Bayesian interpretation of the prefrontal P2 ERP component based on stimulus/response mapping uncertainty

The brain can be seen as a predictive system continuously computing prior information to guess posterior probabilities minimizing sources of uncertainty. To test this Bayesian view of the brain, event-related potentials (ERP) methods have been used focusing on the well-known P3 component, traditionally associated with decision-making processes and sources of uncertainty regarding target probability. Another ERP component linked with decision-making is the prefrontal P2 (pP2) component, which has never been considered within the Bayesian framework. To test which source of uncertainty could be associated with the pP2, uncertainty induced by target probability and stimulus-response (S/R) mapping were modulated in three visuomotor tasks. Results showed that the pP2 had the largest amplitude in the task with the largest uncertainty regarding the S/R mapping and degraded as the S/R mapping became more predictable. The P3 was maximal in the tasks with larger uncertainty regarding the target probability. While we confirmed the P3 association with target probability, we extended our knowledge on the pP2 associating it with S/R mapping uncertainty. This component, which has been previously localized within the anterior insular cortex, may minimize S/R mapping uncertainty allowing response-related evidence accumulation and comparing current events with internal representations to extract action-related probabilities.

From plaque biology to clinical setting

Coronary atherosclerosis may cause acute and chronic ischemic syndromes; the former are caused by "acute plaque events," mostly thrombosis complicating vulnerable ruptured plaques, namely severe lesions with large core, thin cap, and weak shoulder infiltrated by activated inflammatory cells. Plaque rupture may also occur in nonischemic settings and is not obligatorily complicated by thrombosis. Furthermore, plaque rupture is not the only thrombus substrate in acute ischemic syndromes: Superficial erosion of fibrous plaques is found in 44% of acute thrombi in sudden coronary deaths and in 25% of those in acute myocardial infarctions. Coronary thrombosis appears to be triggered by superficial intimal inflammation in plaque ulceration and by neointimal hyperplasia in plaque erosion. "Endogenous" and, recently, exogenous factors, particularly infective intracellular organisms, have been proposed as major contributors to plaque inflammation, activation, and vulnerability. Possible exogenous triggers are DNA and RNA viruses and intracellular bacteria such as Chlamydia pneumoniae, which has been identified with microbiological, ultrastructural, immunohistochemical, and molecular tools in a consistent proportion of human plaque samples. Chlamydia increases local thrombogenicity and is associated with an atherogenic lipid profile. Systemic indexes of inflammation, such as PCR, SAA, and fibrinogen, are also increased in acute syndromes and common infectious diseases with high morbidity and minimal clinical impact are good candidates; Helicobacter pylori is a major one. Infectious agents could link local and systemic inflammation: White cells infected in its target tissue could circulate into the flow and be captured, on a specific local trigger, into vessel walls thus stimulating local inflammation.

Protection by ascorbate against apoptosis of thymocytes: implications of ascorbate-induced nonlethal oxidative stress and poly(ADP-ribosyl)ation

Apoptosis can be triggered in thymocytes with stimuli (6alpha-methylprednisolone, thapsigargin, and etoposide) acting by different mechanisms. In each of these instances cell death is extensively prevented until 5 h of incubation when cells are preincubated with 250 microM ascorbic acid (AA) for 1 h, then washed, and incubated in fresh medium containing the above mentioned apoptotic stimuli. In addition, the degree of spontaneous apoptosis of untreated thymocytes is somewhat lower in the AA-preincubated cells. The protection against apoptosis does not seem to be dependent on the intracellular enrichment of AA, as measured at the end of the preincubation period. On the contrary, such a protection is strictly related to a partial loss of ascorbate in the medium (possibly due to its autooxidation), is catalase-inhibitable, and is reproduced by a preincubation of the cells with nontoxic concentrations of hydrogen peroxide. The AA-supplemented cells show a remarkable decrease in NAD+ levels and a significant increase of poly(ADP-ribose) polymerase (PARP) activity. Consistently with these results, the addition of PARP inhibitors, such as thymidine and 3-aminobenzamide, during the preincubation with AA, prevents NAD+ depletion and abolishes the protective effect of AA against apoptosis. The possibility is discussed that an early activation of PARP by stimuli which are nontoxic per se makes the cells able to withstand subsequent apoptotic stimuli which are otherwise lethal.

[Histopathologic features in atherectomy samples obtained from patient with unstable angina, stable angina and restenosis. Directional Atherectomy Lombardi Group]

BACKGROUND

The present study was aimed at investigating the pathologic features of directional coronary atherectomy (DCA) samples obtained from 194 patients (14 females) with stable (n = 68) and unstable (n = 95) angina, and with restenosis (n = 27).

METHODS

DCA samples were obtained from culprit lesions, using the Simpson technique. Unstable angina was classified according to E. Braunwald criteria. Stable angina was grouped according to the presence or absence of a prior myocardial infarction (MI). DCA samples were fixed, processed, serially cut and stained with hematoxilin-eosin and with Movat pentachrome stain.

RESULTS

The major pathologic findings were thrombosis, inflammation of the superficial plaque layers, and neointimal hyperplasia which often coexisted within a same sample. Their frequencies, in that order, were distributed in the differing groups of patients as follows: 21% (n = 9), 29.2% (n = 12) and 51% (n = 21) of the 41 cases with stable angina without prior MI. 40.7% (n = 11), 40.7% (n = 11), and 51.8% (n = 14) of the 27 cases with stable angina with prior MI. 25% (n = 4), 56.2% (n = 9) and 68.7% (n = 11), of the 16 cases with BI unstable angina. 35.3% (n = 14), 55.8% (n = 19) and 44% (n = 15), of the 34 cases with BII unstable angina. 44.4% (n = 4), 33.3% (n = 3) and 33.3% (n = 3), of the 9 cases with BIII unstable angina. 48.2% (n = 14), 48.2% (n = 14) and 51.8% (n = 15), of the 29 cases with CII unstable angina at 35.8 days after MI. 60% (n = 3), 60% (n = 3) and 40% (n = 2), of the 5 cases with CIII unstable angina at 8.3 days after MI. 26% (n = 7), 48% (n = 13) and 85.1% (n = 23), of the 27 cases with restenosis. According to above observation, the frequency of coronary thrombosis increases with the increase of the severity of myocardial ischemia. However, thrombosis is not found in most unstable angina without prior MI (63% of BI-II-III unstable angina cases do not have thrombus). In addition, thrombus is not a specific finding of unstable angina, given its occurrence, although in a much lower percentage of cases, in stable angina and in restenosis.

CONCLUSIONS

Present data show that different ischemic and plaque lesions. This observation questions on the pathogenetic role of thrombus in unstable angina and calls for further investigations on inflammation and neointimal hyperplasia, as well as on the the reciprocal relation between these findings which are often combined within a same lesion.