Marie Prévost

Oxytocin in pregnancy and the postpartum: relations to labor and its management

The purpose of this study was to examine variations in endogenous oxytocin levels in pregnancy and postpartum state. We also explored the associations between delivery variables and oxytocin levels. A final sample of 272 mothers in their first trimester of pregnancy was included for the study. Blood samples were drawn during the first trimester and third trimester of pregnancy and at 8 weeks postpartum. Socio-demographic data were collected at each time point and medical files were consulted for delivery details. In most women, levels of circulating oxytocin increased from the first to third trimester of pregnancy followed by a decrease in the postpartum period. Oxytocin levels varied considerably between individuals, ranging from 50 pg/mL to over 2000 pg/mL. Parity was the main predictor of oxytocin levels in the third trimester of pregnancy and of oxytocin level changes from the first to the third trimester of pregnancy. Oxytocin levels in the third trimester of pregnancy predicted a self-reported negative labor experience and increased the chances of having an epidural. Intrapartum exogenous oxytocin was positively associated with levels of oxytocin during the postpartum period. Our exploratory results suggest that circulating oxytocin levels during the third trimester of pregnancy may predict the type of labor a woman will experience. More importantly, the quantity of intrapartum exogenous oxytocin administered during labor predicted plasma oxytocin levels 2 months postpartum, suggesting a possible long-term effect of this routine intervention, the consequences of which are largely unknown.

The Reading the Mind in the Eyes test: validation of a French version and exploration of cultural variations in a multi-ethnic city

Introduction The first aim of our study was to validate the French version of the Reading the Mind in the Eyes test, a theory of mind test. The second aim was to test whether cultural differences modulate performance on this test. Methods A total of 109 participants completed the original English version and 97 participants completed the French version. Another group of 30 participants completed the French version twice, one week apart. Results We report a similar overall distribution of scores in both versions and no differences in the mean scores between them. However, 2 items in the French version did not collect a majority of responses, which differed from the results of the English version. Test-retest showed good stability of the French version. As expected, participants who do not speak French or English at home, and those born in Asia, performed worse than North American participants, and those who speak English or French at home. Conclusions We report a French version with acceptable validity and good stability. The cultural differences observed support the idea that Asian culture does not use theory of mind to explain peoples behaviours as much as North American people do.

Schizotypal traits and N400 in healthy subjects

We examined whether correlations previously found between symptoms of schizophrenia patients and the amplitude of an event-related potential (ERP), the N400, could be also found between schizotypal experiences of healthy subjects and the N400. We chose a semantic categorization task previously used with patients. Schizotypal experiences were measured with the schizotypal personality questionnaire (SPQ). The effects of the other factors were controlled for when assessing the correlations between each SPQ factor and N400s. These correlations were assessed at each electrode site to see whether their distribution on the scalp follows that of the N400 effect. Disorganization and interpersonal scores were found to correlate with ERPs in the N400 time window, as previously reported for the comparable symptoms of patients. However, the scalp distribution of these correlations differed from that of the N400 effect.

P300 asymmetry and positive symptom severity: A study in the early stage of a first episode of psychosis

The amplitude of the P300 event-related potential (ERP) has been reported to be reduced over left compared to right temporal sites in schizophrenia patients. This left temporal P300 reduction has been associated with positive symptom severity and gray matter reduction in the left superior temporal gyrus. We investigated a group of patients with a first episode of schizophrenia spectrum psychosis and a group of normal controls to verify if P300 amplitude asymmetry already exists around the time of presentation for treatment. Relative to normal control subjects, no P300 asymmetry was found in patients. Nevertheless, P300 asymmetry was correlated with the severity of positive symptoms and worse global functioning (GAF), a good predictor of poor outcome.

Paranoid induction reduces N400s of healthy subjects with delusional-like ideation.

A previous study suggests that the amplitude of the N400 event-related potentials (ERPs) of healthy subjects does not vary with their delusional-like ideations. This contrasts with the smaller N400 amplitudes observed in more- than in less-deluded schizophrenia patients. Here, we hypothesize that these smaller N400 amplitudes were related to the paranoid feelings patients had during the ERP recording. We thus induced this type of feelings in healthy subjects. Delusional-like ideation was assessed with the schizotypal personality questionnaire. Thirty-four healthy subjects completed a semantic categorization task. Paranoid feelings were significantly enhanced by the induction. In these conditions, greater delusional-like ideation scores were associated with smaller N400 amplitudes and larger late positive components. Controlling for the two other schizotypal factors strengthened these results. These findings may help us understand why delusions persist.

