231 research outputs found
Magnetoencephalography Demonstrates Multiple Asynchronous Generators during Human Sleep Spindles
No full textDehghani N, Cash SS, Rossetti AO, Chen CC, Halgren E. Magnetoencephalography demonstrates multiple asynchronous generators during human sleep spindles. J Neurophysiol 104: 179-188, 2010. First published April 28, 2010; doi:10.1152/ jn.00198.2010. Sleep spindles are similar to 1 s bursts of 10-16 Hz activity that occur during stage 2 sleep . Spindles are highly synchronous across the cortex and thalamus in animals, and across the scalp in humans, implying correspondingly widespread and synchronized cortical generators. However, prior studies have noted occasional dissociations of the magnetoencephalogram (MEG) from the EEG during spindles, although detailed studies of this phenomenon have been lacking. We systematically compared high-density MEG and EEG recordings during naturally occurring spindles in healthy humans. As expected, EEG was highly coherent across the scalp, with consistent topography across spindles. In contrast, the simultaneously recorded MEG was not synchronous, but varied strongly in amplitude and phase across locations and spindles. Overall, average coherence between pairs of EEG sensors was similar to 0.7, whereas MEG coherence was similar to 0.3 during spindles. Whereas 2 principle components explained similar to 50% of EEG spindle variance, similar to 15 were required for MEG. Each PCA component for MEG typically involved several widely distributed locations, which were relatively coherent with each other. These results show that, in contrast to current models based on animal experiments, multiple asynchronous neural generators are active during normal human sleep spindles and are visible to MEG. It is possible that these multiple sources may overlap sufficiently in different EEG sensors to appear synchronous. Alternatively, EEG recordings may reflect diffusely distributed synchronous generators that are less visible to MEG. An intriguing possibility is that MEG preferentially records from the focal core thalamocortical system during spindles, and EEG from the distributed matrix system
Sacred Power, Sacred Space: An Introduction to Christian Architecture and Worship (Jeanne Halgren Kilde)
No full textLooking at Jeanne Halgren Kilde's book, Sacred Power, Sacred Space, Julie Durbin considers issues of sacredness in the spaces where worship happens
Neurolinguistic processing when the brain matures without language
No full textThe extent to which development of the brain language system is modulated by the temporal onset of linguistic experience relative to post-natal brain maturation is unknown. This crucial question cannot be investigated with the hearing population because spoken language is ubiquitous in the environment of newborns. Deafness blocks infants' language experience in a spoken form, and in a signed form when it is absent from the environment. Using anatomically constrained magnetoencephalography, aMEG, we neuroimaged lexico-semantic processing in a deaf adult whose linguistic experience began in young adulthood. Despite using language for 30 years after initially learning it, this individual exhibited limited neural response in the perisylvian language areas to signed words during the 300-400 ms temporal window, suggesting that the brain language system requires linguistic experience during brain growth to achieve functionality. The present case study primarily exhibited neural activations in response to signed words in dorsolateral superior parietal and occipital areas bilaterally, replicating the neural patterns exhibited by two previously case studies who matured without language until early adolescence (Ferjan Ramirez N, Leonard MK, Torres C, Hatrak M, Halgren E, Mayberry RI. 2014). The dorsal pathway appears to assume the task of processing words when the brain matures without experiencing the form-meaning network of a language
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Neural Language Processing in Adolescent First-Language Learners: Longitudinal Case Studies in American Sign Language
No full textOne key question in neurolinguistics is the extent to which the neural processing system for language requires linguistic experience during early life to develop fully. We conducted a longitudinal anatomically constrained magnetoencephalography (aMEG) analysis of lexico-semantic processing in 2 deaf adolescents who had no sustained language input until 14 years of age, when they became fully immersed in American Sign Language. After 2 to 3 years of language, the adolescents' neural responses to signed words were highly atypical, localizing mainly to right dorsal frontoparietal regions and often responding more strongly to semantically primed words (Ferjan Ramirez N, Leonard MK, Torres C, Hatrak M, Halgren E, Mayberry RI. 2014. Neural language processing in adolescent first-language learners. Cereb Cortex. 24 (10): 2772-2783). Here, we show that after an additional 15 months of language experience, the adolescents' neural responses remained atypical in terms of polarity. While their responses to less familiar signed words still showed atypical localization patterns, the localization of responses to highly familiar signed words became more concentrated in the left perisylvian language network. Our findings suggest that the timing of language experience affects the organization of neural language processing; however, even in adolescence, language representation in the human brain continues to evolve with experience
Neurochemical substrates and neuroanatomical generators of the event-related P300
No full textThe present review focuses on the current knowledge of the neurochemical processes and neuronal structures involved in the generation of P300. The increasing knowledge in this area facilitates the physiological interpretation of P300 findings as well as the link between P300 research and other research findings in biological psychiatry. Concerning the question of neurochemical substrates, the glutamatergic, GABAergic, cholinergic, noradrenergic, dopaminergic and serotonergic influences on P300 are reviewed. The knowledge of the generating structures of P300 is summarized from intracranial studies, magnetoencephalographic investigations, lesion and animal studies
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Coaching Practices for Facilitating Reflection Toward Transformative Insight: A Constructive-Developmental Perspective
No full textResponding to gaps in the executive coaching literature, this study’s purpose was to identify coaching practices for facilitating growth in leaders’ developmental capacity to help them more successfully navigate the demands of their increasingly complex contexts.
