Brain Oscillatory Correlates of Visual Short-Term Memory Errors

Brain dynamics of memory formation were explored during encoding and retention intervals of a visual working memory task. EEG data were acquired while subjects were exposed to grayscale images of widely known object categories (e.g., “luggage,” “chair,” and “car”). Following a short delay, two probes were shown to test memory accuracy. Oscillatory portraits of successful and erroneous memories were contrasted. Where significant differences were identified, oscillatory traits of false memories (i.e., when a novel probe item of the same category is recognized as familiar) were compared with those of successful and erroneous memories. Spectral analysis revealed theta (6–8 Hz) power over occipital channels for encoding of successful and false memories that was smaller when compared to other types of memory errors. The reduced theta power indicates successful encoding and reflects the efficient activation of the underlying neural assemblies. Prominent alpha-beta (10–26 Hz) activity belonging to the right parieto-occipital channels was identified during the retention interval. It was found to be larger for false memories and errors than that of correctly answered trials. High levels of alpha-beta oscillatory activity for errors correspond to poor maintenance leading to inefficient allocation of WM resources. In case of false memories, this would imply necessary cognitive effort to manage the extra semantic and perceptual load induced by the encoded stimuli

A direct relationship between oscillatory subthalamic nucleus-cortex coupling and rest tremor in Parkinson's disease

Electrophysiological studies suggest that rest tremor in Parkinson's disease is associated with an alteration of oscillatory activity. Although it is well known that tremor depends on cortico-muscular coupling, it is unclear whether synchronization within and between brain areas is specifically related to the presence and severity of tremor. To tackle this longstanding issue, we took advantage of naturally occurring spontaneous tremor fluctuations and investigated cerebral synchronization in the presence and absence of rest tremor. We simultaneously recorded local field potentials from the subthalamic nucleus, the magnetoencephalogram and the electromyogram of forearm muscles in 11 patients with Parkinson's disease (all male, age: 52-74 years). Recordings took place the day after surgery for deep brain stimulation, after withdrawal of anti-parkinsonian medication. We selected epochs containing spontaneous rest tremor and tremor-free epochs, respectively, and compared power and coherence between subthalamic nucleus, cortex and muscle across conditions. Tremor-associated changes in cerebro-muscular coherence were localized by Dynamic Imaging of Coherent Sources. Subsequently, cortico-cortical coupling was analysed by computation of the imaginary part of coherency, a coupling measure insensitive to volume conduction. After tremor onset, local field potential power increased at individual tremor frequency and cortical power decreased in the beta band (13-30 Hz). Sensor level subthalamic nucleus-cortex, cortico-muscular and subthalamic nucleus-muscle coherence increased during tremor specifically at tremor frequency. The increase in subthalamic nucleus-cortex coherence correlated with the increase in electromyogram power. On the source level, we observed tremor-associated increases in cortico-muscular coherence in primary motor cortex, premotor cortex and posterior parietal cortex contralateral to the tremulous limb. Analysis of the imaginary part of coherency revealed tremor-dependent coupling between these cortical areas at tremor frequency and double tremor frequency. Our findings demonstrate a direct relationship between the synchronization of cerebral oscillations and tremor manifestation. Furthermore, they suggest the feasibility of tremor detection based on local field potentials and might thus become relevant for the design of closed-loop stimulation systems

Statistically Reliable and Fast Direct Estimation of Phase-Amplitude Cross-Frequency Coupling

There is growing interest in phase-amplitude cross-frequency coupling (PAC), which is widely observed in human and animal brain recordings. The choice of the estimation method is vital while extracting accurate PAC parameters from data. Two desired properties of PAC estimators are reliability and computational efficiency. This study offers a methodology called normalized direct PAC (ndPAC) for the rapid and statistically reliable estimation of PAC strength. A plain confidence limit formula, depending solely on data length and confidence level, is derived. Confidence level derivation is validated numerically. It is shown through simulations that ndPAC exhibits high specificity and sensitivity performances. The suggested methodology is also demonstrated on monkey electrocorticogram recorded during a visual task

