The Distribution of Consciousness: A Difficult Cartesian Chart

Abstract: If we were asked to draw a graph to represent the distribution of consciousness in the world around us (from dolphins to honeybees) based on objective criteria, we would definitely be in trouble. The two objective parameters that have been traditionally considered as a guide – the complexity of behavior and brain size – lead to paradoxical conclusions and turn out to be unsatisfactory, to say the least. We need to find novel, reliable metrics. However, these can be identified, validated and calibrated only if we first tackle seriously the problem of recognizing consciousness in our fellow humans, a task which is far from being obvious.Keywords: Consciousness; Animal; Brain; Behaviour; Coma La distribuzione della coscienza: un difficile diagramma cartesiano Riassunto:  Se ci chiedessero di tracciare un grafico per rappresentare la distribuzione della coscienza nel mondo che ci circonda (dai delfini alle api) su una base oggettiva, ci troveremmo sicuramente in difficoltà. I due criteri oggettivi che sono stati tradizionalmente presi in considerazione come guida – la complessità del comportamento e la dimensione del cervello – conducono a conclusioni paradossali rivelandosi, come minimo, insoddisfacenti. È necessario individuare altre misure. Ma queste potranno essere individuate, validate e calibrate soltanto se prima affronteremo seriamente il problema di riconoscere la coscienza nell’uomo, un compito tutt’altro che scontato.Parole chiave: Coscienza; Animale; Cervello; Comportamento; Com

Posterior and anterior cortex — where is the difference that makes the difference?

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Tracking dynamic interactions between structural and functional connectivity : a TMS/EEG-dMRI study

Transcranial magnetic stimulation (TMS) in combination with neuroimaging techniques allows to measure the effects of a direct perturbation of the brain. When coupled with high-density electroencephalography (TMS/hd-EEG), TMS pulses revealed electrophysiological signatures of different cortical modules in health and disease. However, the neural underpinnings of these signatures remain unclear. Here, by applying multimodal analyses of cortical response to TMS recordings and diffusion magnetic resonance imaging (dMRI) tractography, we investigated the relationship between functional and structural features of different cortical modules in a cohort of awake healthy volunteers. For each subject, we computed directed functional connectivity interactions between cortical areas from the source-reconstructed TMS/hd-EEG recordings and correlated them with the correspondent structural connectivity matrix extracted from dMRI tractography, in three different frequency bands (alpha, beta, gamma) and two sites of stimulation (left precuneus and left premotor). Each stimulated area appeared to mainly respond to TMS by being functionally elicited in specific frequency bands, that is, beta for precuneus and gamma for premotor. We also observed a temporary decrease in the whole-brain correlation between directed functional connectivity and structural connectivity after TMS in all frequency bands. Notably, when focusing on the stimulated areas only, we found that the structure-function correlation significantly increases over time in the premotor area controlateral to TMS. Our study points out the importance of taking into account the major role played by different cortical oscillations when investigating the mechanisms for integration and segregation of information in the human brain

Repetitive transcranial magnetic stimulation dissociates working memory manipulation from retention functions in the prefrontal, but not posterior parietal, cortex

Understanding the contributions of the prefrontal cortex (PFC) to working memory is central to understanding the neural bases of high-level cognition. One question that remains controversial is whether the same areas of the dorsolateral PFC (dlPFC) that participate in the manipulation of information in working memory also contribute to its short-term retention (STR). We evaluated this question by first identifying, with functional magnetic resonance imaging (fMRI), brain areas involved in manipulation. Next, these areas were targeted with repetitive transcranial magnetic stimulation (rTMS) while subjects performed tasks requiring only the STR or the STR plus manipulation of information in working memory. fMRI indicated that manipulation-related activity was independent of retention-related activity in both the PFC and superior parietal lobule (SPL). rTMS, however, yielded a different pattern of results. Although rTMS of the dlPFC selectively disrupted manipulation, rTMS of the SPL disrupted manipulation and STR to the same extent. rTMS of the postcentral gyrus (a control region) had no effect on performance. The implications of these results are twofold. In the PFC, they are consistent with the view that this region contributes more importantly to the control of information in working memory than to its STR. In the SPL, they illustrate the importance of supplementing the fundamentally correlational data from neuroimaging with a disruptive method, which affords stronger inference about structure-function relations

