Temporal context and conditional associative learning

<p>Abstract</p> <p>Background</p> <p>We investigated how temporal context affects the learning of arbitrary visuo-motor associations. Human observers viewed highly distinguishable, fractal objects and learned to choose for each object the one motor response (of four) that was rewarded. Some objects were consistently preceded by specific other objects, while other objects lacked this task-irrelevant but predictive context.</p> <p>Results</p> <p>The results of five experiments showed that predictive context consistently and significantly accelerated associative learning. A simple model of reinforcement learning, in which three successive objects informed response selection, reproduced our behavioral results.</p> <p>Conclusions</p> <p>Our results imply that not just the representation of a current event, but also the representations of past events, are reinforced during conditional associative learning. In addition, these findings are broadly consistent with the prediction of attractor network models of associative learning and their prophecy of a persistent representation of past objects.</p

Outcomes of metallic stents for malignant ureteral obstruction.

PURPOSE: Malignant ureteral obstruction often necessitates chronic urinary diversion and is associated with high rates of failure with traditional ureteral stents. We evaluated the outcomes of a metallic stent placed for malignant ureteral obstruction and determined the impact of risk factors previously associated with increased failure rates of traditional stents. MATERIALS AND METHODS: Patients undergoing placement of the metallic Resonance® stent for malignant ureteral obstruction at an academic referral center were identified retrospectively. Stent failure was defined as unplanned stent exchange or nephrostomy tube placement for signs or symptoms of recurrent ureteral obstruction (recurrent hydroureteronephrosis or increasing creatinine). Predictors of time to stent failure were assessed using Cox regression. RESULTS: A total of 37 stents were placed in 25 patients with malignant ureteral obstruction. Of these stents 12 (35%) were identified to fail. Progressive hydroureteronephrosis and increasing creatinine were the most common signs of stent failure. Three failed stents had migrated distally and no stents required removal for recurrent infection. Patients with evidence of prostate cancer invading the bladder at stent placement were found to have a significantly increased risk of failure (HR 6.50, 95% CI 1.45-29.20, p = 0.015). Notably symptomatic subcapsular hematomas were identified in 3 patients after metallic stent placement. CONCLUSIONS: Failure rates with a metallic stent are similar to those historically observed with traditional polyurethane based stents in malignant ureteral obstruction. The invasion of prostate cancer in the bladder significantly increases the risk of failure. Patients should be counseled and observed for subcapsular hematoma formation with this device

Abstract 17460: Initial Clinical Experience with the Medtronic LinQ Loop Recorder: Concerns about Data Deluge

Introduction: Long-term ECG monitoring is often necessary in patients (pts) with unexplained syncope and suspected or known atrial fibrillation (AF). The recently released Medtronic LinQ loop recorder (ILR) accrues ECG data daily; “alert” conditions are wirelessly transmitted to providers. To date, the frequency and characteristics of these alerts are unknown. Hypothesis: We hypothesized that alerts would occur infrequently, thus allowing for remote management of large numbers of pts. Methods: Consecutive pts implanted with the LinQ were assessed. All alerts were collected and analyzed. Alerts ideally reflect a change within the past 24 hours of monitoring. However, some alerts (once triggered) perpetuate daily until cleared by a patient initiating a manual transmission. Results: Our first 100 LinQ pts (mean age 67.5 years; 51% male) implanted within the first 3 months of market release were assessed. The indications for monitoring included suspected AF (cryptogenic stroke, n=10; history of atrial flutter, n=1), known AF (n=61), and unexplained syncope (n=25). During follow-up, an alert occurred in 63 pts; a similar frequency of alerts occurred in AF and syncope pts (Figure). Once present, 29 (46%) alerts perpetuated daily and required manual transmission to clear. Conclusion: We report the initial clinical experience with the LinQ ILR. We found that alerts occurred frequently, irrespective of indication for monitoring. Once present, alerts were frequently perpetuated due to a major design limitation. A more robust system is needed to triage the data being accrued to prevent unnecessary data deluge. </jats:p