A Basic Nietzschean Model in Lieu of the Causal Maxim

Causal knowledge unquestionably provides useful means to describe, explain and predict both natural and daily phenomena. This article addresses whether causality as such may not be ontologically primary and looks for an alternative fundamental mechanism encapsulating the information load of the causal framework. A probabilistic process view of reality asserting the struggle of natural forces is considered along with lines quoted from Nietzsche's posthumously published notebooks and published work. Examples from scientific discoveries, in particular neurosciences, echoing his ontology are provided. Furthermore, I propose a basic number game algorithm to illustrate and model the struggle of forces leading to causal inferences for an external observer. Nietzschean dynamic ontology involving the ceaseless struggle of will-to-power units accords with the emergentist approach to causation, which has been principally employed by the scientists working under the fields of thermodynamics, quantum mechanics and complex dynamical systems

Estimation of nonlinear neural source interactions via sliced bicoherence

Neural oscillations and their spatiotemporal interactions are of interest for the description of brain mechanisms. This study offers a novel third order spectral coupling measure named "sliced bicoherence". It is the diagonal slice of cross-bicoherence allowing an efficient quantification of the nonlinear interactions between neural sources. Our methodology comprises an indirect estimation method, a parametric confidence level formula and a subtracted version for robustness to volume conduction. The methodology provides an efficient estimation of third-order nonlinear cross relations reducing the complexity to the same order of second-order coherence computation. Unlike other bispectral measures, the suggested measure solely holds terms related to cross relations between channel sources and omits the possible strong autobispectral relations. Feasibility and robustness of the methodology are demonstrated both on simulated and publicly available MEG data. The latter were collected for a motor task and an eyes-open resting state. Analytical confidence level marked the non-significant couplings. Simulations confirmed that the subtracted bicoherence enabled robustness to volume conduction by avoiding the spurious nearby channel couplings. Central regions were shown to be coupled with muscular activity by sliced bicoherence. Couplings for spontaneous data occurred particularly at theta and alpha bands. Volume-conduction related bicoherence values originated especially from the low frequencies below 5 Hz. The suggested nonlinear measure is promising to be a part of the rich collection of the multichannel electrophysiological brain connectivity metrics

Spectral Features of Heart Rate Variability Obtained from a Video Camera

In this study, we propose a scheme to investigate the relationship between cognitive tasks and heart beat rate. Accordingly, a video focused on the face was recorded during a working memory experiment. Heart rate was noninvasively estimated from the camera recording. Subsequently, its spectral features were examined. These values were compared with heart rate dynamics obtained from a standard ECG. As a result of the comparison, we observed that the data from the video were compatible with the common heart rhythm, except its spectrum did not have 1/f character

