Thalamic epileptic spikes disrupt sleep spindles in patients with epileptic encephalopathy.

In severe epileptic encephalopathies, epileptic activity contributes to progressive cognitive dysfunction. Epileptic encephalopathies share the trait of spike-wave activation during non-rapid eye movement sleep (EE-SWAS), a sleep stage dominated by sleep spindles, brain oscillations known to coordinate offline memory consolidation. Epileptic activity has been proposed to hijack the circuits driving these thalamocortical oscillations, thereby contributing to cognitive impairment. Using a unique dataset of simultaneous human thalamic and cortical recordings in subjects with and without EE-SWAS, we provide evidence for epileptic spike interference of thalamic sleep spindle production in patients with EE-SWAS. First, we show that epileptic spikes and sleep spindles are both predicted by slow oscillations during stage two sleep (N2), but at different phases of the slow oscillation. Next, we demonstrate that sleep activated cortical epileptic spikes propagate to the thalamus (thalamic spike rate increases after a cortical spike, p≈0). We then show that epileptic spikes in the thalamus increase the thalamic spindle refractory period (p≈0). Finally, we show that in three patients with EE-SWAS, there is a downregulation of sleep spindles for 30 seconds after each thalamic spike (p<0.01). These direct human thalamocortical observations support a proposed mechanism for epileptiform activity to impact cognitive function, wherein epileptic spikes inhibit thalamic sleep spindles in epileptic encephalopathy with spike and wave activation during sleep.

The biological basis of the experience and categorization of colour.

We used the Land Colour Mondrian experiments in a Bayesian context to test the degree to which subjects vary in categorizing the colour of different patches, when each patch is made to reflect light of the identical wavelength-energy composition. The brain uses a ratio-taking mechanism to determine the ratio of light of every waveband reflected from a surface and from its surrounds. Our (Bayesian) hypothesis was that this ratio-taking mechanism is similar in all humans and therefore leads to a constant categorization of colours that differs little between them. The similarly categorized colours are the initial priors, with initial hues attached to them. Twenty subjects of different ethnic and cultural backgrounds, for all but one of whom English was not the primary language, viewed eight patches of different colour in two Mondrian displays; each patch, when viewed, was made to reflect identical ratios of long-, middle- and short-wave light. Subjects were asked to match the colour of the viewed patch with that of the Munsell chip coming closest in colour to that of the viewed patch, without using language. In terms of hue, there was less variability in matching warm hues than cool ones. In terms of colour categorization, there was little variability overall. We take the lack of significant variability between subjects in the matches made as a pointer to similar computational mechanisms being employed in different subjects to perceive colours, thus permitting them to assume that their categorization of colours has universal agreement and assent.

Pupil responses to colorfulness are selectively reduced in healthy older adults.

The alignment between visual pathway signaling and pupil dynamics offers a promising non-invasive method to further illuminate the mechanisms of human color perception. However, only limited research has been done in this area and the effects of healthy aging on pupil responses to the different color components have not been studied yet. Here we aim to address this by modelling the effects of color lightness and chroma (colorfulness) on pupil responses in young and older adults, in a closely controlled passive viewing experiment with 26 broad-spectrum digital color fields. We show that pupil responses to color lightness and chroma are independent from each other in both young and older adults. Pupil responses to color lightness levels are unaffected by healthy aging, when correcting for smaller baseline pupil sizes in older adults. Older adults exhibit weaker pupil responses to chroma increases, predominantly along the Green-Magenta axis, while relatively sparing the Blue-Yellow axis. Our findings complement behavioral studies in providing physiological evidence that colors fade with age, with implications for color-based applications and interventions both in healthy aging and later-life neurodegenerative disorders.

Single-trial magnetoencephalography signals encoded as an unfolding decision process.

The model of a stochastic decision process unfolding in motor and premotor regions of the brain was encoded in single-trial magnetoencephalographic (MEG) recordings while ten healthy subjects performed a sensorimotor Reaction Time (RT) task. The duration of single-trial MEG signals preceding the motor response, recorded over the motor cortex contralateral to the responding hand, co-varied with RT across trials according to the model's prediction. Furthermore, these signals displayed the same properties of a "rising-to-a-fixed-threshold" decision process as posited by the model and observed in the activity of single neurons in the primate cortex. The present findings demonstrate that non-averaged, single-trial MEG recordings can be used to test models of cognitive processes, like decision-making, in humans.

Blue-green color categorization in Mandarin-English speakers.