Human Cortical Excitability Increases with Time Awake

Prolonged wakefulness is associated not only with obvious changes in the way we feel and perform but also with well-known clinical effects, such as increased susceptibility to seizures, to hallucinations, and relief of depressive symptoms. These clinical effects suggest that prolonged wakefulness may be associated with significant changes in the state of cortical circuits. While recent animal experiments have reported a progressive increase of cortical excitability with time awake, no conclusive evidence could be gathered in humans. In this study, we combine transcranial magnetic stimulation (TMS) and electroencephalography (EEG) to monitor cortical excitability in healthy individuals as a function of time awake. We observed that the excitability of the human frontal cortex, measured as the immediate (0-20 ms) EEG reaction to TMS, progressively increases with time awake, from morning to evening and after one night of total sleep deprivation, and that it decreases after recovery sleep. By continuously monitoring vigilance, we also found that this modulation in cortical responsiveness is tonic and not attributable to transient fluctuations of the level of arousal. The present results provide noninvasive electrophysiological evidence that wakefulness is associated with a steady increase in the excitability of human cortical circuits that is rebalanced during slee

Consciousness Regained: Disentangling Mechanisms, Brain Systems, and Behavioral Responses

How consciousness (experience) arises from and relates to material brain processes (the "mind-body problem") has been pondered by thinkers for centuries, and is regarded as among the deepest unsolved problems in science, with wide-ranging theoretical, clinical, and ethical implications. Until the last few decades, this was largely seen as a philosophical topic, but not widely accepted in mainstream neuroscience. Since the 1980s, however, novel methods and theoretical advances have yielded remarkable results, opening up the field for scientific and clinical progress. Since a seminal paper by Crick and Koch (1998) claimed that a science of consciousness should first search for its neural correlates (NCC), a variety of correlates have been suggested, including both content-specific NCCs, determining particular phenomenal components within an experience, and the full NCC, the neural substrates supporting entire conscious experiences. In this review, we present recent progress on theoretical, experimental, and clinical issues. Specifically, we (1) review methodological advances that are important for dissociating conscious experience from related enabling and executive functions, (2) suggest how critically reconsidering the role of the frontal cortex may further delineate NCCs, (3) advocate the need for general, objective, brain-based measures of the capacity for consciousness that are independent of sensory processing and executive functions, and (4) show how animal studies can reveal population and network phenomena of relevance for understanding mechanisms of consciousness.European Union's Horizon 2020 Research and Innovation ProgrammeHermann and Lilly Schilling FoundationGerman Research FoundationCenter for Nanoscale Microscopy and Molecular Physiology of the BrainNational Institutes of Health/National Institute of Neurological Disorders and StrokeSao Paulo Research FoundationJames S. McDonnell Foundation Scholar AwardEU Grant H2020-FETOPENCanadian Institute for Advanced ResearchAzrieli Program in Brain, Mind and ConsciousnessFLAG-ERA JTC project CANONNorwegian Research CouncilNetherlands Organization for Scientific ResearchUniv Oslo, Inst Basal Med Sci, Div Physiol, Dept Mol Med, POB 1103 Blindern, N-0317 Oslo, NorwayUniv Wisconsin, Dept Neurol, Madison, WI 53705 USAUniv Wisconsin, Dept Psychiat, Madison, WI 53719 USAUniv Fed Sao Paulo, Inst Sci & Technol, BR-12231280 Sao Jose Dos Campos, SP, BrazilUniv Milan, Dept Biomed & Clin Sci Luigi Sacco, I-20157 Milan, ItalyFdn Don Carlo Gnocchi ONLUS, Ist Ricovero & Cura Carattere Sci, I-20162 Milan, ItalyUniv Amsterdam, Swammerdam Inst Life Sci, Cognit & Syst Neurosci Grp, NL-1098 XH Amsterdam, NetherlandsUniv Amsterdam, Res Prior Program Brain & Cognit, NL-1098 XH Amsterdam, NetherlandsUniv Med Goettingen, Dept Cognit Neurol, D-37075 Gottingen, GermanyLeibniz Inst Primate Res, German Primate Ctr, D-37077 Gottingen, GermanyLeibniz Sci Campus Primate Cognit, D-37077 Gottingen, GermanyUniv Fed Sao Paulo, Inst Sci & Technol, BR-12231280 Sao Jose Dos Campos, SP, BrazilEuropean Union's Horizon 2020 Research and Innovation Programme: 720270German Research Foundation: WI 4046/1-1National Institutes of Health/National Institute of Neurological Disorders and Stroke: 1R03NS096379FAPESP: 2016/08263-9EU Grant H2020-FETOPEN: RIA 686764Web of Scienc