Through the lenses of transformative learning (Mezirow, 1978, 1991, 2000) and constructive-developmental theory (Kegan, 1982, 1994), this study aimed to identify and understand coaching practices for facilitating reflection (at content, process, and premise levels) toward transformative insight, conceptualized as an insight occurring at the heart of Mezirow’s perspective transformation and Kegan’s subject-object move. Also, using constructive-developmental theory, this study explored how a select sample of executive coaches with various developmental capacities or forms of mind differ in their understanding of these practices.
This exploratory multiple-person case study investigated the experiences of 21 executive coaches via semi-structured interviews. Thematic data analysis revealed 16 coaching practice themes across all three levels of reflection. Given the importance of premise reflection in the literature, an unexpected finding was that these practices were used less than 10% of the time. An overarching process and coaching practices model for facilitating transformative insight emerged, describing the movement from a client’s current way of knowing (experienced as limiting) to a new way of knowing (seen as more desirable and effective).
Using constructive-developmental theory’s methodology, the Subject-Object Interview (Lahey, et al., 1988), participants’ forms of mind were identified. A comparative developmental analysis revealed that coaches with different forms of mind used reflective practices (from all themes and levels of reflection) to a similar extent and with similar intent. However, the qualitative differences that emerged followed the “transcend and include” principle, meaning that coaches, with each subsequent (and more complex) form of mind, expanded upon the ways in which these practices were used by coaches with a less complex form of mind.
Findings confirmed and expanded upon the coaching processes and practices related to transformative learning and the constructive-developmental literature, uniting them in similarities and differences and integrating them into an overall system for facilitating transformative insight. Implications for scholars, practitioners, and coach educators interested in transformative coaching with developmental impact are discussed
Memory and Epileptogenesis in Complex Biological and Simulated Systems
No full textOscillations of neural activity may bind widespread cortical areas into a neural representation that encodes disparate aspects of an event. In order to test this theory we have turned to data collected from complex partial epilepsy (CPE) patients with chronically implanted depth electrodes. Data from regions critical to word and face information processing was analyzed using spectral coherence measurements. Similar analyses of intracranial EEG (iEEG) during seizure episodes display HippoCampal Formation (HCF)—NeoCortical (NC) spectral coherence patterns that are characteristic of specific seizure stages (Klopp et al. 1996). We are now building a computational memory model to examine whether spatio-temporal patterns of human iEEG spectral coherence emerge in a computer simulation of HCF cellular distribution, membrane physiology and synaptic connectivity. Once the model is reasonably scaled it will be used as a tool to explore neural parameters that are critical to memory formation and epileptogenesis
Large Scale Simulations of Hippocampal-Neocortical Interactions in a Parallel Version of Genesis
No full textA hippocampal-CA3 memory model was constructed with PGENESIS, a recently developed version of GENESIS that allows for distributed processing of a neural network simulation. A number of neural models of the human memory system have identified the CA3 region of the hippocampus as storing the declarative memory trace. However, computational models designed to assess the viability of the putative mechanisms of storage and retrieval have generally been too abstract to allow comparison with empirical data. Recent experimental evidence has shown that selective knock-out of NMDA receptors in the CA1 of mice leads to reduced stability of firing specificity in place cells. Here a similar reduction of stability of input specificity is demonstrated in a biologically plausible neural network model of the CA3 region, under conditions of Hebbian synaptic plasticity versus an absence of plasticity.\ud
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The CA3 region is also commonly associated with seizure activity. Further simulations of the same model tested the response to continuously repeating versus randomized nonrepeating input patterns. Each paradigm delivered input of equal intensity and duration. Non-repeating input patterns elicited a greater pyramidal cell spike count. This suggests that repetitive versus non-repeating neocortical inpus has a quantitatively different effect on the hippocampus. This may be relevant to the production of independent epileptogenic zones and the process of encoding new memories
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