The six cortical layers have distinct anatomical and physiological properties, like different energy use and different feedforward and feedback connectivity. It is not known if and how layer-specific ...neural processes are reflected in the fMRI signal. To address this question we used high-resolution fMRI to measure BOLD, CBV, and CBF responses to stimuli that elicit positive and negative BOLD signals in macaque primary visual cortex. We found that regions with positive BOLD responses had parallel increases in CBV and CBF, whereas areas with negative BOLD responses showed a decrease in CBF but an increase in CBV. For positive BOLD responses, CBF and CBV increased in the center of the cortex, but for negative BOLD responses, CBF decreased superficially while CBV increased in the center. Our findings suggest different mechanisms for neurovascular coupling for BOLD increases and decreases, as well as laminar differences in neurovascular coupling.
► High-resolution fMRI allows visualization of laminar differences in BOLD, CBV, and CBF ► CBF is decreased for negative BOLD while CBV is increased ► Positive and negative BOLD signals have different neurovascular coupling mechanisms ► Neurovascular coupling differs depending on cortical depth
Goense et al. use high-resolution fMRI to show that positive and negative BOLD responses have different neurovascular coupling mechanisms and that neurovascular coupling is cortical layer dependent. This potentially allows disentangling of feedforward, feedback, excitatory, or inhibitory processes using fMRI.
Functional magnetic resonance imaging (fMRI) is currently the mainstay of neuroimaging in cognitive neuroscience. Advances in scanner technology, image acquisition protocols, experimental design, and ...analysis methods promise to push forward fMRI from mere cartography to the true study of brain organization. However, fundamental questions concerning the interpretation of fMRI data abound, as the conclusions drawn often ignore the actual limitations of the methodology. Here I give an overview of the current state of fMRI, and draw on neuroimaging and physiological data to present the current understanding of the haemodynamic signals and the constraints they impose on neuroimaging data interpretation.
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DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Neuronal discharges in the primate temporal lobe, but not in the striate and extrastriate cortex, reliably reflect stimulus awareness. However, it is not clear whether visual consciousness should be ...uniquely localized in the temporal association cortex. Here we used binocular flash suppression to investigate whether visual awareness is also explicitly reflected in feature-selective neural activity of the macaque lateral prefrontal cortex (LPFC), a cortical area reciprocally connected to the temporal lobe. We show that neuronal discharges in the majority of single units and recording sites in the LPFC follow the phenomenal perception of a preferred stimulus. Furthermore, visual awareness is reliably reflected in the power modulation of high-frequency (>50 Hz) local field potentials in sites where spiking activity is found to be perceptually modulated. Our results suggest that the activity of neuronal populations in at least two association cortical areas represents the content of conscious visual perception.
► Single- and multiunit discharges reflect visual consciousness in the macaque LPFC ► Gamma (>50 Hz) power reflects visual consciousness in the macaque LPFC ► Subliminal spiking activity reflects weak traces of nonconscious processing
Ambiguous visual stimulation provides a window into the neural correlates of visual consciousness. Panagiotaropoulos et al. show that neuronal discharges and gamma oscillations in the macaque lateral prefrontal cortex during rivalrous visual stimulation reflect the content of subjective visual perception.
The anterior insular cortex (AIC) and its unique spindle-shaped von Economo neuron (VEN) emerged within the last decade as having a potentially major role in self-awareness and social cognition in ...humans. Invasive examination of the VEN has been precluded so far by the assumption that this neuron occurs among primates exclusively in humans and great apes. Here, we demonstrate the presence of the VEN in the agranular anterior insula of the macaque monkey. The morphology, size, laminar distribution, and proportional distribution of the monkey VEN suggest that it is at least a primal anatomical homolog of the human VEN. This finding sheds new light on the phylogeny of the VEN and AIC. Most importantly, it offers new and much-needed opportunities to investigate the primal connections and physiology of a neuron that could be crucial for human self-awareness, social cognition, and related neuropsychiatric disorders.
► Von Economo neurons (VENs) occur in the anterior insula in macaques ► Concentrated VEN populations in primates are not an exclusivity of hominids ► The VEN's phylogeny needs to be reexamined ► Much-needed examinations of the VEN's connections and physiology are now possible
The von Economo neuron (VEN) in the anterior insula has been proposed to play a role in self-awareness and social cognition but had been presumed to occur only in humans and great apes. Evrard et al. demonstrate anatomical evidence for a macaque VEN, opening the way for functional tests of its role in cognition.
Awakening Deco, Gustavo; Cruzat, Josephine; Cabral, Joana ...
Proceedings of the National Academy of Sciences - PNAS,
09/2019, Letnik:
116, Številka:
36
Journal Article
Recenzirano
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A fundamental problem in systems neuroscience is how to force a transition from one brain state to another by external driven stimulation in, for example, wakefulness, sleep, coma, or ...neuropsychiatric diseases. This requires a quantitative and robust definition of a brain state, which has so far proven elusive. Here, we provide such a definition, which, together with whole-brain modeling, permits the systematic study in silico of how simulated brain stimulation can force transitions between different brain states in humans. Specifically, we use a unique neuroimaging dataset of human sleep to systematically investigate where to stimulate the brain to force an awakening of the human sleeping brain and vice versa. We show where this is possible using a definition of a brain state as an ensemble of “metastable substates,” each with a probabilistic stability and occurrence frequency fitted by a generative whole-brain model, fine-tuned on the basis of the effective connectivity. Given the biophysical limitations of direct electrical stimulation (DES) of microcircuits, this opens exciting possibilities for discovering stimulation targets and selecting connectivity patterns that can ensure propagation of DES-induced neural excitation, potentially making it possible to create awakenings from complex cases of brain injury.