Observers are faster to detect a target among a set of distracters if the targets and distracters come from different color categories. This cross-boundary advantage seems to be limited to the right visual field, which is consistent with the dominance of the left hemisphere for language processing [Gilbert et al., Proc. Natl. Acad. Sci. USA 103, 489 (2006)]. Here we study whether a similar visual field advantage is found in the color identification task in speakers of Mandarin, a language that uses a logographic system. Forty late Mandarin-English bilinguals performed a blue-green color categorization task, in a blocked design, in their first language (L1: Mandarin) or second language (L2: English). Eleven color singletons ranging from blue to green were presented for 160 ms, randomly in the left visual field (LVF) or right visual field (RVF). Color boundary and reaction times (RTs) at the color boundary were estimated in L1 and L2, for both visual fields. We found that the color boundary did not differ between the languages; RTs at the color boundary, however, were on average more than 100 ms shorter in the English compared to the Mandarin sessions, but only when the stimuli were presented in the RVF. The finding may be explained by the script nature of the two languages: Mandarin logographic characters are analyzed visuospatially in the right hemisphere, which conceivably facilitates identification of color presented to the LVF.

Sources of Variation in the Spectral Slope of the Sleep EEG.

The 1/f spectral slope of the electroencephalogram (EEG) estimated in the γ frequency range has been proposed as an arousal marker that differentiates wake, nonrapid eye movement (NREM) sleep, and rapid eye movement (REM) sleep. Here, we sought to replicate and extend these findings in a large sample, providing a comprehensive characterization of how slope changes with age, sex, and its test-retest reliability as well as potential confounds that could affect the slope estimation. We used 10,255 whole-night polysomnograms (PSGs) from the National Sleep Research Resource (NSRR). All preprocessing steps were performed using an open-source Luna package and the spectral slope was estimated by fitting log-log linear regression models on the absolute power from 30 to 45 Hz separately for wake, NREM, and REM stages. We confirmed that the mean spectral slope grows steeper going from wake to NREM to REM sleep. We found that the choice of mastoid referencing scheme modulated the extent to which electromyogenic, or electrocardiographic artifacts were likely to bias 30- to 45-Hz slope estimates, as well as other sources of technical, device-specific bias. Nonetheless, within individuals, slope estimates were relatively stable over time. Both cross-sectionally and longitudinal, slopes tended to become shallower with increasing age, particularly for REM sleep; males tended to show flatter slopes than females across all states. Our findings support that spectral slope can be a valuable arousal marker for both clinical and research endeavors but also underscore the importance of considering interindividual variation and multiple methodological aspects related to its estimation.

No Difference in Outcomes Between Suspensory (Fixed-Loop Cortical Button) Versus Expandable Anteromedial Femoral Fixation in Anterior Cruciate Ligament Reconstruction With Autologous Hamstring Tendons: A Prospective, Randomized, Controlled Study in Male Patients.

PURPOSE: To compare anterior cruciate ligament (ACL) autograft reconstruction using fixed-looped suspensory versus expandable femoral fixation through the anteromedial portal. METHODS: After we performed prospective power analysis and obtained institutional review board, 70 patients with ACL rupture were block randomized to the expandable or suspensory femoral fixation group (35 in each group). All patients received autologous hamstring autograft through the anteromedial portal and fixed with a sheath-screw system in the tibia. The primary outcome measures were anteroposterior knee stability at 2 years' follow-up measured using the KT-1000 arthrometer and the degree of femoral and tibial tunnels' widening measured by the use of computed tomography imaging performed immediately postoperative and 12 months postsurgery. Secondary outcome measures included pain score on a visual analog scale, the subjective International Knee Documentation Committee 2000 assessment form, the Lysholm score, and the Tegner activity scale at 3, 6, 12, and 24 months. RESULTS: Twenty-four patients were excluded from further analysis, leaving a total of 48 patients (24 in each group) for the final evaluation. The anteroposterior knee stability (KT-1000) showed no difference between groups at 24 months' follow-up (P = .31). The percentile widening (%) of femoral and tibial tunnel at 1-year follow-up showed no difference also, except for greater values at the tibial coronal point T2 (P = .065) and tibial sagittal point T1 (P = .033) in the group of cortical buttons. Secondary clinical outcomes showed no statistical differences between groups at 3, 6, 12, and 24 months' postoperatively. Numerical pain scale (visual analog scale) was similar in both groups except for postoperative day 7, where the AperFix group showed better results (P = .014). There were no major intraoperative and late postoperative complications in any of the groups. CONCLUSIONS: Our results showed no significant differences in knee anteroposterior stability, tunnel enlargement or other clinical outcomes comparing expandable versus cortical button fixation in anteromedial hamstrings ACL reconstruction. LEVEL OF EVIDENCE: Level II, randomized controlled trial.

Coherence of achromatic, primary and basic classes of colour categories.

A range of explanations have been advanced for the systems of colour names found in different languages. Some explanations give special, fundamental status to a subset of colour categories. We argue that a subset of colour categories, if fundamental, will be coherent - meaning that a non-trivial criterion distinguishes them from the other colour categories. We test the coherence of subsets of achromatic (white, black and grey), primary (white, black, red, green, yellow, blue) and basic (primaries plus brown, orange, purple, pink and grey) colour categories in English. Criteria for defining colour categories were expressed in terms of behavioural, linguistic and geometric features derived from colour naming and linguistic usage data; and were discovered using machine learning methods. We find that achromatic and basic colour categories are coherent subsets but not primaries. These results support claims that the basic colour categories have special status, and undermine claims about the fundamental role of primaries in colour naming systems.

