A statistical technique for measuring synchronism between cortical regions in the EEG during rhythmic stimulation

The coherence function has been widely applied in quantifying the degree of synchronism between electroencephalogram (EEG) signals obtained from different brain regions. However, when applied to investigating synchronization resulting from rhythmic stimulation, misleading results can arise from the high correlation of background EEG activity. The authors, thus propose a modified measure, which emphasizes the synchronized stimulus responses and reduces the influence of the spontaneous EEG activity. Critical values for this estimator are derived and tested in Monte Carlo simulations. The effectiveness of the method is illustrated on data recorded from 12 young normal subjects during rhythmic photic stimulation

Cerebral Synchrony Assessment Tutorial: A General Review on Cerebral Signals' Synchronization Estimation Concepts and Methods

The human brain is ultimately responsible for all thoughts and movements that the body produces. This allows humans to successfully interact with their environment. If the brain is not functioning properly many abilities of human can be damaged. The goal of cerebral signal analysis is to learn about brain function. The idea that distinct areas of the brain are responsible for specific tasks, the functional segregation, is a key aspect of brain function. Functional integration is an important feature of brain function, it is the concordance of multiple segregated brain areas to produce a unified response. There is an amplified feedback mechanism in the brain called reentry which requires specific timing relations. This specific timing requires neurons within an assembly to synchronize their firing rates. This has led to increased interest and use of phase variables, particularly their synchronization, to measure connectivity in cerebral signals. Herein, we propose a comprehensive review on concepts and methods previously presented for assessing cerebral synchrony, with focus on phase synchronization, as a tool for brain connectivity evaluation

Aerospace medicine and biology: A continuing bibliography with indexes, supplement 125

This special bibliography lists 323 reports, articles, and other documents introduced into the NASA scientific and technical information system in January 1974

Spectral and coherence estimates on electroencephalogram recordings during arithmetical tasks

Dissertação apresentada na Faculdade de Ciências e Tecnologia da Universidade Nova de Lisboa para obtenção do Grau de Mestre em Engenharia Biomédic

Electric Aspects of Neurophysiological Action of Certain Amines and Steroids NB: All pages that have a series, that is to say a numbered page with addition pages after (CF: 97, 97A, 97B), were scanned. However, if in copy 2 there is a page 98 outside of 98A and 98B, that needs to be scanned as it was not found in copy 1.

Thesis (M.A.)--Boston Universit

Neuronal Coding of Low Frequency Complex Stimuli at the Cochlear Nucleus and Inferior Colliculus of Cat Brain

Articles have recently appeared by Erickson (1968) and Pfaff (1969) which propose that the study of the activity of a large population of neurons may contribute information about sensory coding which is supplementary to data obtained from single neuron studies. These authors propose that there are not enough neurons in the primary sensory pathways so that every stimulus can be represented by a separate neuron. They maintain that over-all measures of neuronal activity will be more fruitful in the study of sensory coding. The present study used such a measure (multiple unit techniques) to monitor the over-all discharge characteristics of neuronal pools at the cochlear nucleus and inferior colliculus of cat brains to aural stimulation. Measures of spike discharge frequencies were obtained from four adult cats. Stimuli consisted of recorded male and female voices presenting the words one through ten . Data was collected from four sites: left and right cochlear nuclei and left and right inferior colliculi. The dependent variable was the number of neuronal spike discharges counted during each 500 millisecond recording period. The basic hypothesis of the experiment was that the large multiple unit spike bursts to aural stimulation consistently observed at.the sites investigated represented a stimulus coding mechanism. If such a mechanism was operating, it was predicted that analysis of discharge patterns would reveal that the subcortical auditory nuclei discharge differentially to the different stimuli. It was also thought that different voices presenting the same stimuli would evoke very similar patterns of activity both within and between anatomical sites tested. The following effects were investigated: laterality of stimulation; stimuli; voices presenting the stimuli; and anatomical sites both within and between cats. Results clearly indicated that at the level of the cochlear nuclei ipsilateral stimulation evoked a sustained multiple unit spike burst while contralateral stimulation had no observable effect on the on-going neuronal activity. The importance of laterality of stimulation was also clearly confirmed at the inferior colliculi level. Only rarely did ipsilateral stimulation at the inferior collicular level cause any detectable change in the on-going level of neuronal discharge. Contralateral stimulation, however, was consistent in evoking a sustained spike burst. The experiment demonstrated that the multiple unit spike bursts ! observed at the cochlear nucleus and inferior colliculus have a functional significance. Different stimulus words generated discharge patterns which differed from each other. Different voices presenting identical stimuli also generated responses having a moderate to very high similarity to each other. The spike discharge patterns were highly similar at both cochlear nucleus and inferior colliculus in all experimental animals. There was also a very close association between anatomical sites within each cat. The results contributed evidence that the original hypothesis of the existence of a neuronal coding mechanism was confirmed. This phenomenon appeared to be a prominent feature of the neuronal response to low frequency complex stimuli through the level of the inferior colliculus. Low frequency.sounds which are coded at the cochlear nerve by frequency of nerve fiber discharge appear to be encoded in the same way by groups of neurons at the dorsal cochlear nucleus and the inferior colliculus. The fact that the encoding mechanism occurs only below the level of the thalamus suggested that pitch discrimination may be essentially completed before the neuronal discharges arrive at the medial geniculate body of the thalamus