The past decade has witnessed a renewed interest in cortical local field potentials (LFPs)--that is, extracellularly recorded potentials with frequencies of up to ~500 Hz. This is due to both the ...advent of multielectrodes, which has enabled recording of LFPs at tens to hundreds of sites simultaneously, and the insight that LFPs offer a unique window into key integrative synaptic processes in cortical populations. However, owing to its numerous potential neural sources, the LFP is more difficult to interpret than are spikes. Careful mathematical modelling and analysis are needed to take full advantage of the opportunities that this signal offers in understanding signal processing in cortical circuits and, ultimately, the neural basis of perception and cognition.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Electrical microstimulation and more recently optogenetics are widely used to map large-scale brain circuits. However, the neuronal specificity achieved with both methods is not well understood. Here ...we compare cell-targeted optogenetics and electrical microstimulation in the macaque monkey brain to functionally map the koniocellular lateral geniculate nucleus (LGN) projection to primary visual cortex (V1). Selective activation of the LGN konio neurons with CamK-specific optogenetics caused selective electrical current inflow in the supra-granular layers of V1. Electrical microstimulation targeted at LGN konio layers revealed the same supra-granular V1 activation pattern as the one elicited by optogenetics. Taken together, these findings establish a selective koniocellular LGN influence on V1 supra-granular layers, and they indicate comparable capacities of both stimulation methods to isolate thalamo-cortical circuits in the primate brain.
•Konio cells of the macaque LGN directly influence the supra-granular layers of V1•CamKII-selective, AAV-mediated optogenetics can be used to activate the konio system•Electrical stimulation of konio cells affirms selective V1 supra-granular activation•Both methods prove highly comparable in eliciting selective feedforward activation
Klein et al. show a selective influence of the lateral geniculate nucleus koniocellular projections on the supra-granular layers of visual cortex in the macaque, using cell-specific optogenetics and electrical microstimulation. Both stimulation methods result in similar feedforward activation selectivity.
Although the electroencephalogram (EEG) is widely used in research and clinical settings, its link to the underlying neural activity during sensory processing remains poorly understood. To ...investigate this, we made simultaneous recordings of surface EEG, intracortical local field potential, and multiunit activity (MUA) in the alert monkey visual cortex during presentation of natural movies. Using a general linear model, we show that in single trials, EEG power in the gamma band (30–100 Hz) and phase in delta band (2–4 Hz) are significant predictors of the MUA response. Specifically, we found that the MUA response was strongest only when increases in EEG gamma power occurred during the negative-going phase of the delta wave, thus revealing a frequency-band coupling mechanism that can be exploited to infer population spiking activity. This finding may open up a new dimension in the use and interpretation of EEG in normal and pathological conditions.
Short-term memory requires communication between multiple brain regions that collectively mediate the encoding and maintenance of sensory information. It has been suggested that oscillatory ...synchronization underlies intercortical communication. Yet, whether and how distant cortical areas cooperate during visual memory remains elusive. We examined neural interactions between visual area V4 and the lateral prefrontal cortex using simultaneous local field potential (LFP) recordings and single-unit activity (SUA) in monkeys performing a visual short-term memory task. During the memory period, we observed enhanced between-area phase synchronization in theta frequencies (3-9 Hz) of LFPs together with elevated phase locking of SUA to theta oscillations across regions. In addition, we found that the strength of intercortical locking was predictive of the animals' behavioral performance. This suggests that theta-band synchronization coordinates action potential communication between V4 and prefrontal cortex that may contribute to the maintenance of visual short-term memories.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Simultaneous intracortical recordings of neural activity and blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) in primary visual cortex of anesthetized monkeys ...demonstrated varying degrees of correlation between fMRI signals and the different types of neural activity, such as local field potentials (LFPs), multiple-unit activity (MUA), and single-unit activity (SUA). One important question raised by the aforementioned investigation is whether the reported correlations also apply to alert subjects.
Monkeys were trained to perform a fixation task while stimuli within the receptive field of each recording site were used to elicit neural responses followed by a BOLD response. We show – also in alert behaving monkeys – that although both LFP and MUA make significant contributions to the BOLD response, LFPs are better and more reliable predictors of the BOLD signal. Moreover, when MUA responses adapt but LFP remains unaffected, the BOLD signal remains unaltered.
The persistent coupling of the BOLD signal to the field potential when LFP and MUA have different time evolutions suggests that BOLD is primarily determined by the local processing of inputs in a given cortical area. In the alert animal the largest portion of the BOLD signal's variance is explained by an LFP range (20–60 Hz) that is most likely related to neuromodulation. Finally, the similarity of the results in alert and anesthetized subjects indicates that at least in V1 anesthesia is not a confounding factor. This enables the comparison of human fMRI results with a plethora of electrophysiological results obtained in alert or anesthetized animals.
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