Efficient Prestimulus Network Integration of Fusiform Face Area Biases Face Perception during Binocular Rivalry.

Ongoing fluctuations in neural excitability and connectivity influence whether or not a stimulus is seen. Do they also influence which stimulus is seen? We recorded magnetoencephalography data while 21 human participants viewed face or house stimuli, either one at a time or under bistable conditions induced through binocular rivalry. Multivariate pattern analysis revealed common neural substrates for rivalrous versus nonrivalrous stimuli with an additional delay of ∼36 msec for the bistable stimulus, and poststimulus signals were source-localized to the fusiform face area. Before stimulus onset followed by a face versus house report, fusiform face area showed stronger connectivity to primary visual cortex and to the rest of the cortex in the alpha frequency range (8-13 Hz), but there were no differences in local oscillatory alpha power. The prestimulus connectivity metrics predicted the accuracy of poststimulus decoding and the delay associated with rivalry disambiguation suggesting that perceptual content is shaped by ongoing neural network states.

No behavioural evidence for rhythmic facilitation of perceptual discrimination.

It has been hypothesized that internal oscillations can synchronize (i.e., entrain) to external environmental rhythms, thereby facilitating perception and behaviour. To date, evidence for the link between the phase of neural oscillations and behaviour has been scarce and contradictory; moreover, it remains an open question whether the brain can use this tentative mechanism for active temporal prediction. In our present study, we conducted a series of auditory pitch discrimination tasks with 181 healthy participants in an effort to shed light on the proposed behavioural benefits of rhythmic cueing and entrainment. In the three versions of our task, we observed no perceptual benefit of purported entrainment: targets occurring in-phase with a rhythmic cue provided no perceptual benefits in terms of discrimination accuracy or reaction time when compared with targets occurring out-of-phase or targets occurring randomly, nor did we find performance differences for targets preceded by rhythmic versus random cues. However, we found a surprising effect of cueing frequency on reaction time, in which participants showed faster responses to cue rhythms presented at higher frequencies. We therefore provide no evidence of entrainment, but instead a tentative effect of covert active sensing in which a faster external rhythm leads to a faster communication rate between motor and sensory cortices, allowing for sensory inputs to be sampled earlier in time.

Prestimulus feedback connectivity biases the content of visual experiences.

Ongoing fluctuations in neural excitability and in networkwide activity patterns before stimulus onset have been proposed to underlie variability in near-threshold stimulus detection paradigms-that is, whether or not an object is perceived. Here, we investigated the impact of prestimulus neural fluctuations on the content of perception-that is, whether one or another object is perceived. We recorded neural activity with magnetoencephalography (MEG) before and while participants briefly viewed an ambiguous image, the Rubin face/vase illusion, and required them to report their perceived interpretation in each trial. Using multivariate pattern analysis, we showed robust decoding of the perceptual report during the poststimulus period. Applying source localization to the classifier weights suggested early recruitment of primary visual cortex (V1) and ∼160-ms recruitment of the category-sensitive fusiform face area (FFA). These poststimulus effects were accompanied by stronger oscillatory power in the gamma frequency band for face vs. vase reports. In prestimulus intervals, we found no differences in oscillatory power between face vs. vase reports in V1 or in FFA, indicating similar levels of neural excitability. Despite this, we found stronger connectivity between V1 and FFA before face reports for low-frequency oscillations. Specifically, the strength of prestimulus feedback connectivity (i.e., Granger causality) from FFA to V1 predicted not only the category of the upcoming percept but also the strength of poststimulus neural activity associated with the percept. Our work shows that prestimulus network states can help shape future processing in category-sensitive brain regions and in this way bias the content of visual experiences.

From the dry lab to the operating room: the first transferability study of hysteroscopic skills.

