However, these rats were also impaired at the initial acquisition of spatial water maze, thereby confounding clear assessment of how aging may specifically alter extinction. Previous deficits in the extinction of escape from spatial water maze have been reported in aged rats 28, 29. Although a substantial progress has been made in recent years on understanding the processes mediating extinction of learned threat 2, 27, the impact of healthy aging on the context-dependent extinction of threat memories has been relatively unexplored. Of these, prefrontal cortex and hippocampus-dependent behaviours are preferentially vulnerable during aging, suggesting that impairments within these structures could underlie extinction deficits in advanced age 25, 26. Furthermore, considerable research in animals and humans reveals that contextual regulation of extinction memory requires coordinated activity of regions of prefrontal cortex, hippocampus, and amygdala 20. Declines in the ability to process contextual information, and flexibly adapt behaviour to situational changes, may represent a fundamental mechanism of age-related cognitive alterations 24. It is widely agreed that aging is accompanied by a cognitive decline in laboratory animals, as well as in humans 21, 22, 23. This “ABA renewal effect” has been repeatedly demonstrated in both rats 14, 15, 16 and humans 17, 18, and suggests that extinction involves just one more form of learning that is particularly context-dependent (for excellent comprehensive reviews on threat extinction and renewal, see 2, 19, 20). For example, a renewal of responding is observed 11, 12, 13 when, after extinction in a context (Context B) different from the acquisition context (Context A), the CS is presented in the original acquisition context (Context A). During this competition, contextual information appears to be a critical regulatory factor in determining whether the original threat memory or the new extinction memory should control defensive CS responses. Instead, there is converging evidence from animal 5, 6, 7, 8 and human 9, 10 studies that the mechanisms supporting extinction entail new learning (i.e., CS-no US) that competes, and temporarily interferes, with the expression of the original conditioning trace. Several key studies 3, 4 indicate that extinction does not involve permanent erasure (i.e., unlearning) of the original associative (i.e., CS-US) memory. During extinction, repeated presentation of the conditioned stimulus (CS) alone after Pavlovian or classical, threat conditioning (CS–unconditional stimulus (US) pairings) causes attenuation of defensive responses 1 (see ref. These results reveal that aging affects the capacity to use context to modulate learned responses to threat, possibly due to changes in brain structures that enable context-dependent behaviour and are preferentially vulnerable during aging.Įxtinction of threat memories is a phenomenon that allows animals and humans to adapt their behaviour to a changing environment. In addition, there were no age group differences in fear ratings and contingency awareness, thus revealing that aging selectively impairs extinction memories as indexed by autonomic responses. On Day 2, however, older adults showed impaired recall of extinction memory, with increased SCR to the extinguished stimulus in the ‘safe’ context, and reduced ability to process context properly. CONTEXT DEPENDENT MEMORY SKINSkin conductance response (SCR data revealed no significant differences between age groups during acquisition and extinction of threat conditioning on Day 1. Physiological and verbal report measures of threat conditioning were collected throughout the experiment. On Day 2, the extinguished stimulus was presented to assess extinction recall (safe context), and threat renewal (danger context). On Day 1, conditioned stimuli were paired with an aversive electric shock in a ‘danger’ context and then extinguished in a different ‘safe’ context. We used a 2-day differential threat conditioning and extinction procedure to determine whether young and older adults differed in the contextual recall of conditioned responses after extinction. Although a substantial progress has been made in recent years on understanding the processes mediating extinction of learned threat, little is known about the context-dependent extinction of threat memories in elderly individuals.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |