Breakdown of Cortical Effective Connectivity During Sleep.

University of Milan, Milano, Lombardy, Italy
Science (Impact Factor: 33.61). 10/2005; 309(5744):2228-32. DOI: 10.1126/science.1117256
Source: PubMed


When we fall asleep, consciousness fades yet the brain remains active. Why is this so? To investigate whether changes in cortical information transmission play a role, we used transcranial magnetic stimulation together with high-density electroencephalography and asked how the activation of one cortical area (the premotor area) is transmitted to the rest of the brain. During quiet wakefulness, an initial response (approximately 15 milliseconds) at the stimulation site was followed by a sequence of waves that moved to connected cortical areas several centimeters away. During non-rapid eye movement sleep, the initial response was stronger but was rapidly extinguished and did not propagate beyond the stimulation site. Thus, the fading of consciousness during certain stages of sleep may be related to a breakdown in cortical effective connectivity.

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Available from: Giulio Tononi, Oct 06, 2015
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    • "Similar to the hypothesis underlying regional homogeneity (ReHo), functional connectivity should occur in clusters, exhibiting intrinsic local boundaries between connected brain areas (Zang et al., 2004). Previously, Massimini measured a localized electrical response instead of long-distance propagation in human premotor cortex using transcranial magnetic stimulation during sleep (Massimini et al., 2005). Lu et al. (2007) also observed that long-distance somatosensory connections in rats were reduced with increasing anesthesia levels, while short-distance connections remained relatively unaffected. "
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    • "This alteration has been detected by analyzing functional connectivity within cortical networks in resting condition (Boly et al., 2012; Spoormaker et al., 2011; Tagliazucchi et al., 2013) and becomes obvious when one applies perturbations directly to the cerebral cortex. Hence, measurements performed with transcranial magnetic stimulation (TMS) and electroencephalography (EEG) have shown that a single magnetic pulse triggers a complex chain of causal interactions that propagate through a distributed network of cortical areas during wakefulness , but a simple response that remains either local (Massimini et al., 2005) or spreads like an oil-spot (Massimini et al., 2007) during NREM. This altered response to TMS has been subsequently observed in other conditions in which consciousness is lost, such as general anesthesia and the vegetative state (Casali et al., 2013; Rosanova et al., 2012). "
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    ABSTRACT: During non-rapid eye movement (NREM) sleep (stage N3), when consciousness fades, cortico-cortical interactions are impaired while neurons are still active and reactive. Why is this? We compared cortico-cortical evoked-potentials recorded during wakefulness and NREM by means of time-frequency analysis and phase-locking measures in 8 epileptic patients undergoing intra-cerebral stimulations/recordings for clinical evaluation. We observed that, while during wakefulness electrical stimulation triggers a chain of deterministic phase-locked activations in its cortical targets, during NREM the same input induces a slow wave associated with an OFF-period (suppression of power>20Hz), possibly reflecting a neuronal down-state. Crucially, after the OFF-period, cortical activity resumes to wakefulness-like levels, but the deterministic effects of the initial input are lost, as indicated by a sharp drop of phase-locked activity. These findings suggest that the intrinsic tendency of cortical neurons to fall into a down-state after a transient activation (i.e. bistability) prevents the emergence of stable patterns of causal interactions among cortical areas during NREM. Besides sleep, the same basic neurophysiological dynamics may play a role in pathological conditions in which thalmo-cortical information integration and consciousness are impaired in spite of preserved neuronal activity. Copyright © 2015. Published by Elsevier Inc.
    NeuroImage 03/2015; 6. DOI:10.1016/j.neuroimage.2015.02.056 · 6.36 Impact Factor
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    • "Transcranial magnetic stimulation (TMS) is a non-invasive technique to stimulate the brain [1e3]. Applications of TMS range from studies of cortical effective connectivity [4] [5] to presurgical mapping [6] [7] and treatment of major depression [8]. In TMS, a strong, brief current pulse driven through a coil is used to induce an electric field (E-field) stimulating neurons in the cortex. "
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    ABSTRACT: In transcranial magnetic stimulation (TMS) a strong, brief current pulse driven through a coil is used for non-invasively stimulating the cortex. Properties of the electric field (E-field) induced by the pulse together with physiological parameters determine the outcome of the stimulation. In research and clinical use, TMS is delivered using a wide range of different coils and stimulator units, all having their own characteristics; however, the parameters of the induced E-field are often inadequately known by the user.
    Brain Stimulation 01/2015; 8(3). DOI:10.1016/j.brs.2015.01.004 · 4.40 Impact Factor
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