Corticosterone exposure and the retention of long-lasting memory in free-living Florida scrub-jays (<em>Aphelocoma coerulescens</em>). — ASN Events

Corticosterone exposure and the retention of long-lasting memory in free-living Florida scrub-jays (Aphelocoma coerulescens). (#49)

Blake C Jones 1 , Sara E Bebus 1 , Stephen M Ferguson 1 , Philip W Bateman 2 , Stephan J Schoech 1
  1. University of Memphis, Memphis, TENNESSEE, United States
  2. Environment and Agriculture, Curtin University, Perth, Western Australia, Australia

Stress can facilitate memory formation and retention via glucocorticoids (GCs), which are released at low baseline concentrations, but increase in response to a stressor. Exposure to increased levels of circulating GCs shortly after learning typically enhances long-term memory formation. Long-term memories last hours to weeks, whereas memories that persist for months to years are known as long-lasting memories. Despite considerable knowledge of the effects of GCs on short- and long-term memory, understanding of the effects of GCs on long-lasting memory is essentially nonexistent. The goal of this study was to understand the effects of GCs on the acquisition and retention of long-lasting memory. We asked: do circulating glucocorticoids affect the long-lasting memory of an emotionally arousing event? We exposed free-living Florida scrub-jays (Aphelocoma coerulescens; FSJs) to a modified fear conditioning protocol that used a novel ‘predator’ as the conditioned stimulus. Endogenous and manipulated levels of corticosterone (CORT; the primary avian GC) immediately after conditioning were compared to the FSJs’ long-lasting response to the novel ‘predator’ using flight initiation distance (FID). Our results indicate that CORT has an inverted U-shaped relationship with the retention of long-lasting memory with low and high levels impairing memory formation or retention. Additionally, FSJs with a moderate stress-response phenotype display an intensified conditioned response with time (i.e., FID increases over time), superficially similar to sensitization, but occurring after associative learning in the absence of reinforcement and over a much longer time frame. This suggests that FSJs can experience a type of memory modification that amplifies their original perception, which challenges the conventional wisdom that memory tends to either remain static or decay with time.