From N400 to N300: variations in the timing of semantic processing with repetition.

The present study aimed to explore the variations of semantic processing according to the number of target words (i.e., 4, 12 and 24) and according to the number of repetitions (i.e, 1 to 15). The number of targets had no impact on the N400 brain potential, the index of semantic processing, nor on the late positive component (LPC), an index of episodic encoding and retrieval. Analyses of the effects of the number of repetitions showed that the duration of semantic processes--assessed by measuring N400 latency--was linearly shortened along repetitions while their extent--as indexed by N400 amplitude--remained constant after the second presentation. In contrast, the extent of episodic processes--as indexed by LPC amplitude--was found to increase linearly with repetition. By showing that N400 latency may be much less stable than previously thought, these results bring new constraints on the functional correlates of this key stage in the processing of semantic information. They also suggest that semantic processes can be studied at high repetition rates whatever the number of target stimuli. Finally, our findings show that each episode of prior presentation has an impact on the late processing of a stimulus despite the absence of an explicit memory task.

On the Functional Significance of the P1 and N1 Effects to Illusory Figures in the Notch Mode of Presentation

The processing of Kanizsa figures have classically been studied by flashing the full “pacmen” inducers at stimulus onset. A recent study, however, has shown that it is advantageous to present illusory figures in the “notch” mode of presentation, that is by leaving the round inducers on screen at all times and by removing the inward-oriented notches delineating the illusory figure at stimulus onset. Indeed, using the notch mode of presentation, novel P1and N1 effects have been found when comparing visual potentials (VEPs) evoked by an illusory figure and the VEPs to a control figure whose onset corresponds to the removal of outward-oriented notches, which prevents their integration into one delineated form. In Experiment 1, we replicated these findings, the illusory figure was found to evoke a larger P1 and a smaller N1 than its control. In Experiment 2, real grey squares were placed over the notches so that one condition, that with inward-oriented notches, shows a large central grey square and the other condition, that with outward-oriented notches, shows four unconnected smaller grey squares. In response to these “real” figures, no P1 effect was found but a N1 effect comparable to the one obtained with illusory figures was observed. Taken together, these results suggest that the P1 effect observed with illusory figures is likely specific to the processing of the illusory features of the figures. Conversely, the fact that the N1 effect was also obtained with real figures indicates that this effect may be due to more global processes related to depth segmentation or surface/object perception.

Judging Strangers’ Trustworthiness is Associated with Theory of Mind Skills

Trusting people requires evaluating them to assess their trustworthiness. Evaluating a stranger’s intentions is likely to be one method of assessing trustworthiness. The present study tested the hypothesis that judgments of trustworthiness are associated with mind reading skills, also called theory of mind (ToM). We tested a group of healthy participants and a group of patients with paranoid schizophrenia. Both groups made ToM judgments and judged the trustworthiness of strangers. Participants were also assessed for their disposition to trust as well as levels of paranoid belief. As anticipated, healthy participants had a normal ToM scores and patients with paranoid schizophrenia had poor ToM scores. In paranoid patients, better ability to read others’ minds was associated with judging others as more trustworthy, while the reverse was found in the healthy participants (better mind reading was associated with judging others as less trustworthy), suggesting a non-linear relationship between trust in others and being able to read their intentions.

The influence of contour fragmentation on recognition memory: An event-related potential study

The present study was carried out to examine how the event-related potentials to fragmentation predict recognition success. Stimuli were abstract meaningless figures that were either complete or fragmented to various extents but still recoverable. Stimuli were first encoded as part of a symmetry discrimination task. In a subsequent recognition phase, encoded stimuli were presented complete along with never presented stimuli and participants performed an old/new discrimination task. Fragmentation stimuli elicited more negative ERPs than complete figures over the frontal, central and parietal areas between 180 and 260 ms, and over the occipito-temporal areas between 220 and 340 ms. Only this latter effect was modulated as a function of whether stimuli were recognized or not during the recognition phase of the memory test. More specifically, the effect occurred for stimuli that were later forgotten and was absent for stimuli that were later recognized. This ERP to fragmentation, the occipito-temporal N(frag), possibly reflects the brain response to encoding difficulty, and is thus predictive of recognition performance.