Sözel Bellek Performansının Nicelenmesi Ve Frontal İzdüşümü

İşleyen bellek (working memory) sözel, görsel ve mekansal bilgilerin kısa süreli olarak kayıt altına alındığı ve kullanılabildiği bellek sistemidir. İnsan beyni uygun şekilde uyarıldığında hafızası ‘yanlış’ olarak yönlendirilebilmektedir. Projenin temel amacı kısa süreli yanlış ve doğru bellek performansının bellek yoğunluğuna bağlı olarak frontal bölgelerdeki etkinliğini fNIR (functional near-infrared spectroscopy – işlevsel kızılötesi ışık tayf ölçümü) nörogörüntüleme modalitesi kullanarak nicelemektir. fNIR hem zararsız hem de maliyeti düşük olarak beyin aktivasyonunu ölçebilmeye olanak vermektedir. Ayrıca kısa süreli bellek çalışmalarında da verimli sonuçlar verebilmektedir. Bellek güvenilirliğinin nörolojik bir imza ile belirlenimi bellek aktarımına dair yanılsamanın beyinle ilişkisi hakkında özgün bilgi edinimini sağlayacaktır. Bellek yanılsamasını indükleyecek Türkçe’ye özgü veri tabanı oluşturulacaktır. İlksel sözcük kümesi 2’şerli, 3’erli ve 4’erli sözcükler olarak gerçeklenecektir. Oluşturulacak her bir kümenin ayrı sözcüklere sahip ve ortak semantik bağlamda olmasına özen gösterilecektir. Bellek kümeleri kullanılarak, uygun bir paradigma ile bilgisayarda E-prime ortamında gerçeklenecektir. Sunulan sözcüklerin arasına bilişsel bir aktivasyon olarak basit bir aritmetik sorusu konacaktır. Her bir deneme için ‘ilintili tuzak’, ‘pozitif hedef’ ve ‘ilintisiz tuzak’ soruları dengeli olarak dağıtılacaktır.Tüm denemeler boyunca frontal korteks aktivasyonu fNIR ile hemoglobin seviyesine bağlı olarak kaydedilecektir. Korteks aktivasyonuyla eş zamanlı olarak, deneklerin ‘evet’ ve ‘hayır’ cevapları ile ‘uyarana verdikleri tepki süreleri’ bilgisayar seri portuna bağlı bir buton kutusu üzerinden ayrıca kaydedilecektir. fNIR verileri, denek cevapları ve cevap süreleri dikkate alınarak gerçeklenecektir. fNIR verilerinden elde edilen aktivasyon uygun bir metrikle nicelendirilip, yukarıda saydığımız soru çeşitlerine bağlı olarak değerlendirilecektir. Aynı değerlendirme tepki süreleri için de gerçeklenecek ve aktivasyon-süre ilintileri hesaplanacaktır. Bulunan sonuçların istatiksel güvenilirliği ANOVA ve t-testi gibi yöntemlerle tespit edilecektir. Proje kapsamında ilk kez frontal aktivite ile kısa süreli bellek yanılsaması ilişkilendirilecektir. Şu ana kadar yapılan nörogörüntüleme çalışmaları genellikle yanlış bellek söz konusu olduğunda uzun süreli bellek paradigmaları ile kısıtlanmıştır. Son çalışmalardan feyz alarak DRM paradigmasını Strenberg testi ile birleştirerek gerçekleyeceğimiz bellek yanılsaması deneyleri, yüklenilen bellek yoğunluğuna bağlı olarak frontal aktivitede nasıl değişikliklere yol açacağı hakkında özgün bilimsel bulgulara alan açacaktır. Araştırma sonuçları ilk defa beyin aktivasyonu kaynaklı bir bellek sınama imzası (marker) gerçekleme potansiyeline de sahipti

Bellek performansını arttırıcı dokunsal ve işitsel ritmik uyaran parametrelerinin belirlenimi

Canlı organizmalarda çeşitli kompleks ritimlerin varlıkları tespit edilmiş ve özellikleri incelenegelmiştir. EMDR (Göz Hareketleriyle Duyarsızlaştırma ve Yeniden İşleme) tekniği beynin iki yarımküresinin ritmik olarak çift taraflı görsel, işitsel ya da dokunsal uyarımlarına dayanmaktadır. Klinik ortamda kullanılan ritmin modalitesi, frekansı ve büyüklüğü rastgele ya da pratisyenin tecrübesine göre afaki olarak uygulanmaktadır. Literatürde bunların optimal değerlerine dair kapsamlı bir çalışma henüz mevcut değildir. Çalışmamız bir uzun süreli bellek yüz tanıma deneyini tasarlayıp, gerçekleyerek optimal EMDR parametrelerini belirlemeyi amaçlamaktadır. Bellek performansını arttırabilmenin yanı sıra, çalışmanın sonuçları potansiyel olarak bizzat beyin dalgalarındaki değişimleri anlamak için de temel oluşturacaktır