OBJECTIVE: The aim of this study is to prove that a short dry lab training prior to the surgery is efficient to acquire basic hysteroscopic skills and that these skills are transferable directly to the operation theater. METHODS: Thirty-nine gynecologists who never attended a training course or practiced hysteroscopy before were evaluated. Participants were randomly divided into trainees (n = 21) and control (n = 18). Trainees attended a short time dry lab prior the exposure to the OR. The controls went directly to the OR. Participants were asked to identify the different landmarks of the uterine cavity and to perform a punch biopsy under the supervision of a gynecologist expert in hysteroscopy. A video recording for all the exercises was done, and showed independently to two expert surgeons in hysteroscopy for evaluation. The experts were also asked to distinguish between the trainees and the control. RESULTS: For both experts, the trainees' performance was statistically better than that of the controls (p < 0.001) for the identification of the uterus land marks and the punch biopsy. The two experts identified 80.9 and 85.7%, respectively, of the trainees. The participants' subgroup ID and the experts' identification were statistically correlated (p < 0.001). CONCLUSION: A short time dry lab is efficient to acquire basic hysteroscopic skills and these skills are transferable directly to the OR.

Validation Study of a Portable Home Trainer Using a Pad for Laparoscopic Practice.

The aim of this study was to describe and validate a homemade laparoscopic trainer. The abdominal cavity is simulated within a 3-mm-thick stainless steel model. Thirty-four participants were evaluated in a pilot study to validate our model. Participants were divided into experts (n = 19) and novices (n = 15) to perform basic and complex laparoscopic skills. The comparison between the homemade trainer (HT) and the standard laparoscopic trainer showed no significant differences for the 2 tasks performed for each group ( P > .05). The experts' performance of the 2 tasks was statistically different from the novices ( P < .05) on both trainers. Both experts (84%) and novices (87%) approved the HT as an effective home trainer. Our HT seems to fulfill the conditions of performing the basic and complex laparoscopic psychomotor skills at a low cost and similar efficiency.

Common neural mechanisms supporting time judgements in humans and monkeys.

There has been an increasing interest in identifying the biological underpinnings of human time perception, for which purpose research in non-human primates (NHP) is common. Although previous work, based on behaviour, suggests that similar mechanisms support time perception across species, the neural correlates of time estimation in humans and NHP have not been directly compared. In this study, we assess whether brain evoked responses during a time categorization task are similar across species. Specifically, we assess putative differences in post-interval evoked potentials as a function of perceived duration in human EEG (N = 24) and local field potential (LFP) and spike recordings in pre-supplementary motor area (pre-SMA) of one monkey. Event-related potentials (ERPs) differed significantly after the presentation of the temporal interval between "short" and "long" perceived durations in both species, even when the objective duration of the stimuli was the same. Interestingly, the polarity of the reported ERPs was reversed for incorrect trials (i.e., the ERP of a "long" stimulus looked like the ERP of a "short" stimulus when a time categorization error was made). Hence, our results show that post-interval potentials reflect the perceived (rather than the objective) duration of the presented time interval in both NHP and humans. In addition, firing rates in monkey's pre-SMA also differed significantly between short and long perceived durations and were reversed in incorrect trials. Together, our results show that common neural mechanisms support time categorization in NHP and humans, thereby suggesting that NHP are a good model for investigating human time perception.

ß Band Rhythms Influence Reaction Times.

Despite their involvement in many cognitive functions, ß oscillations are among the least understood brain rhythms. Reports on whether the functional role of ß is primarily inhibitory or excitatory have been contradictory. Our framework attempts to reconcile these findings and proposes that several ß rhythms co-exist at different frequencies. ß Frequency shifts and their potential influence on behavior have thus far received little attention. In this human magnetoencephalography (MEG) experiment, we asked whether changes in ß power or frequency in auditory cortex and motor cortex influence behavior (reaction times) during an auditory sweep discrimination task. We found that in motor cortex, increased ß power slowed down responses, while in auditory cortex, increased ß frequency slowed down responses. We further characterized ß as transient burst events with distinct spectro-temporal profiles influencing reaction times. Finally, we found that increased motor-to-auditory ß connectivity also slowed down responses. In sum, ß power, frequency, bursting properties, cortical focus, and connectivity profile all influenced behavioral outcomes. Our results imply that the study of ß oscillations requires caution as ß dynamics are multifaceted phenomena, and that several dynamics must be taken into account to reconcile mixed findings in the literature.

Distinct beta frequencies reflect categorical decisions.