A Brain-computer Interface Architecture Based On Motor Mental Tasks And Music Imagery

This present research proposes a Brain-Computer Interface (BCI) architecture adapted to motor mental tasks and music imagery. For that purpose the statistical properties of the electroencephalographic signal (EEG) were studied, such as its probability distribution function, stationarity, correlation and signal-to-noise ratio (SNR), in order to obtain a minimal empirical and well-founded parameter system for online classification. Stationarity tests were used to estimate the length of the time windows and a minimum length of 1.28 s was obtained. Four algorithms for artifact reduction were tested: threshold analysis, EEG filtering and two Independent Component Analysis (ICA) algorithms. This analysis concluded that the algorithm fastICA is suitable for online artifact removal. The feature extraction used the Power Spectral Density (PSD) and three methods were tested for automatic selection of features in order to have a training step independent of the mental task paradigm, with the best performance obtained with the Kullback-Leibler symmetric divergence method. For the classification, the Linear Discriminant Analysis (LDA) was used and a step of reclassification is suggested. A study of four motor mental tasks and a non-motor related mental task is performed by comparing their periodograms, Event-Related desynchronization/synchronization (ERD/ERS) and SNR. The mental tasks are the imagination of either movement of right and left hands, both feet, rotation of a cube and sound imagery. The EEG SNR was estimated by a comparison with the correlation between the ongoing average and the final ERD/ERS curve, in which we concluded that the mental task of sound imagery would need approximately five times more epochs than the motor-related mental tasks. The ERD/ERS could be measured even for frequencies near 100 Hz, but in absolute amplitudes, the energy variation at 100 Hz was one thousand times smaller than for 10 Hz, which implies that there is a small probability of online detection for BCI applications in high frequency. Thus, most of the usable information for online processing and BCIs corresponds to the α/µ band (low frequency). Finally, the ERD/ERS scalp maps show that the main difference between the sound imagery task and the motor-related mentaltasks is the absence of ERD at the µ band, in the central electrodes, and the presence of ERD at the αband in the temporal and lateral-frontal electrodes, which correspond tothe auditory cortex, the Wernickes area and the Brocas area

Neuronal oscillations, information dynamics, and behaviour: an evolutionary robotics study

Oscillatory neural activity is closely related to cognition and behaviour, with synchronisation mechanisms playing a key role in the integration and functional organization of different cortical areas. Nevertheless, its informational content and relationship with behaviour - and hence cognition - are still to be fully understood. This thesis is concerned with better understanding the role of neuronal oscillations and information dynamics towards the generation of embodied cognitive behaviours and with investigating the efficacy of such systems as practical robot controllers. To this end, we develop a novel model based on the Kuramoto model of coupled phase oscillators and perform three minimally cognitive evolutionary robotics experiments. The analyses focus both on a behavioural level description, investigating the robot’s trajectories, and on a mechanism level description, exploring the variables’ dynamics and the information transfer properties within and between the agent’s body and the environment. The first experiment demonstrates that in an active categorical perception task under normal and inverted vision, networks with a definite, but not too strong, propensity for synchronisation are more able to reconfigure, to organise themselves functionally, and to adapt to different behavioural conditions. The second experiment relates assembly constitution and phase reorganisation dynamics to performance in supervised and unsupervised learning tasks. We demonstrate that assembly dynamics facilitate the evolutionary process, can account for varying degrees of stimuli modulation of the sensorimotor interactions, and can contribute to solving different tasks leaving aside other plasticity mechanisms. The third experiment explores an associative learning task considering a more realistic connectivity pattern between neurons. We demonstrate that networks with travelling waves as a default solution perform poorly compared to networks that are normally synchronised in the absence of stimuli. Overall, this thesis shows that neural synchronisation dynamics, when suitably flexible and reconfigurable, produce an asymmetric flow of information and can generate minimally cognitive embodied behaviours

Aerospace Medicine and Biology: A continuing bibliography with indexes, supplement 142

This bibliography lists 256 reports, articles, and other documents introduced into the NASA scientific and technical information system in May 1975 for aerospace medicine and biology