FDI: a MATLAB tool for computing the fractal dimension index of sources reconstructed from EEG data

Background: The fractal dimension (FD) is a valuable tool for analysing the complexity of neural structures and functions in the human brain. To assess the spatiotemporal complexity of brain activations derived from electroencephalogram (EEG) signals, the fractal dimension index (FDI) was developed. This measure integrates two distinct complexity metrics: 1) integration FD, which calculates the FD of the spatiotemporal coordinates of all significantly active EEG sources (4DFD); and 2) differentiation FD, determined by the complexity of the temporal evolution of the spatial distribution of cortical activations (3DFD), estimated via the Higuchi FD [HFD(3DFD)]. The final FDI value is the product of these two measurements: 4DFD × HFD(3DFD). Although FDI has shown utility in various research on neurological and neurodegenerative disorders, existing literature lacks standardized implementation methods and accessible coding resources, limiting wider adoption within the field. Methods: We introduce an open-source MATLAB software named FDI for measuring FDI values in EEG datasets. Results: By using CUDA for leveraging the GPU massive parallelism to optimize performance, our software facilitates efficient processing of large-scale EEG data while ensuring compatibility with pre-processed data from widely used tools such as Brainstorm and EEGLab. Additionally, we illustrate the applicability of FDI by demonstrating its usage in two neuroimaging studies. Access to the MATLAB source code and a precompiled executable for Windows system is provided freely. Conclusions: With these resources, neuroscientists can readily apply FDI to investigate cortical activity complexity within their own studies

Studying functional networks in human brain through intracerebral spontaneous EEG

none6G.Arnulfo; A.Pigorini; M.Massimini; L.Nobili; A.Schenone; M.M. FatoArnulfo, Gabriele; Pigorini, A.; Massimini, M.; Nobili, L.; Schenone, Andrea; Fato, MARCO MASSIM

Consensus Paper: Probing Homeostatic Plasticity of Human Cortex With Non-invasive Transcranial Brain Stimulation

AbstractHomeostatic plasticity is thought to stabilize neural activity around a set point within a physiologically reasonable dynamic range. Over the last ten years, a wide range of non-invasive transcranial brain stimulation (NTBS) techniques have been used to probe homeostatic control of cortical plasticity in the intact human brain. Here, we review different NTBS approaches to study homeostatic plasticity on a systems level and relate the findings to both, physiological evidence from in vitro studies and to a theoretical framework of homeostatic function. We highlight differences between homeostatic and other non-homeostatic forms of plasticity and we examine the contribution of sleep in restoring synaptic homeostasis. Finally, we discuss the growing number of studies showing that abnormal homeostatic plasticity may be associated to a range of neuropsychiatric diseases

Electrophysiological findings in migraine may reflect abnormal synaptic plasticity mechanisms. A narrative review

Background: The cyclical brain disorder of sensory processing accompanying migraine phases lacks an explanatory unified theory. Methods: We searched Pubmed for non-invasive neurophysiological studies on migraine and related conditions using transcranial magnetic stimulation, electroencephalography, visual and somatosensory evoked potentials.We summarized the literature, reviewed methods, and proposed a unified theory for the pathophysiology of electrophysiological abnormalities underlying migraine recurrence. Results: All electrophysiological modalities have determined specific changes in brain dynamics across the different phases of the migraine cycle. Transcranial magnetic stimulation studies show unbalanced recruitment of inhibitory and excitatory circuits, more consistently in aura, which ultimately results in a substantially distorted response to neuromodulation protocols. Electroencephalography investigations highlight a steady pattern of reduced alpha and increased slow rhythms, largely located in posterior brain regions, which tends to normalize closer to the attacks. Finally, nonpainful evoked potentials suggest dysfunctions in habituation mechanisms of sensory cortices that revert during ictal phases. Conclusion: Electrophysiology shows dynamic and recurrent functional alterations within the brainstem-thalamuscortex loop varies continuously and recurrently in migraineurs. Given the central role of these structures in the selection, elaboration, and learning of sensory information, these functional alterations suggest chronic, probably genetically determined dysfunctions of the synaptic short- and long-term learning mechanisms