Inflammation Causes a Long-Term Hyperexcitability in the Nociceptive Sensory Neurons of Aplysia

Nerve injury, tissue damage, and inflammation all cause hyperalgesia. A factor contributing to this increased sensitivity is a long-term (>24 hr) hyperexcitability (LTH) in the sensory neurons that mediate the responses. Using the cluster of nociceptive sensory neurons in Aplysia californica as a model, we are examining how inflammation induces LTH. A general inflammatory response was induced by inserting a gauze pad into the animal. Within 4 days, the gauze is enmeshed in an amorphous material that contains hemocytes, which comprise a cellular immune system. Concurrently, LTH appears in both ipsilateral and contralateral sensory neurons. The LTH is manifest as increased action potential discharge to a normalized stimulus. Immunocytochemistry revealed that hemocytes have antigens recognized by antibodies to TGFβ1, IL-6, and 5HT. When a localized inflammation was elicited on a nerve, hemocytes containing the TGFβ1 antigen were present near axons within the nerve and those containing the IL-6 were on the surface. Western blots of hemocytes, or of gauze that had induced a foreign body response, contained a 28-kD polypeptide recognized by the anti-TGFβ1 antibody. Exposure of the nervous system to recombinant human TGFβ1 elicited increased firing of the nociceptive neurons and a decrease in threshold. The TGFβ1 also caused an activation of protein kinase C (PKC) in axons but did not affect a kinase that is activated in axons after injury. Our findings, in conjunction with previous results, indicate that a TGFβ1-homolog can modulate the activity of neurons that respond to noxious stimuli. This system could also contribute to interactions between the immune and nervous systems via regulation of PKC.     

Effects of priming and suppression of worry

High and low worriers were primed by a short period of worry, suppression of worry, or the same period of non-worrying thought. Analysis of thoughts during the period following showed that worriers had more than twice as many unpleasant thoughts as did controls, across all prior conditions. Priming condition had little effect on this difference, although worry suppression was associated with a slight increase in the frequency of neutral or pleasant thoughts in high worriers, and a slight decrease in controls. These results are taken as evidence against the hypothesis that suppression of upsetting thoughts increases their intrusive quality, and thereby contributes to anxiety disorders.     

Biased cognitive operations in anxiety: Accessibility of information or assignment of processing priorities?

There is considerable evidence that anxiety is associated with a cognitive bias favouring the processing of threat-related information. Bower's (1981) network model attributes this bias to the enhanced availability of mood congruent information from memory. However, certain experimental tasks do not reveal such a bias, when this effect is strongly predicted by the model. We note that all tasks which have demonstrated such mood congruent processing effects in anxious subjects share the requirement that these subjects must assign priorities to simultaneously available, and differentially valenced, alternative processing options. This feature has been consistently lacking in those paradigms we have found insensitive to the influence of anxiety. It is therefore suggested that anxiety is associated with the assignment of high processing priorities to threat-related options, rather than with the facilitated availability of threat-related information from memory. This proposal was experimentally tested using a lexical decision task, which is sensitive to the accessibility of information from memory, under conditions which either do or do not introduce the requirement to assign priorities to alternative processing options. The results indicate that the facilitated processing of threat related stimulus words, shown by generalised anxiety patients, does indeed appear to reflect a bias in the assignment of processing priorities, rather than the enhanced availability of this information from memory.     

Facilitative interactions of model- and experiencebased processes: Implications for type and flexibility of representation

People are often taught using a combination of instruction and practice. In prior research, we have distinguished between model-based knowledge (i.e., acquired from explicit instruction) and experience-based knowledge (i.e., acquired from practice), and have argued that the issue of how these types of knowledge (and associated learning processes) interact has been largely neglected. Two experiments explore this issue using a dynamic control task. Results demonstrate the utility of providing model-based knowledge before practice with the task, but more importantly, suggest how this information improves learning. Results also show that learning in this manner can lead to "costs" such as slowed retrieval, and that this knowledge may not always transfer to new task situations as well as experientially acquired knowledge. Our findings also question the assumption that participants always acquire a highly specific "lookup" table representation while learning this task. We provide an alternate view and discuss the implications for theories of learning.     

Suppression of attentional bias in PTSD

Sixty combat veterans with posttraumatic stress disorder performed an emotional Stroop task under 1 of 4 contextual conditions designed to test theoretical explanations for an attentional bias suppression effect. Results revealed that when the emotional Stroop task was performed under conditions involving a future threat of either watching a combat video or giving a speech, attentional bias was inhibited. There was limited support for the prediction that the suppression effect was strongest when stressor content matched word content on the Stroop. In contrast to participants in the threat conditions, veterans who believed that they would receive additional compensation for speeded color naming or who believed that they would have no other experimental demands were slower when color naming combat-threat words. Potential theoretical explanations of the findings are discussed.     

Effects of model-based and memory-based processing on speed and accuracy of grammar string generation

Learners are able to use 2 different types of knowledge to perform a skill. One type is a conscious mental model, and the other is based on memories of instances. The authors conducted 3 experiments that manipulated training conditions designed to affect the availability of 1 or both types of knowledge about an artificial grammar. Participants were tested for both speed and accuracy of their ability to generate letter sequences. Results indicate that model-based training leads to slow accurate responding. Memory-based training leads to fast, less accurate responding and highest achievement when perfect accuracy was not required. Evidence supports participants' preference for using the memory-based mode when exposed to both types of training. Finally, the accuracy contributed by model-based training declined over a retention interval.     

Take a closer look: emotion modifies the boundary extension effect

Evidence has accumulated showing that central aspects of negative emotional scenes are remembered better than equivalent aspects of nonemotional scenes. Previous work, and an attentional account of these findings, led the authors to predict that anxiety-prone individuals would remember extremely negative emotional pictures as if seen from a closer perspective (i.e., with a less extended background) than other pictures. Findings showed that boundary extension was indeed reduced in high-trait-anxious individuals for very negative scenes, and this was more generally true for arousing scenes, with the exception of those with positive content. These findings are taken to be support for the view that attending to central aspects of emotionally arousing scenes can restrict the usual extended impression of surrounding space.