Categorical colour geometry.

Ordinary language users group colours into categories that they refer to by a name e.g. pale green. Data on the colour categories of English speakers was collected using online crowd sourcing - 1,000 subjects produced 20,000 unconstrained names for 600 colour stimuli. From this data, using the framework of Information Geometry, a Riemannian metric was computed throughout the RGB cube. This is the first colour metric to have been computed from colour categorization data. In this categorical metric the distance between two close colours is determined by the difference in the distribution of names that the subject population applied to them. This contrasts with previous colour metrics which have been driven by stimulus discriminability, or acceptability of a colour match. The categorical metric is analysed and shown to be clearly different from discriminability-based metrics. Natural units of categorical length, area and volume are derived. These allow a count to be made of the number of categorically-distinct regions of categorically-similar colours that fit within colour space. Our analysis estimates that 27 such regions fit within the RGB cube, which agrees well with a previous estimate of 30 colours that can be identified by name by untrained subjects.

Large-scale structure and individual fingerprints of locally coupled sleep oscillations.

Slow oscillations and sleep spindles, the canonical electrophysiological oscillations of nonrapid eye movement sleep, are thought to gate incoming sensory information, underlie processes of sleep-dependent memory consolidation, and are altered in various neuropsychiatric disorders. Accumulating evidence of the predominantly local expression of these individual oscillatory rhythms suggests that their cross-frequency interactions may have a similar local component. However, it is unclear whether locally coordinated sleep oscillations exist across the cortex, and whether and how these dynamics differ between fast and slow spindles, and sleep stages. Moreover, substantial individual variability in the expression of both spindles and slow oscillations raises the possibility that their temporal organization shows similar individual differences. Using two nights of multichannel electroencephalography recordings from 24 healthy individuals, we characterized the topography of slow oscillation-spindle coupling. We found that while slow oscillations are highly restricted in spatial extent, the phase of the local slow oscillation modulates local spindle activity at virtually every cortical site. However, coupling dynamics varied with spindle class, sleep stage, and cortical region. Moreover, the slow oscillation phase at which spindles were maximally expressed differed markedly across individuals while remaining stable across nights. These findings both add an important spatial aspect to our understanding of the temporal coupling of sleep oscillations and demonstrate the heterogeneity of coupling dynamics, which must be taken into account when formulating mechanistic accounts of sleep-related memory processing.

The Constancy of Colored After-Images.

We undertook psychophysical experiments to determine whether the color of the after-image produced by viewing a colored patch which is part of a complex multi-colored scene depends on the wavelength-energy composition of the light reflected from that patch. Our results show that it does not. The after-image, just like the color itself, depends on the ratio of light of different wavebands reflected from it and its surrounds. Hence, traditional accounts of after-images as being the result of retinal adaptation or the perceptual result of physiological opponency, are inadequate. We propose instead that the color of after-images is generated after colors themselves are generated in the visual brain.

Judging the judges' performance in rhythmic gymnastics.

INTRODUCTION: Rhythmic gymnastics (RG) is an aesthetic event balancing between art and sport that also has a performance rating system (Code of Points) given by the International Gymnastics Federation. It is one of the sports in which competition results greatly depend on the judges' evaluation. In the current study, we explored the judges' performance in a five-gymnast ensemble routine. METHODS: An expert-novice paradigm (10 international-level, 10 national-level, and 10 novice-level judges) was implemented under a fully simulated procedure of judgment in a five-gymnast ensemble routine of RG using two videos of routines performed by the Greek national team of RG. Simultaneous recordings of two-dimensional eye movements were taken during the judgment procedure to assess the percentage of time spent by each judge viewing the videos and fixation performance of each judge when an error in gymnast performance had occurred. RESULTS: All judge level groups had very modest performance of error recognition on gymnasts' routines, and the best international judges reported approximately 40% of true errors. Novice judges spent significantly more time viewing the videos compared with national and international judges and spent significantly more time fixating detected errors than the other two groups. National judges were the only group that made efficient use of fixation to detect errors. CONCLUSIONS: The fact that international-level judges outperformed both other groups, while not relying on visual fixation to detect errors, suggests that these experienced judges probably make use of other cognitive strategies, increasing their overall error detection efficiency, which was, however, still far below optimum.

Dynamic analysis of EEG signals during spatial working memory used for either perception discrimination or planning of action.

We analysed multi-channel electroencephalographic (EEG) recordings during a spatial Working Memory (WM) task in order to test the hypothesis that segmentation of perception and action is present when the visual stimulus has been stored in spatial WM. To detect the interactions between different regions of the brain depending on the task we employed both Short Time Fourier Transformation (STFT) and the concept of Granger Causality (GC). Our computational analysis supports evidence that the Parietal Cortex (PC) is involved in WM processing.