Attenuation of age-related conditioning deficits in humans by extension of the interstimulus interval

Cognitive Deficits, Changes in Synaptic Function, and Brain Pathology in a Mouse Model of Normal Aging(1,2,3)

Age is the main risk factor for sporadic Alzheimer's disease. Yet, cognitive decline in aged rodents has been less well studied, possibly due to concomitant changes in sensory or locomotor function that can complicate cognitive tests. We tested mice that were 3, 11, and 23 months old in cognitive, sensory, and motor measures, and postmortem measures of gliosis and neural activity (c-Fos). Hippocampal synaptic function was also examined. While age-related impairments were detectable in tests of spatial memory, greater age-dependent effects were observed in tests of associative learning [active avoidance (AA)]. Gross visual function was largely normal, but startle responses to acoustic stimuli decreased with increased age, possibly due to hearing impairments. Therefore, a novel AA variant in which light alone served as the conditioning stimuli was used. Age-related deficits were again observed. Mild changes in vision, as measured by optokinetic responses, were detected in 19- versus 4-month-old mice, but these were not correlated to AA performance. Thus, deficits in hearing or vision are unlikely to account for the observed deficits in cognitive measures. Increased gliosis was observed in the hippocampal formation at older ages. Age-related changes in neural function and plasticity were observed with decreased c-Fos in the dentate gyrus, and decreased synaptic strength and paired-pulse facilitation in CA1 slices. This work, which carefully outlines age-dependent impairments in cognitive and synaptic function, c-Fos activity, and gliosis during normal aging in the mouse, suggests robust translational measures that will facilitate further study of the biology of aging.

Etiology, Composition, Development and Maintenance of Misophonia: A Conditioned Aversive Reflex Disorder

Misophonia is a recently identified condition in which an individual has an acute reaction of hatred or disgust to a specific commonly occurring sound. We propose that misophonia is a form of conditioned behavior that develops as a physical reflex through Pavlovian conditioning. Although misophonia is generally considered to be a one-step reaction, in which the sound elicits rage or disgust, as well as typical autonomic responses associated with these emotions, we propose that misophonia is a two-step reaction, in which the sound elicits an aversive conditioned physical reflex, and the aversive conditioned physical reflex elicits hatred or disgust. We also propose that the emotional response to trigger stimuli creates a Pavlovian conditioning paradigm that maintains or strengthens the misophonic physical reflex. Finally, we propose that new misophonic trigger stimuli are developed through the pairing of a neutral stimulus with a misophonic trigger stimulus. We suggest that a better name for misophonia is Conditioned Aversive Reflex Disorder (CARD) since it focuses attention on the reflexive nature of this condition and incorporates multiple stimuli modalities. A counterconditioning treatment for misophonia is presented with brief case descriptions which demonstrate the conditioned reflex nature of this disorder.

Pavlovian eyeblink conditioning in combat veterans with and without post-traumatic stress disorder

Several recent studies have investigated relationships between post-traumatic stress disorder (PTSD) and learning and memory problems. These reports have found in general that not only does PTSD affect trauma-related memories, but when patients with PTSD are compared with similar trauma patients without PTSD, general memory impairments have been found. The present paper reports a study in which associative learning, using Pavlovian eyeblink conditioning, was investigated in combat veterans with and without chronic PTSD, using interstimulus intervals of 500 and 1000 msec in two separate experiments. Although several recent reports suggest that larger-magnitude autonomic conditioned responses occur in patients with PTSD during Pavlovian conditioning, the present study found evidence of impaired Pavlovian eyeblink conditioning in combat veterans with and without PTSD, compared to non-combat veterans. Although these data suggest that combat leads to an impaired associative learning process regardless of whether PTSD is apparent, a group of community-dwelling combat veterans not under medical treatment showed normal conditioning, suggesting that variables other than prior combat must also be involved.

Aging and the Detection of Contingency in Causal Learning

Young and older participants' ability to detect negative, random, and positive response-outcome contingencies was evaluated using both contingency estimation and response rate adaptation tasks. Age differences in contingency estimation were consistently greater for negative than positive contingencies, and these differences, though still present, were smaller when response rate adaptation was used as the measure of contingency learning. Detecting causal contingency apparently becomes more difficult with age, especially when an oven numerical estimate of contingency must be provided and when the relationship between a causal event and an outcome is negative. A model that incorporates features of both associative and rule-based approaches to contingency learning (e.g., P. C. Price & J. F. Yates, 1995; D. R. Shanks, 1995) provides the best explanation for this pattern of findings.

Awareness in classical differential eyeblink conditioning in young and aging humans

The role of awareness and its impact on learning the conditioned eyeblink response was investigated in both trace and delay discrimination eyeblink conditioning in young and aging participants, in 4 paradigms: delay 750, delay 1,250, trace 500, and trace 1,000. Participants concurrently watched a silent movie about which they were questioned afterward. Acquisition in both the trace and delay discrimination task was correlated with awareness of conditioning stimulus contingencies, regardless of age. Age-dependent deficits were observed in trace discrimination but not in delay discrimination, with more severe deficits appearing at the longer trace interval. The percentage of aware participants was also found to be greater in the young population than in the aging population. These results indicate that awareness or knowledge of stimulus contingencies may be an important contributor to successful acquisition in higher order discrimination tasks.

A behavioral stages model of classical (Pavlovian) conditioning: application to cognitive aging

In the present article, it is argued that a five-stage sequential model of the behavioral and neurophysiological events that occur when organisms are exposed to signals predicting significant events suggests that classical conditioning produces multiple memory traces involving both excitatory and inhibitory processes. Further, these multiple brain structures and associated neurophysiological mechanisms are beginning to be understood; thus, using Pavlovian conditioning techniques to study aging and cognitive functions may provide insights into which brain structures or mechanisms are responsible for more general age-related declines in associative learning and memory. The evidence for this model is briefly reviewed and studies suggesting age-related effects on classical conditioning of various response systems are described within the context of the brain structures implicated by the model.