Based on prior findings of content-specific beta synchronization in working memory and decision making, we hypothesized that beta oscillations support the (re-)activation of cortical representations by mediating neural ensemble formation. We found that beta activity in monkey dorsolateral prefrontal cortex (dlPFC) and pre-supplementary motor area (preSMA) reflects the content of a stimulus in relation to the task context, regardless of its objective properties. In duration- and distance-categorization tasks, we changed the boundary between categories from one block of trials to the next. We found that two distinct beta-band frequencies were consistently associated with the two relative categories, with activity in these bands predicting the animals' responses. We characterized beta at these frequencies as transient bursts, and showed that dlPFC and preSMA are connected via these distinct frequency channels. These results support the role of beta in forming neural ensembles, and further show that such ensembles synchronize at different beta frequencies.

Synthol systemic complications: Hypercalcemia and pulmonary granulomatosis. A case report.

INTRODUCTION: Synthol injection for body contouring has been used by bodybuilders for some time. We report two extremely rare systemic complications; pulmonary granulomatosis and hypercalcemia, in a woman who has received Synthol injections for buttocks augmentation. PRESENTATION OF CASE: The case discussed in this report is of a 36-year-old lady who presented for severe hypercalcemia and nephrocalcinosis. Subsequent workup revealed granulomas in the buttocks and in the lungs. Upon questioning, it was discovered that she had received Synthol injection for buttocks augmentation a few months earlier. Labs were consistent with calcitriol mediated hypercalcemia, a phenomenon observed in granulomatous diseases. A diagnosis of foreign body granulomatosis with pulmonary migration and secondary hypercalcemia was made. The patient was started on prednisone and showed an initial positive response. DISCUSSION: Reported complications of Synthol include pain, muscle deformity, and ulceration at the injection site. Hypercalcemia secondary to foreign body granulomatosis after Synthol injection has been reported only once previously, and here we report a second case. The hypercalcemia is thought to be calcitriol mediated, where overexpression of CYP27B1 in the macrophages forming the granulomas leads to pathological extrarenal calcitriol production. Pulmonary granulomatosis, theorized to be secondary to hematologic migration of the injected material, has never been reported previously with Synthol use. CONCLUSION: Synthol injection for body contouring may be a cause of extensive local and pulmonary foreign body granulomatosis leading to calcitriol mediated hypercalcemia. History of cosmetic injections should not be disregarded during history taking.

Detecting Pre-Stimulus Source-Level Effects on Object Perception with Magnetoencephalography.

Pre-stimulus oscillatory brain activity influences upcoming perception. The characteristics of this pre-stimulus activity can predict whether a near-threshold stimulus will be perceived or not perceived, but can they also predict which one of two competing stimuli with different perceptual contents is perceived? Ambiguous visual stimuli, which can be seen in one of two possible ways at a time, are ideally suited to investigate this question. Magnetoencephalography (MEG) is a neurophysiological measurement technique that records magnetic signals emitted as a result of brain activity. The millisecond temporal resolution of MEG allows for a characterization of oscillatory brain states from as little as 1 second of recorded data. Presenting an empty screen around 1 second prior to the ambiguous stimulus onset therefore provides a time window in which one can investigate whether pre-stimulus oscillatory activity biases the content of upcoming perception, as indicated by participants' reports. The spatial resolution of MEG is not excellent, but sufficient to localise sources of brain activity at the centimetre scale. Source reconstruction of MEG activity then allows for testing hypotheses about the oscillatory activity of specific regions of interest, as well as the time- and frequency-resolved connectivity between regions of interest. The described protocol enables a better understanding of the influence of spontaneous, ongoing brain activity on visual perception.

Coupling and Decoupling between Brain and Body Oscillations.

Cross frequency coupling is used to study the cross talk between brain oscillations. In this paper we focus on a special type of frequency coupling between brain and body oscillations, which is reflected by the numerical ratio (r) between two frequencies (m and n; n > m). This approach is motivated by theoretical considerations, indicating that during alert wakefulness brain-body oscillations form a coupled hierarchy of frequencies with integer relationships that are binary multiples (r = n:m = 1:2, 1:4, 1:8…..). During sleep we expect an irrational relationship (r = n/m = irrational number) between brain and body oscillations that reflects decoupling. We analyzed alpha frequency, heart rate, breathing frequency during performance of a memory tasks and in addition spindle frequency from data collected by the SIESTA sleep research group. As predicted, our results show a binary multiple frequency relationship between alpha, heart rate and breathing frequency during task performance but an irrational relationship between spindle frequency, heart rate and breathing frequency during sleep.