common sense' notions about memory. However, these notions are not in agreement with findings from neuroscientific and behavioural studies of memory development. Without expert guidance, judges and jurors may have difficulty in properly adjudicating the weight of memory evidence in cases involving adult recollections of childhood experiences

Behavioral expression of learned fear: Updating of early memories

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Comparison of cytotoxicity test models for evaluating resin-based composites

Objectives: This study compared different cytotoxicity test models for evaluating resin-based composites (RBCs) and assessed the biocompatibility of standard and bulk-fill RBCs. Methods: A standard (spectrum TPH) and a bulk-fill (smart dentin replacement (SDR)) RBC were selected. Disc-shaped specimens (7 mm diameter) of 2 and 4 mm thickness were polymerized for 20 s with a LED curing light of 700 mW/cm2 irradiance. The specimens ( n = 5) were subjected to micro-hardness testing and three cytotoxicity test models (direct contact, indirect contact and extract tests) with the established L-929 cell line. Hardness ratios of top and bottom surfaces of specimens were computed to assess the effectiveness of cure. For the direct and indirect contact tests, the cells were stained and zones of inhibition were analyzed after material contact for 24 h. For the extract test, cells were exposed to extracts for 24 h, and cell viability was measured. Data was analyzed using analysis of variance/Scheffe’s post hoc test and Pearson’s correlation ( p &lt; 0.05). Results: The lowest mean hardness ratio and highest cytotoxicity were observed for TPH at 4 mm. At 4-mm thickness, SDR was found to be biocompatible with all three models. Correlations between hardness ratio and cell viability ranged from r = 0.89–0.96 for the various tests. A significant correlation ( r = 0.97) was also observed between the three test models. Conclusion: Our data indicated consistency between direct contact, indirect contact and extract test models for cytotoxicity testing of RBCs. Bulk placement and curing at 4 mm for the bulk-fill RBC evaluated did not result in undue cytotoxicity. </jats:sec

The effect of adverse rearing environments on persistent memories in young rats: removing the brakes on infant fear memories

Mental health problems are often assumed to have their roots in early-life experiences. However, memories acquired in infancy are rapidly forgotten in nearly all species (including humans). As yet, a testable mechanism on how early-life experiences have a lasting impact on mental health is lacking. In these experiments, we tested the idea that infant adversity leads to an early transition into adult-like fear retention, allowing infant memories to have a longer-lasting influence. Rats were exposed to maternal separation (3 h per day) across postnatal days (P) 2–14, or their mother was given corticosterone in her drinking water across the same period. Infant rats were then trained to fear a conditioned stimulus (CS) paired with an aversive unconditioned stimulus (US) on P17. Retention of the fear association was then tested 1–55 days later. When tested one day after the CS–US association was formed, both standard-reared (SR) and maternally-separated (MS) rats exhibited strong memory. However, when tested 10 days later, SR rats exhibited robust forgetting, whereas MS rats exhibited near-perfect retention. These effects were mimicked by exposing the mother to the stress hormone corticosterone in the drinking water. Finally, fear associations in P17 MS rats were retained for up to 30 days. Our findings point to differences in retention of fear as one factor that might underlie the propensity of stress-exposed individuals to exhibit early anxiety symptoms and suggest that manipulations of the corticosterone system may hold the key to ameliorating some of the effects of early stress on persistent retention of fear

Early experiences and the development of emotional learning systems in rats

Research first reported nearly 50 years ago demonstrated that infant and young animals (including humans) exhibit profoundly faster rates of forgetting (i.e., infantile amnesia) than do adults. In addition to these differences in retention, more recent research has shown that inhibition of fear learning is also very different in infancy than in adulthood. Specifically, extinction of fear early in life is much more resistant to relapse than is extinction later in life. Both of these findings suggest that young animals should be especially resilient to the emergence of mental health disorders, which appears to be at odds with the view that early-life experiences are particularly important for the development of later psychopathologies (such as anxiety disorders) and with the finding that the majority of anxiety disorders first emerge in adolescence or childhood. This apparent paradox might be resolved, however, if exposure to chronic stress early in life affects the maturation of the fear retention and extinction systems, leading to a faster transition to the adult form of each (i.e., long-lasting fear memories and relapse-prone extinction). In several recent studies we have found exactly this pattern; that is, infant rats exposed to maternal-separation stress exhibit adult-like fear and extinction learning early in development. Further, we have demonstrated that some of these effects can be mimicked by exposing the mother to the stress hormone corticosterone in their drinking water (in lieu of the separation procedure). These findings suggest that early-life exposure to stress and stress hormones may act as a general signal that can alter the developmental trajectory of emotional systems and potentially place animals at greater risk for the development of anxiety. The implications of these recent findings for our understanding of the developmental origins of health and disease, and for enhancing preventative and therapeutic treatments across the lifespan, are considered

Impaired Extinction Retention in Adolescent Rats: Effects of D-Cycloserine

The developmental trajectory of the prefrontal cortex (PFC) in both rats and humans is nonlinear, with a notable decline in synaptic density during adolescence, potentially creating a ‘natural lesion' preparation at this age. Given that the PFC is critically involved in retention of extinction of learned fear in adult humans and rodents, the present study examined whether adolescent rats exhibit impaired extinction retention. The results of experiment 1 showed that adolescent rats were impaired in extinction retention, compared with both younger and older rats. The partial NMDA receptor agonist D-cycloserine (DCS) improved extinction retention in adolescent rats (experiment 2), but only if administered immediately after extinction training (experiment 3). In addition, providing extended extinction training improved extinction retention in adolescent rats in a manner similar to that of DCS (experiment 4). The results of this study show that adolescent rats exhibit impaired extinction retention, and that this can be reduced through either DCS or extended extinction training. These novel findings have potential implications for clinical treatments of fear and anxiety disorders in adolescent patients